mexico, between 19º–23ºn - Instituto de Geología

45
Carranza-Castañeda, Óscar, 2006, Late Tertiary fossil localities in central Mexico, between
19°–23°N, in Carranza-Castañeda, Óscar, and Lindsay, E.H., eds., Advances in late Tertiary
vertebrate paleontology in Mexico and the Great American Biotic Interchange: Universidad
Nacional Autónoma de México, Instituto de Geología and Centro de Geociencias, Publicación
Especial 4, p. 45–60.
Late Tertiary fossil localities in central Mexico, between 19º–23ºN
Óscar Carranza-Castañeda*
ABSTRACT
Only 35 years ago, the continental late Tertiary biostratigraphy of Mexico was almost
unknown. Most of the information regarding previous reports came from the Yepómera
fauna, located in northwest Chihuahua. From central Mexico, the only known faunas were
Tehuichila in the State of Hidalgo, Rancho La Goleta in the State of Michoacán and Rancho
El Ocote in the State of Guanajuato, with the inconvenience that these faunas were referred
only to the Pliocene age. Recent studies in the sedimentary basins of central Mexico
(between latitudes 19°N and 23°N) have shown a wealth of diversity and abundance of
Cenozoic vertebrates that represent the Hemphillian and the Blancan mammalian ages.
Besides, our results have yielded relevant new information, revealing central Mexico as an
important area for mammalian migrations during the Blancan.
Key words: stratigraphy, paleontology, mammals, fossils, basins, Hemphillian, Blancan,
Mexico.
RESUMEN
La estratigrafía continental del Terciario tardío de México, hasta los años setenta del
siglo pasado, estuvo basada en la información de la fauna de Yepómera en el noroeste
de Chihuahua. En el centro de México, la información sobre la estratigrafía y contenido
fósil de las cuencas, fue escasa y se basó sólo en la información disponible de las faunas
de Tehuichila en el estado de Hidalgo, la fauna de La Goleta en el estado de Michoacán y
la fauna de Rancho El Ocote, en el estado de Guanajuato, todas referidas al Plioceno. Los
trabajos recientes efectuados en las cuencas sedimentarias del centro de México, entre los
paralelos 23° y 19°N, han demostrado la diversidad y abundancia de vertebrados fósiles,
que están representando dos edades de Mamíferos, Henfiliano y Blancano, además de
proporcionar información acerca de las migraciones de faunas hacia el centro de México,
durante el Blancano.
Palabras clave: estratigrafía, paleontología, mamíferos, fósiles, cuencas, Hemphilliano,
Blancano, México.
INTRODUCTION
The continental late Tertiary stratigraphy of Mexico for
many years was based mainly on the published papers
of the Yepómera fauna, northwestern Chihuahua. The
*Centro de Geociencias, Campus Juriquilla, Universidad Nacional Autónoma de
México, Querétaro, Mexico.
E-mail address: [email protected]
late Tertiary stratigraphy of central Mexico was poorly
known until the second half of the past century; it was
biased, incomplete and based on isolated fossil findings
without any stratigraphic control, which did not allow
to make any correlations between the Mexican faunas.
The results of the investigations carried out in
the sedimentary basins of central Mexico, between 19º
and 23º N, have shown that in these basins there is a
large fossil diversity that will contribute to a better un-
Carranza-Castañeda, Óscar, and Lindsay, E.H. eds., Advances in late Tertiary vertebrate paleontology in Mexico
2006
Carranza-Castañeda
46
derstanding of migrations and the evolution of diverse
taxonomic groups. Besides, the fossil material has been
important to establish the age of the basins, which for
many years were considered filled only by Quaternary
alluvium in the geologic maps, and that their origin and
sedimentation were the result of a single geologic event.
The purpose of this paper is to communicate the recent
advances in the knowledge of the better studied basins
from the Transmexican Volcanic Belt and the latest fossil discoveries of their faunal content. In the second half
of the last century, the Instituto de Geología, UNAM,
started the study of the main basin in central Mexico,
and now is sponsored by the Centro de Geociencias,
UNAM, Campus Juriquilla, Querétaro.
Abbreviations
COLO
GTO
HGO
HUAN
JAL
JUCH
MICH
NAY
QRO
TEO
TECO
ZAC
Colotlán
Guanajuato
Hidalgo
Huanusco
Jalisco
Juchipila
Michoacán
Nayarit
Querétaro
Teocaltiche
Tecolotlán
Zacatecas
GUANAJUATO STATE
San Miguel de Allende Basin
Previous works. The first mention of the San Miguel de
Allende area was made by Arellano (1951), who talked
about the Rancho El Ocote horses and some glyptodont
scutes from Rancho Viejo. Later, Mooser (1958, 1959,
1963, 1964, 1973) and Dalquest and Mooser (1980) describe the fauna of Rancho El Ocote. They suggest the
fauna corresponds only to one age, late Hemphillian,
and that is younger than the Yepómera fauna.
The results of the research done in this basin have
demonstrated the importance of it. For better under-
standing, in this paper the study area has been separated in the most complete stratigraphic sequences.
Rancho El Ocote Area
The field work carried out at Rancho El Ocote allowed
to establish that in this locality two stratigraphic levels
occur, each with a different lithology and faunal content. In addition, an unconformity is present, which
separates the strata that bear the early Blancan fauna.
The results of the taphonomic analysis made in
the GTO 2B locality showed that only in the basal
layer, named Rhino Level (because it is the only layer
where it is possible to find rhinoceros material), the
genera Nannippus minor (=Nannippus aztecus), and
Neohipparion are abundant, and Teleoceras, Osteoborus,
Agriotherium, Machairodus, and Megalonyx are present. A late Hemphillian age was determined for this
layer.
In the overlying bed, named White Layer because
of its lithology of fine grained sand with volcanic ash, the
equids Dinohippus mexicanus and Astrohippus stockii
are abundant, also a fibular fragment of Glossotherium
was recovered in the top of the section. Based on the
equid species, the age of this layer was determined as
latest Hemphillian.
The volcanic ash lenses present in this sequence
were dated by the fission-track method, giving an age of
4.8 ± 0.2 Ma, which corroborates the late Hemphillian age
based on the fauna described in previous papers (Table
1) (Carranza-Castañeda and Ferrusquía-Villafranca,
1978, 1979; Miller and Carranza-Castañeda, 1984;
Carranza-Castañeda, 1989; Carranza-Castañeda and
Walton, 1992; Carranza-Castañeda and Miller, 1996;
Miller and Carranza-Castañeda, 1996; MacFadden and
Carranza-Castañeda, 2002; Flynn et al., 2005).
Los Corrales stratigraphic sequence is at the top
of this section in erosional discordance. In it molariforms of Nannippus peninsulatus and molars of Equus
simplicidens were found. One complete osteoderm and
fragments of other assigned to the pampathere Plaina
have been recovered. Radiometric dating of the volcanic ashes of this layer gave an age of 4.70 ± 0.07
by 40Ar/39Ar, and 4.6 ± 0.3 by the fission-track method
(Kowallis et al., 1998) (Figure 1).
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Late Tertiary fossil localities in central Mexico, between 19°–23°N
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Table 1. Faunal list for Hemphillian and Blancan mammalian taxa from central Mexico.
Carranza-Castañeda, Óscar, and Lindsay, E.H. eds., Advances in late Tertiary vertebrate paleontology in Mexico
2006
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Carranza-Castañeda
Table 1. Faunal list for Hemphillian and Blancan mammalian taxa from central Mexico (continued).
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Figura 1. Stratigraphic sequence of the Rancho El Ocote area.
Late Tertiary fossil localities in central Mexico, between 19°–23°N
Carranza-Castañeda, Óscar, and Lindsay, E.H. eds., Advances in late Tertiary vertebrate paleontology in Mexico
2006
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50
It is important to point out that the HemphillianBlancan boundaries in these localities are more reduced
than in any other research area. Also, in the upper part
of this layer, a Pleistocene sandy clay, brown in color,
covers all the section (Figure 2).
Locality GTO 2 Rancho El Ocote
Locality GTO 2B Type section
21°05.28’N, 100°41.01’W
Blanco layer Rhino layer Pleistocene
latest H
late H
vore diversity of the Mexican Hemphillian localities
(Carranza-Castañeda, 1992; Carranza-Castañeda and
Miller, 1996; Miller and Carranza-Castañeda, 1996),
also the badger Taxidea was collected recently. The
horses are abundant, mainly Dinohippus mexicanus,
Astrohippus stockii and Neohipparion eurystyle. The
radiometric date gave a Hemphillian age (Kowallis et
al., 1998).
Locality GTO 43 Rinconada 21°03.44’N, 100°47.81’W
H
Los Galvanes Area
The stratigraphic sequences of the localities from GTO
12 La Pantera are in erosional discordance. Here, abundant material of Nannippus peninsulatus has been recovered, a skull fragment and isolated molars of Equus
simplicidens as well as undescribed remains of rodents,
amphibians and reptiles. The two ash layers present were
dated by fission-tracks, giving an age of 3.9 ± 0.3 Ma.
At the base of this sequence is the Rinconada fauna
(locality GTO 43), which bears the largest carni-
Locality GTO 12 La Pantera A and B
21°03.78’N, 100°46.13’W
Locality GTO 2 Los Corrales
early Blancan
Locality GTO 83 (GTO 2D Plaina)
21°05.26’N, 100°41.30’W
early Blancan
Figure 2. Stratigraphic sequence of the Los Galvanes area.
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Late Tertiary fossil localities in central Mexico, between 19°–23°N
The localities from GTO 4 Arroyo El Tanque correlate
with GTO 12. On different places of El Tanque, abundant fossils of Blancan age have been recovered, such
as birds and reptiles, skeletal elements of Hemiauchenia
blancoensis and Platygonus, molars and mandibles
of Nannippus peninsulatus and Rhynchotherium,
Neochoerus cordobai molars and Glossotherium material (Montellano-Ballesteros and Carranza-Castañeda,
1986); the last two represent the first records of South
American immigrants integrated with the Holartic faunas (Flynn et al., 2005).
Locality GTO 4 Arroyo El Tanque
21°04.03’N, 100°46.12’W
The basal bed of locality GTO 47 Arroyo Belén corresponds to the same stratigraphic level of GTO 4.
Glyptotherium, Neochoerus elements and the most significant remains of a pampathere tentatively referred to
Plaina have been recovered in this locality. They represent the oldest records of South American immigrants
in North America; the bearing bed has an age of 3.6 ±
0.04 Ma. This sequence is covered by sandy clay with
Equus sp. molars and remains of the rodent Thomomys
sp. (Figure 2).
Locality GTO 47 Arroyo Belén 21°04.69’N, 100°46.41’W
early Blancan
Rancho Viejo Area
In the base of this sequence is locality GTO 44 La
Presa, where molars of Calippus (Grammohippus)
castilli and diverse elements of Dinohippus interpolatus have been collected. The locality was assigned
to the earliest late Hemphillian (Carranza-Castañeda
and Espinosa-Arrubarrena, 1994). Other localities
of the same age where these species were recorded
are GTO 50 La Cancha EW and GTO 69 Arroyo
Sorpresa.
Locality GTO 44 La Presa
21°00.86’N, 100°47.19’W
earliest late H
Locality GTO 50 La Cancha EW
earliest late H
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In the Comonfort area, distant just 35 km, in the La
Nopalera locality (Ranchería de Neutla), similar molars to those of Calippus have been recovered.
In Rancho Viejo are the localities of GTO 42
Rancho San Martín, where besides Astrohippus stockii
and Dinohippus mexicanus molars, a skull, a mandible and different skeletal elements of Canis ferox
were collected. This fauna correlates with the one of
Arroyo Tepalcates (GTO 52), which bears abundant
material of Astrohippus stockii, Dinohippus mexicanus,
Machairodus cf. M. coloradensis, Desmathyus brachidontus and Megatylopus matthewi. The age of these
localities is late Hemphillian.
Locality GTO 42 Rancho San Martín 21°01.36’N, 100°46.00’W
late H
Locality GTO 52 Arroyo Tepalcates 21°01.25’N, 100°45.46’W
late H
The early Blancan locality GTO 11 Garbani is just 800
m to the north of GTO 42; here an age of 4.1 ± 0.5 Ma
was estimated by a dated volcanic ash (Kowallis et al.,
1998). In this locality Nannippus peninsulatus, Equus
simplicidens molariforms and undescribed rodent and
bird material are abundant.
Locality GTO 11 Garbani 21°01.12´N, 100°45.46’W
early Blancan
Three kilometers to the southeast, the localities GTO 5
Miller Place, GTO 33 Pork Chop and GTO 14 Cuesta
Blanca are located, where the largest amount of the
capybara Neochoerus cordobai and some elements of
Glossotherium have been collected.
Locality GTO 14 Cuesta Blanca 21°01.26’N, 100°45.24’W
early Blancan
Locality GTO 6 Arrastracaballos is towards the south
of this sequence, which bears the largest Blancan faunal diversity of the San Miguel de Allende basin. The
best collected material are the horses Equus simplicidens and Nannippus peninsulatus, the carnivores
Borophagus diversidens, Felis studeri, Pliotaxidea
Carranza-Castañeda, Óscar, and Lindsay, E.H. eds., Advances in late Tertiary vertebrate paleontology in Mexico
2006
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Carranza-Castañeda
sp., Trigonictis sp., and Canis cf. C. lepophagus, the
artiodactyls Hexobelomeryx fricki, Hemiauchenia
blancoensis, and Platygonus sp. Besides, undescribed
rodent material, as well as the lagomorph Hypolagus
vetus come from this locality.
Locality GTO 6 Arrastracaballoslate H – early Blancan
21°00.92’N, 100°45.31’W
It is important to point out that the Pleistocene localities where isolated teeth and a partial skull of Equus
material have been collected are only 400 m north of
this locality (Figure 3).
Coecillos Area (20º59.93’N, 100º46.06’W)
Locality GTO 69 Arroyo Sorpresa is situated at
the base of the same sequence, and is of early late
Hemphillian age. Its fauna is represented by the most
complete palate of Dinohippus interpolatus, with both
P2-M3 series, and a maxillary fragment of a gomphothere.
Figure 3. Stratigraphic sequence of the Rancho Viejo area.
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Late Tertiary fossil localities in central Mexico, between 19°–23°N
Above these stratigraphic sequences there are different sites within the Coecillos area where abundant
material has been collected of Dinohippus mexicanus,
Astrohippus stockii, Neohipparion eurystyle, Nannippus
minor (=N. aztecus), Teleoceras, a Machairodus incisor, numerous rodent remains, specially few skulls and
jaws of Paenemarmota, the lagomorphs Notolagus
velox, Hypolagus and the artiodactyls Hemiauchenia,
Texoceros, Hexobelomeryx, Megatylopus and
Desmathyus. All these collecting sites were named locality GTO 30 Coecillos.
Recent work in the ravine named GTO 75 Arroyo
de Emilio (20º59.97N and 100º45.88’W), where a
diversity of fossils was found, made this locality important. Here were collected a Dinohippus mexicanus
skull fragment and mandibles, a complete and articulated skeleton of the peccary Desmathyus. Some jaws,
a partial skull, an almost complete skeleton, mandibles,
skull and other elements of Paenemarmota, a new indeterminate mustelid, and the badger cf. Taxidea and
the first record of the possible skunk Conepatus, a
Hemiauchenia mandible and another jaw of a probable
Texoceros. Undoubtedly, all the material corresponds
to the Hemphillian.
Pleistocene sediments, in erosional discordance,
are in the same ravine. In them, an Equus mandible associated with a more or less complete Glyptotherium
cf. G. floridanus carapace, including the mandible of
the same individual, were collected. In the same area,
the locality GTO 36 Palma Sola has a similar stratigraphy; Astrohippus molars have been collected in the
basal Hemphillian sediments, and molars of Equus sp.
in the Pleistocene ones.
Recently, Blancan fossils were recovered in the
locality GTO 79 La Perdida, consisting of isolated
molars of Nannippus peninsulatus. This shows that in
the Coecillos area there is a complete stratigraphic sequence from early late Hemphillian, late Hemphillian,
Blancan to Pleistocene.
Discussion
The most complete stratigraphic sequences known at
present in Mexico and probably in North America occur in the San Miguel de Allende basin. Of the four
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sections, the most complete is the one from Rancho
Viejo area, with representative faunas of the early
late Hemphillian, late Hemphillian, early Blancan and
Pleistocene. The age of these localities has been confirmed by radiometric dates of volcanic ashes intercalated with the bearing beds.
In all four stratigraphic sections there is evidence of South American immigrants. Without doubt,
they represent the first fossil evidences that during the
Hemphillian-Blancan boundary the Panamian land
bridge had an efficient terrestrial corridor, through
which the American faunal interchange began (Miller
and Carranza-Castañeda, 1999; Carranza-Castañeda
and Miller, 2004).
HIDALGO STATE
Zacualtipán Basin
Accidental fossil findings made by coal miners during
their work in the Zacualtipán mines, exploited during
the second half of the xix century, are among the first
descriptions of fossil material of the Mexican Miocene.
This fossil material without stratigraphic control (Leidy,
1882; Cope, 1885, 1886) is known as the Tehuichila
fauna. In the first descriptions, the age was assigned
to the Miocene. Ferrusquía-Villafranca (1978), in the
revision of the Miocene faunas, established their age
as Pliocene.
During the research carried out in the 1990’s,
sponsored by the Universidad Autónoma del Estado
de Hidalgo, a new locality, HGO 2 Potrero de Zietla,
20º36.40’N, 98°36.25’W, was discovered. The fauna
consists of Dinohippus interpolatus and Calippus
(Grammohippus) castilli upper molars, molar fragments
of Agriotherium and Teleoceras?, a Hexobelomeryx
molar and calcaneum and molar fragments of cf.
Prosthennops. This fauna correlates with the one from
the San Miguel de Allende basin, GTO 44 La Presa,
assigned to the early late Hemphillian (CarranzaCastañeda and Espinosa-Arrubarrena, 1994).
The revision of the equid fauna from Tehuichila
(MacFadden, 1984; Carranza-Castañeda and EspinosaArrubarrena, op. cit.) showed that in this basin two
mammal ages exist: late Hemphillian (late Miocene),
Carranza-Castañeda, Óscar, and Lindsay, E.H. eds., Advances in late Tertiary vertebrate paleontology in Mexico
2006
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Carranza-Castañeda
represented by the fauna of Potrero de Zietla, and early
Blancan (early Pliocene), by the presence of Nannippus
peninsulatus.
Actopan-Ixmiquilpan Basin
This is one of the largest ancient paleolakes in central Mexico. The fluvio-lacustrine sediments extend
by thousands of square kilometers, and the thickness
in some areas is more than 100 m, covered by early
Pleistocene volcaniclastic sediments.
At several sites in the surrounding of the
Lagunillas village, unidentified mammalian fossil fragments have been collected. In the locality HGO 7 La
Suerte, 10º51.35’N and 99º01.36’W, a lower molar
fragment of Rhynchotherium and molar fragments of
unidentified equids were recovered.
In the ravine Bodandha of the Ixmiquilpan region (20°24.22’N, 99°14.56’W), just 2 km south of the
ranchería de Xothi, the locality HGO 27 Las Arcinas was
discovered. Its fauna consists of upper molar fragments
of Nannippus peninsulatus, Equus cf. simplicidens and
Platygonus, which are Blancan fossil indexes.
In the Santa María Amajac region, 20º18.27’N,
98º42.50’W, there is a sequence of clay, sandy clay and
gravel which bears fossils. The ash that is at the base
of this sequence was dated, giving an age of 4.2 ± 0.3
Ma by fission-tracks, and of 4.57 ± 0.02 Ma by 40Ar/
39
Ar, which indicates an early Blancan age. The collected fauna includes Equus simplicidens, Nannippus
peninsulatus and Rhynchotherium fragments. These
fossils reinforce the early Blancan age assignment. In
the upper strata, a Tremarctus maxilla was recovered.
Sediments that bear fragments of the rhino Teleoceras,
a Hemphillian index fossil, are found to the west of
these localities. The sequence has just been preliminary
explored (Carranza-Castañeda and Miller, 1998).
Tepeji del Río-Tula Basin
The Tepeji del Río area, in the southwestern region of
the Hidalgo State, is where the lacustrine sequence is
best exposed, with a thickness of more than 100 m in
some sites. This sequence is covered by volcaniclastic
sediments of the locality HGO 20 Tacos y Tortas, where
Equus sp. upper molars were collected. The presence
of this genus indicates a Pleistocene age.
In the Tula area, locality HGO 24 El Bagre, fish
remains of the genera Ictiobus (Alvarado-Ortega and
Carranza-Castañeda, 2002a, 2002b; Alvarado-Ortega
et al., in press) and Ictalurus have been recovered in
Blancan age beds. Also, in surrounding sites there are
fish fossils that now are under study. Other important
localities are HGO 21 Los Fragmentos and HGO 22
Los Tepalcates, where Nannippus peninsulatus material, proboscidean fragments possibly of Rhynchotherium
and Platygonus molariforms have been recovered
(Figure 4).
Locality HGO 25 La Plegaria is southwest of Tepeji
del Río city. Its fauna is represented by Astrohippus
stocki, Neohipparion eurystyle, Dinohippus mexicanus, Machairodus cf. M. coloradensis, Canis ferox,
Megalonyx, Teleoceras fossiger, cf. Megatylopus matthewi, Hemiauchenia vera, Alforjas sp., Hexobelomeryx
fricki and cf. Texoceros sp., of late Hemphillian age.
It correlates with the faunas of Rinconada, Arroyo
Tepalcates and Rancho El Ocote, from Guanajuato
State (Padilla-Gutiérrez, 2004).
JALISCO STATE
Large sedimentary basins occur in this state. The updated results of the prospecting work are given according to the regions where these basins are located.
Tecolotlán Basin
During the last years an extensive investigation was
carried out in this area, located 100 km southwest of
Guadalajara city. The stratigraphy of the basin is composed of two sedimentary sequences; the lower was determined as late Hemphillian because of the associated
fauna and 40Ar/39Ar ash dating, which yielded an age
of 4.89 ± 0.016 Ma, and the upper, Buenaventura, assigned to the late Blancan also by its faunal content and
the ash dating that gave an age of 2.6 Ma.
The Hemphillian sequence consists of three sections. The lower, named JAL TECO 9 Santa María, is
composed of red oxidized clay and sandy clay, as well
as gravels that represent paleochannels. The abundance
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Late Tertiary fossil localities in central Mexico, between 19°–23°N
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Figure 4. Main basins in central Mexico.
of Nannippus minor (=N. aztecus) is notable; it exceeds
any locality from central Mexico, including the localities from Guanajuato. In contrast with other Mexican
Hemphillian localities, in this layer few specimens of
Astrohippus stockii have been collected. The sequence
is interrupted by lacustrine sediments that crop out in
almost all the southwestern part of the basin and cover
this sequence; they do not have fossil mammals, but in
the upper bed some crystallized gastropods have been
recorded.
Covering these lacustrine sediments, the upper
section consists of clay bed sequences named JAL
TECO 20 La Hacienda, JAL TECO 26 Kowallis, where
the ash gave an age of 4.89 ± 0.16 Ma by the 40Ar/39Ar
method. In this stratigraphic level, numerous micro vertebrate remains have been collected, such as rodents,
lagomorphs, amphibians, reptiles and birds, which have
not yet been described. It is interesting to point out that
Astrohippus stocki is very rare in this part of the section
and Nannippus minor has never been collected.
Unconformably, the sequence of gravel and finegrained sand, whose radiometric date gave an age of
2.6 Ma, allows to situate it in the late Blancan. From
this sequence, in the locality JAL TECO 7 Las Gravas,
equid molars were found with less progressive characters than those of Equus simplicidens, besides
Platygonus, Hemiauchenia blancoensis.
In JAL TECO 44 Las Placas and the most important locality JAL TECO 53 Lic. Preciado, proboscidean
tusks, horse teeth fragments and the noteworthy South
American immigrants Glyptotherium, Neochoerus
and pampathere remains of cf. Plaina have been recovered. It is important to note that all along the sequence there are fossils of crocodilian and turtle material, but no remains of Nannippus peninsulatus were
observed (Kowallis et al., 1998, 2003, in press; Miller
and Carranza-Castañeda, 1998a, 1998b, 1999, 2001a,
2001b; Carranza-Castañeda, 2002; Carranza-Castañeda
et al., 2002) (Figure 5). The known fauna is listed in
Table 1.
Carranza-Castañeda, Óscar, and Lindsay, E.H. eds., Advances in late Tertiary vertebrate paleontology in Mexico
2006
Carranza-Castañeda
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Figure 5. Composite stratigraphic sequence of the Tecolotlán Basin.
Colotlán-Tlaltenango Basin
The locality JAL COLO 17 Los Vélez is located eight kilometers south of Colotlán city. Here the Neohipparion
eurystyle, Astrohippus stockii and Desmathyus fossils have been collected; these taxa establish a late
Hemphillian age.
In the state border of Jalisco and Zacatecas, just
3 km south of Los Vélez locality, the locality ZAC 18
Santo Domingo is found, where also the late Hemphillian
equids Nannippus minor, Neohipparion eurystyle and
Astrohippus stockii were recorded. In the locality JAL
COLO 9 Los Corrales (= ZAC JUCH 9 Sanidad Animal,
21º57.56´N, 103º18.27´W), molars of Dinohippus interpolatus and Calippus cf. C. castilli have been recovered,
which represent the earliest part of the late Hemphillian.
It is important to point out that these equid species represent the oldest horses in central Mexico.
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Late Tertiary fossil localities in central Mexico, between 19°–23°N
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Teocaltiche-Xalostitlán Basin
QUERÉTARO STATE
In different places located between these two cities,
different specimens were collected. In the Teocaltiche
area, Osteoborus cyonoides (=Borophagus secundus),
Astrohippus stockii, Dinohippus mexicanus and cf.
Hexobelomeryx fricki fossils were found. This fauna is
of late Hemphillian age (Montellano-Ballesteros, 1997;
Aguirre-Díaz and Carranza-Castañeda, 2001).
In recent field work carried out by the author, a new
locality was discovered, JAL TEO 2 El Libramiento,
that allowed to recover an equid upper molar with
close characters to those of Calippus, a carnivore tibia,
a second molar of probable gomphothere and bird remains. The age of this fauna is the earliest part of the
late Hemphillian.
There have been several reports of Pleistocene fossils
from different places in this state. The only locality with
late Tertiary fossils is QRO 1 Landa de Matamoros,
which is in the Sierra Gorda of Querétaro. The recovered fossils include a gomphothere mandible and maxilla, a Nannippus minor lower molar and an astragalus
of a possible Hexobelomeryx. The fauna was assigned
to the late Hemphillian.
MICHOACÁN STATE
Late Tertiary localities from the Michoacán State are
very scarce, but there are several reports of Pleistocene
fossils.
Charo Depression
The town of Charo is located 14 km south of Morelia
city. In the locality MICH 1 Rancho La Goleta is found
the only late Tertiary fauna. It has been mentioned
since the second half of the past century, but the age
assignment always was ambiguous (Reppening, 1962;
Howard, 1965; Ferrusquía-Villafranca, 1978). New
investigations carried out with UNAM’s support, allowed to prospect the area and to collect early Blancan
fossils (Carranza-Castañeda, 1976). Besides, there are
abundant unpublished rodent remains. The radiometric date gave an age of 3.6 Ma. Unconformably, late
Pleistocene sediments with Equus sp. molars cover the
Blancan sediments.
The locality MICH 2 Cinqua, 19°45.43’N,
100°14’32”W, was discovered 160 km southeast
of Morelia city. Its associated fauna consists of
Neohipparion eurystyle, Dinohippus interpolatus (?),
Teleoceras fossiger, Desmathyus and Megatylopus cf.
M. matthewii, with an age corresponding to the earliest
late Hemphillian (Figure 4).
NAYARIT STATE
In the 1960’s, Dr. Theodore Downs and Harley J.
Garbani collected material from the locality Valle de
Los Gigantes that is now housed in Los Angeles County
Natural History Museum; the locality is recorded in
Centro de Geociencias, UNAM as NAY 1.
Los Gigantes Basin (21º27.69´N, 104º04.70´W)
This fauna has not been described, but a preliminary study
of the present author allowed to identify Dinohippus
mexicanus, Neohipparion eurystyle, Agriotherium,
Megalonyx, Rhynchotherium, Megatylopus, and a felid,
probably Machairodus. During the spring field work of
2005, a lower molar of Dinohippus and turtle (probably
Geochelone) carapace fragments were collected. The
associated fauna suggests a late Hemphillian age.
As part of the recent prospecting work, two new
late Hemphillian localities were discovered in the top
of the southwestern Sierra Madre. The most interesting one is found in the Huajimic basin, where some
fossils were collected. This locality was named as
NAY 2 El Huichol, and Dinohippus mexicanus and
Rhynchotherium fossils were identified.
It is important to note that in all these localities volcanic ash is intercalated with the bearing beds (Figure 4).
ZACATECAS STATE
Juchipila-Jalpan-Tabasco Basin
This is a large geologic structure about 120 km long
with a NE orientation, where lacustrine sediments have
Carranza-Castañeda, Óscar, and Lindsay, E.H. eds., Advances in late Tertiary vertebrate paleontology in Mexico
2006
58
Carranza-Castañeda
a thickness greater than 70 m, and in some areas the
clay sediments bear abundant root traces and other evidences of fossil plants, such as in locality ZAC JUCH
29 Raíces, in the ranchería of Mezquituta. In other
areas only the lacustrine sediments with ostracodes
crop out, as in localities ZAC JUCH 24 La Cofradía
(21º37.53’N, 103º01.85´W) and ZAC JUCH 27 La
Chimenea (21º27.25’N, 103º05.54W).
Along this basin, several localities with fossil mammals have been discovered. Among the most
important is locality ZAC JUCH 30 Las Lomas del
Valle, where upper molars of a possible Calippus and
antilocaprid molars were collected; this large area
with exposed sediments has diverse fossil mammals.
In the locality ZAC JUCH 25 Arroyo Los Fragmentos,
Dinohippus mexicanus molars and a tibia, and
Astrohippus stockii molars were recovered; the abundance of fragments also suggests a diverse fauna. Other
localities are ZAC JUCH 22 Camino de Piedra and
ZAC JUCH 23 El Pájaro (21º37.53´N, 103º01.85´W),
where bird elements, specially coracoids and an upper
molar probably of Dinohippus were recovered.
To the north of Jalpan city are localities ZAC
JUCH 28 La Canica, where a Neohipparion eurystyle
molar and other fragments were collected, and locality
ZAC HUAN 5 Yerbaniz, with fragments of a possible
Rhynchotherium. Locality ZAC HUAN 6 Hilda, with
Equus sp. upper molars, is north of Tabasco city, where
only Pleistocene sediments crop out (Aguirre-Díaz and
Carranza-Castañeda, 2000; Carranza-Castañeda and
Aguirre-Díaz, 2000, 2001).
BAJA CALIFORNIA SUR
In the southern part of the Baja California Peninsula,
the late Tertiary Las Tunas fauna was for several years
the only extensively described fauna (Miller, 1980).
Prospecting work done north of San José del Cabo allowed to recover Blancan fossil mammals. This area is
being systematically worked now, and abundant Equus
simplicidens, Rhynchotherium, a canid material, a Felis
lacustris partial jaw, and lagomorphs, rodents and bird
specimens have been collected (Carranza-Castañeda
and Miller, 1999; Miller and Carranza-Castañeda,
2001a, 2001b, 2002).
CONCLUSIONS
The carried out research of the continental late Tertiary
basins of central Mexico has shown the importance
of this region due to the abundance of fossils and the
faunal diversity. The faunal associations represent two
mammal ages: late Hemphillian (late Miocene) and
Blancan (Pliocene), although Pleistocene mammals are
also present. In some basins, the superposition of late
Hemphillian-Blancan faunas has demonstrated that the
San Miguel de Allende and Tecolotlán basins are the
most complete stratigraphic late Tertiary continental
sequences in Mexico. This superposition opens the possibilities of studying the extinctions that occurred in the
boundary between the mammal ages. Also, the abundance of rodent fossils, of which most part has not been
described, constitutes an opportunity to study different
biological events, such as the evolution of cricetid rodents, which are common in these basins. Collaterally,
the boundaries of large lakes that were present in central Mexico during late Tertiary have been defined.
The continuity of researching in basins of Mexico
will contribute to precise the migrating routes of the
first South American immigrants from the early Blancan
faunas of central Mexico to the late Blancan faunas of
Texas, Arizona, New Mexico and Florida.
ACKNOWLEDGMENTS
The research of the sedimentary basins from central Mexico began with the support of the Instituto
de Geología, UNAM, and continues with that of the
Centro de Geociencias, UNAM, Campus Juriquilla,
Querétaro. Mr. Harley J. Garbani, since the beginning,
has been working in the San Miguel de Allende Basin.
I am very grateful to Dr. Wade Miller and Dr. Bart
Kowallis, from Brigham Young University; their support and participation in the research have been significant in the success of the results here presented. In the
last years, Miss Hilda Troncoso has been prospecting
and collecting. I want to express my special thanks for
their financial support to the investigations to the following institutions: Centro de Geociencias, Campus
UNAM, Juriquilla; National Geographic (Grant 344386); CONACYT (Project 1466 and Project 47071);
Universidad Nacional Autónoma de México, Instituto de Geología and Centro de Geociencias
Publicación Especial 4
Late Tertiary fossil localities in central Mexico, between 19°–23°N
National Science Foundation (Grants EAR 8620155,
EAR 9316895, and EAR 9902898), and The Earth
Watch Institute.
Finally, I acknowledge Luis Burgos and Fernando
Vega for drawing the illustrations. Also, I thank all participants during the field work, Gerardo Álvarez-Reyes,
students and researchers, which have collaborated in
different phases of the studies of central Mexico.
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