and archaeostomatopods (Hoplocarida, Crustacea)

Transcription

Contributions
Zoology,
to
SPB Academic
Palaeo-
and archaeostomatopods
Gulch Limestone,
Mississippian (Namurian),
for Systematics
1090 GT Amsterdam,
and Population
Schram
Stomatopoda,
phylogeny,
&
ic composite
arose
from
now
the
seen as a
the
from
herein
are
described
&
palaeostomatopod Bairdops beargulchensis Schram
Horner,
1978 and
a new
species
acanthocercus.
of archaeostomatopod,
Tyran-
Tyrannophontes acanthocercus
is
quite distinct from the Pennsylvanian archaeostomatopod
T.
nophontes
theridion
from
the
fauna (Mazon Creek),
Essex
originally compared. Bairdops beargulchensis
ilar
to
the Mississippian palaeostomatopod,
the Scottish Glencartholm
jected.
of B.
A
theridion
pods
preliminary restudy
and
A
Perimecturus
rapax
interpretations
of
genetic analysis
resolves
hoplocarid
of the
the
and
P.
very
sim-
syn-
therefore
is
theridion
of the
re-
archaeostomatopods
and the
parki,
of those taxa
is
and
evolution.
the
yielded
largest
ver-
Prominent among the Bear
are
ten
some
species of mala-
costracan crustaceans, five of which
ida. The rest
array
of fish, conodonts,
and
gastropods
are
of the fauna consists of
molluscs
Hoplocar-
an
extensive
(cephalopods,
bivalves), brachiopods, annelids, xi-
phosurans, sponges and various unidentified, eniggroups (e.g.,
1969; Schram
Melton,
see
Horner,
1978; Factor & Feldmann,
Morris,
1990).
&
1985; Conway
The Bear Gulch Limestone beds
are
part
of the
Bear Gulch Member of the Heath Formation in the
T.
Big Snowy Group of central and
Other limestone
some
novel
cladistic phylo-
Hoplocarida including
the
of the
beds and black
newly
some
suggests
higher level relationships
fact has
eastern Montana.
palaeostomato-
reveals
A
Gulch invertebrates
it
elegans, from
previously proposed
T.
Gorgonophontespeleron,
recognized characters
forms
fauna.
beargulchensis with
B.
fauna in
diverse collection of Carboniferous
tebrates in the world.
matic
which
with
was
onymy
Box 94766.
taxonom-
the confusion of specimens of two
distinct hoplocarid species. These species
as
beargulchensis
(Malacostraca, Hoplocarida)
Gulch Limestoneis
Bear
that
Bairdops
crustacean
1978
Horner,
P.O.
Bear Gulch
1983). This
Mississippian
Hague
The Netherlands
and most
palaeostomatopod
(1998)
The
of central Montana
University of Amsterdam,
Abstract
The
155-185
Schram
Biology,
Malacostraca, Hoplocarida,
Keywords:
(3)
(Hoplocarida, Crustacea) from the Bear
Ronald+A. Jenner
& Frederick+R.
, Cees+H.J. Hof
Institute
67
Publishing bv,
Paleozoic
hoplocarids
(palaeostomatopods, archaeostomatopods, aeschronectids,
shales
comprise
the
remaining part of the Bear Gulch Member (Fac-
tor
& Feldmann,
crops
out on
50
mately
Bear Gulch Limestone
1985). The
Potter Creek Dome
km
1), approxi-
(Fig.
southeast of Lewistown
in
Fergus
and
County,
unipeltatans).
Montana. The
exact
age and
stratigraphic
relationships of the Bear Gulch Limestone have
been the
Introduction
1981 for
Dome
The Bear Gulch
are
late
part of
an
palaeo-
extensive
Mississippian
and
archaeostomatopods
invertebrate fauna of the
(Namurian)
Bear Gulch
Lime-
stone of central Montana. This Carboniferous Kon-
servat-Lagerstdtte preserves
community (Schram
Feldmann,
species
1985).
In
&
a
near-shore marine
Horner,
quality
of
diversity, it is comparable
Limestone
of the Jurassic
1978;
Factor &
preservation
to
and
the Solnhofen
of Bavaria
(Williams,
most
subject of
a
some
summary),
strongly
suggest
Mississippian)
Limestone
was
debate
age
a
the result of
(Fig. 2). The
deposited in
high
with low oxygen
terface
a
low-energy, shallow,
and
the excellent
sedimentation rates
at the
1983;
(upper-
Bear Gulch
Bear Gulch fossils
levels
(Williams,
Williams,
late Chesterian
tropical marine environment,
preservation of the
(see
but the fossils of Potter Creek
is
perhaps
combined
sediment-water in-
Factor
&
Feldmann,
1985).
The Bear Gulch fauna, the Middle
Pennsylvani-
156
R.A.
Jenner
et
al.
-
Fossil
of
stomatopods from the
Carboniferous chronofauna and
a
hibit
similarity in both ecologic
striking
and taxonomic
pervasive
composition
of the
stability
communities
crustacean
ex-
structure
1981). The
(Schram,
and taxonomic
ecologic
near-shore
such
as
these three
at
spatio-temporally distinct localities qualify them
the invertebrate
fauna
of
analogue
a
1966). Briggs & Clarkson (1990)
(Olson,
indicated that
subsequently
represented by the trophic
ecologic
The maintenance of taxonomic
remains
time, however,
The faunas
or
even
on
as
crus-
of the various
1981)
localities could not be maintained
stability,
(based
structure
feeding types; Schram,
tacean
as
vertebrate chrono-
unambiguously.
stability through
essentially
unquestioned.
the different localities share genera
at
Crangopsis eskdalensis is part of
species.
the Bear Gulch and Glencartholm faunas and BeFig.
I.
Creek
extent of the Bear Gulch
Map showing the
Montana
Dome,
(modified
from
Beds
Williams,
at Potter
1983).
lotelson magister is
present in both the Bear Gulch
and Mazon Creek
As
an
(Westphalian)
Creek
Essex
assemblage
region of Illinois,
the three
&
gerstätten). These Lagerstdtten
exceptional
both in the
1991
Briggs,
complete list of Phanerozoic
more
Konser-
major Carboniferous
vat-Lagerstdtten (see Allison
their
Viséan (Middle
the
Glencartholm fauna from Scotland
Mississippian)
represent
and
of the Mazon
are
for
a
Konservat-La-
well known for
exquisite quality of the fossils
data obtained from the
stätten
should be
Diversity
and their
in
and
more
Lagerstdtten
onomic
ferent
1989,
One of the
ary
first endeavours to
utilizing
patterns
gerstdtten
in
servation
of
a
a
data
from
Konservat-La-
led to Schram’s ob-
systematic way,
Carboniferous
continuum (Schram,
study
evolution-
near-shore
faunal
1979b). This Laurentian Car-
sonal
arise
the
use
large
when the
preferences
camps
of
for the
single
a
problems have
care.
of data
contrast
Lagerstdtten
& Clark-
quality
of fossils
strongly influence
are
taxa
splitting
taxon
polarized
arisen in
the Bear Gulch
to be
under
profound preservational
ing them into
into
also
preservational histories
exhibit
1990).
special
the
by
to
preservational
can
quality,
tax-
when individual fossils with dif-
practice
Problems
&
The
from
quantity, both in absolute numbers of
Clarkson,
with
be distorted
typical fossil outcrops (Briggs
son,
and
(Briggs
study
approached
can
1990).
organisms
diversity
studies
exceptional
of Kons erv at- Lager-
information content between the
remarkable
taxonomic
faunas.
their
consequence of
from these kinds of faunas due
which is reflected
preservation,
a
compared.
comparison
differences.
of
taxa
Per-
lump-
easily divide workers
interpretation.
the
or
taxonomic
Similar
history of
tyrannophontids.
boniferous faunal continuum denotes the similari-
ty in ecological and
near-shore
taxonomic
composition
marine fauna from
Europe
to
of the
North
America, extending from at least the Viséan through
the
Westphalian. Briggs
& Gall
(1990) showed
fauna
(near-shore
can
to
terrestrial)
and the associated
be extended from the late Paleozoic into
the Mesozoic. The
Bear Gulch
crustacean
fauna, the
Essex
communities of the
fauna of the
Creek and the Scottish Glencartholm fauna
Mazon
are
phylogenetic background
of the
that
the concept of a continuum in transitional environments
Taxonomic and
Hoplocarida
part
The classification of the
story of continuous
change
(Schram, 1986). Prior
of extant and fossil
the
at
order
hoplocarids
to
since
the
1962, only
a
has been
early
a
1960s
limited array
stomatopods occurred within
Stomatopoda Latreille, 1817. However,
present the subclass Hoplocarida Caiman,
1904
Contributions
Zoology,
to
is divided into three
67
(3)
1998
-
separate orders: Stomatopoda
1817, Aeschronectida Schram, 1969, and
Latreille,
Palaeostomatopoda
matopoda
Brooks,
1962. The order Sto-
is further subdivided into
1925 and
Unipeltata Latreille,
1969. The
dea Schram,
suborders;
two
Archaeostomatopo-
aeschronectids,
matopods and archaeostomatopods
ed
157
palaeosto-
are
represent-
exclusively by late Paleozoic forms.
at least 412
Presently,
species within five
super-
families and 109 genera constitute the extant uni-
peltatan
fossil
ambiguous
Jurassic
sozoic
tatans
1995). Their
stomatopods (Manning,
record
goes back
Me-
1886, all unipel-
be accommodated within modern fami-
can
lies. The
taxonomy
has been in
flux
of the
for
at
unipeltatan stomatopods
least the past
Much has been achieved since the
vertebrate
Paleontology
1969) recorded the
matopods
un-
early
the extinct
(Sinemurian). Except for
family Sculdidae Dames,
the
to
that
were
24
years.
In-
on
Manning,
unipeltatan
sto-
known at the time. Since then,
substantial contributions to the
tant and extinct
&
(Holthuis
genera of
thirty
Treatise
description of
unipeltatans have been and
are
ex-
be-
ing made. These developments, however, have
been paralleled
netic
by investigations into
within the
relationships
the
not
phyloge-
stomatopods (Hof,
in
1962, H.K. Brooks erected the order Palaeoto accommodate the
stomatopoda
turus
genera
1908 and Archaeocaris
Peach,
Brooks listed the following features
istic of the
somites
four
posterior
freely articulated, thoracic
five
to
(Brooks,
subchelate
1962:
72).
In
1872.
character-
as
and
thoracic
somites
subequal
Montana
after Williams,
in
[s7c]
size.”
1969, Brooks’ list of palae-
rus
in his
(Peach,
“Thoracopods subchelate,
subequal,
early
work
on
Peach (1908)
and Brooks
the
(1962),
Peach
of the
In
a
and
species
of
(modified
currently only Perimecturus parki
1882) is retained in
cies
or
are
Bairdops
name,
elegans
(Peach,
pattoni (Peach,
1908)
over-splitting
and revised Brooks’
of Archaeocaris.
Perimectu-
re-
spe-
(see
“Perimec-
does not allow
therefore retained incerta sedis
that of
1908)
1979c). The single specimen of
styliof
while the
subsumed in either this
pairs
removed much
(1908) had placed the genus
Dome
“Mysid-group” which, combined with his
definitive placement in
any
series
mainly
substantial
(especially by Peach),
descriptions
spine
to
1979c) re-evaluated the
palaeostomatopods,
ambiguity caused by
of taxa
second to fifth
1969: 535).
Schram (1979a,
papers,
complementary
telson with fixed median
form furca.” (Brooks,
mid-Carboniferousrocks
Potter Creek
1981).
maining species
turus"
partially
on
1817). Of his six initially described species
treille,
Schram,
was
exposed
of Perimecturus,
that of
it:
as
“Euphausid-group”, comprised the schizopods (La-
ostomatopodan characters differed somewhat from
1962 and
section of the
Stratigraphic
Perimec-
Meek,
“Carapace shallow
Palaeostomatopoda;
with articulated rostrum,
two
2.
central
press).
In
Fig.
for
a
higher category and was
(Schram,
1979c).
The structure of the tail fan and the fact that all
but
the most anterior thoracic
free (not fused to the carapace)
segments
suggested
appeared
to Peach
(1908) close affinity of the perimecturids and
nodactyloids
Fabricius,
(especially
1781).
about the exact
Gonodactylus
However, Peach
relationship
was
of the
go-
chiragra
not
certain
perimecturids
and the modern forms, but he did remark
that, “....it
158
is
that
highly probable
[Perimecturidae]
gave
characteristic
Archaeocaris
the
regarded
to
convergent
a
groups,
a
a
phy-
accommo-
of
forms
some
of
insuffi-
an
homologous
between
conclusively
some
or
phylogenetic
the fos-
prove
modern crusta-
classification
of the
would obscure the tentativeness of the in-
fossils
ferred
phylogenetic
for
an
erected
a
relationships.
superorder,
new
commodate the
cephalomorpha
fossil
and
He
therefore
horizontal classification:
alternative,
the
-
Fossil
Eocarida,
to
orders Eocaridacea,
Palaeostomatopoda.
ac-
Pygo-
He did not
stomatopods from the Bear Gulch Limestone
carnivores characterized
late
thoracopods
(e.g.,
the aeschronectids
thoracopods.
by the
1986), detritus
Clarkson, 1990),
omnivorous
or
1981).
placed within three fam-
are
ilies: Kallidecthidae Schram,
Schram
&
1979.
Schram,
macarididae
Horner,
The
are
1969; AenigmacaridAratidecthidae
1978;
Kallidecthidae
and
an
elongated, stenopodous maxillary palp, subequal
in
length
to the
macarids
thoracopods.
uniquely
possess
but
lary palp,
not
and
do possess
so
specialized
intermediacy
is
as
a
morphological
palaeostomatopods and
The
stomatopods.
unipeltatan
particularly
morphological
from
apparent
ages. The combination of
present,
1969).
within three genera ( Per-
species
imecturus, Bairdops and Archaeocaris)
within
the
Palaeostomatopoda
1986). The species
(Schram,
of Perimecturus
ized by their dorsoventrally
grouped
are
flattened
1979a,
character-
are
body
and the
distinct structure of their tail fans. Members of the
Bairdops and Archaeocaris have
genera
lindrical
bodies, but the greater complexity of
fans of Perimecturus and
tail
genera
apart
Bairdops
from Archaeocaris.
reduced carapace of Archaeocaris
it
es
the
more
more
other
closely
to the
The
sets
the)
these
posteriorly
apparently plac-
archaeostomatopods
palaeostomatopod
cy-
than
(Schram,
genera
Schram
(1969)
recognized
the first
species
of
Aeschronectida, Kallidecthes richardsoni Schram,
1969 and Aratidecthes
tes
as
the first
johnsoni Schram,
archaeostomatopod
theridion Schram,
ception of hoplocaridan
hoplocarids
are
1969,
as
Tyrannophon-
1969. The aeschronectids
diverged rather strikingly
which
an
subchelate
a
regionalized thorax (di-
and
thoracopods
from
the standard
con-
morphology, according
depicted
as
to
active, rapacious
the
append-
anterior tagma of segments
a
bearing
posterior tagma of
larger “abdominalized” segments with locomotory
limbs)
and
apparently
closely
a
posterior reduction of
links
to the
the
carapace
archaeostomatopods
the
more
than to the
palaeostomatopods.
In
1978,
Schram &
Horner described the
mala-
costracan fauna from the Bear Gulch Limestone of
central
Montana, which included
ostomatopod species
matopod
and
of uncertain
tentatively
one
phontes cf.
some
new
palae-
tyrannophontid
Schram &
affinity.
T.
theridion
In
sto-
Horner
at
with the
newly
as
Tyranno-
T. theridion in
com-
described archaeostomato-
pod Gorgonophontes peleron
revision tended to
hand
1984, Schram revised
morphological details of
parison
two
designated the small number of tyran-
nophontid remains they had
1979a).
well
vided into
an-
1969 is
as
Schram
interpreted by
was
intermediate between the
the
second
enlarged
an
maxil-
enlarged
an
Tyrannophontes theridion Schram,
quite
aenig-
stenopodous pleopods.
The aratidecthids do not carry
tenna.
the
addition,
In
ida until
six
Aenig-
distinguished by the possession of
structure of the thorax and the associated
1969 (Brooks,
emerg-
life-styles,
place the palaeostomatopods within the Hoplocar-
At
that
(achelate)
feeding (Schram,
The aeschronectids
idae
in
1969),
viz., nektonic,
&
feeding (Briggs
(Kunze,
Moore,
see
of subche-
variety of suggestions have
A
filter
epibenthic,
presence
have “unmodified”
ed for the aeschronectid
proper way
similarity
to be actual ancestors to
opted
as
He believed that until addi-
tional evidence could
cean
1962). However,
recent
deciding
for
similarity.
or-
crustacean groups. He
existing
more
on
sto-
erecting the
evidently committed to
cient basis
he
(Brooks,
morphological
fossil forms
sils
unipeltatan
to
crustaceans, he felt uneasy
the fossils in
dating
structure
thoracopod
vertical classification
or
arranging
the
was
Squillid stock...”
the basis for
Palaeostomatopoda
family
(1962) discovery of the
suggested affinity
although Brooks
of
rise to the
subchelate
matopods and formed
logenetic
member of the
some
Brooks’
1908: 5).
(Peach,
der
Jenner et al.
R.A.
Schram,
1984. This
emphasize the overall similarity
of T. theridion from the Mazon Creek and the Bear
Gulch
tyrannophontid.
However,
the Bear Gulch
hoplocarids
were
re-
Contributions
evaluated
basis
by
Factor
of then
concluded that
&
the
Feldmann
at
doubtful
and
their
Furthermore,
on a
the
on
Bairdops
a
at
Type species.
be
cannot
Mazon
1969 with the
tyrannoThe differences be-
These
preservation.
ascribed
the
to
vagaries of
now
studied
Tyrannophontes acanthocercus,
Naturale,
Synonymy.
sils
used
previously
undescribed
&
(Italy).
original
beargulchensis,
(Schram
fossils
from
the Bear Gulch
In
addition,
description
Tyrannophontes
theridion Schram
theridion
Tyrannophontes
examined. -
11997, i
34453
34462;
Homer,
Homer, 1978,
text-
Factor
sensu
&
7.
Tyrannophontes
can
P
of
the
Tyranno-
1985). First,
be
now
i
(holotype),
CM
i
8785,
12017,
i
11841,
12145,
UM
UM 6492
part
are
and
counterpart
i
11979,
i
12444;
11978,
12433,
CM
34454-34456,
32093, 32095-32098;
i
i
34458, 34459,
5541, 6022, 6114, 6123,
6138, 6145, 6149, 6205, 6267, 6271, 6290, 6492 (P
Museum
Carnegie
-
locality
of the
same
6123
6205,
6267
from
recorded
are
UM
32095
and
fossil).
material
locality
number SL
from
is
the
574; Field
University
of
5541, 6114, 6149, 6138, 6492, 6271,
locality
the exact
unknown;
Museum
designated T14N, R22E;
Montana specimens
MV
7106;
site MV
while
7001;
UM
exact
locality within the
6022, 6145,
UM 6290
locality
Bear Gulch
of the
area
unknown.
seen
Diagnosis.
Second,
Bairdops
1978
beargulchensis
pace
was
a
of
derived from
composite
a
an
Tyrannophontid
-
Schram &
extends
Propodi
genuine palaeostomatopod
archaeostomatopod
from the Bear Gulch
Limestone. Thus B.
beargulchensis is neither
Bear Gulch
synonym of the
jun-
tyrannophontid,
one
side and
row
of
one row
large,
median
used
tology, University
seum
Civico
of
in
this
Natural
di Storia
of
three
study
are
deposited in
Chicago (P),
Museum
the
of
Naturale,
Pittsburgh
Milan
(CM),
and
the
Mu-
Museo
(Italy) (MSNM).
Suborder
spines
on
outer
on
inner side of
and
pleomeres with
ridge, ridge
into
passes
cesses
projecting
of
dorsal,
pleomere,
posteriorly
on
submedian
in
from
posterior
son
margin. Uropodal protopod with dorsal
process
tergite beyond
over
ridges
line with two pro-
gin
projecting posteriorly
posteri-
pleomeres
of sixth
pleorneral
antero-
mar-
anterior telprocess
exopod, and larger
ven-
projecting posteriorly under endopod.
1904
Caiman,
Order Stomatopoda Latreille,
Pair
sixth
on
Field
Paleon-
tral
Subclass Hoplocarida
six.
to
present
Montana, Missoula (UM), Carnegie
History,
spines
orly directed anteroventral spine
Systematic description
Natural History,
sized
unequally
moveable
longitudinal plane of propodus. Pleura of
ventral furrow and
of
thoracopods with
of
rows
of smaller
exposed thoracomeres
specimens
stomatopod. Cara-
the level of fifth tho-
nor
theridion.
Museum
to
of subchelate
submedian
parallel,
spines;
a
mid-dorsally
con-
two
The
&
1969
Schram,
MSNM i
12002, i 12004,
racomere.
T
T.
Feldmann, 1985, figs. 6,1, 6.S-6.6,
Italian
fusing specimens
ior
cf.
&
Schram
beargulchensis
3.
distinct taxon from the Mazon Creek T. therid-
Horner,
and
1, fig,
fos-
theridion
T.
phontes theridion (Factor & Feldmann,
ion.
re-
Bairdops
1978) and those used for
Horner,
the Bear Gulch
sp.
5.
Occurrence,
of
cf.
Tyrannophontes
construction of the revised
concept
as a
have
we
palaeo- and archaeostomatopod
for the
n.
and Pis. I-III)
Bairdops
-
1978, in part, pi.
i
acquired by the Museo Cívico di Storia
examined the
5.1
(Figs. 3, 4,
CM
in Milan
of Illinois
Pennsylvanian
Creek area).
(Mazon
Material
archaeostomatopod
Limestone
from the Middle
specimens represent different
altogether.
have
Tyrannophontes theridion Schram,
-
actually hinges
equation of the
Mazon Creek and Bear Gulch
tyranno-
phontids
1969
they
beargulchensis
synonymy
Bear Gulch.
Tyrannophontes Schram,
1969,
Tyran-
of what
most
Genus
Feldmann
fig.
tween the
We
&
in fact material of
B.
not
Creek T. theridion Schram,
species
that
was
their
premise:
phontid from the
(1985)
Our re-examination of the
study
tyrannophontid
true
all.
hand for their
159
of
synonym
junior
a
specimens they used reveals
had
1998
-
palaeostomatopod
was
theridion.
nophontes
(3)
material. Factor
new
beargulchensis
67
Zoology,
to
Uropodal
1817
Archaeostomatopodea
mounted
Schram, 1969
Family Tyrannophontidae Schram,
1969
rami
on
Articulated
broadly
endopod
blade-like
and inner
with
setae
margin of exopod.
spines mounted on approximately
tal four fifths of outer
dis-
margin of uropodal exopod.
160
R.A.
Robust telson with
submedian
spike flanked by four pairs of
in size
spines decreasing
distance
ing
from median
telson defined
with increas-
Median
spike.
two submedian and
by
al.
et
subrectangular base tapering off
terminal median
to
Jenner
crest
Fossil
solateral carapace
carina.
margins slightly converging
the anterior
to
approximately
and 8
cm
body length
i
(MSNM
ranges
between 2
11979 and CM 34459
thoracomere
(MSNM i
respec-
are
triflagellated
visible
antennae
two
This scale widens from
and setae
UM
UM
by
compound
MSNM
not
i
directed
third
one
a narrow
are
eyes
oval
broad as
as
base to
is
long.
rounded
a
margins (UM
scaphocerite
scale
of
1-2). The
(PI.
reniform
or
large
(CM 34453,
1-1). Ocular peduncles
are
clearly preserved.
The
through
the
carapace
and
are
approxi-
from
the
posterior
carapace
margin (CM
1-4). The mandibles mainly consist of
(PI.
and massive mandibular
body with
rior
dorsal
margin and
a narrow
a
cave
changing
dibular
more
body
a
the
margins
relatively heavily
UM
directed
6492,
anterodorsally
34454,
UM
curvature
of the
carapace is
triangular
incisor
12444) and
directed
a
subtriangular
approximately
and
of,
in lateral
In dorsal
halfway
subrectangular
sig-
convex
the absence of
on
a
thoracomeres three
least,
at
i
carapace
and
CM
P
12145,
32095),
we
con-
is free from all but the
flattened
34454)
an-
in
tapers into
11853,
i
more
MSNM i
UM
12002a,
one
a
fourth
long
(PI.
narrow,
rounded
tip (MSNM i
MSNM i
12433a, MSNM
rostrum is about
11841b,
the mid-dorsal
as
approximately
length of the
one
and
half times
two
distinct tagmata:
a
broad.
as
anterior
region of small but distinct and unfused
segments (at least thoracomeres
5) bearing
of
subchelate
five) (PI.
two to
thoracopods,
and
a
larger segments (thoracomeres six
MSNM i
in
the broad rostral base
The thorax is divided into
area
(CM
aspect
6149) (PI. 1-2). The
long
as
carapace and
lateral
1-4) and subtriangular
dorsal view. In dorsal aspect,
12017 and
(PI.
i
MSNM
MSNM
12002,
especially
MSNM i
1-5) indicate the unfused
I-
posterior
to
i
eight).
11997,
12145 and
and distinct
i
appearance of the anterior thoracomeres. MSNM
ridg-
a
(CM
(CM
or
tagma exhibit
ra
and the anterior thoracomeres
deep,
as
those
an
aspect,
view, the
between sub-
in form with the dor-
anterior deflection of their
more
posterior.
not
are
pleu-
high,
as
Consequently,
or
the
cephalothorax tapers anteriorly while the sternites
of the anteriormost thoracomeres show
shift relative to the
longer than high.
a
11841b preserves the unfused sternites of the ante-
slight anteriorly
molar process
region and
The
rior thoracomeres. The thoracomeres of the anteri-
body. The ven-
process
view is
man-
6492).
The carapace is
only slightly
i
smooth
34458,
P32095
con-
portion of the mandible shows indications of
34454,
is
Specimens
At least
sclerotized
less distinct central
posteroventrally
or
The
large
poste-
margin is
34458) with
ventrally.
are
surrounding
tral
CM
(CM 34454,
a
convex
tip (Fig. 3).
the dorsalmost part of the anterior
es
34454)
convex.
lateral
teriormost thoracomeres. The articulated rostrum
an
mately three fifths of the length of the carapace
furrow is
specimens and the distinct and
through eight (MSNM
clude that the
i
the anteri-
A
slightly
in
Based
corner.
some
unfused nature
impressed
located at
are
on
carapace
MSNM
margin. The dor-
carapace
dorsal
concave
ventrolateral
as
heavily sclerotized mandibles
a
posteriad
11841b,
laterally.
and
margin
carapace
moid, with
small basal segment
a
large flap-like
12002b) (PI.
A
scaphocerite
The
1-2, 3).
composed of
a
peduncles
segments (CM
the
along
present
6149) (PI.
6149 is
followed
are
segments
6149) (PI. 1-1, 2).
UM
ventrolaterally
i
(PI. 1-1). The
34453)
slender
elongated
noted (P 32096) almost
6022,
peduncular
CM
posterior
annu-
length (MSNM
directed ventrad and their
are
34453, CM 34458,
subovate
robust
(CM 34455,
have at least two
tip
in
flagella (PI. 1-2) subequal
11978). At least
with the
thora-
margin of the
carapace encloses
dorsally
sal surface of the carapace is
The antennules
are
thorax both
present along the entire
tively).
lated
or
wings
the anterolateral
to
12145) (PI. 1-1). The
The
-
extend
an-
approx-
margin of the fifth
comere, while the lateral
sixth
Description.
teriorly. Mid-dorsally, the carapace extends
imately
on
median
one
-
i
12145,
MSNM i
34454) (PI. 1-4).
comeres
ventral
are
12017,
The
rounded
marginal
an
anterior
position of the tergites (MSNM
MSNM
pleurae
of the
ventrally
furrow and
i
11997, CM
exposed thora-
and have
ridge (PI.
an
antero-
1-1). The
Contributions
PI.
I.
Zoology,
to
67
(3)
—
n. sp.;
peduncular segments of antennules (arrows)
6149,
dorsal
bar
0.3
=
3,
cm;
thoracomeres,
D
=
UM
6022,
anterior to
arrowhead
dactylus,
scaphocerite.
2 and
4
photographed under
and slender
E
=
distorted cephalic appendages
right, scale
=
abdomen -
eye,
IM
=
bar
=
0.2
thorax
cm;
5,
P
transition,
ischiomerus,
M
=
water:
peduncular segment
view of anterior cephalothorax with cephalic appendages,
cephalothorax,
coxa,
161
1998
and
scale bar
P
slender
subchelae, scale
32095, lateral
mandible,
note
I, holotype:
of antenna
=
view
bar
propodus,
=
R
=
0.8
the size
antennular
=
rostrum,
lateral
34453,
scale
segments of
peduncular
showing
1.6 cm. AF
=
CM
(arrowhead),
cm;
4,
CM
difference
flagellum,
SB
=
B
bar
view,
0.75
antenna
note
cm;
anterior
basis,
scaphocerite
CA
basal
broad
2,
UM
(arrows), scale
34454, lateral
of the
=
=
=
and
view
of
posterior
carpus,
segment,
CO
SC
=
=
162
R.A.
of the sixth thoracomere
pleura
ly
than that of the seventh and
(CM 34453, MSNM i
12004,
eighth
MSNM
et
al.
-
Fossil
thoracomere
types of
i
able.
12444) (PI.
the thora-
on
comeres.
There is
ages
no
indication of the
the first
on
to five each bear
that
(Pis.
pairs
indicated
as
The rims
by
11841, UM
thoracopodal
(MSNM
The
i
thoracopods
The ischiomerus
in size and somewhat
mal segments
CM
UM
34454,
podus is
and carpus
1
i
UM
6138,
subrectangular,
three times
MSNM
1978,
i
being
and
two
longer than wide, with
qually
lus
sized
the surface
on
that may extend
where the
self
spines
somewhat
distalmost
surface of the
propodus.
the inside of the median
propodus, while
on
A
a
row
the outside of this
The six
or
spines alternate with
PI. II.
to
i
six,
more numerous
n. sp.;
scale
2,
indicating subchela,
scale
bar
1.2
=
12004, lateral view
of sixth
pleomere
first pleomere,
cm;
3,
=
telson,
1.75 cm;
CM
of pleural
and
note
bar
is the
the
34456,
P
smaller
rae
on
3-6
spines (arrows)
note
processess
anteroventrally
directed
on
on
is the
heav-
more
with
the pro-
outer mar-
convex
aligns itself parallel
and
III-l).
Indications
to the
The form of the ap-
to slender and
point
UM
approximately
All
cephalothorax.
as
a
an-
6492).
one
third
pleomeres
longer
larger
are
However, the first pleomere
of the abdominal segments
consequence
They
are
of
possessing dor-
processes.
in lateral aspect
subquadrate
are
into
es
on
decorated with
a
an
The
pleu-
with rounded
anteroventral
three
pleomeres
view of
water:
I,
UM
arrows
bar
pleomeres three through five, scale
=
0.14
and
view
=
0.16
cm. AM
=
=
0.15
6,
cm;
CM
The sixth
(counterpart
anterior
5,
the first
posteriorly,
pleural spines (arrows)
cm;
=
MSNM i
34459,
pass-
spine
11-2, 4). The height
indicate large spines, scale bar
sixth pleomere (arrows), scale bar
scale bar
(PI.
pleomeres.
6492, lateral
subequal subchelae
of propodus spines,
to six
decreases
pleomeres generally being higher
than the last three
spines
directed anteroventral
posteriorly
pleomeres three
of the
largest
spines (arrows),
robust and
marginal furrow and ridge (PI. II-4).The ridge
to
photographed under
lateral view
somewhat to-
the posterior thoracomeres is not clear-
on
largest
corners.
sized
32093, lateral
curves
sal, posteriorly directed tergal
plane. The larger
unequally
con-
(shortest dorsal margin), while the sixth pleomere
of small,
regularly spaced
seven
II-1
is often the smallest
it-
larger spines appears
found in
articulation
as
dactylus
than the thoracomeres.
longitudinal plane of the I
of
of these consists of two classes of
spines.
row
Some-
34456).
are
appendages (CM 34459,
than the
point
to
more
the
distally,
The abdomen is
une-
apposed spines is positioned
closely
be located
parallel
runs
nulate
mas-
the outer lat-
on
the
ly preserved.
dacty-
the
beyond
A furrow
propodus
axis of the
longitudinal
fine and
facing
the
to
large spines
propodal surface
CM
spines
dactylus
near
than it is
pendages
pro-
upper
of
rows
the
on
34453,
dactylus is
propodus (Pis.
tip of the dactylus aligns
along the propodus.
eral
submedian
two
CM
apposition
the
propodus and is about four-fifths of its
12444,
convex
the result of the form
in close
gin of the dactylus (P 32095). When the subchela
half to
a
thin, sharp
a
with the empty sockets (MSNM i 12145).
is closed,
(facing the dactylus) and lower margins. It is
sive and armed with
ily
are
disarticulated
proxi-
6492) (PI. 1-4).The
that
sockets
12145,
sclerotized
podus
subequal
are
robust than the
more
(MSNM
coxa,
more
When disarticulated,
The
length.
shorter ischiomerus and
a
large spines is
cup-shaped
wards the
a
not
are
spines. The wide spacing of the
The thin, blade-like
Fig. 5.1).
sized
moderately
a
long basis, followed by
carpus.
1-4 and
34454) (PI.
have
of the
junction
sclerotized
heavily
are
widely spaced
times the
6271) (see Fig. 5.1).
robust, heav-
a
tip. The large spines
leave
diverge
two
move-
to
(MSNM i
posterior
These
11-3).
conically shaped with
are
each other.
pairs
12145) (PI.
ily sclerotized roundedbase tapering
apices
surrounding the holes into
coxae
CM
11841,
the
appear articulated and
large spines
They
of the robust bases
thoracopods
the coxal holes that
the sternites
on
than
MSNM i
than the smallest
subequal in size
The anterior
III-l).
laterally
more
anteriad (MSNM i
the
2 and
1-1, 3, 4, 11-1,
positioned
are
pair
a
similar in appearance and
are
of append-
structure
thoracomere. Thoracomeres two
of subchelate
(CM 34456,
sharp-
more
tapers
1-1). No tergal decoration is present
Jenner
pleomere
of PI.
on
deeper
or
1-5),
arrow
pleomeres
0.35
cm;
4,
three
MSNM
11841a, dorsal view
lateral view
margin of pleomere 4,
of pleopod
CA
=
on
carpus,
4
D
=
dactylus,
DR
=
posterodorsal spine,
=
thoracopod,
VM
diagonal ridge,
PM
=
IR
3
=
inner
posterior margin
=
ventral
margin
of
ramus
of pleopod, OR
of pleomere
pleomere.
3,
PVS
=
outer ramus
of pleopod,
posteroventral spine,
=
Pr
=
P
=
3
4
propodus,
S
=
pleomere 3,
4
small spines,
T
or
=
6,
PDS
telson,
=
Th
Contributions
to
Zoology, 67 (3)
-
1998
163
164
R.A.
has
a
in line with two processes
are
projecting
posteriorly from the posterior margin of the tergite
the anterior
beyond
as
cess
a
the
on
i
further
No
tergal decoration is present
large
coxal
CM
holes
sclerotized
in
pleopod
and has
a
detail
indicating
i
11841b). Specimens
P 32095 and P
massive
heavily
CM 34459 preserves the first
11-6). The limb is biramous
(PI.
stomatopods from
the inner
spine
projects
process
A small-
protrude from
seems to
by
of the
corner
located
rest of the
III-4)
the distal
four fifths
ramus
can
be
detected
The telson is
tapering
robust with
fourth and
one
fifth
II-6 and
more
heavily
III-l). The inner ramus
robust and lobate.
sclerotized,
the
subequal
in
of the inner ramus
on
are
length.
The
anterior
(PI. III-5).
pairs of moveable submedian spines
in
crease
size
The terminal
with
spines
directed
spines. The
be twisted
appear to
spines
agonal ridge
The
margin
the median
corner
is not clear. The
of
an
ment. A
a
somewhat
approximately
of
surface
one
median crest.
laterally
on
The
a
directed
34454,
11841).
margin
MSNM i
A
appears
11841a) (PI. II-5).
(i
pair
over
The telson
longitudinal carinae;
and
of submedian,
length
mesiad
one
pair
one
dor-
the dorso-median
ramus
spines
projecting
over
the
are
converge upon
extends
12145,
larger ventral
dopod (UM 6149) (PI.
onto
Fig.
seg-
tes
located
uropodal
process
on
the telson,
the
the dorso-median carina that in
the terminal telson
4
shows
a
reconstruction of
acanthocercus
and its
representative
on
the
Etymology.
spike (PI.
III-
tail fan.
TyrannophonTable I offers
measurements.
Combination of the Greek akanthos
-
and
(thorn, prickle)
i
area
(see Fig. 4). The
posteriorly
MSNM
elevated
an
The sublateral and submedian cari-
consist
to
larger posterior
gation projects posteriorly under
are
one
obliquely
3,5).
uropods have single-segment protopods with
posterior
sclerotized di-
sixth the
ramus
margin of this segment.
dorsal process
a
the
some
anterior
the
slight-
spike. The pair of
so-median. The submedian and
single large, apparently undivided segment
forms the distal part of the
anteroventrally
from
are
unmoveable. From each
of the telson
is ornamented by five
with the anterodistal part of the
proximal part
anterior and
by
that de-
two dis-
segmentation of the inner
exact
distance
increasing
be
may
is
The
turn
ramus.
flanked
spike (MSNM i 12433) and that
ly curved towards
nae
specimen, together
spike is
CM 24459 shows indications
anteroventrally
talmost
length of the telson
four
carinae define
of five
spike that is between
base
of sublateral,
rami
subrectangular base
a
terminal median
to a
the dorsal
specimens (Pis.
UM
5541,
6205).
several
on
(PI. III-4).
of the outer
UM
34453,
of the telson base extends
This annulated
is
portion
ram-
It consists of at least fifteen annulated segments.
us.
outer
membranous inner part
more
(CM 34455, CM
protopod. The
the outer
probably represents
ramus
sclerotized
thick-
a
flattened medi-
a
(CM 34455, CM 34453)
anterolateral
slender
and
margin of the exopod bears articulated spines (PI.
smallest
plane of the body than the
the
Approximately
protopod. This lat-
towards the median
more
entire
from
furrow
a
median
ter process is
The
part of the
outer
exopod is divided in
marginal ridge
narrow
are
endopod. The heavily sclero-
tized outer half of the
part.
and
decorated with
heavily sclerotized than
more
its inner part and the
an
exopod
(PI. III-4). The
setae
pos-
posterodorsally
posterior margin of the protopod.
posteroventral
margin
of the
uropodal exopod is
ened
the Bear Gulch Limestone
(PI. III-3, 4). The uropodal endopod
long delicate
one
A
single-segment protopod.
ventrally directed
the
the size of the
the presence of massive,
pleopods.
protopodal
from the
undecorated and
are
34455, CM 34459,
32096 indicate
Fossil
separated
abdominal sternites
UM 5541,
er
processes
directed pro-
12004, MSNM i 12145, CM 34453,
pleopodal protopods (MSNM
sible
i
pleomeres.
The
show
(MSNM
view, these
single, dorsal, posteriorly
(MSNM
32095).
P
margin
In lateral
11841a) (PI. II-5).
appear
of the telson
—
in outline
pair of dorsal, longitudinal submedian ridg-
They
es.
Jenner et al.
the
MSNM i
basal
prolon-
uropodal
en-
111-2). The uropodal rami
unisegmental and broadly blade-like
to
(tail), referring
the
to
spined telson.
the
exopod (CM
12002,
or
from
kerkos
lobate
Remarks.
Horner
was
-
In
the
original
study of Schram &
(1978) the tyrannophontid they recognized
among
the
rarer
faunal elements
present
in the
collections made up until that time. Thus their
certainty
mens.
It
as
to
now
the taxonomic
turns
un-
affinity of the speci-
out, after many
more
years
of
Contributions to
PI. III. Tyrannophontes
nght,
scale
scale bar
bar
=
pleopod,
Se
=
DMC
setae,
=1.2
0.35
uropodal rami,
cm;
scale
=
SEC
67
Zoology,
(3)
acanthocercus
cm;
3,
bar
2,
UM
UM
=
6149,
6149,
0.2
cm;
sublateral
carina,
n.
1998
sp.;
4,
5
165
photographed under
ventral view
5,
MSNM i
En
SMC
=
tailfan'(part
of uropod, Ex
subraedian carina,
T
=
=
1,
dorsal
of
UM
5541,
lateral
and ventral
III-2), scale
12433a, dorsal view telson,
endopod
=
water:
of partial tailfan with
dorsal view of partial
dorsomedian carina,
=
-
scale
bar
bar
=
=
Th
=
0,58
0.18
exopod of uropod, MC
telson,
view with
processes
thoracopod.
=
on
cm;
cm.
AR
median
the anterior curved
to
the
uropodal protopod (arrows),
4,
=
CM
34455, lateral
annulate
crest,
P
=
or
view
of
outer ramus of
protopod
of uropod,
166
R.A.
in
collecting
the
area
and
a
of the world,
is among the
Gulch
that
more
fauna. The
common crustaceans
of the
bles in
of the Bear
evi-
species
now one
anatomically of all the Paleozo-
tyrannophontid stomatopods has
in
the literature
the two
1979a). The mandibles of Archaeo-
well
as
as
than
thoracopod protopods
farther
the
are
mandibles. The mandibles of the
be located
appear to
alon than those of
of the
proximal
ing
and the
1962;
mandibular
large
position of the
(Brooks,
body bearing
As
at least
pointed
an
by
out
this mandibular form is
1962),
to that of
comparable
Archaeocaris, consist-
for mastication.
unipeltatan stomatopods.
In
addition, the mandibles of unipeltatan stomatopods
possess
a
the Bear Gulch
tant issues
a
molar process
tyrannophontids raises impor-
concerning the evolution of the
stoma-
topod mouth field.The unipeltatan stomatopods
unique
among
having
extending
a
the
process
that characterizes
unipeltatans.
The
by the molar
served
the
a
the mandibles
specializa-
feeding apparatus of
enlargement
of the anterior
inside of which food is masticated
processes
of the
mandibles. As
above, the position of the mandibles
chaeocaris indicates that the mouth is
edly displaced posteriad,
the
1981,
(Kunze,
series of
posterior position of the mouth
associated with the
proventriculus,
on
proventriculus
1983). This feature is part of
tions
are
large-food feeding malacostracans
large molar
into
development
of
a
Reconstruction
acanthocercus
IP
mm.
=
n.
incisor
sp.
and the
of
the
process,
MB
mandible
to the
(anterior
may
indicate that these
=
of
mandibular
Tyrannophontes
scale
right),
bar
=
0.85
body.
possess
triculus. The
more
not
so
apparent
ob-
feature of
a
the tentative
molar process could
ginning of
an
proventriculus and the
enlarged
some
on
specimens
used for the
mens
as-
analysis of
Tyrannophontes theridi-
original description of the species
partially
confirms
this.
Speci-
PE 25507 and PE 25502 reveal mandibles and
show the
impression of
Flowever,
ture
of
we
a
large and massive jaw.
wish to stress
of these observations
the
for
provide
more
the exact
thorax.
Second, other hoplocaridan
in
regard
to
a
mark-
ation of the
feeding apparatus
Schram’s
the
hypothesis
in
the
(Schram,
and
position
laboratory
with
on
SEM in-
constructive line
points of the radi-
of
findings
cephalo-
taxa should be
our
mouthpart morphology
dicates that this indeed would be
Nevertheless,
the
concerning
mandibular
morphology. Preliminary work in
unipeltatan
First,
mandibular molar process and
position of the mandible
examined
reasons.
na-
specimens should
conclusive evidence
of the
morphology
provisional
two
study of other tyrannophontid
in Ar-
mandibular molar process
identification
sociated mandibular apparatus. Further
of the
proven-
possibly indicate the be-
of research to elucidate the finer
lack of
large
a
posteriorly positioned tyranno-
phontid mandibles and
of
did not
palaeostomatopods
the distinctive
by Schram (1969)
molar process.
The uncertain identification of
in
3.
Fig.
to the anterior
Structurally, how-
thoracopod segments.
incisor process
Brooks
tyrannophontid
(Brooks,
Archaeocaris
resembles the mandible of
a
from the
tyrannophontid mandible (Fig. 3) closely
the
of
away
posteriorly in the ceph-
more
céphalothorax
margin of
tyrannophontids
1979a), both with respect
Schram,
ever,
1984),
is confined to
be closer to the anterior
to
seem
céphalothorax
part
been
species of the genus Archaeocaris (Brooks,
1962; Schram,
the
it
never
1969;
(Schram,
palaeostomatopods
while among
caris
sclerotized mandi-
of heavily
preservation
reported
is
Fossil
hoplocarids.
The
in
-
museums
preservation
dent in these strata also makes this
of the best known
al.
acanthocercus
Tyrannophontes
quality
et
considerable number
specimens having accumulated in the
of
ic
Jenner
stomatopods.
here
1969)
consolidate
of the
mor-
Contributions
67
Zoology,
to
(3)
1998
-
167
phological intermediacy of tyrannophontid
topods between
the
tatans exhibit
stoma-
palaeostomatopods and the
is
un-
ipeltatans.
exhibits
of
grade
among
structure of the biramous
larity
that
may prove to be of
is
the
pleopods.
than
more
superficial
acanthocercus to the
petasma
of male
unipeltatans.
pods.
It
can
be
now
reconstruction
Creek in 1984
are
of
pleopods
T.
theridion
mented
of
protopod (Schram,
are
The
possession of
thoracic and abdominal
hoplocarids
ported the
on
1984),
text.
are
seg-
1984). The pleo-
annulate outer rami
of
appendages
presence of annulate
Bairdops elegans, but their
Schram’s
by
gested
the
by Briggs
encountered the
nulate
&
Clarkson
same
flagella of the
situation
as
are
from which arises
apódeme
over
also have
a
on
sug-
an-
5 of 71
still
coxa.
be
lacking in
a
see
Unipeltatans
posterior ridge with
anteriorly directed apodemes, but these appear
T. acanthocercus. In
to
addition, unipel-
ster-
first
indeed modimore
body
medi-
preserva-
specimens preserved
show
to
telson with
a
but
this
along the anterior-posterior
actually
are
preserved
in
However,
other
specimens
vations (MSNM i
In these
are
this
along
would be
true
MSNM i
11979,
specimens,
is seen, which extends
a
parallel
12444,
single
regarded
as
axis,
as
a
lateral
upon the median
interpretation
are
some
different
UM 6149
ro-
carina
seems
clear
is
also
carinae
that
plane of the-
compatible with
on
the spec-
dorsoventrally preserved (MSNM i
11841, MSNM i
There is
being
this
dorsomedian
the reconstruction of the telson based
imens that
carina
median carina, but rather
longitudinal
posteriorly
and CM
however, these carinae
posteriorly,
paired
specimens.
to the upper surface
incorrectly interpreted
not a
(P
lateral preser-
the upper telson surface. Thus it
are
12433) (Fig. 4).
variation in telson form apparent
specimens.
For
example, the telson
of
(PI. I1I-3) is somewhat more rounded than
that of MSNM i
11841
ex-
manner
longitudinal
the anteroposterior
More
converge
on
rotat-
of Factor & Feld-
is consistent with these kinds of
on
hangs
axis and thus
32098). The telson reconstruction
34455).
their
on
longitudinal
a
apparent dorsal telson surface. Some spec-
an
imens
there
crucial
interpretation
ed
poses
was
assumption that the telson is actually
that there is
can
kinds of
the
telson. This
we
two distinct
on
join
in
the
on
that the
proper reconstruction of the tail fan could
physical-
seen
me-
unipeltatans.
dorsomedian carina,
carina.
posteriorly directed, finger-like
well-developed
a
sides appear
the inside of the sternite
the entry into the
are
also
through
longer than anything
ridge
a
How-
antennae.
unipeltatan (Fig. 5). Nevertheless,
distinct anterior
was
regarding the
in
seen
be undertaken. The
tated
(1985) when they
The sternites of thoracomeres 2
acanthocercus
was
seen
was
to the
of the second
indicates
of the telson. If the telson is
re-
exo-
presence
(1979c) restudy.
original description,
on
rapacious
thoracopodal
This
appears
heavily scle-
onciling the differences between these
before
mann
with
appendages
the material may have deteriorated
ly since
a
on
Bi-
the Mazon
might be primitive. Peach (1908)
not confirmed
ever,
1969;
and
maxillipede, but its location is
a
There
branch
two
as
and those
(Fig. 5.1)
at
fifth. The
tion in these fossils, lateral and dorsoventral. Rec-
pleo-
theridion
through
narrower
of T acanthocercus
thoracopod
not-
seen
and
positioned closer
are
unipeltatans.
al than that
mention in the
biramous
nites of
Horner
14394).
a
ridges that
fied
flap-like rami that provide the attachment site
gills.
pods
be
thoracomere is
plane of the sternite than those
pair of
1969 and
unisegmental with
pods of unipeltatans
broad
from
rami of T.
pleopodal
being
as
PE
of the first
to possess small coxal holes with less
thoracomere
also indicated in the revised
however, without any explicit
described
can
see
structure
that
in T. acanthocercus. Further-
sternite is much shorter
dial
varies from the
(compare Schram,
In any case, the
one
telescoping of these segments
variance with that of the second
rotized
of T.
ramus
of the
ramus
pleopod distinctly
pleopods
pass-
(1985) already
Gorgonophontes peleron (e.g.,
ramous
just
first
demonstrated that
annulate form. Similar
simi-
Schram &
ed the presence of the annulate
of the biramous
the
on
Factor & Feldmann
(1978) and
A
resemblance of the
irregular distal tip of the inner pleopod
pleopods
inter-
no
these is the most sin-
gular
ing interest
also
between both these
organization
Most notable
groups.
acanthocercus
Tyrannophontes
unique characteristics that form
mediate
the
more,
However,
a
completely lacking
(PI. II-5)
12433 (PI. III-5). That of MSNM i
appears
intermediate. The sublat-
eral and submedian carinae of UM 6149 (PI. III-3)
R.A.
168
I, Lateral reconstruction of Tyrannophontes
4.
Fig.
dorsal
are
Jenner et al.
tailfan
more
carina
reconstruction
of T. acanthocercus
acanthocercus
new
species, scale
closely associated with the dorsomedian
than those of MSNM
MSNM
i
118419
i
12433a (PI.
1II-5).
apparently shows only the sub-
median and dorsomedian carinae. Thus, variation
is
expressed
in telson outline
differences
as
and
of the elements of the telson
spatial relationships
Body size is quite variable (see Table I), but the
opposite
at
ends of the spectrum
markably isomorphic (e.g., compare
UM 6492).
on
prominence
The
pleomeres three
i
pare MSNM
of the
distal
to
shows
a
a
of the
six also
12004 and P
more
32093). The
even
among
of such
a
large spine
on
on
which
uncertain taxonomic
affinity.
the carapace
extending
third the
on
this
possible
the
un-
however, is of
specimen
gastric
grooves
posteriorly for ap-
length of the
transverse cervical
ticulated rostrum
very
from both sides of the
base of the articulated rostrum
one
only
appear
Finally,
dorsal
on
34454
34457 is
carpal spines
1 1853 shows two
possible
6271
thoracopo-
is
UM 6492 possesses
ambiguously. This latter specimen,
a
UM
the
carpal spines, but CM
only specimen
proximately
the subche-
tergal ridges
pertinent thoracopod
faintly preserved.
and
com-
curvature
and 6. Furthermore CM
5
dal carpus, but the
on
spines
(e.g.,
remarkable difference with indica-
apparently displays
MSNM i
pleural
specimen (UM 6022).
single
pleomeres
scars
re-
6138 and
UM
varies
tions of the presence of submedian
both
are
tip of the dactyli of the thoracopods
also differ somewhat,
can
lae of
Fossil
n.
scale
sp.,
bar
=
0.5
bar
=
0.95
carapace
groove. The
ar-
specimen is large and sub-
rectangular and thus differs somewhat from the
lines
(dotted
cm
usually observed subtriangular
exact
rostrum outline.The
affinity of this specimen also is
6149 also
displays possible gastric
We record all
carapace.
we
uncertainty); 2,
denote
cm.
of
recognition
to
serve
justify
other than
anything
not clear. UM
grooves
on
the
these variations here, but
believe these do not
As mentioned
ornament.
specimens
-
this time
at
single species.
a
above, Factor & Feldmann (1985)
believed that the Mazon Creek and Bear Gulch ty-
rannophontids belonged
revised
(1984)
theridion Schram,
This
peleron.
T.
larity of
to
the
same
taxon. Schram
details of
morphological
some
1969 in his
revision
comparison
increased the overall
simi-
theridion from the Mazon Creek
the Bear Gulch
tyrannophontid.
T.
with G.
and
Factor & Feldmann
ascribed observed differences between the Mazon
Creek and Bear Gulch
garies of preservation.
revised aspects
late
Schram’s
of the initial
ridion (Schram,
fine
description of
to be
more
described. In addition,
spines
racopodal
was
a
dal
single
observed to be present
The
propodus.
protopod seemed
on
uropod rami
exopod
How
is
possible
only faintly
indicated.
tyrannophontids
only
a
In
the-
row
a
fact, it
as
were
that
appears
general resemblance
rendering of the
to
Bear Gulch
T.
less
uropo-
slight posterior
on
the
morphology of the
described by
of
the tho-
uropodal
closely does this revised concept of
ridion resemble the
mann?
to have had
diaeresis
A
T.
massive than
styliform than originally described and the
extension.
va-
re-examination
1969). The propodus of the subche-
thoracopods appeared
previously
to the
tyrannophontids
T. the-
Bear Gulch
Factor
& Feld-
theridion shows
Factor & Feldmann’s
tyrannophontid.
The
Contributions
Table
/.
to
Zoology
Measurements
(excl. telson),
Te
of
(cm)
Ro
telson,
=
Specimen
67
,
=
(3)
1998
-
Tyrannophontes
rostrum,
Ur
=
169
acanthocercus
n.
sp.
All
uropod, exopod margin,
Pr
measurements
=
are
Ca
Ab
Te
Ro
Ur
Ca
lengths.
propodus thoracopod,
=
CeThor
carapace,
=
Ab
cephalon
=
abdomen
+ thorax.
Pr
CeThor
MSNMi
11979
0.41
1.18
0.42
-
0.45
-
MSNMi
12017
0.57
1.23
0.48
0.10
-
-
1.04
MSNMi
12002
0.53
1.39
0.53
0.23
0.40
-
1.14
MSNMi
11841
0.73
1.35
0.71
0.18
-
-
1.16
MSNMi
11978
0.60
1.43
0.55
0.16
0.40
0.32
1.75
MSNMi
12145
-
1.92
0.75
-
-
-
1.41
MSNM i
12433
0.99
2.29
1.03
0.33
0.52
1.74
MSNMi
12004
0.90
2.52
0.89
0.42
MSNM i
12444
1.24
2.62
0.88
11997
0.99
2.76
1.35
2.81
MSNMi
MSNM
i
8785
MSNMi
11853
0.81
-
0.43
-
0.58
0.22
-
0.70
2.17
1.13
0.26
0.69
0.49
2.04
1.45
0.32
-
-
0.20
-
-
-
CM
34453
1.17
3.27
1.31
0.34
1.06
CM
34459
1.26
3.62
1.57
0.34
0.92
CM
34455
1.73
3.65
1.56
-
CM 34457
CM
1.76
34456
-
-
-
1.22
-
2.42
-
0.73
2.20
-
0.72
2.34
-
2.41
0.68
1.50
0.66
1.30
1.00
0.21
CM 34454
0.74
1.88
0.78
0.19
P
32098
0.99
2.51
0.84
-
-
P
32093
4.49
-
-
-
P
32095
-
-
-
P
32096
-
-
-
1.22
UM 6123
2.05
4.66
4.82
2.00
-
UM
6205
-
UM
6271
-
UM
6149
-
UM
6138
0.74
1.94
0.83
UM
6492
1.73
4.72
2.12
UM
6145
-
4.41
-
1.73
number of
cluding
1.20
-
1.04
-
2.50
of:
1) pleural spines
setae
gin
of the
the
on
the
on
on
on
exopod, 3) spines
of
racopods.
Gulch
ces
The
pair
on
of submedian
new
median
6)
ridges
median telson
and
spines
two
the
8) the form and
on
the Bear
only increase the differenfrom the
structure
on
a
observations here
tyrannophontid
the
margin of
the propodi of the subchelate tho-
between the taxa
include:
and
one
spines
mar-
posterior processes
uropodal protopods, and 5)
spike with
rows
4)
five, 2)
inner
the outer
on
two
material
three to
uropodal endopod and the
uropodal exopods,
the
details in-
the Bear Gulch
pleomeres
of the
two
localities
pleopods, 7)
and
the sub-
tergite of the sixth pleomere,
ornament
-
-
of the telson.
1.37
0.93
-
1.30
-
-
-
-
-
-
-
0.96
-
0.68
-
0.60
0.44
1.35
-
-
0.95
3.40
-
-
it
However,
grained
stone
should be noted that the very fine-
micrite sediment of the Bear Gulch Lime-
cuticle
on
preservation than the
nodules of the
Feldmann,
show
1.90
-
together with the occasional
eralized
ly
2.46
-
-
-
important morphological
the presence
1.32
-
1.30
-
Mazon Creek and the Bear Gulch specimens differ
a
1.14
0.44
-
2.00
6267
in
-
-
1.46
UM
-
-
0.30
•
-
-
3.46
-
-
1.10
CM 34458’
-
2.85
0.80
-
-
1.84
more
its
more
Mazon
1985).
presence of min-
fossils
provides
better
coarse-grained siderite
Creek
deposits (Factor
Bear Gulch
fossils
preserved morphology,
and
&
therefore
more
clear-
than the Mazon Creek fossils.
so,
The
sils
zon
question then is,
justify
Creek
Feldmann
a
can
taphonomy
of the fos-
synonymy of the Bear Gulch and Ma-
tyrannophontids? This is what Factor &
(1985)
did when
they concluded that the
observed differences between these forms
result of differences in
were
preservation. However,
the
we
believe that the Bear Gulch and Mazon Creek forms
R.A.
170
different taxa for the
are
Because both faunas
faunal continuum
quently
exhibit
are
the
of
part
Carboniferous
a
and
reasons
tions
can
for
the
splitting
only depend
are
Such
taxa.
principle, the morphological data
can
be
ed in two ways. Observed differences
either to
cal
preservational
viewed
variation,
If differences
differences.
or
in
we
priori exclude characters
forms from
seen
In
be due
can
are
be
to
a
preserved
taxonomic
as
projecting
of the subchelate
of
leron is
the reconstruction
observed between the Bear Gulch and
Mazon Creek
garded
separating them
anatomical variation
preservation,
in
for
Under the terms of the
taxa.
that
sufficient
as
the
tinctness becomes
of
terms
assuming
becomes
as
re-
distinct
priori assumption
a
from
results
possibility
impossible
potential meaning,
tinctness
could then be
tyrannophontids
to
differences
It
seum.
the
a
14344;
the
to
be tested
by
evaluation of all the evidence.
can
be
preserved.
absolute
preservation
Creek fossils.
by
at
the
This
indicates
and tufted
that there
gills
is
no
taphonomic boundary that could have pre-
vented the
on
structures as setae
of details
Until further
on
the Mazon
analysis yields
new
data
preservational quality of both localities (e.g.,
comparing the preservation
both
localities),
assume
clusive
that
there is
preservational
cause
no
of
species present
compelling
differences
reason
the
are
to
ex-
of the observed differences.
overall
close
a
similarity
similarity
comparison.
to
Gorgonophontes peleron.
of the tail fan
Both
subrectangular base tapering off
spike;
they share the lobate
rami and the setose
inner
part
of the
margins
exopod.
A
The
especially suggests
species have
a
to
telson with
a
median
nature of the
of the
larger
bear two
parallel
propodus
endopod of G.
pe-
depicted in
on re-ex-
narrow
4C in
the
may
being
In
only appears
of
as
a
discontinuity
mineralized cuticle
original
the presence of
against
be
appears to
uropodal endopod
(PE
cam-
the
as
a
dopod
to
incorrectly
proximal inner part of the
exopod
as
uropo-
peleron
define
may
an
elevated
the telson in the way of the Bear Gulch
PE
beyond
the
nent
dorsal
posterior
14319) along
in
of the
margin
the
Bear Gulch
sclerotized,
by proximal
positioned
tergite (PE
14319). The pleural
19259, and specimen
heavily
(PE
ridges which might extend
pleomeres of G. peleron
as
taxon
with indications of submedian telson
19251, PE
spines (PE
of the
ca-
area on
14341), and the sixth pleomere shows
submedian,
two
en-
diaeresis. The two telson
a
to
diaeresis.
exopod, thus suggesting the transition from
rinae of G.
PE
that,
now
transverse groove, the
genuine
a
addition,
drawings of G. peleron adds support
the argument
The
1984).
uropodal exopod of
An examination of Schram’s
lucida
era
the
on
PE
19259,
tip (PE
Schram,
by
acanthocercus
be absent, since it appears
preservation
14344).
T.
distal
underneath
a
PE
14259,
14394 shows robust,
rami
accompanied
slender annulate
the
ridges
equally promi-
specimens,
PE
pleopodal
remnants of
are
anteriormost
ramus
pleo-
meres.
Tyrannophontes acanthocercus also shows substantial
propodi
(Schram, 1984), based
diaeresis
presumed
14259,
The aeschronectids from the Mazon Creek prove
that such delicate
peleron
in
a
fig.
see
dal
option
(PE
The
and the
spines
uropodal
supposed diaeresis
support. Under the
possibility
viable
in
terminating
interpreted
of taxonomic dis-
exopod
a
equally massive (although dif-
differs from that of
of taxonomic dis-
that observed differences have
prolonga-
amination of material available from the Field Mu-
rather than
are
the
1984).
rounded and lobate than
more
G.
that
basal
endopod while
over
Schram,
sized
The
size).
crete observed differences in anatomy have poten-
tial taxonomic value. Therefore, detailed differenc-
a
thoracopods
unequally
in
fering
in
fig. 3D
see
descriptors. The alternative explanation is that dis-
es
projects
process
14319;
be
to
seems
underneath the
and carpus appear
real anatomi-
better
on
meaningful employment
protopod
distinc-
vagaries of preservation, that would
as
tion
rows
interpret-
form
Fossil
insuffi-
data.
morphological
on
-
smaller
conse-
temporal dis-
tinctness of the localities in themselves
cient
al.
uropodal
taxonomic similarities,
geographic
et
reasons.
1979b), and
(Schram,
striking
that
recognize
following
Jenner
uropod
endopod and
process
of the
The main differences
tylus
of the subchelate
tion of the
pleurae,
the ornaments of the
dal
spines
exopod
the
length of the dac-
thoracopods, the segmenta-
thoracopods, the form of the abdominal
the presence
moveable
are
on
or
absence of
the outer
of the Bear Gulch
exact carination and
pleural spines,
uropodal rami (serration and
spination
margin of the uropotyrannophontid),
the
of the telson and the
Contributions
Zoology, 67 (3)
to
size of the lateral carapace
sis
(see below) indicates
1998
-
171
wings. Cladistic analy-
that these differences
rather broad
are
sufficient to retain the Bear Gulch
tyrannophontid
within the genus
However,
Tyrannophontes
study of all the original
material
would be recommended. For
useful to look at the exact
thoracopodal propodi
subchelae of the
.
of
a
re-
example, it would be
spination pattern
body length than those of
T.
are
larger relative
theridion and T.
to
acan-
thocercus.
segments. Specimen
prevents
estimation of the
accurate
of the mandible
large, massive
a
The distorted carapace,
body.
an
P 32094 possess-
and reveals
large rounded eye
mandibular
the
along
howev-
position
length of the cephalo-
thorax.
the
on
and to determine whether the
thoracopods
a
er,
peleron
G.
es
The carapace is
large, elongated and subrectan-
ki lateral view and
gular
aspect,
margin is slightly
sigmoid
lateral
and
corner
a
almost the entire
covers
thorax. In lateral
the
posterior
with
slightly
a
carapace
ventro-
convex
posterodorsal
concave
region (UM 6217) (PI. IV-2). Both in lateral
Order
Palaeostomatopoda
Family Perimecturidae Peach,
Genus
1962
Brooks,
dorsal
1908
ly
Bairdops Schram, 1979
aspect, the anterior carapace margin is
tends
UM
(UM 6217,
concave
approximately
eighth thoracomere and laterally
Type
species.
Perimecturus
-
1908), from the Visean of
elegans
Scotland
(Peach,
(Glencartholm
fauna).
rolateral
4).
P
(Figs.
6 &
5.2,
1978, in part, pi. 1, fig.
1985,
in
Schram
beargulchensis
&
Horner,
theridion Schram,
1969senjM
Factor & Feld-
meres
Material
examined.
P
-
32092,
UM
32094;
6194,
6217
(holotype).
(probably
UM
-
32094
are
6194,
6217
come
from
locality
MV
Diagnosis.
tending dorsally
to
anterior
laterally
pleomere.
Four
racopods.
Posteriorly
pairs
carapace
ex-
margin of eighth tho-
to anterior
of first
margin
of unarmed subchelate
directed processes
tho-
right and
ed
to
segments
The
project-
exact
structure of the
At least four
is
part
preserved. Specimens
not
6217 and
possibly
UM 6194 show
P
(PI. IV-1). These
parts of
an
an
antennal
antennular
are
for the
32094, UM
remnants
elongated peduncular segment
ond antennae
displays
cephalic appendages
of the
specimens
scaphocerite.
also
of
at
sec-
pre-
UM 6194
peduncle consisting of three
are
located lateral
are
32094 suggests
The
ster-
(to
the
surround-
to the
ster-
nites.
pleomeres. Uropodal protopods with posterior di-
-
narrow
by well-sclerotized apodemes. Remnants of tho-
racopod
rected dorsal process.
Description.
thoraco-
somewhat
UM 6194 and P
respectively) that
but the nature of their
serve
eighth)
are
distorted stemites
laterally
the left,
ing from dorsal, posterior margins of fifth and sixth
one
to
thora-
tagmatization of the
(P 32092) (Fig. 5.2 and PI. V-2, 3).
Palaeostomatopod with
-
racomere and
least
large size difference
6194) with rounded coxal holes
P
7106;
R22E.
length than
The posteriormost
the sixth
third
larger than the anterior thoracomeres (P 32092) (PI.
32092 possess
most
of
degree
nites (P 32092, UM
from TI4N,
a
spatulate.
smaller in
a
V-
(UM 6217,
pleomere and the eighth
modest
ante-
UM 6217 and
V-3). The anterior thoracomeres have
Occurrence.
32092,
first
thorax is observable.
6.2.
are
and there is
5.
part, fig.
on
lateral view it appears
pleomeres,
between the
A
furrow
carapace, appears
All the thoracomeres
comere.
Tyrannophontes
mann,
the
as
to about the
pleomere (Pis. IV-2,
marginal
a
ex-
margin of the
large articulated rostrum, about
A
UM 6194. In
Pis. IV, V)
Bairdops
-
carapace has
long
the
Synonymy.
margin
32094).
as
Bairdops beargulchensis Schram & Horner, 1978
The
of the first
slight-
Dorsally it
6194).
the anterior
to
and
unclear
There
pairs
to
seems
they
are
which
to be
a
thoracopods is
folding
are
on
subchelate
(PI. IV-1,
preserved (UM
thoracomeres
and carpus and
dactylus.
sible
a
2).
6217), but it
they
moderately sized
long basis, followed by short, subequal
us
vague,
UM 6217 and P
belong.
coxa
and
a
ischiomer-
longer, unarmed propodus and
UM 6217 shows
some
remains of
a
pos-
eighth thoracopod underneath the eighth tho-
racomere.
The pleomeres decrease both in
height and width
172
Fig.
R.A.
5.
thorax
Camera
lucida
bar
=
0.12
cm;
et
al.
-
Fossil
2, Bairdops beargulchensis
anteriorthoracal stemites; I, Tyrannophontes
of the
drawings
segments, scale
Jenner
Schram &
acanthocercus
Homer, 1978, scale
n.
sp.,
Roman
bar =0.25
cm.
numerals
CH
=
denote the
coxal
M
hole,
=
mandible.
have
pleurae
running
32094
a
directed process
posteriorly
five and six
these
on
furrow and
dorsal,
posterior,
a
the
tergites of ple-
(PI. IV-1). This may be indica-
tive of the presence of one
ridges
marginal
on
margins,
with rounded
axis,
to have
pleomeral
ventral
straight
moderate
seems
The
32092).
to the trunk
They have
P
omeres
relatively
parallel
corners.
ridge.
P
(UM 6217,
posteriorly
or
two submedian tergal
pleomeres with
extend-
processes
ing beyond the anterior margin of the sixth pleomere or
very
on
telson
unclearly shows
six.
pleomere
P 32092
margin, respectively.
two submedian
unknown. UM 6217 shows
a
heavily
part of
a
pleomere, which
The
pleopod.
large (UM 6194,
The tail
fan is
telson is not
P
spike
delicate:
converging
by
the
particularly massive
flanked
a
represent
are
by
body of the
robust.
nor
to a
two
The
long median
slender lobes
or
A median telson crest
median carina and
lateral carinae
process
projecting
have
to
over
outer
approximately
as
long
posteriorly directed
The
and blade-like.
The
attaches to
part
membranous inner
more
a
the rami (UM 6194).
is slender
uropodal exopod
well-sclerotized
as
The
portion.
endopods appear
Fig.
6 shows
a
as
a
narrow,
exopod
the distance from the
terior telson base to the submedian
The
small
spines
is
an-
furca.
or
membranous
flaps.
schematic reconstruction of Bair-
dops beargulchensis.
Table II offers
some
repre-
sentative measurements.
Remarks.
more
two
posteriorly
(UM 6194). The
uropo-
-
cean
While Bairdops
clearly
characters,
it also becomes
its affinities to the Scottish
As
one
of the
now
defining
rarer
species,
crusta-
palaeostomatopods
B.
elegans, and
is apparent.
discussed above, Factor & Feldmann
concluded that
ior
beargulchensis is
understood in terms of its
elements in the Bear Gulch fauna. However,
the other
spines (UM 6194) (PI. V-l).
is defined
between
32092).
rather
that is
may
sclero-
pleopodal coxal holes
subrectangular telson base tapers
telson
is
pleopods
tized structure underneath the boundary
the fifth and sixth
protopods appear
tergal ridges
The structure of the
robust
only
dal
synonym
of
Tyrannophontes theridion. Unfor-
tunately, they did
not
underlying
restudy
of the fossils
scription
explicitly
elaborate
on
their conclusion. However,
reasons
of B.
(1985)
Bairdops beargulchensis is the jun-
originally
beargulchensis
used for
sheds
light
the
our
the deon
how
Contributions
PL IV.
and
to
Zoology, 67 (3)
Bairdops beargulchensis
=
Schram &
1998
173
1978:
Horner,
indicating antennal peduncular segment, scale
arrow
eye, M
-
mandible,
Factor &
P,
beargulchensis
taxon.
clearly
confused
=
Feldmann could have
and
We
1, R
pleomere
=
now
T. theridion
see
specimens of
description of B.
rostrum,
T
=
P
32094,
=
0.55
thoracomere
lateral
cm;
view, arrowheads indicating
2, holotype,
UM
6217,
lateral
dorsal
view,
pleomere
scale bar
=
processess
0.97
cm.
E
=
8.
8
concluded that B.
were
in
the
that Schram &
two
1,
bar
distinct
beargulchensis.
same
Horner
taxa in
their
Consequently,
Schram & Horner
Bear
Gulch
(1978, plate
tyrannophontid
1, fig. 3) depict
instead
of true
the
B.
beargulchensis, and Factor & Feldmann (1985, fig.
6.2) depict
on.
Thus B.
B.
beargulchensis
beargulchensis
instead of T. theridi-
in 1978
was
a
compila-
174
R.A.
Jenner
et
al.
-
Fossil
Contributions
6.
Fig.
I,
Zoology, 67 (3)
to
Lateral
Table II. Measurements
=
Ro
telson,
specimen
1998
=
of Bairdops
(cm)
Ur
rostrum,
=
UM 6194
of B.
beargulchensis. All
P 32092
1.70
3.57
P 32094
1.75
3.19
Gulch
B.
of
with
a
&
Feldmann,
both the Bear
beargulchensis
As
were
present
beargulchensis
Despite this confusion,
are
that
characterized
are
by
all
of the
B.
to
large
a
thorax.
distinct
to
beargulchensis
rannophontid by
tween the
V.
dorsal
P,
=
easily distinguished
the
large
view
view
telson,
telson
pleomere 1,
arrows
difference in
arrows
(part
SC
=
Schram
indicating
indicating
size
Homer,
T
1978:
anterior thorax
anterior
of V-3), scale
scaphocerite,
&
bar
=
=
thorax
0.65
telson,
-
-
T
g
=
the
lesser
of the
B.
The
over-
beargulchensis
is
compared with those of tyran-
morphology of
to
slender telsons
by spines
mentioned in its
is
crest
more,
both
species
podal exopod
part and
UM
6194,
scale
sternites, scale bar
coxal
thoracomere
hole
8.
dorsal
bar
=
=
1.0
0.7
with
a more
view,
cm;
with
tail fan.
cm;
P
4,
P
of pleopod, En
=
B.
re-
spike
elegans also
the telson.
on
in
species
median
long
a
Both
IS
Although
original description (Schram,
defined
by three carinae:
in
B.
This
closely
beargulchensis.
share
a
a more
Further-
blade-like
narrow,
heavily
one
resem-
uro-
sclerotized outer
membranous inner part. The endo-
scale
3,
beargulchensis
caudal furca.
or
median crest
a
B.
elegans, especially
structure of the
the
bles the situation
ty-
=
thoracopods of
modest when
1979c) this
be-
I,
1.98
2.01
degree of thoracic tagmatiza-
median and two submedian.
B.
sternites,
cm. CH
and
mass
not
pleomere and the eighth thoraco-
of V-l),
-
possesses
their
from the
status.
-
flanked
sufficiently
addition,
(counterpart
ventral
first
are
In
justify separate
is
but
resemblance,
ornament
-
have
carapace
superficial
a
size, form, and
3.30
-
gard
The telsons of
opods show
relative
2.20
of B.
very similar to that
bear-
tyrannophontids and palaeostomat-
CeThor
-
-
The overall
the Bear Gulch
Pr
nophontid stomatopods.
palaeostomatopods
genuine
the presence of
almost
covering
we
(excl. telson),
-
also
confirm that in fact
specimens attributable
some
gulchensis
PI.
all
Tyrannophontes.
were
abdomen
tion characteristic of palaeostomatopods.
a
fossils
on
=
thorax.
-
mere
denote
cm.
Ab
cephalon +
lines
(dotted
cm
0.47
carapace,
=
1.00
0.80
1.5
=
=
Ur
0.55
noting that charac-
in
=
CeThor
Ro
1.40
bar
scale bar
Ca
lengths.
are
propodus thoracopod,
tyrannophontid morphology, concluded that
all the B.
there
on
measurements
=
scale
1978,
Homer, 1978,
-
tyrannophontid and palaeostomatopod.
result, Factor
ters
be found
Homer,
1.40
3.80
5.30
to
&
Schram &
Te
2.60
tion of characters
Pr
Ab
1.92
UM 6217
Schram
beargulchensis
uropod, exopod margin,
Ca
*
175
dorsal tailfan reconstruction
uncertainty); 2,
Te
of
reconstruction
-
bar
=
0,8
cm;
32092,
ventral
32092,
dorsal
endopod
of
2,
UM
6194,
ventral
view abdomen and
view
abdomen
uropod, Ex
=
and
view
carapace,
carapace,
exopod of uropod,
176
R.A.
pod of both species appears reduced
of
B.
specimens of
more
is
podal endopod
only partially
of the
species
of the
lateral
in size.
to whether the
as
of B.
wing
carapace
B.
of that of B.
beargulchensis
be armed
with
gulchensis
logical
appear unarmed.
pleopods
B.
elegans)i
the presence of
B.
tergite ridges
the
sis,
on B.
possible
B.
may
bear-
species
are
fairly
beargulchensis
and
carapace,
propodus spines
on
of submedian
presence
pleomeres five and six that form
on
presence of
podal protopod
elegans
the outline of the
directed processes
posteriorly
(1985)
Currently, the morpho-
thoracopodal
the
elegans,
reminis-
(excluding cephalic append-
exclusively observed
on
of the
mass
also
is
those of
differences between the
limited. These include
ages
while
size
beargulchensis
of B.
thoracopods
spines,
larger
& Clarkson
elegans. Briggs
indicated that the
or
The carapace silhouette
preserved.
being the main difference. The small
cent
uro-
substantially reduced in size
also differs somewhat, the
thoracopods of
Study
should
beargulchensis
additional evidence
provide
Jenner et al.
B.
on
the nature of the
genuine
a
B.
on
-
Fossil
has five carinae (one median and
instead of four
(Schram,
rinae
the
15A). Two small
fig.
1979c:
lateral
two
described in
is
as
pairs)
literature
antennal
extending posteriad from the base of the
tennae
also
are
indicated.
render the carapace of P.
These
parki
ca-
an-
observations
similar
more
to
the
revised reconstruction of P. rapax (Factor & FeldIn
1985).
mann,
(and
to
lesser
a
GSE
abdominal ornaments of P.
to those of P. rapax than
tween the
parki
of the
the
also
now
appears
1985) (PI. VI-1).
perimecturids
presence of spines,
part of
similar
more
described. Be-
previously
those observed
to
Feldmann,
character
are
pair of submedian carinae and the
of nodes similar
&
that the
5892) indicate
laterally located pair of carinae
tor
ofGSE 4663
addition, photographs
degree
on
to
a row
P. rapax
final
A
is the
apparently
possibly movable,
the distal
on
demonstrated to be
present
(Fac-
uniting
margin of the uropodal
outer
more
be
on
exopod,
P.
parki
(PI. VI-2).
beargulchen-
process
beargulchensis,
the
on
and
uro-
possibly
Discussion
uropodal endopods.
Body form inference
Genus Perimecturus Peach,
1908 (PI. VI)
It
Remarks.
some
Some
on
fossils of Perimecturus rapax from the Bear
sides
preliminary
Gulch Limestone in
of P.
parki
land reveal
some
fossils in
CM
cesses as
potentially interesting
detailed
a
rapax)
two
possess
observed
by
Factor & Feldmann
est
to the telson is
smaller process is
Detailed
of all the
perti-
directed pro-
posteriorly
basal
dorsal
probably
analysis
uropodal
Schram & Horner (1978) and
(1985). The large
a
a
of
or
reasonable to
positioned
as
G.
process clos-
prolongation
projection
while the
over
the
the situation in T.
exo-
acan-
are
indicator of
an
additional factors
body
to the
photographs
of P.
parki
in-
frequency of ani-
their ventral
or
body form (dorsoventrally
changes
Among these post
changes
in
lateral sides.
shrimps
the
click-joint
explain
crustaceans
Experimental,
repositioning
(Briggs
decay
thoracopods.
(1908) argued for post
form to
body
that many fossil
to
of the
unfolding
&
of the
Kear,
are
preserved
on
body after death in
1994).
In
stomatopods,
muscles
mechanism of the
releases
thoracopods
P.
This
These differences
carapace,
can
are
be
decreased
centered
abdominal and tail
photograph
on
considerably.
the details of
fan ornaments.
The
of GSE 5896 shows that the carapace
can
its side
A
sils
lead
(Hof
to
&
the
Briggs,
in
result from the
the
resultmerus.
repositioning of the animal
potentially important
may
their
taphonomic data also
of the
propodal
mortem
the observation
ing in the unfolding of the propodus and
probably
These
reposition the animal from its normal
may
life mode. Peach
point
influencing the attitude of the
sediment surface.
dicate that the number of purported differences with
rapax
lateral
factors may be flexion of the abdomen and
mortem
the
peleron.
on
the
use
either
laterally flattened or cylindrical). However, there
the telson and
shows that the
pod. This clearly resembles
thocercus and
restudy
char-
new
this genus.
33934 (P.
protopods
comparison with photographs
from the Glencartholm fauna of Scot-
acters that invite
nent
observations
seems
mals
-
on
press).
source
for
arthropod fos-
molting process. Shed
ex-
Contributions to
PI.
VI. Perimecturus
with
arrows
indicating spines
uviae may be
tual animals,
Molts of
on
the Glencartholm
intermediate and lateral
fossils from
as
crustaceans and
exhibit
characteristically
and abdomen
unipeltatan
well (MSNM i
as
ac-
Rea-
1990;
(Mikulic,
sto-
separated
a
1975). Such separation is observed
record
of Scotland:
I,
(arrowhead); 2,
GSE
GSE
4663,
in the fossil
11978, MSNM
i
11979),
suit of
liams,
1983).
ever, indicate
eral
a
of the animal relative
difficult to
the sediment, but it is very
to
In addition to these
gy-based explanations,
tors,
as
some
catastrophic
preservation of the body in
an
served animals is
not
burial,
evant
(e.g.,
may
in
see
also be
Simple
may
cause
“unnatural” attitude.
necessarily
indicator of
body form.
morpholo-
environmental fac-
Thus, the frequency of ventrally
form
positioning
distinguish molts from similarly orient-
ed actual animals.
such
the
on
or
a
laterally
pre-
straightforward
observation of
body
misleading. This is certainly rel-
interpreting
Schram,
the
1979c:
Bear Gulch
fig.
16a, for
an
unusual
substantially
vation
recently,
the excellent
was
preservation
more
preservation
diagenesis
direct control
of the
largely the
re-
of
on
poten-
organic
preserva-
indirectly by facilitating the formation of
that the
salinity levels
at the
three
major Carbonif-
near-shore marine communities (Bear Gulch,
erous
Glencartholm and Essex fauna of the Mazon
suggests
factor
&
a
role
tures
for
lowered
salinity
a
an
abiotic
1989).
number of instances apparent structural fea-
on
the fossils
fossils,
UM 6217
interpreted
probably represent
to
B.
(PI. IV-2) and
masked
beargulchen-
P 32092
show cuticular structures that
as
lateral and
specimen, and they
(PI.
V-
might
dorsomedian carinae.
However, their relative position
men
as
facilitating exceptional preservation (Briggs
Clarkson,
In
Creek)
lower than normal marine levels
probably
were
4) apparently
considered
a
enhance
Mineral
diagenetic mineral precipitates. In addition, the fact
be
Bear Gulch fossils
gen-
tion. Anoxic conditions may then enhance
preser-
sis
Until
a
1988b). These studies reveal that anoxic conditions
taphonomic artefacts. Among the
Taphonomic considerations
as
preservation-promoting factor (Allison, 1988a;
do not
hoplocarids
lateral preservation of Perimecturus parki).
(Wil-
taphonomy, how-
less direct role for anoxia
material exerts
effect
studies of
Recent
articulation
an
posterior abdomen and
oxygen levels at the sediment-water interface
tial of soft tissue.
have
of abdominal ornaments
of
high sedimentation rates combined with low
(Mikulic, 1990; Schram, 1979c: fig. 16a). Such discan
dorsal view
5892, dorsal view
the distal part of the uropodal exopod.
indistinguishable
céphalothorax
fauna
carinae
especially if they remain articulated.
decapod
matopods
and
177
1998
-
parki (Peach, 1882) from
submedian carinae (arrows)
tailfan,
ka,
Zoology, 67 (3)
can
varies from
speci-
be inconsistent in
R.A.
178
form
even
on
a
omere
lateral
that
tergites
Similarly
looking
positions
distributed
over
P 32092 for
single specimen.
ample, shows median ridges
not
are
on
well but
the
the first
three
et
al.
they
in
present
are
more
inconsistently
are
-
Fossil
tergites.
the
Traditionally,
ex-
ple-
in line with each other.
structures
as
Jenner
pods
pods
of
of
racopods
thoracopod
on
and
structure
suggested
more
lack
bly
function
above.
We
what does the structure of the
might ask,
terior subchelate
an-
of archaeostomato-
thoracopods
and
second
are
akin to those
of
thoracopods
cludes
a
tively
short
seen
on
thoracopodal segments
the third to fifth
unipeltatan stomatopods.
relatively
long
pairs of
slender basis and
ischiomerus
and
(merus)
in-
This
rela-
a
carpus
so
thoracopod
subchelate limbs.
further
requires
is not
unipeltatans
but it may
spondence,
relative
parison
strict
a
to the
for
point
warrant
point
corre-
functional
a
second
specialized
com-
pair of
thoracopods present in unipeltatans.
The
unipeltatan second pair of thoracopods
in both
extremely specialized
The whole limb is
connects to
formed
may
or
large
by
a
short
carpus.
not possess
may
teristic of these
through
the
A
ever, based
the structure of the
on
rapid
prey
The
capture
specialized
strike charac-
stomatopods (Burrows,
articulating
are
1969). The
connected
by
are
conforma-
tion of the muscles and associated exoskeletal
a
spe-
accommodated in
large ischiomerus. The specialized
is termed
a
joint. This joint is operated
set of muscles that
parts
click-joint mechanism.This mechanism
allows the build up of tension in the muscles and
released when the mechanism is
suddenly
locked. As
a
result
forward. This
reported
limbs
are
ture and
for
the carpus and subchela
un-
swing
organization and the associated abil-
ity for ballistic
movement of the
thoracopods three
employed
tearing
in
thoracopods, that
the
possibly
palaeosto-
well, could have functioned
tunistic scavengers,
in
specialized
dead food, while the later
the
unipeltatans
cialized
for the
active
ballistic
second
thoracopods.
Phylogenetic
capture
of
as
oppor-
handling of
became spe-
using their
prey
to
manipulating
it apart (Kunze,
analysis
Schram (1986)
sis
subchela is
five.
not
The latter
food after cap-
1981).
of all
solved
performed the first cladistic analy-
the crustacean
some
of the
higher
classical
analysis,
ly
method of
evolutionary
fossil and
to cover
history of
proved
as
much
extant
as
for
a
taxa
effort
more
“subjective”
In his
systematics.
were
treated
equal-
Inclusion of fossil
and
proper
standing of the phylogenetic
Schram & Hof
His
possible of the evolutionary
crustaceans.
to be vital
taxa.
problems inherent in the less
rigorously defined and therefore
(in press)
complete
forms
under-
history of the group.
have
essentially built
that initial effort and achieved much the
same
on
re-
sults.
It is
tendons before the actual strike. The stored energy
is
as
and
how-
developed and
large subchela is
spines.
ischiomerus and the carpus
a
well
unipeltatan second thoracopods fa-
cilitates the very
be pur-
form and function.
large propodus and dactylus, which
a
anatomy of the
cialized
is
matter that
a
cannot
are
relative to the other tho-
The ischiomerus
racopods.
enlargement of the
that
investigation
matopods
in
unipelta-
sued here. We could then venture to suggest,
pods of tyrannophontids
to five
more
the reduction of the other
Obviously this is
archaeostomatopods,
pair three
outlined
as
clearly
are
ar-
proba-
unipeltatans then may
much the
as
(Kunze, 1981). The similarity between the thoracoand
The limbs of
fifth of the
through
The evolution of the
not have involved
of the
the situation
mechanism
click-joint
pods reveal about their function? The relationship
comparisons
palaeostomatopods
Nevertheless, these limbs
and the
proportions
Such
than that.
complex
the
palaeostomato-
through fifth tho-
function. However,
robust than the third
tans.
and
third
unipeltatans.
similar
chaeostomatopods
Notes
to the
compared
are
seems
battery of subchelate thoraco-
archaeostomatopods
in any
particularly important
analysis
the three
order
of
hoplocarid relationships. Two of
currently recognized orders and the sub-
Archaeostomatopodea
Paleozoic.
In
are
as
also extinct and
peltatan
are
exclusively
addition, phylogenetically
unipeltatan forms such
da
to include fossil forms
stomatopods
Sculda and Pseudoscul-
new
are
Late
important
fossil
species of uni-
continuously
being de-
Contributions
Table
Zoology,
to
III. Data matrix of the
67
(3)
1998
-
179
of Fig. 7.
phylogenetic analysis
See
for annotated
appendix
list
of characters.
1
i
1
1
1
i
1
1111111
1
2
3
12345678901
4
5
6
7
8
9
0
i
23
2
3
4
5
6
euphausian
euphausian
7
0
0
0
00007003000
0
0
0
0
0
0
3
00
0
0
0
11
2
K.
richardsoni
7
0
0
0
0
0
00007003000
0
3
0
0
0
00
0
0
7
7
I1
2
A.
vermiformis
7
1
0
0
1
0
1
0
0
10010100070
0
0
00
0
0
7
7
1
1
7
B.
B.
elegans
0
0
00010100001
0
1
0
1
0
0
0
0
1
011
0
7
0
0
B.
beargulchensis
0
0
0
1
0
0
7
00010000071
0
0
0
1
7
0?
0
7
7
0
0
0
0
rapax
rapax
0
7
7
7
7
7
000177772?
0
0
1
2
11i
1
i1
0
0
0
P.
P.
parki
0
0
0
7
00010000071
1
0
0
0
0
0
1
11i
1
i1
0
0
G.
peleron
2
0
0
1
0
2
20010201010
0
i
0
i
0
00
0
0
7
7
0
11
T. theridion
7
2
0
0
1
0
2
0
0
20010200170
1
0
00
0
0
7
7
0
0
11
T.
2
0
0
1
0
2
0
0
1
i
20010200110
0
10
1
0
i1
0
0
1
7
2
1
1
1
7
7
21111707071
1
0
0
1
10
1
0
i1
0
0
2
10
1
0
i1
I
2
1
i1
0/1
0/1
2
P.
acanthocercus
Ps.
Ps. laevis
laevis
S.
7
2
1
1
1
21117
pennata
unipeltatans
unipeltatans
scribed
from
taxa
(e.g.,
1
Hof &
see
significantly
1
Schram,
contributing
available for
tribute
netic
2
2
7
7
111
1
in
1/3
press). Apart
to the
numbers of
study, the fossil forms also
data to any
unique morphological
con-
focused
a
on
cladistic
phyloge-
analysis that specifi-
the Paleozoic
characters in 13 taxa
(Table III)
Some
were
treated
groups.
were
analysed
states
were
appendix. Our analysis yielded three
trees with
a
length of
RI of 0.865 and
a
shows the strict
character state
a
RC
31
changes plotted
as
exclusion
Cl
Fig.
7
unambiguous
the branch-
along
palaeo- and archaeostomatopods.
described
with
two
species
were
exceptions.
chaeocaris
graffhami
The
is
of the
Therefore all
included
in
the
analysis
palaeostomatopod
known
only
Ar-
from
four
the preservation of which allowed
only
partial reconstruction of the thoracopods
and
specimens,
the tail fan
(Schram, 1979a). Consequently,
imately 60 percent of the characters
“unknown” for this
species.
we
were
Inclusion of taxa with'
high proportion of missing characters
obfuscation of
approx-
scored
can
lead to
phylogenetic signal present in
a
of
some
most-
1995). However,
analysis
an
relationships
contribute
not
the
also result
can
remaining
taxa.
rules for “safe taxonomic
unique character combinations to the
data
safely be excluded from
can
analysis because they do
not
contribute
information to the reconstruction
relationships.
A.
Following
graffhami
cladistic
unique
phylogenetic
these rules,
the
was
of
we
decided
The
archaeostomatopod
of
equivalent
vermiformis and could therefore be safely
ex-
Tyrannophontes
fraiponti similarly is only incompletely known and
does not contribute essential
the
analysis. Finally,
malacostraca)
five
relationships
(Wilkinson,
trees
of taxa from
altered
cluded.
most-
a
0
by increasing the number of equally
parsimonious
that A.
given
steps,
of 0.725.
tree with
consensus
We wanted to elucidate the
a
matrix
0/2
0/2
0
the
es.
the
0/3
All
anno-
tated list of characters and character states is
of 0.839,
000
0
0
0
2
data matrix. Such taxa
treated
polymorphisms employing ACCTRAN. The
parsimonious
?
0/1
0/1
us-
unordered and equally
as
weighted. Multiple character
in the
7
reduction” that allow the detection of taxa that do
16
ing PAUP with the Branch-and-Bound option.
characters
7
Wilkinson devised
We undertook
cally
7
in
analysis.
1
1
7
was
superfamilies
a
data
phylogenetic
to
generalized euphausian (Eu-
used
of
as
an
out-group
and
the
stomatopods
extant
are
lumped under “unipeltatans” in the analysis. Finally, Kallidecthes richardsoni
it
is
one
of the
most
was
included because
completely
described
ae-
schronectids.
The basic
topology of the strict
resembles that of Schram’s
hoplocarid relationships (Schram,
The first
tree
analysis
1986:
of
fig. 43-4).
split is between the rapacious forms with
subchelate
late
consensus
order-level
thoracopods
thoracopods.
The
forms is characterized
and the forms
large
clade of
with ache-
rapacious
by the possession of
matized thorax with subchelate
thoracopods
a
tag-
on
the
180
Fig.
R.A. Jenner
7.
Strict
consensus
tree
with
13
taxa
Uniquely derived characters uniting two
a
particular
character
anterior tagma.
vermiformis
This
not known
The next
A.
one
size of the lateral
parent
situation
seen
of
a
in
A.
forms.
rapacious
it
from
of which is
carapace
a
unambig-
wings and
tyrannophontids.
dorsal telson
a
se-
the other
the roundness of the carapace unite it with the
absence
Fossil
are
state
changes
are
plotted along the
underlined. Asterisks indicate
that
the
branches.
character
state for
depicted clade members.
aeostomatopods, but the lobate uropod rami
ble the
-
(synapomorphies)
Palaeostomatopoda
that separate
al.
characters. Unambiguous character
taxa
vermiformis contains
palaeostomatopods, only
The
all
16
dichotomy separates
the order
taxon.
of characters
uous.
in
from the rest of the
would make
paraphyletic
ries
is
and
or more
et
ridge
pal-
resem-
The
sets
ap-
A.
vermiformis apart from the other palaeostomatopods and tyrannophontids.
Among the other rapacious
three terminal clades emerge:
dops-clade (P-B clade),
tyrannophontid
clade
(U clade). The
possession
like
clade
Blade-like
the fossil
a
our
analysis
archaeostomatopod
(T clade),
and
a
or
unipeltatan
supported by the
uropodal endopods, blade-
large median telson spike.
uropodal exopods
unipeltatan
in
Perimecturus-Bair-
P-B clade is
of reduced
exopods, and
an
taxa
a
are
also
Pseudosculda,
present
but the
on
com-
Contributions
to
67
Zoology,
(3)
1998
-
bination ofblade-like exopods with
uropodal
bers
endopods
of the P-B
greatly reduced
characterizes
uniquely
clade. B.
181
elegans
mem-
off
splits
endopod although,
served
the
as
Because
sister taxon to the other members of the P-B clade
speaking
with its
in
di. The
perimecturids
session of armed
able
of
possession
distinguished by the
are
spines). Although the complex and
included
united
are
anteroposteriorly
thoracopodal propodi and
spike. The singular
son
shared
The
by
least G.
at
to be addressed
tation
pleopods in
small
to a
on
larger proximal segment.
that
ever,
fine the
the very least
at
and
It
laterally
is
or
sep-
Tyrannophon-
hinge
can
on
three
seg-
attached to
are
more
clearly de-
thusly:
seventh
carapace
thoracomere
thoracomere;
ly tagmatized into anterior (thoracomeres
and
tagma;
the
ma
a
relative size ratio of the first
eighth
thoracomere of
with four
thoracopods;
biramous
to
maximally
a
a
to
ramus
and
subrectangular
fourth the
not
on
the
T.
telson.
appear
Uropodal
theridion, and
longation. Uropodal
with setose
slender
telson base
if present,
with dorsal posterior process, which is
on
a
length of the telson base.
spike. Telson carinae,
indicated
to
pleopods consisting of one
T. theridion does
median crest
pleomere
1.4; anterior tag-
moderately sized median spike of
one
At this time
1.1
lobate inner
annulate outer ramus;
such
to
pairs of subequal, armed, subchelate
well-sclerotized
tapering
one
posterior (thoracomeres six through eight)
rami
a
to
exhibit
define
a
protopods
only faintly
The data
the
out
pair of
a
margins of exopod (median part) and
an
dorsoventrally flattened
divided in three fields
possess
are
members possess
by
very
gas-
group
enlarged tho-
contains
set
enough information to
of the
relationships
larger
groups
sort
(palaeo-
stomatopods, archaeostomatopods, aeschronectids,
unipeltatans
including Sculda and Pseudosculda),
provide enough resolurelationships
unipeltatans. This would require
trix
least
at
families
or
character
the level
on
It would
that
Our
our
a
with
clade,
true
clades.
or
super-
accommodate
taxonomic lev-
higher
however, that the palaeostomat-
separate
P-B
the
and Archaeocaris
analysis suggests, therefore,
of the
higher taxonomy of the
Hoplocarida needs revision.
of
to
ma-
grade of organization rather than
cladistic
concepts
visions
unipeltatan
genera,
on
within the
larger data
press).
appear,
opods delineate
a
a
of the
polymorphism
els (see Hof, in
We
see
in
Hoplocarida
two
Fig.
7:
major dithe
Ae-
schronectida, and the line of stem-group rapacious
forms
could
leading
to the
crown
call this
possibly
sensu
name.
Under this scheme,
a
Plesion
Purists
topodea
could then
sensu
stricto
(= Family
Archaeostomatopodea,
topoda and prefer
to
we
sense
and
create
recognize
Archaeocaris and three suborders:
might object
ditional
a
We
lato, broadening the definition of that
laeostomatopodea
turidae),
Unipeltata.
group
rapacious line the Stomat-
opoda
to
and
Pa-
Perimec-
Unipeltata.
to this redefinition of Stoma-
to
maintain that
name
in its tra-
link the suborders Archaeostoma-
Unipeltata.
new
“carnocarids”
name
that is
In that case,
for
a
we
would need
superordinal
the sister
clade of
group to the
Ae-
schronectida.
ventral basal pro-
broadly lobate, usually
character states
racopods.
families,
large flap-like scaphocerite; thoracomeres distinct-
five)
is
changes
support-
as
grooves. At least Pseudosculda and the
tric
Tyrannophontes
about the fifth
to
the sixth
to
peleron
would appear, how-
we
Archaeostomatopodea
extending dorsally
carapace, which
Its
reduced,
anteroposteriorly
regarded
some
U-clade.
tion for the elucidation of
segments that
two
the
T. theridion needs
larger proximal
ment, while the subchelae of the
a
pleopods
not ob-
are
trichotomy, strictly
a
be
can
but this data base does not
G. peleron
segments that attach
species hinge
pecti-
setae
character state
T. acanthocercus.
of G.
thoracopods
The subchelae of
tes.
form of the
it from members of the genus
arates
and
by additional studies. The segmen-
of the
pattern
by
small median tel-
a
for
“unipeltatans”
the posses-
spined
peleron and
form of the
exact
was
clade is
unambiguous
ing the clade. However,
reduced carapace. The
members of the T clade
possess
nate
perimectu-
ornament
the U
no
limited matrix
our
unique
explicitly in the analysis.
The T and the U clades
sion of an
body
pos-
mov-
very similar
of the
ornament
this clade,
species supports
not
propo-
uropodal exopods (probably
patterns of abdominal
rid
spined thoracopodal
such
again,
T. theridion.
on
We hesitate to do
As
this paper
anything formally
points
out, there
tions that need to be addressed
are
at
this time.
specific
ques-
concerning the
spe-
182
Fig.
R.A.
8.
sp.
uropodal protopod,
D
=
telson
dorsal
ornaments
Perimecturus
on
cies of the genus Perimecturus and the
elegans. For example,
known
a
species
of
at
palaeostomatopods
differences between
the
tened Perimecturus and the
cies of
would
Bairdops
In
status.
addition,
there
and
the Mazon Creek
uncertainties about
our
be restudied,
phies unite
Our
this
genus
also
of
T.
Finally,
now
a
in
species,
these
possible
of the
analysis
some
suggests
should
that apomor-
of anatomical structures be-
particular features of the
tail fan. The aeschronectids have very
decorated,
forms
uropodal
acquire
laeo- and
a
very
with
ventral
projection
peltatans
protopods.
distinct
a
small
dorsal
or
broad
retain the basic
elaborations.
Usually they
prolongation
or
have
un-
rapacious
organization. The
archaeostomatopods
topods
The
simple,
pa-
uropodal pro-
projection and
a
larger
prolongation. The uni-
arrangement
possess
a
forked process.
with
some
bifurcated ba-
to the
This
to
the
the
process
unipeltatans
such
possess
they
distal
are
on
Not all
uropodal exopod.
or-
the
present,
tip of the 1-segmented
Perimecturus and T.
holds true also
for
with
proximal segment (except
and
possess
spines
some
acan-
Sculda
unipeltatans
superfamily Bathysquilloidea,
2-
confined
members of
which have
uropodal exopods) (Fig. 8).
1-
However,
uropodal exopod spines of palaeostomatopods
and
as
numerals
possession of spines
segmented uropodal exopods
stomatopods
is
may have
independently evolved,
suggested by the cladogram.
The
palaeostomatopods
con-
Roman
of forked
uropodal exopod.
Pseudosculda. The other
segmented
phylogeny of the hoplocari-
tween different groups, in
unipeltatan stomatopod
prolongation
where
uropodal exopod (e.g.,
given the
intriguing possibilities
on
of the
However,
the
too
basal
spines
margin
theridion
knowledge of the details of
with the
the outer
thocercus).
con-
undertake
=
a
indicated.
Another consistent feature of all
prominent feature of the stem-group
cious taxa is
cerning homologies
sal
family
separate
B
(left),
are
since the Mesozoic is the
spines continue
other uncertainties
still
=
naments.
stricto.
sensu
dans
it is
since
S
spe-
faunas.
anatomy of Archaeocaris
unipeltatan.
cylindrical
collections
private
homologies
palaeo- and archaeostomatopods
superfi-
study of all the available material
museums
from
placed
even
in
and
median spike,
B.
species
are
=
acanthocercus
Possible
parki (right).
MS
the Bear Gulch Limestone
stomatopods from
dorsoventrally
more
be addressed. Someone should
careful
Fossil
archaeostomatopod
the anatomy of the British forms that must
cerning
-
flat-
warrant
are
the
four of the six
present
single family, Perimecturidae, but
cial
al.
uropodal protopod,
on
process
et
archaeostomatopod Tyrannophontes
(middle) and the palaeostomatopod
possible homologous
connote
on
of the
Schematic tailfan representations
Squitla
Jenner
a
telson bearing
a
terminal
rapa-
spike. This
spike is flanked in the palaeostomatopods by
of
gle pair
four
sets
of furca.
glance has
with
deed
a
a
a
very
posterior
and
is
unipeltatan telson
different form
no
four
at
by
first
from the above
median terminal
spike (in-
median excavation often
teeth: submedian,
It
The
broad width,
denticles),
eral.
sin-
a
furca, but in the archaeostomatopods
pairs of variously
bearing
developed
intermedian, lateral, and pre-lat-
tempting
to
see
possible homologies be-
tween the four sets of furca of
Tyrannophontes and
the four teeth of
The issue of
is
an
never
so
unipeltatans.
straightforward.
Unipeltatans
course
display
incredible amount of variation in the telson deco-
Contributions
to
61
Zoology,
(3)
1998
-
ration both within and between the
perfamilies. However,
be
to bear
brought
gies from
on
some
183
recognized
useful information
Acknowledgements
su-
can
We wish
this issue of tail fan homolo-
careful consideration of the
form, loca-
Teruzzi
to extend
tion, and orientation of carinal ornament among all
collection to
groups, fossil and recent,
the material.
well
as
as
documentation of the
anatomy
Sculda and
genera
What is
important
careful
analysis
genetic
context
of
elucidation and
of the
Pseudosculda (Hof,
to note in all
of characters in
can not
on
new
or
Without
a
us
hypotheses
lines of
Allison,
1988a.
P.A.,
Allison, P.A.,
1988b.
P.A.
&
concerns
the increased coherence of the clade that includes
palaeostomatopods
must be
in
the
future
Scotland.
some
more
the
concerning
Earth
Briggs,
G.P.
ion
from
peleron
observations
new
the Mazon Creek and
Briggs,
of
accurate
formulation
of
a
archaeostomatopods.
We present
a
beargulchensis
as
a
Bairdops
genuine palaeostomatopod.
to B.
E.N.K.
about the
generalize
group.
ently
aberrant
of
D.E.G. &
other, Archaeocaris has
possess
transition series
along
an
as
part
with
the crown-group
the
of
very
apparpa-
tyrannophontids,
stomato-
and
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thoracomeres
6-8
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Contributions
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185
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Carapace
0
67
Zoology,
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9
which
carapace
(thoracopod
the
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coxae
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from
Pleural
and
0
under-
1
carapace)
flattened
(dorsoventrally)
carapace
=
on
pleomeres
2
=
on
all
3
=
on
pleomere
Pleural
3
Carapace
fields
0
=
no
1
=
carapace
nal
fields
tripartitioned by gastric
Thorax
tagmata (defined by
1
=
segment
and/or
=
absent
anterior
tagma
terior
subchelate thoracopods and
with
larger segments
with
=
=
11
0
=
=
1
size
0
subchelate
(sub)equal
one
pair
=
=
2
thoracopods
=
Propodus
0
1
very
12
enlarged
second
spined margin
3
=
pectinate
and
13
spined
pectinate
Pectinate
refers
to
short
interspaces)
refers to the
the
Dactylus
0
=
1
=
and
relatively
blunt
spines, while spined
possession of slender, sharp spines
=
1
=
2
3
=
=
outer
ramus,
robust,
lobate
inner
ra-
form
lobate, 1-segmented
blade-like, 1-segmented
2-segmented
smooth
outer
armed outer
margin
margin (spines, serration)
Uropod, endopod form
0
=
1
=
that
may
14
be
second
0
thoracopod
15
smooth
=
=
a
pointed tip
smooth
dorsal
Telson
0
=
and
crest
or
ventral protrusions
or
processes
present
ridge
longitudinal dorsal median
crest
or
ridge present
on
telson
spined
subchela
lobate
simple,
reduced with
form
Uropod, protopod
1
Conformation
0
=
=
1
8
rami
slender
possession of closely apposed (no
movable.
7
annulate,
margin
smooth
=
=
abdomi-
Uropod, exopod decoration
1
thoracopod
=
2
postero-
thoracopods
0
6
or
of the
form
simple flap-like
Uropod, exopod
1
Relative
margins
pos-
non-subchelate
appendages
5
the ventral
mus
of
tagma
sharp protrusions, posteriorly
from
directed
pleurae.
Pleopod
0
appendage
1
tagmata
6
are
grooves
differentiation)
0
3-6
pleomeres
spines
ventrally
JO
4
spines
absent
=
second
=
absent
thoracopod
hinged
on
2
segments
subchela hinged
on
3
segments
subchela
hinged
on
1
achelate
thoracopods
segment
16
Median telson
0
=
1
=
2
=
spike
spike
a third
spike
a
absent
or more
fourth
or
less
the
length
telson
base
the
length of the telson
of the
base
the

and archaeostomatopods (Hoplocarida, Crustacea)

Transcription

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