Phytosaurs were a geographically widespread group of semiaquatic reptiles that thrived in the Late Triassic. Everything Dinosaur team members look at the remarkable phytosaur Colossosuchus techniensis and other related genera.

The phylogenetic position of the phytosaurs remains disputed. This is in part as little is known about their ancestral forms. For example, some scientists classify phytosaurs as members of the Archosauria, uniting them in the same clade as crocodiles, pterosaurs, dinosaurs and birds. However, other researchers, notably the American palaeontologist Sterling Nesbitt does not define the Phytosauria as archosaurs, but as close relatives to the Archosauria (Archosauriformes).

Often depicted with a sprawling gait, a trackway assigned to a phytosaur (Apatopus) indicates that these reptiles adopted a “high walk” gait.  They had an erect stance, albeit with a tail drag, and a parasagittal gait, much as crocodiles do today.

Phytosaurs Resembled Extant Crocodilians

These animals superficially resembled crocodilians, although they were not closely related to modern crocodiles. This is an example of convergent evolution.  Convergent evolution is the process through which distantly related or unrelated organisms evolve similar characteristics or adaptations in response to similar environmental pressures.  For instance, most phytosaurs were probably aquatic ambush predators.  They occupied an environmental niche in ancient ecosystems similar to the niche occupied by extant crocodilians.

A museum exhibit featuring a typical phytosaur. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Characteristics of Phytosaurs

Although superficially resembling crocodiles there were notable differences.  For example, the nostrils of phytosaurs were located high up on the skull, almost between the eyes. The nostrils were located atop a dome-like structure towards the posterior of the snout. In crocodilians, the nostrils are located at the tip of their long snouts.

The location of the nostrils in a phytosaur. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

In addition, phytosaurs lacked the bony secondary palate found in crocodilians.  Although, they probably possessed a fleshy secondary palate that enabled them to breathe whilst they had water in their mouths.  Unfortunately, the presumed presence of a fleshy palate is not confirmed in the fossil record, probably due to this structure’s poor preservation potential.

The arrangement of dermal armour was probably different too. Phytosaurs probably had a paired row of armoured scutes running down their backs. In contrast, crocodilians have multiple rows of scutes.

The manus (hand) of these reptiles such as the phytosaur Colossosuchus techniensis consisted of five digits.

A description of the phytosaur manus:

• The manus is short and rounded with digit III being longest.
• Digits II and IV are approximately the same length.
• Moreover, digit V is the smallest digit. Digit I (pollex) is short but robust.
• Claws are present on digits I to IV.
• The largest claws being located on digit I and II.

A description of the phytosaur pes:

• The pes had five digits.
• Digit I was short and quite robust.
• Digits II, III and IV were long and slender.
• Digit IV was the longest.
• It is believed that all the digits had claws.
• Digit V was much reduced and the shortest digit. It did have a small claw.

How Big were the Largest Phytosaurs?

Scientists remain uncertain over the size of the largest taxa.  Some phytosaurs may have been bigger than the largest living crocodilian the Saltwater crocodile (Crocodylus porosus) which rarely exceeds six metres in length. For example, Rutiodon carolinensis from the southeastern United States is thought to have measured about eight metres long.  It is known from numerous fossil specimens including skull material. The largest skull measures seventy-seven cm in length.

Furthermore, Smilosuchus gregorii is thought to have reached a length of around eight metres.  Some body length estimates for this species exceed twelve metres. However, these estimates are based on highly fragmentary specimens. The recently described Indian phytosaur Colossosuchus techniensis is also estimated to have reached a length of around eight metres.

The 2023 scientific paper describing the phytosaur Colossosuchus techniensis:

“A giant phytosaur (Diapsida, Archosauria) from the Upper Triassic of India with new insights on phytosaur migration, endemism and extinction” by Debajit Datta and Sanghamitra Ray published in Papers in Palaeontology.

Mike from Everything Dinosaur commented:

“Intriguingly, there are numerous examples of at least two phytosaur species being coeval.  One species is often narrow-snouted [Dolichorostral] with teeth that are very similar.  The second species often has a much more robust snout [Brachyrostral] with differently shaped teeth.  Often the robust snouted forms have long fangs at the end of their jaws.  This suggests that these two phytosaurs evolved to take advantage of different food resources although they shared the same environment. Niche partitioning seems to have taken place quite frequently within the Phytosauria.”

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Palaeontologists explain this niche partitioning phenomena by suggesting that the ancestral phytosaur species specialised in eating different things.  They eventually diverged into two closely related but different species. It is remarkable that this evolutionary pattern is repeated so often within the Phytosauria fossil record.