Lecture PDF - Revealed Singularity

Theropods I: Basal Theropods –
Ceratosauria, Early Tetanurans, and
Carnosauria
Dinosaur Cladogram – Last Time
Therodopoda – Terrors of the Dinosaurs

Theropods are the dinosaurs we’ve all been waiting for –
theropods are the group that contained all of the
predatory dinosaurs to live.



Note that while all predatory dinosaurs were theropods, not
all theropods were predatory.
“Theropod” literally means “beast foot”.
The earliest Eutherpods (true theropods) are the
Coelophysids, but their
placement is in dispute.
The Old Junk Group

Carnosaurs essentially used to be a dumping ground for
large theropods.

These were reclassified in the 1980s/90s




Many were reclassified to a more primitive status
Some were placed in Coelurosauria if they were close to birds, such
as Tyrrannosaurids
Others underwent a Great Shuffle
Now, Carnosauria is not even a root clade; it is a sub-clade
(“Infraorder”) of Tetanurae (“stiff tails”)
Tetanurae

Most of the theropods we are familiar with are called
“tetanurans”.

The clade “Carnosaurs” has been refined to “Carnosauria”, a
group that splits off from Coelurosauria at the Neotetanurae
node.



Animals from before this split are still Tetanurans, but not part of
“neotetanurae”.
Neotetanurae is also called “Avetheropoda”, but “Neotetanurae”
reached publication first.
In contrast, “Ceratosauria” are their own group
Grey Areas
If we were to zoom into our cladogram, we could see that we are in a bit of a grey area in the cladistic charts.
Effective Class Cladogram
For the purposes of this class, this is a simplified cladogram that highlights the most relevant groups and their
most accepted current arrangement.
Ceratosauria

Ceratosaurs are a bit of an ill-defined group. While they
are formalized to be those closer to Ceratosaurus over
birds, there is no formal diagnostic listing

In addition, some analyses include Coelophysoids in this group,
but recent studies imply Coelophysoids should be more basal
(thus this is a paraphyletic situation)
Ceratosaurs, con’t

By now, Ceratosaurs are a
fairly small group.

Their primary members are
Ceratosaurus, Abelisaurus,
and arguably the one with
the most name recognition:
Dilophosaurus


Dilophosaurs was much
larger than in Jurassic Park.
It was approximately 6 m
long and 500 kg in mass.
Abelisaurs included the
Carnotaurs, with vestigial
arms and prominent horns.
Spinosaurids – Largest Land Predator?

Spinosaur’s names say it all – they were basal tetanurans
with a large sail of neural spines that protruded from the
backs of many species


Spinosaurs also had distinctive teeth; their front teeth fanned
out, and their jaw often had a notch by the dentary
Their skull was distinctly crocodiliform
Spinosaurids, con’t


Spinosaurus aegypticus
was possibly the largest
land carnivore to ever live,
coming in at 16-18 m and
9t
Baryonyx was a type of
spinosaurid that was
initially misclassified due
to its large claws on its
hands
Baryonyx
Carnosauria– not quite birds



Carnosauria is the group of predatory dinosaurs that
were theropods, but are more closely related to
Allosaurus than birds.
We will not discuss Sinraptoridae, as they only have a
single genus and are generally unremarkable.
Diagnostic characters include skull shape
and the leg/pelvic
structure.

For example,
the femur is longer than
the shin
Allosaurids

Allosaurs were the largest theropods of the late Jurassic



They averaged in length to about 8.5 meters, (max: ~12 m)
There has been some debate over the species counts – many
look rather similar, and have been alternately named individuals
vs. spieces
One notable difference
from most Coleusaurs
that shows up in
Allosaurids is a small
horn above the eyes.
Allosaurus vs. Tyrannosaurs
Can you see some difference in the skulls in this picture?
Carcharodontids – Giants Apply Here

Carcharodontids are a large group of carnosaurs that
included many members who eclipsed T. Rex in size.

One of the most notable of these is Giganotosaurus, who was
possibly the second largest land carnivore to live.



He lived during the late Cretaceous, until about 80 MYA
The term “carcharodon” may sound familiar: it is because it
means “shark-toothed”.
Some recent
phylogenetic analysis by
Sereno (2005) suggests
Carcharodontosauridae
may be its own clade.
Sorry, you’re not a raptor

These particular groups of animals have been notoriously
misclassified


In addition to the problems in determining their cladistic
relationships, there is the problem with Allosaurs mentioned.
Another problem has been the misclassification of a few of
these as members of the dromaeosaur
family.


Baryonyx was thought to be a dromaeosaur
based on the hand claws to the right.
Megaraptor isn’t a raptor at all – its single
large claw was on its hands.
Dinosaur Cladogram – Finished Today
Next Time

Coelurosaurs: Maniraptorforms and Theropod
biomechanics.

Consider the proposition on how these large animals caught
fast prey!
Additional Reading


Many relevant articles are too old to be available online.
Phylogenies


Padian, Hutchinson, Holtz. “Phylogenetic definitions and
nomenclature …” 1999
Gauthier, JA. “Saurischian monophyly and the origin of birds.”
1986