Episode 142 – Phytosaurs

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Travel back in time to the Late Triassic, and the waters were home to animals you’d easily mistake for crocs. This episode, we discuss the fossil record, lifestyles, and uncanny croc-ness of Phytosaurs.

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Crocs Before Crocs

Phytosaurs are an extinct group of carnivorous reptiles. They’re famous for being found on nearly all continents; they’re famous for being among the most abundant and important predators of the Late Triassic; but mostly, they’re famous for their uncanny resemblance to crocodilians.

Top: Skeleton of the phytosaur Redondasaurus by Piotrus, CC BY-SA 3.0
Bottom: Artist’s reconstruction of the phytosaur Protome by Smokeybjb, CC BY-SA 3.0

If you caught a glimpse of a living phytosaur (or even a skeleton), you could easily mistake it for a croc. They have large, low bodies, sprawling limbs, long tails, long toothy snouts, and backs covered in osteoderm armor. Phytosaurs even came in similar sizes to crocs, ranging from a few meters long to over 10 meters. It’s an incredible case of convergent evolution.

But despite these differences, phytosaurs are NOT crocs. They’re generally thought to be an earlier branch of archosaurs, or perhaps close relatives of true archosaurs. And since the entire phytosaur fossil record is restricted to the Triassic Period, this means that not only are phytosaurs not all that closely related to crocs, they also went extinct more than 100 million years before true crocodilians as we know them evolved.

The most obvious difference between phytosaurs and crocodilians is in the skull. A croc’s upper jaw is mostly comprised of the maxillary bone, while in phytosaurs it’s mainly the premaxillary bone. A side effect of this is that phytosaur nostrils are not down at the tip of the snout, but up by the eyes.
Top: Phytosaur (Rutiodon) skull by Ryan Somma, CC BY-SA 2.0
Bottom: Modern gharial skull by Andrew R. Cuff and Emily J. Rayfield, CC BY 2.5

Looks can be deceiving, and some scientists have cautioned that it might not be accurate to assume phytosaurs lived exactly like modern crocs just because of their physical similarity. That said, there is evidence that, in many ways, phytosaurs were doing many of the same things crocs would do millions of years later.

Phytosaurs were most likely at least partially aquatic. Not only do they have a good body shape for it, like modern crocs, but their fossils and even trackways are typically found in lake and river deposits. Many phytosaurs, like Rutiodon (pictured here) were likely semi-aquatic.
Image by Dmitry Bogdanov, CC BY-SA 3.0

Phytosaurs were predators. This is evident from the shape and wear patterns of their teeth, from occasional phytosaur stomach contents, and from some examples of phytosaur bite marks on other animals. Most of them were also probably quite capable swimmers, and the fact that their eyes and nostrils are elevated on the skull suggests they spent lots of their time submerged just under the surface like modern crocs do. Some phytosaurs were well-adapted for a more aquatic lifestyle, like Mystriosuchus with its more paddle-like limbs, and certain others are thought to have perhaps been more terrestrial, like Nicrosaurus.

Sometimes, multiple phytosaur fossils are found in close proximity, which has led paleontologists to wonder if some phytosaurs might have been gregarious, gathering in groups like some crocs do today. At least one case of young and old phytosaurs found together might be an indication of parental care. If that’s true, then phytosaurs might have been even more croc-like than their anatomy alone would suggest!

Learn more

Diandongosuchus—the strange-faced transitional phytosaur

Brain anatomy convergence between crocodylians and phytosaurs

The Last Phytosaur

Phytosaurs, (mostly) gharial-snouted reptiles of the Triassic

Phytosauria, a major overview from 2013 (technical)

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