Pristichampsus
Name:
Pristichampsus
(Saw crocodile).
Phonetic: Priss-tee-champ-sus.
Named By: Gervais – 1853.
Synonyms: Crocodilus rollianti.
Classification: Chordata, Reptilia,
Crocodylomorpha, Crocodylia, Pristichampsidae.
Species: P. rollinatii
(type), P. geiseltalensis, P. vorax.
Diet: Carnivore.
Size: About 3 meters long.
Known locations: Eurasia and North America.
Particularly well-known from the USA.
Time period: Throughout the Eocene.
Fossil representation: Many individuals.
Pristichampsus
is a crocodile
that bears all of the hallmarks of a terrestrial
lifestyle rather than an aquatic one like todays crocodiles. The key
clues to this lifestyle can be seen in the legs which are longer than
those of semi-aquatic crocodiles to allow for more terrestrial
locomotion. Additionally the ends of the toes were hoof-like for
better traction on the land. The tail of Pristichampsus
is was
also round rather than flattened, probably because it was not used
for swimming like its semi-aquatic cousins. Although a bipedal
posture is theoretically possible for a Pristichampsus
running at high
speed, palaeontologists are confident that for most of the time and
in standard low speed locomotion, Pristichampsus
would have been
quadrupedal due to the centre of gravity being well forward of the
hips.
Support
for the idea of a terrestrial lifestyle comes from the teeth of
Pristichampsus which were laterally compressed
(broad when seen from
the side, but thin when viewed from the front) and had well
developed serrations. These kinds of teeth are perfect for slicing
through flesh, particularly the relatively soft and unarmoured bodies
of mammals. Aquatic crocodiles however have more conical teeth which
are stronger and better able to grip a struggling animal as the
crocodile holds it under the water to drown it. In addition
Pristichampsus is often credited with having teeth
like large theropod
dinosaurs, particularly the tyrannosaurids, though really this is a
poor analogy. Tyrannosaurids like Tyrannosaurus
had round conical
teeth for crunching bones, not slicing flesh like Pristichampsus.
A
better analogy would be that of the carcharodontosaurids, another
group of theropods which did have serrated and laterally compressed
teeth.
The
temporal and geographical ranges as well as the number of individuals
of Pristichampsus indicate that it was a very
capable predator. The
early Eocene is marked by abundant warm forests which would have
provided plenty of ambush locations for a predator like Pristichampsus
to use to surprise prey. The warm climate also helped with a
reptilian cold blooded metabolism so that crocodiles like
Pristichampsus could be more active.
As
the Eocene progressed however things began to change in that global
temperatures began to slowly drop which triggered a shift towards a
cooler and drier climate. First, crocodiles are cold blooded, so
those like Pristichampsus would have steadily
become more lethargic,
meaning slower reactions and movements. Second, the forests that
held so many hiding places began to thin out and become replaced by
grasslands, though not yet to the extent of later periods. Third,
the animals that Pristichampsus preyed upon were
also changing,
developing longer legs to help cover the wider distances between
growths, which also meant that they were becoming faster and harder
to catch. Additionally the mammals were also proving to be more
competition as more highly developed predators such as creodonts and
nimravids
began appearing. Although crocodiles would continue
into modern times, they would do so by being more specialised hunters
of aquatic environments while the terrestrial crocodiles like
Pristichampsus would steadily decline.
Further reading
- Studies on Cenozoic crocodiles: 5. Biomechanical investigation on the
postcranial skeleton of the Palaeogene crocodile Pristichampsus
rollinatii (Eusuchia: Pristichampsidae). - Neues Jahrbuch
fuer Geologie
und Pal�ontologie Abh. 217 (3) 289-300. - T. Russmann - 2000.
- Phylogenetic relationships of Palaeogene ziphodont eusuchians and the
status of Pristichampsus Gervais, 1853. - Earth and
Environmental
Science Transactions of the Royal Society of Edinburgh: 1. - C. A.
Brochu - 2013.
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