Rutiodon: Beast of the Week

 This week we'll be checking out a prehistoric beast that was a crocodilian before crocodilians existed.  Take a look at Rutiodon carolinensis!

Rutiodon grabbing a late Triassic pterosaur (based on Caelestiventus) reconstruction in watercolors by Christopher DiPiazza.

Rutiodon was a carnivorous prehistoric reptile that lived during the late Triassic Period, between 237 and 208 million years ago in what is now the east coast of the United States, with fossils found in New York, New Jersey, and North Carolina.  From snout to tail Rutiodon shows variation among adult lengths,  ranging from about ten to as large as twenty-six feet.  The name, Rutiodon, translates to "wrinkled tooth" in reference to the grooves along the length of some of its teeth.  

Rutiodon belonged the family of reptiles called phytosaurs.  Phytosaurs are fascinating because they looked and likely behaved very much like modern crocodilians...but weren't even closely related to them!  In fact, modern crocodilians are more closely related to dinosaurs(including birds) and pterosaurs than they are to phytosaurs.  During the Triassic the ancestors of crocodilians were actually generally small, land-dwelling creatures.  It wasn't until the end of the Triassic, when phytosaurs went extinct, that the crocodile group appears to have taken advantage of that ecological niche and eventually evolved a very similar body plan for a very similar lifestyle. Despite the similarities, the most notable difference between phytosaurs, like Rutiodon, and crocodilians is the nostril placement.  Phytosaurs had their nostrils closer to the base of the skull, near the eyes, while crocodilians have their nostrils at the tip of the snout.  Both placements allowed the animals to breathe while mostly submerged underwater.  

During the time of Rutiodon, the true crocodilians were small land-dwellers.

Rutiodon likely spent most of its time in or near fresh water.  Its eye sockets and nostrils were both at the highest point of its skull so it would have been able to remain almost completely hidden in murky water while still being able to see and breathe.  This would have been a helpful adaptation if it was trying to get close enough to snatch prey as it drank at the water's edge.  Rutiodon also almost certainly ate plenty of fish and other aquatic animals and maybe even occasionally snatched careless pterosaurs perched on low-hanging branches or as they flew too close to the water's surface.  Rutiodon's teeth showed some diversity depending on their placement in the mouth which give us hints as to how exactly it fed.  The teeth at the very tip of the jaws were the longest, which could have concentrated more pressure to that point as the animal bit into struggling prey.  The needle-like teeth in the middle of the snout were more for holding on and making sure food didn't escape once bitten.  

Rutiodon skeleton at the American Museum of Natural History in New York.

Like modern crocodilians, Rutiodon was adorned with bony armor plates, called osteoderms.  This armor would have served as protection against predators when Rutiodon was still young and small, and possibly against other members of its own species if adults engaged in any kind of fighting over territory or dominance.  If modern crocodilians are any indicator of its behavior, then they probably did. 

References

Colbert, E. H. (1947). Studies of the phytosaurs Machaeroprosopus and Rutiodon. Bulletin of the American Museum of Natural History 88:53-96. 

Michelle R. Stocker (2010). "A new taxon of phytosaur (Archosauria: Pseudosuchia) from the Late Triassic (Norian) Sonsela Member (Chinle Formation) in Arizona, and a critical reevaluation of Leptosuchus Case, 1922". Palaeontology. 53 (5): 997–1022. 

Stocker, M. R. (2012). "A new phytosaur (Archosauriformes, Phytosauria) from the Lot's Wife beds (Sonsela Member) within the Chinle Formation (Upper Triassic) of Petrified Forest National Park, Arizona". Journal of Vertebrate Paleontology. 32 (3): 573–586.