Name: Acrocanthosaurus
(High spined lizard).
Phonetic: Ak-row-can-fo-sore-us.
Named By: John Willis Stovall & Wann
Langston, Jr. - 1950.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Carcharodontosauridae.
Species: A. atokensis
(type).
Type: Carnivore.
Size: Up to 11.5 meters long.
Known locations: USA, Oklahoma, Antlers
Formation, and the Texas, Twin Mountains Formation. Some
specimens from other parts of the US.
Time period: Aptian to Albian of the Cretaceous.
Fossil representation: Several specimens of partial
remains. Combined study of all these specimens has allowed
Acrocanthosaurus to be very well reconstructed.
Acrocanthosaurus
immediately sticks out from other large theropods with its high
dorsal spines than run from the neck to the tip of the tail. There
have been many artistic representations for this structure from the
spines standing proud from the body, to supporting a flap of skin.
Modern thinking however comes from the examination of the lower spines
that have attachments for muscles. This has led to the suggestion
that the spines supported a hump of tissue that ran down the length of
Acrocanthosaurus.
The
purpose of the hump of Acrocanthosaurus has been
subject to a lot of
speculation. Some have said that it would provide a larger surface
area than Acrocanthosaurus would have had without
it, helping with
temperature exchange and reducing negative effects of gigantothermy.
It could have been composed of fatty tissue and used to keep
Acrocanthosaurus going for extended periods without
eating. It may
have also been a form of visual display for other Acrocanthosaurs
to
gauge its level of health, perhaps even having a different colour or
markings to the rest of its body.
It
is possible that the hump served double duty. If composed of fatty
tissue, Acrocanthosaurus would have had to eat
more than the minimum
it would have had to just to survive. This would then result in a
large and well maintained hump that would speak along the lines of
'Look at my hump. That is how much of a successful predator I am.
That’s why I am more worthy of passing my genes down to the next
generation'. It could have also worked in dominance displays
between two Acrocanthosaurus, with the larger
hump meaning that they
were a more capable hunter and knew what to do when things came to a
fight. The Acrocanthosaurus with the smaller hump
would then probably
back down instead of go up against what appeared to be a stronger and
more capable Acrocanthosaurus.
Acrocanthosaurus
was big for its time, a family trait that is shared with some other
carcharodontosaurids
such as Carcharodontosaurus
and Giganotosaurus.
At eleven and a half meters, Acrocanthosaurus
would have
been the largest
predator of its time and locale. Its diet as a result probably
consisted of hadrosaurs and smaller sauropods, dinosaurs that were
large enough to provide sufficient sustenance, while being too slow
to escape. Study of the area that the main Acrocanthosaurus
remains
come from suggest that it was probably the apex predator of its
location, with most other predators such as Deinonychus
being much
smaller.
The
skull of Acrocanthosaurus featured large fenestra,
a necessary
adaptation to reduce the weight of its huge skull that could approach
up to a one hundred and thirty centimeters long. The teeth of Acrocanthosaurus
were
curved and serrated like other members of the carcharodontosaurid
group. The maxilla and premaxilla contained a total of around
thirty-eight
teeth. The teeth in the lower jaw are generally smaller than those
above and can approach up to thirty in number. Another
carcharodontosaurid trait is the bony brow ridge above the eye,
formed by the lacrimal and postorbital bones coming together.
Computer
reconstruction of the inner ear has shown that the 'resting
position' of the head of Acrocanthosaurus was
twenty-five degrees
below zero horizontal. This may give the impression that
Acrocanthosaurus usually walked around looking
slightly towards the
ground.
Reconstruction
of an Acrocanthosaurus forelimb suggests that there
would have been
large amounts of cartilage between the bones. This comes from the
fact that bones themselves do not make perfect joints and would need
the extra cartilage in order to articulate properly. The arms of
Acrocanthosaurus did not have a huge range of
motions. The arm could
not fully extend and could only manage limited flexing. The humerus
could retract back quite away, as if Acrocanthosaurus
was pulling
something towards its chest. As is commonly seen in larger
theropods, the fore arm could not twist like a human arm can. When
at rest the arms would have faced medially inwards, like when you
clap your hands together. Acrocanthosaurus had
three digits on the
end of its arms with the first and second claws probably being
permanently flexed. The third and smallest claw may have been able to
retract as well.
Altogether,
Acrocanthosaurus may have grabbed large prey such
as sauropods
like Sauroposeidon
with
its jaws and then
latched onto it with its claws. The neck vertebrae also interlocked
together for greater rigidity which means that Acrocanthosaurus
could hold onto large prey with its jaws without sustaining injury to
the neck. Lighter prey such as ornithopod dinosaurs like Tenontosaurus
may have been pulled
towards Acrocanthosaurus while it continued to work
with its jaws,
whereas it would probably have to pull itself onto heavier prey.
Alternatively it may have held its prey with its jaws while repeatedly
slashing at it with its claws, the more the prey struggled, the
worse its wounds became.
Further reading
- Acrocanthosaurus atokensis, a new genus and
species of Lower
Cretaceous Theropoda from Oklahoma. - American Midland Naturalist
43(4):686-728. - J. W. Stovall & W. Langston Jr. - 1950.
- A reanalysis of Acrocanthosaurus atokensis, its
phylogenetic status,
and paleobiological implications, based on a new specimen from Texas. -
New Mexico Museum of Natural History and Science Bulletin. 13: 1–75.. -
Jerald D. Harris - 1998.
- Estimating Mass Properties of Dinosaurs Using Laser Imaging and 3D
Computer Modelling. - PLoS One. 2009; 4(2): e4532. - Karl T. Bates,
Phillip L. Manning, David Hodgetts & William I. Sellers,
(Ronald Beckett, ed.) - 2009.
- A new specimen of Acrocanthosaurus atokensis
(Theropoda, Dinosauria)
from the Lower Cretaceous Antlers Formation (Lower Cretaceous, Aptian)
of Oklahoma, USA. - Geodiversitas 22(2):207-246. - P. J. Currie
& K. Carpenter - 2000.
- Acrocanthosaurus and the maker of Comanchean
large-theropod
footprints. - James O. Farlow - 2001.
- Range of motion in the forelimb of the theropod dinosaur
Acrocanthosaurus atokensis, and implications for
predatory behaviour. -
Journal of Zoology. 266 (3): 307–318. - Phil Senter & James H.
Robins - 2005.
- Cranial endocast of the Cretaceous theropod dinosaur Acrocanthosaurus
atokensis. - Journal of Vertebrate Paleontology. 25 (4):
859–864. -
Jonathan Franzosa & Timothy Rowe - 2005.
- New Information on the Cranial Anatomy of Acrocanthosaurus
atokensis
and Its Implications for the Phylogeny of Allosauroidea (Dinosauria:
Theropoda). - PLoS ONE. 6 (3): e17932. - Drew R. Eddy & Julia
A. Clarke, (Andrew Farke, ed.) - 2011.
- Paleobiology and geographic range of the large-bodied Cretaceous
theropod dinosaur Acrocanthosaurus atokensis. -
Palaeogeography,
Palaeoclimatology, Palaeoecology. 333–334: 13–23. - Michael D. D’Emic,
Keegan M. Melstrom & Drew R. Eddy - 2012.