While the crocodilians of today are often mislabeled as prehistoric holdovers, the
larger group they were a part of, Crocodylomorpha, was far more diverse. Among the most successful
crocodylomorphs was Araripesuchus. Araripesuchus is not a single species but a genus consisting of
multiple species of small reptiles, all of whom lived during the Cretaceous period.
Some of these have been given colorful nicknames, such as “DogCroc” and “RatCroc”.
While Araripesuchus was more closely related to crocodilians than any other living reptile,
it differed from them considerably. It belonged to Notosuchia, which consisted of generally
terrestrial species, and Araripesuchus was no exception. One of the traits that does make
Araripesuchus exceptional is how it contained six species, which is more than any other
notosuchian genus. While there were differences between these species, their overall anatomy
was largely similar. As Araripesuchus split from other notosuchians early on, the genus provides a
window into what the early notosuchians were like before they diversified. Like most notosuchians,
Araripesuchus had long limbs held in an erect, upright stance, as opposed to the semi-erect
stance of their closest living relatives. This gave Araripesuchus much greater speed on land.
None of the species were particularly large, ranging from 1 to 1.8 meters long,
with Araripesuchus buitreraensis being the largest known species. Araripesuchus is thought to have
had large eyes given the large orbits in its skull. The most distinguishing trait of the
genus from other notosuchians is how the edges of the snout bulge outwards, which is most prominent
near a pair of large, canine-like teeth. Like many other notosuchians, the teeth of Araripesuchus
were heterodont, meaning they had several distinct shapes. This is in contrast to the uniform conical
teeth of crocodilians. While they varied depending on the species, Araripesuchus teeth came in three
basic shapes: conical, crocodile-like incisiforms at the front of the jaw, the pair a larger
caniniform teeth in both the upper and lower jaws, and a variety of different teeth behind them that
are referred to as post-caniniform teeth. These range from lance shaped teeth to the leaf shaped
teeth of plant eaters. While their teeth were not those of dedicated herbivores, they do suggest
an omnivorous diet. As the teeth of the species differed, it seems they filled somewhat different
niches. Unfortunately, most of the more rigorous testing is limited to Araripesuchus gomesii.
A study of the teeth of various crocodylomorphs found the teeth of Araripesuchus gomesii to be
within the range of insectivores and omnivores, with the authors concluding it was a generalist.
However, this study was limited to the teeth of a juvenile, and juveniles, including modern
crocodilians, sometimes have different niches than their parents. A finite element analysis
of an Araripesuchus gomesii’s skull likewise found it had a weak bite force, suggesting
it wasn’t adapted to hunt large animals, instead preying upon small vertebrates and insects.
The largest outlier is RatCoc, Araripesuchus rattoides. While none of its actual teeth have
been preserved, the first and fourth tooth sockets indicate it they were much larger
than in other Araripesuchus species. The tooth sockets suggest the fourth pair of teeth were
closer to the size to those of large carnivores like the baurusuchids and peirosaurids. The
teeth at the front of RatCoc’s jaw also pointed forwards, likely to dig for plants and insects.
However, while the teeth of Araripesuchus were a lot more variable than those of crocodilians,
they still paled in comparison to the even more specialized teeth of most other notosuchians.
One of the traits Araripesuchus shared with modern crocodilians was their metabolism.
Examination of the bone structure of Araripesuchus and other notosuchians has revealed that they had
an ectothermic, or “cold blooded” metabolism, relying on the environment for thermoregulation
like modern crocodilians. While this is the norm among modern reptiles,
early crocodylomorphs had a high metabolism, though not as high as modern birds or mammals.
A lower metabolism costumes a lot less energy. This means Araripesuchus would not have needed to
consume nearly as much food as its similarly sized warm blooded ancestors. However, it also meant it
would have been less active and would have grown at a much slower rate than mammals or dinosaurs.
Therefore, while today’s omnivorous mammals may provide an analogue for Araripesuchus’s diet,
in many other ways monitor lizards provide a better indication of its activity level. Like many
other crocodylomorphs, Araripesuchus possessed osteoderms, which are bony plates on the skin.
Araripesuchus’s osteoderms were arranged into multiple rows across the back, tail, and belly. In
addition to providing protection, the osteoderms of modern crocodilians are vascularized to aid in
heat exchange. However, like those of their more active ancestors, the osteoderms of Araripesuchus
were thinner, lacking the vascularization critical to heat exchange in modern crocodilian
osteoderms. This shows that even though Araripesuchus already had a low metabolism,
it took time for crocodylomorphs to optimize their anatomy for an ectothermic lifestyle.
All of the locations Araripesuchus fossils have been found were formerly part of the
supercontinent Gondwana, which was formed from what are now the southern continents.
The oldest species were Araripesuchus gomesi and an unnamed species nicknamed the Crato form,
both of which lived in South America 115 to 108 million years ago. Araripesuchus wegeneri,
the DogCroc, whose nickname is derived from its soft dog-like nose, lived about 112 million years
ago. Its fossils are found in what is now North Africa in the Elrhaz Formation. Araripesuchus
patagonicus and Araripesuchus buitreraensis are both from the Candeleros Formation in Argentina,
which was formed between 99 to 97 million years ago. At roughly the same time Araripesuchus
rattoides, the RatCroc, lived in North Africa. Its fossils are found in the famous Kem Kem beds,
which contains fossils of many famous species, including the iconic dinosaur Spinosaurus.
The last known species of Araripesuchus is Araripesuchus tsangatsangana, who lived in
Madagascar not long before the extinction of the non-avian dinosaurs and most of the other
notosuchians 66 million years ago. Araripesuchus tsangatsangana extends the range of the genus to
about forty to fifty million years, an exceptional amount of time for a single genus to survive. Even
among crocodilians, who are often mislabeled “living fossils”, no living genus has lasted
so long. However, examination of Araripesuchus’s closest relativities indicates the genus didn’t
suffer from evolutionary stasis. Araripesuchus belongs to the clade Uruguaysuchidae.
The namesake of the clade, the South American Uruguaysuchus, consists of two species who were
not that different from Araripesuchus. However, the third and final genus in Uruguaysuchidae,
the African Anatosuchus, was very much an outlier. Anatosuchus had a broad, duck-like snout, for
which it has been nicknamed “DuckCroc”, though it is thought to have been more of a heron analogue.
Notably, some papers have found it nested within Araripesuchus, suggesting that Anatosuchus is
descended from a species of Araripesuchus. If so, some members of Araripesuchus not only changed
enough to warrant a new genus, but evolved in a very unusual direction. It has also been suggested
RatCroc may deserve its own genus as well. Regardless, other descendants of Araripesuchus
changed so little that they remained within the genus for an extraordinary length of time.
In conclusion, Araripesuchus’s basic body plan was both long lasting, but also capable of
evolving in surprising ways. The survival of at least one species of Araripesuchus into the very
end of the Cretaceous period suggest it took a meteor to finally bring about the extinction
of this enduring reptile. Thank you for watching. I hope you learned something interesting. Have a
great day, and, if you enjoyed the video, please remember to hit the like button.