The First Crocodiles

Before the first true crocodiles emerged on the prehistoric scene, there were the phytosaurs ("plant lizards"): archosaurs that looked very much like crocodiles, except that their nostrils were positioned on the tops of their heads rather than the tips of their snouts. You might guess from their name that phytosaurs were vegetarians, but in fact they subsisted on fish and marine organisms in freshwater lakes and rivers worldwide. Among the most noteworthy phytosaurs were Rutiodon and Mystriosuchus.

Rutiodon (Greek for "wrinkled tooth"); pronounced roo-TIE-oh-don

Habitat: Swamps of North America
Historical Period: Late Triassic (225-215 million years ago)
Size and Weight: About 8 feet long and 200-300 pounds
Diet: Fish
Distinguishing Characteristics: Crocodile-like body; nostrils on top of head

About Rutiodon:

Although it's technically classified as a phytosaur rather than a prehistoric crocodile, Rutiodon cut a distinctively crocodilian profile, with its long, low-slung body, sprawling legs, and narrow, pointed snout. What set the phytosaurs (an offshoot of the archosaurs that preceded the dinosaurs) apart from early crocodiles was the position of their nostrils, which were located on the tops of their heads rather than on the ends of their snouts (there were also some subtle anatomical differences between these two types of reptiles, which only a paleontologist would be much concerned with).


Mystriosuchus (Greek for "spoon crocodile"); pronounced MISS-tree-oh-SOO-kuss

Habitat: Swamps of western Europe
Historical Period: Late Triassic (215-205 million years ago)
Size and Weight: About 13 feet long and 1,000 pounds
Diet: Fish
Distinguishing Characteristics: Long, narrow snout with numerous teeth

About Mystriosuchus:

Perhaps it has something to do with the way they live, but of all the animals that have persisted from the Mesozoic Era down to the present day, the crocodiles seem to have changed the least. A good example is Mystriosuchus, whose pointy, tooth-studded snout bears a remarkable resemblance to the modern gharial of central and southern Asia. Like the gharial, Mystriosuchus is believed to have been an accomplished swimmer, spearing and eating fish as it plied the ancient rivers of western Europe.

Technically, Mystriosuchus is classified as a phytosaur, a type of archosaur (the family of ancient reptiles preceding the dinosaurs) that differed from primitive crocodiles in that their nostrils were positioned on top of the skull, between the eyes, rather than on the ends of their snouts. So rather than a direct ancestor of modern crocodiles, Mystriosuchus can be considered a great-great-great, etc. uncle.

Oddly enough, except for the location of their nostrils, phytosaurs looked more like modern crocodiles than the first true crocodiles did. The earliest crocodiles were small, terrestrial, two-legged sprinters, and some of them were even vegetarians (presumably because their dinosaur cousins were better adapted to hunting for live prey). Erpetosuchus and Doswellia are two leading candidates for the honorific of "first crocodile," though the exact evolutionary relationships of these early archosaurs are still uncertain. Another likely choice is the recently reclassified Xilousuchus, from early Triassic Asia, a sailed archosaur with some distinctly crocodilian characteristics.

Later Crocodiles

By the start of the Jurassic period (about 200 million years ago), crocodiles had mostly abandoned their terrestrial lifestyles. This is when we begin to see the marine adaptations that characterize modern crocodiles and alligators: Long bodies, splayed limbs, and narrow, flat, tooth-studded snouts with powerful jaws (a necessary innovation, since crocodiles feasted on dinosaurs and other animals that ventured too close to the water). There was still room for innovation, though: for example, paleontologists believe that Stomatosuchus subsisted on plankton and krill, like a modern grey whale.

About 100 million years ago, toward the middle of the Cretaceous period, some crocodiles had begun to imitate their dinosaur cousins by evolving to enormous sizes. The king of the Cretaceous crocodiles was the enormous Sarcosuchus, dubbed "SuperCroc" by the media, which measured about 40 feet long from head to tail and weighed in the neighborhood of 10 tons. And let's not forget the slightly smaller Deinosuchus, the "deino" in its name connoting the same concept as the "dino" in dinosaurs: "terrible" or "fearsome."

One way in which prehistoric crocodiles were indeed more impressive than their terrestrial relatives was their ability, as a group, to survive the K/T Extinction Event that wiped the dinosaurs off the face of the earth 65 million years ago (why this is so remains a mystery, though it may be an important clue that no plus-sized crocodiles survived the meteor impact). Today's crocodiles and alligators are little changed from their prehistoric ancestors, a telling clue that these reptiles were (and remain) extremely well adapted to their environment. (See this article for possible theories about why crocodiles survived into the Cenozoic Era.)

Here's a list of the most notable crocodiles and phytosaurs


Aegisuchus Better known as the "ShieldCroc."

The specimen — a hefty hunk of fossilized skull, first discovered years ago in southeastern Morocco — was re-discovered by evolutionary biologist Casey Holliday, who happened upon it while searching through unlabeled specimens in The Royal Ontario Museum. The specimen is thought to come from a previously undescribed species (the researchers have dubbed it Aegisuchus witmeri) dating to the Late Cretaceous period, approximately 95 million years ago. According to the researchers, that makes it the earliest true crocodile specimen ever recovered from Africa.

But in terms of uniqueness, this skull fragment has way more going for it than its age; it also features a unique arrangement of bumps and dents, left by blood vessels centered in the roof of A. witmeri's cranium, seen here.

These blood vessels, explains Holliday — along with co-author Nick Gardner — in the latest issue of PLoS ONE, were likely necessary for delivering blood to a thick, circular, shield-like mound of skin atop the creature's skull — a physiological feature never before seen in a crocodile.This fleshy anatomical feature has earned A. witmeri the nickname of "Shieldcroc" — a misleading name, perhaps, given that Holliday suspects the croc used its fleshy headgear not for physical protection, but as a visual display for attracting mates or warding off predators.

Granted, Shieldcroc would have looked pretty intimidating even without its shield. Analyses of the skull fragment suggest that this prehistoric creature was positively massive. By comparing the skull fragment to those of numerous other species, Holliday and Gardner were able to estimate that the creature's head was somewhere in the range of 2.08—2.86 meters long. A head that size would put the reptile's total length at somewhere between 15 and 22 meters. As a point of reference, your typical city bus is about 10 or 11 meters long.

Araripesuchus This long-legged crocodile hunted its prey on land

Baurusuchus A land-dwelling crocodile of Cretaceous South America.  
Bernissartia One of the smallest of all the Cretaceous crocodiles.  
Champsosaurus A crocodile-like reptile of the late Cretaceous period.  

Chimaerasuchus The first vegetarian crocodile ever to be discovered.

Dakosaurus This fierce marine crocodile had a dinosaur-like head.  
Deinosuchus One of the biggest crocodiles of the Cretaceous period.  

Desmatosuchus A crocodile-like archosaur with a fish-like head.

Diplocynodon A prehistoric alligator of western Europe.  

Doswellia This may (or may not) have been one of the earliest crocodiles.

Erpetosuchus This tiny reptile may have been the ancestor of all crocodiles.  

Geosaurus This aquatic reptile may have spent its entire life in the sea.

Goniopholis A widespread crocodile of the late Jurassic period.  

Gracilisuchus One of the most dinosaur-like of all the Triassic crocodiles.

Kaprosuchus This "BoarCroc" had some very big teeth.  
Metriorhynchus One of the most common crocodiles of the Jurassic period.  
Mystriosuchus This Triassic archosaur looked a lot like a modern gharial.  
Notosuchus Did this ancient crocodile have a pig-like snout?  
Pakasuchus This tiny crocodile had distinctly mammalian teeth.  
Pristichampsus A hooved crocodile of the Eocene epoch.  
Protosuchus This land crocodile competed for prey with early dinosaurs.  
Purussaurus A giant caiman of the Miocene epoch.  
Quinkana A terrestrial crocodile from Down Under.  
Rhamphosuchus Once thought to be the biggest crocodile that ever lived.  
Rutiodon This crocodilian's nostrils were located on top of its head.  
Saltoposuchus This "leaping crocodile" spent most of its time on two legs.  
Sarcosuchus A Cretaceous "SuperCroc" that put modern crocodiles to shame.  
Simosuchus This ancient crocodile had an unusually short skull.  
Stagonolepis This crocodile-like archosaur was actually a vegetarian.  
Steneosaurus An ocean-going crocodile of the Mesozoic Era.  
Stomatosuchus This giant crocodile fed on tiny plankton, like a baleen whale.  
Terrestrisuchus Otherwise known as "the greyhound of the Triassic."  
Xilousuchus One of the earliest archosaurs in the fossil record.