The Phytosaurs

Phytosaurs were large, heavily-armored, (mostly) semi-aquatic predators of the Late Triassic. When their remains were first discovered, they were erroneously thought to belong to an herbivore, hence the name ‘phytosaur’ – which literally means ‘plant reptile.’ The fact that these creatures were feisty predators is, then, rather ironic. Generally speaking, phytosaurs were long-snouted, covered in armor, and upon a quick glance resembled modern crocodiles in plenty of aspects. This is an example of convergent evolution, in that phytosaurs were adamantly not crocodiles. Though they were distantly related to the crocodiles we know today, they weren’t ancestral. The crocodilian ancestors of the Triassic – the crocodylomorphs, or ‘proto-crocs’ – lived side-by-side with the phytosaurs but resembled reptilian wolves. It wasn’t until the Early Jurassic that proto-crocs became ‘crocodilian’; or, to put it in a more honest way, became ‘phytosaur-like’! It isn’t that phytosaurs resemble crocodiles; it’s that crocodiles resemble phytosaurs! Phytosaurs, after all, came first. 

a phytosaur takes center-stage among early crocodilians
and a Coelophysis

The phytosaurs first appear in the Carnian stage of the Late Triassic. They have no welcoming committee, no ‘transitional fossil’ heralding their arrival. They show up on the scene as full-fledged, highly-specialized semi-aquatic predators unlike most of their contemporary terrestrial archosaurs. They spread across Pangaea like kudzu, gaining a nearly global distribution during the Triassic. Only in southern Pangaea, where the environment was much drier, were they hard-pressed to thrive. The first phytosaurs were ‘basal’ in the sense that they weren’t highly-specialized for particular environments (despite being specialized for semi-aquatic living). In the late Carnian, more specialized forms emerged, such as Rutiodon, Leptosuchus, and Smilosuchus. These specialized phytosaurs died off in the Carnian-Norian extinction, and the surviving phytosaur lineages were more basal and thus more able to adapt to changing environments (the more specialized you become, the harder catastrophe hits). By the middle of the Norian stage of the Late Triassic, advanced and specialized phytosaurs were reemerging, such as the highly successful fish-eating Mystriosuchus. Phytosaurs underwent rapid diversification and specialization throughout the Norian and into the Rhaetian, but their star-studded rise to fame died out in the twinkling of a geologic eye at the Triassic-Jurassic Extinction Event. Crossing into the Jurassic Period, phytosaurs are nowhere to be found. Sure, some paleontologists have argued that a lineage or two survived into the early Jurassic, but evidence is lacking or at least misleading. For example, what looks like phytosaurs teeth have been found in early Jurassic rocks, but these could easily be misidentified; and the remains of a supposed phytosaur from the Early Jurassic turned out to be, upon closer examination half a century later, the remains of a sauropodomorph dinosaur. 

Phytosaurs grew between two to twelve meters in length and averaged three to four meters. These creatures come in three different morphologies centered around differences in their skulls due to changes related to feeding and habitat. Interestingly enough, modern crocodiles also share diverging morphological characteristics: compare the broad-snouted alligator and the long-snouted gavial. 

The Dolichorostral Morphology contains the ‘long snouted’ phytosaurs. These organisms had a long, slender snout with homodont conical teeth (homodont meaning that all teeth were the same). These phytosaurs were most likely piscivores (fish eaters) and were adapted to seize fast aquatic prey. However, they wouldn’t have fared well against land-dwelling prey, unlike their brachyrostral cousins. Long-snouted phytosaur species include Paleorhinus, Rutiodon, and Mystriosuchus (the latter of which became almost fully aquatic with paddle-like limbs and a laterally-compressed tail used for marine locomotion). 

a school of Mystriosuchus hunting in the Late Triassic seas

The Brachyrostral Morphology contains the ‘short snouted’ phytosaurs. These phytosaurs were adapted to hunting and eating terrestrial prey. They had massive, broad snouts and strong skulls and jaws. Their front teeth were prominent fangs, and their rear teeth were blade-like, designed for slicing food into easily-swallowed chunks. Though some short-snouted phytosaurs – such as Nicrosaurus and Smilosuchus – seemed more designed for life on land than in the water, many of its brethren likely hung around shorelines and watering holes to snatch unwary prey coming to the water to drink – much like modern crocodiles in Africa. 

a pair of Smilosuchus prowling a herd of Placerias

The Altirostral Morphology contains the ‘high snouted’ phytosaurs. These are viewed as intermediates between the long-snouted and short-snouted phytosaurs. Their teeth were heterodont (not all alike), but they weren’t as developed as those of their short-snouted cousins. The ‘hybrid’ morphology may indicate a ‘generalist’ feeding style, in which they would prey on marine creatures as well as smaller terrestrial ones. An example of this morphology is the phytosaur Pseudopalatus.

a Rutiodon growls at a flock of Fabrosaurus

The three main morphologies aside, all these phytosaurs have at least one thing in common: were we to step back in time today, our gut instinct would tell us they were crocodiles. Nevertheless, they were not crocodiles and not even ancestral to them. There are several key differences between phytosaurs and crocodiles. Phytosaurs had primitive ankles, and they lacked the bony secondary palate that enables crocodiles to breathe even when their mouths are full of water (though some scientists speculate they had a fleshy palate rather than a bony one, as many Mesozoic crocodiles are thought to have had). Phytosaurs were more heavily armored than crocodiles: phytosaurs were protected by heavy bony scutes, and their bellies were reinforced with a thick arrangement of abdominal ribs called gastralia. Crocodile nostrils are placed near the end of the snout, but phytosaur nostrils were placed on a crest high on the skull near or above the eyes (presumably to enable them to breathe while they floated just underneath the surface of the water). And, unlike crocodiles, phytosaurs had an erect gait with their legs positioned directly beneath their bodies rather than sprawled to the side. Thus phytosaurs could move easily about on land, though they were at home in the water, too; phytosaur ‘swim tracks’ have been found in the fossil record. Though it’s likely that they reproduced the same way as modern crocodiles – laying eggs – no nests have been found. Some paleontologists speculate that phytosaurs provided parental care for their young like modern crocodilians.