Those Crocodile-Like Creatures of the Past — The Phytosaurs

When people think of crocodiles, a very specific image usually appears: a long snout, a powerful jaw full of teeth, short limbs, and a body covered with heavy scales and bony armor. With these features in mind, almost anyone could instantly recognize a crocodile.

But what if I told you that modern crocodiles are not the only animals that possessed this distinctive body plan? There was once another group of reptiles that looked even more “crocodile-like” than crocodiles themselves. These animals are the subject of today's story—the phytosaurs.

Figure 1. Life reconstruction of Rutiodon, showing the typical characteristics of phytosaurs.（圖片來源：Nobu Tamura，採用 CC BY-SA 3.0 授權）

Why Are They Called Phytosaurs?

The order Phytosauria, represented by species such as Phytosaurus cylindricodon, carries a name that originated from a rather dramatic misunderstanding.

The name Phytosaurus literally means “plant lizard.” It arose from an error made in 1828 by the German paleontologist Georg Friedrich Jäger (1785–1866). Jäger discovered the first fossil remains of this animal—a tooth and a fragment of the lower jaw—in Württemberg, Germany. The tooth fossil appeared flattened on one side and tapered below, resembling the teeth of herbivorous animals. Based on this apparent tooth morphology, Jäger concluded that the animal must have been plant-eating and named it Phytosaurus.

Figure 2. Early record of a phytosaur tooth, illustrated by Georg Friedrich Jäger.（圖片來源：Verlag der Metzler'schen Buchhandlung，CC0 1.0 公共領域）

Figure 3. Phytosaur tooth incorrectly described as having a flattened structure, illustrated by Georg Friedrich Jäger.（圖片來源：Verlag der Metzler'schen Buchhandlung，CC0 1.0 公共領域）

What Jäger did not realize was that the flattened surface he observed was actually sediment stuck to the fossil. The true tooth beneath it was conical in shape, typical of carnivorous predators. By the time the mistake became clear, however, the name had already been formally published. According to the rules of zoological nomenclature, the name had to remain in use despite the misunderstanding.

Figure 4. One of the early records of phytosaur teeth; the pointed portion represents the actual tooth, illustrated by Georg Friedrich Jäger（圖片來源：Verlag der Metzler'schen Buchhandlung，CC0 1.0 公共領域）

Diet and Classification within the Phytosaur Lineage

At present, all phytosaurs are generally placed within a single family, Phytosauridae, yet this family displays considerable diversity. In total, twenty-six species have been recognized. Based on the shape of the snout, phytosaurs can be broadly grouped into three morphological types: long-snouted forms, short-snouted forms, and high-snouted forms. Each corresponds to a different feeding strategy.

Much like modern crocodilians, phytosaurs were semi-aquatic ambush predators. Long-snouted species such as Rutiodon likely fed primarily on fish, much like the modern gharial (Gavialis gangeticus). Their narrow snouts and conical teeth were well suited for gripping slippery prey.

Short-snouted forms such as Smilosuchus probably occupied a role similar to that of the saltwater crocodile (Crocodylus porosus) or the American alligator (Alligator mississippiensis). These animals likely ambushed terrestrial vertebrates that approached water sources. Their broad snouts could withstand the mechanical stress of powerful bites, while their robust skulls and jaws allowed for large muscle attachments that increased bite force. In these species, the teeth were also differentiated into two types: conical teeth at the front of the mouth for grasping prey and blade-like teeth toward the rear for slicing tendons and flesh.

High-snouted forms combined features of the other two types. One example is Angistorhinus, which possessed a moderately elongated snout and heterodont dentition. Its feeding strategy may have resembled that of the modern false gharial (Tomistoma schlegelii), feeding on both fish and terrestrial animals.

Figure 5. Environmental adaptations within the genus Smilosuchus, showing divergence into long-snouted and short-snouted forms.（圖片來源：Dr. Jeff Martz，採用 CC BY-SA 4.0 授權）

Figure 6. Diversity of phytosaur snout morphologies.（圖片來源：RobinGoodfellow_(m)，CC0 1.0 公共領域）

When Did Phytosaurs Appear, and Why Did They Disappear?

The evolutionary origin of phytosaurs remains uncertain. What is known is that they belonged to Archosauria, the broader lineage that also includes the crocodile-line archosaurs (Pseudosuchia) and the bird-line archosaurs (Avemetatarsalia), the latter including dinosaurs.

The earliest known phytosaur is Diandongosuchus, discovered in Middle Triassic deposits of Yunnan, China. Compared with later phytosaurs, this species was relatively small and lacked one of the most distinctive traits seen in later members of the group—the position of the nostrils near the top of the head.

The marine sediments in which Diandongosuchus fossils were found, along with fish remains preserved in its stomach contents, suggest that it lived in environments composed of shallow coastal waters and islands. Such habitats may have provided the ecological conditions that encouraged the early evolution of phytosaurs.

Figure 7. Holotype specimen of Diandongosuchus, showing the primitive skull and preserved stomach contents（圖片來源：Michelle R. Stocker, Li-Jun Zhao, Sterling J. Nesbitt, Xiao-Chun Wu & Chun Li，採用 CC BY 4.0 授權）

The major diversification of phytosaurs likely occurred during the Carnian stage of the Late Triassic. During this time, Earth experienced a climatic episode known as the Carnian Pluvial Episode. The climate of the supercontinent Pangaea shifted from predominantly arid conditions to a more humid regime, resulting in increased rainfall and the formation of numerous wetlands, rivers, ponds, and swamps.

These environments created ideal habitats for semi-aquatic predators like phytosaurs. They also supported abundant prey, including fishes and large amphibians such as temnospondyls.

Figure 8. Changes in species diversity and climate indicators from the Carnian to the Norian; the orange box highlights fluctuations in phytosaur species diversity（圖片來源：Jacopo Dal Corso, Massimo Bernardi, Yadong Sun, Haijun Song，採用 CC BY 4.0 授權）

This flourishing period for phytosaurs continued until the Rhaetian stage at the end of the Triassic. Prior to the end-Triassic mass extinction, phytosaurs remained a successful and widespread group. However, following the extinction event, their diversity declined dramatically. By the Early Jurassic, phytosaur fossils appear only sporadically in the geological record, marking the disappearance of this once-dominant lineage.

How Phytosaurs Differ from Crocodiles

Perhaps the most striking difference between phytosaurs and modern crocodilians lies in the position of the nostrils.

In living crocodilians, the nostrils sit at the very tip of the snout. When the animal lies submerged in water, only the eyes and nostrils remain visible above the surface.

Phytosaurs, however, possessed nostrils located far back on the skull, positioned close to the eyes and near the top of the head. This arrangement resembles the breathing openings of whales and dolphins and may have allowed phytosaurs to breathe efficiently while remaining mostly submerged in deeper water during ambush.

Another difference involves the palate. Modern crocodilians possess a fully developed bony secondary palate, a structure that separates breathing from swallowing. Phytosaurs lacked this bony structure, although they may have possessed a softer, fleshy secondary palate. This condition is generally considered more primitive.

Their teeth also differed from those of crocodiles. Phytosaurs possessed serrated teeth similar to those of carnivorous dinosaurs, whereas modern crocodilians have smooth, conical teeth. Conical teeth are excellent for gripping prey and distributing mechanical stress during biting, but crocodiles must often perform a “death roll” to tear flesh from their victims.

Phytosaur teeth, by contrast, functioned more like serrated steak knives. Paleontologists believe these teeth were less capable of withstanding strong biting forces but were highly effective at slicing through flesh and causing significant bleeding.

Figure 9. Comparison between phytosaur teeth and those of living species. A, predator of relatively “soft” invertebrates (Varanus prasinus, emerald tree monitor); B, piscivore (Gavialis gangeticus, gharial); C, carnivore (Varanus rudicollis, rough-necked monitor); D, predator of relatively “hard” invertebrates (Crocodylus acutus, American crocodile); E, generalist carnivore (Varanus olivaceus, Gray's monitor). F–J, phytosaurs: F, Machaeroprosopus pristinus; G, Mystriosuchus planirostris (no. 6); H, Nicrosaurus kapffi (no. 7); I, Nicrosaurus meyeri (no. 14); J, Smilosuchus lithodendrorum（圖片來源：Jordan Bestwick, Andrew S. Jones, Mark A. Purnell, Richard J. Butler，採用 CC BY 4.0 授權）

In body posture, phytosaurs retained a more primitive stance than modern crocodilians. Their limbs were typically held in a sprawling posture rather than the semi-upright gait seen in many pseudosuchians, including crocodilians, birds, and pterosaurs. Most phytosaurs retained ancestral pelvic and ankle structures, suggesting that they diverged relatively early within the archosaur lineage. Because they spent much of their time in water, buoyancy likely reduced the need for an upright terrestrial posture.

Modern crocodilians, despite their semi-aquatic lifestyle, evolved from later pseudosuchians that had already developed more advanced ankle joints and a more upright gait. As a result, even after returning to aquatic habitats, crocodilians retained many derived archosaur features.

Figure 10. Schematic comparison of gait and pelvic structure among amniotes: (left) phytosaurs and basal archosaurs; (center) dinosaurs and mammals; (right) pseudosuchians（圖片來源：Fred the Oyster，採用 CC BY-SA 4.0 授權）

Figure 11. Comparison of ankle joints in phytosaurs and pseudosuchians: (left) the phytosaur ankle showing the primitive parallel configuration; (right) the more derived mesotarsal-style ankle of pseudosuchians（圖片來源：Philcha，CC0 1.0 公共領域）

Phytosaurs also possessed heavier armor than modern crocodiles. While crocodilians have dermal armor composed of osteoderms along the back, phytosaurs had both dorsal armor and specialized abdominal ribs that formed a protective “plastron-like” structure across the underside of the body—an anatomical feature absent in modern crocodilians.

Figure 12. 3D skeletal reconstruction of Redondasaurus bermani, illustrating the distinctive armor and nostril structure of phytosaurs（圖片來源：Piotrus，採用 CC BY-SA 3.0 授權）

Figure 13. Skeletal and skin specimens of Caiman crocodilus（圖片來源：Eden, Janine and Jim，採用 CC BY 2.0 授權）

Phytosaurs in Popular Culture and Future Research

Among prehistoric reptiles depicted in documentaries and educational media, phytosaurs are relatively well known. Species such as Rutiodon have appeared in television programs like Discovery Channel’s When Dinosaurs Roamed America and Animal Armageddon. The IMAX film Dinosaurs Alive! also featured the phytosaur Redondasaurus. Many dinosaur books likewise introduce phytosaurs alongside other pseudosuchian reptiles. For many readers, including the author of this article, phytosaurs were first encountered through such books.

For many decades, phytosaur fossils were primarily discovered in Europe and North America. More recent discoveries from India, Madagascar, North Africa, Thailand, and Yunnan in China have significantly expanded our understanding of their evolutionary history. In particular, research published in 2021 on Diandongosuchus helped fill an important gap in the early evolutionary history of phytosaurs.

Figure 14. Life reconstruction of Diandongosuchus（圖片來源：Smokeybjb，採用 CC BY-SA 3.0 授權）

This concludes our introduction to phytosaurs. Yet within the Triassic world, they were only one branch of a much larger archosaur lineage—the pseudosuchians. This diverse group produced not only crocodile-like reptiles but also forms that superficially resembled dinosaurs, and even the true ancestors of modern crocodiles themselves.

In the upcoming articles of this series, Rodrigo will continue exploring these remarkable reptiles and the strange evolutionary experiments that once thrived in the Triassic world.

Author: Rodrigo

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