During the Early Triassic period, before the evolution of the dinosaurs,
the apex predator of southern Pangea was Proterosuchus. It looked similar to a crocodile
with a longer neck and a hooked snout that formed a massive overbite. Proterosuchus is known to the
public at large mostly from its appearance in BBC’s Walking with Monsters, although it was
called Chasmatosaurus during the program. While Proterosuchus was a terror in its own time,
it was also a herald of what was to come. It was part of the clade Archosauriformes,
the clade which includes dinosaurs, crocodilians, and their close relatives who already had most
of the traits that set them apart from other reptiles. Proterosuchus was one of the first
archosauriforms to reach large body size. It was also one of the first new species to evolve after
the Permian Mass Extinction, the most devasting extinction event known to science. Combined with
a number of good specimens, Proterosuchus is uniquely informative in understanding the rise
of one of the most important groups of reptiles. So, what was Proterosuchus itself actually like?
It was about three and a half meters long and held its limbs in a sprawling stance.
While this is similar to most of other reptiles, the limbs of more derived archosauriforms were
usually held in more erect stance. Proterosuchus’s skull was large, deep, and filled with recurved,
serrated teeth. This proportionally large skull is thought to have been the result of
Proterosuchus evolving to hunt larger prey in the wake of the extinction of most of the top Permian
carnivores. Some of the later, more derived archosauriforms, such as the erythrosuchids,
took this a step further, possessing almost comedically oversized skulls. Perhaps the
most prominent feature of Proterosuchus’s skull is the long, hooked snout and its resulting overbite.
While a hooked snout is also present in some other early archosauriforms and their relatives,
Proterosuchus is one of the most extreme examples. As for what it was used for, the snout was
highly resistant to bending and created a notch comparable to those in Conger eels, spinosaurids,
and crocodilians. However, Proterosuchus’s teeth do not have similar wear patterns as these taxa.
It could be that the notch was merely a byproduct of the downturned snout, which Proterosuchus
used to keep its prey from escaping. Another possibility is that the snout could have been a
display feature used to attract mates. Another key feature of the skull was the antorbital fenestra,
an opening in the skull in front of the eyes. While perhaps less striking than the hooked snout,
this feature is one of the identifying traits of Archosauriformes. While most extinct reptiles
are assumed to have been ectothermic, or “cold blooded”, this was not the case
for Proterosuchus. Examination of its bone histology show that its metabolism was much
higher than most reptiles, instead being closer to that of endothermic, or “warm blooded”, species.
Indeed, a high metabolism seems to have been an ancestral trait in Archosauriformes,
with most other members, including dinosaurs and even the ancestors of crocodilians possessing
a high metabolism. While an endothermic metabolism requires a lot more energy to maintain,
there are several reasons why it is advantageous. For instance, it allows an animal to be much more
active and to inhabit colder environments. Animals with a high metabolism are also able to grow much
faster than those with lower metabolisms. In Proterosuchus’s case, in a single year
it was able to reach two thirds of its full adult size. In contrast, the ectothermic Komodo dragon
takes at least eight years to reach its full size despite being slightly smaller.
Such quick growth is thought to be helpful in unpredictable conditions like those during the
End Permian Mass Extinction and its aftermath in the Early Triassic. Indeed, the other major group
of large vertebrates to survive the extinction, the synapsids, were also endothermic. Furthermore,
out of all the synapsids, the survivors were only from the two clades with the highest metabolisms:
the tusked dicynodonts and more mammaliam eutheriodonts. However, when compared to other
members of Archosauriformes, Proterosuchus’s metabolism was still rather low. While early
archosauriforms did have lower metabolisms than many of the later ones, Proterosuchus’s metabolic
rate was even lower than that of Prolacerta, who was not a true archosauriform but a
close relative of the group. This suggests that Proterosuchus evolved to have a lower metabolism
than its direct ancestors, although it remained higher than most other reptiles.
While not as large as later Triassic carnivores such as erythrosuchids or rauisuchids,
let alone many of the later theropod dinosaurs, there is no question that
Proterosuchus was capable of hunting the largest prey of the earliest
Triassic, such as the extremely common dicynodont Lystrosaurus. The question is how it killed them.
Proterosuchus has variously been proposed to have been a terrestrial hunter or a semi-aquatic
predator analogous to crocodilians, which is how it was portrayed in Walking with Monsters.
Among the evidence used to support an amphibious mode of hunting is the shape of its brain casts.
Proterosuchus’s olfactory bulbs, which were responsible for its sense of smell,
were smaller than those of closely related species and are instead more like those of crocodilians.
Also like crocodilians, the length of the cochlear ducts in its ears suggest it was best adapted
for detecting low frequency sounds. Some paleontologists have suggested that the neutral
position of Proterosuchus’s head, inferred from its ear canals, would have been stilted upward.
Such a position is ideal for a semi-aquatic predator, as it would leave its nostrils above
the water while the rest of the body remained obscured beneath it. However,
the connection between ear canals and the neutral position of the head is looser than was thought
when this idea was first proposed. There are also arguments against an amphibious Proterosuchus.
Crocodilian nostrils are on the top of the snout, which allows them to easily remain above water.
Because of Proterosuchus’s hooked snout, its nostrils were angled much lower than in most
terrestrial species. Even if they were angled above the water, its head would have been much
easier to see than a crocodilian’s. Proterosuchus also lacks many of the other morphological traits
that make crocodilians so effective in the water. For instance, when swimming,
a crocodilian’s primary source of propulsion is its large tail, which is tall and flattened. In
contrast, the shape of Proterosuchus’s tail was more like that of terrestrial reptiles.
Its recurved and serrated teeth are also typical of terrestrial archosauriforms,
as opposed to the straight and conical teeth in most semi-aquatic ones. This means that
even if Proterosuchus caught its prey in a manner similar to crocodilians,
it would have killed them with more direct wounds rather than drowning them. Furthermore,
its bone histology and the ossification of its legs were more like those of terrestrial species.
The environment Proterosuchus lived in was also arid and prone to droughts. While crocodilians do
sometimes live in similar climates, Proterosuchus is the only known large carnivore in the region
for much of its evolutionary history, making a semi-aquatic mode of existence a questionable
strategy in such conditions. Finally, its metabolism was also higher than that
of most semi-aquatic predators. A high metabolism is far from ideal for an aquatic ambush predator,
as it would result in a lot of wasted energy while simply waiting for prey to approach. However,
a lower metabolism might have meant Proterosuchus would have been unable to grow fast enough to deal
with the unstable world of the Early Triassic. Therefore, its comparatively high metabolism
may have been a compromise between two different evolutionary considerations. Additionally, if it
was a crocodile analogue, this could explain why its metabolism was so low for an archosauriform.
Another explanation is that there simply weren’t enough large herbivores to support a fully
endothermic carnivore of its size. Overall, while not definitive, the evidence does not
seem to strongly suggest that Proterosuchus was an amphibious predator, though it cannot yet be
ruled out. If was a semi-aquatic predator, it does not seem to have been as well adapted for the role
as crocodilians, perhaps because it was still in the early stages of adapting to the niche.
Regardless of how adult Proterosuchus hunted, it would seem that the juveniles behaved differently.
Their skulls were far less robust, closer to those of their more primitive relatives
such as Prolacerta. Also like them, the back teeth were not curved as strongly as those in the front,
in contrast to the more uniform teeth of the adults. As their skulls were similar to
their smaller relatives, it is likely the juvenile Proterosuchus lived accordingly. Once they reached
larger size and gained their proportionally larger skulls, they shifted to hunting larger species.
This mirrors the changes today’s crocodilians go through as they grow. While Proterosuchus has been
treated as one species so far, it was actually a genus that consisted of at least three similar
species. Proterosuchus fergusi is the type species and is the one known from the most fossils.
The other two species, Proterosuchus goweri, and Proterosuchus alexanderi, are only known
from one specimen each. Proterosuchus alexanderi had a longer snout. The skull of Proterosuchus
goweri had a small, toothless gap in the upper jaw before the transition to the hooked snout.
All three species have only been found in Early Triassic rocks from South Africa.
However, most Early Triassic fossils are from South Africa, and the world’s
continents were combined into Pangea at the time, so Proterosuchus was likely far more widespread.
Fossils of a species similar to Proterosuchus have also been found in Early Triassic India,
and may even be Proterosuchus itself. There may be a fourth species of Proterosuchus.
The type species of the “Chasmatosaurus” genus, “Chasmatosaurus vanhoepeni”, turned out to instead
be a specimen of Proterosuchus fergusi, which is why Proterosuchus was called Chasmatosaurus
in Walking with Monsters. While this means “Chasmatosaurus” is no longer a valid genus,
another species formerly assigned to it, “Chasmatosaurus” yuani, is a genuinely
unique species. It lived after the others, in Middle Triassic China. Whether it is a species of
Proterosuchus or it warrants its unique own genus has yet to be determined. Either way, this Chinese
species was more closely related to Proterosuchus goweri than to the other species of Proterosuchus,
indicating it was at least a direct decedent of Proterosuchus. Proterosuchus is the namesake
of the clade Proterosuchidae, which was the first clade to branch off of Archosauriformes.
There are some other species that may or may not be part of Proterosuchidae, the most notable being
Chasmatosuchus, who shouldn’t be confused with the now invalid Chasmatosaurus. The only definitive
proterosuchid besides Proterosuchus and the unnamed Chinese species is Archosaurus. It lived
during the Permian Period in what is now Russia and Poland. Although Archosaurus was similar
to Proterosuchus, its head was proportionately smaller, reflecting its lower place in the food
chain. Since Archosaurus lived during the very end of the Permian, Proterosuchidae split from
the rest of Archosauriformes before the beginning of the Triassic Period. Furthermore, both other
early archosauriforms and a very close relative of the clade, the Australian Tasmaniosaurus,
were also very similar to Proterosuchus. This means that the direct ancestor of the crocodilians
and dinosaurs, including birds, at some point looked very similar to Proterosuchus.
All definitive species of Proterosuchus are 251 to 249 million years old and are from
Lystrosaurus Assemblage Zone in the Karoo Supergroup. This site is one of the few,
and by far the best sites containing fossils from the Early Triassic. On account of directly
following the end-Permian mass extinction, this environment was not very diverse.
Among its inhabitants was a close relative of the archosauriforms, the previously mentioned
Prolacerta. But like during the proceeding Permian Period, most of the large fauna were synapsids.
The namesake of the assemblage zone, the dicynodont Lytrosaurus was extremely common,
both in South Africa and the rest of the world. There was also a second,
less common dicynodont named Myosaurus. Eutheriodonts were also present. Indeed,
the therocephalian Moschorhinus was initially the top predator of the region. However, it was
eventually replaced by Proterosuchus. Moschorhinus may have been the first synapsid to be outcompeted
by an archosauriform, but it would not be the last. Soon, the roles would be reversed,
with synapsid increasingly reduced to bit players in a world dominated by archosauriforms
and their relatives, who belonged to the larger clade Archosauromorpha. However, neither
Proterosuchus nor the rest of Proterosuchidae would live to see it. Just as they replaced
large synapsid predators such as Moschorhinus, later archosauriforms such as the erythrosuchids
replaced them. These predators were in turn replaced by even more derived archosauriforms.
As time went on, Archosauriformes would continue to diversify into a number of roles beyond that
of small and large predators. They ruled for the rest of the Triassic Period and beyond,
culminating in the dinosaurs’ rise to dominance. While not the direct descendants of Proterosuchus,
the fact that the archosaurs were all descended from a similar, closely related species means
that Proterosuchus’s legacy, in a way, lives on not just in its fossilized bones
but in the crocodilians and birds of today. Thank you for watching. I hope you learned something
interesting. Also, a thank you to Domenic Pennetta for making art of Proterosuchus specifically
for this video. If you would like to see more of his art, be sure to check out his website.
There is a link to it in the description. This video is a remake of an earlier video I made.
While that video is now unlisted, it can still be viewed from the link in the description if
you wish to compare the two. If you enjoyed this video, please remember to hit the like button
and subscribe if you want like to see more. Finally, be sure to have a great day!