Before There Were Dinosaurs, There Was This Weird Crocodile-Looking Thing

Everybody knows about dinosaurs. How could we not? They’re everywhere, from museum halls and Hollywood blockbusters to city sidewalks where their modern, feathery representatives pick up crumbs with their beaks. But even while we adore the terrifying Tyrannosaurus and breathtaking Brachiosaurus, we still know next to nothing about the earliest dinosaurs that arose over 235 million years ago—and who exactly they evolved from.

That may be about to change, thanks to a new analysis of an enigmatic creature from the ancient rock of Tanzania. This crocodile-like beast, it turns out, plays a starring role in the origin story of the terrible lizards.

The story of this new dinosaur predecessor, described by Virginia Tech paleontologist Michelle Stocker and colleagues in a Nature study published today, picks up in 1933. That’s when British paleontologist Rex Parrington collected some unusual bones from the 245 million-year-old rock of southern Tanzania. Those bones rested in storage until 1956 when paleontologist Alan Charig categorized them as some sort of archosaur, part of the major group of reptiles that includes dinosaurs and other lineages—but it was difficult to say where exactly the species fell.

Nonetheless, Charig proposed a name for the animal in his unpublished research: Teleocrater, or “finished bowl,” in reference to the saurian’s closed hip socket.

The reptile’s hip may have been finished, but the story wasn’t: Charig never published his research on the animal, and so the mystery of Teleocrator remained unresolved. It wasn’t until 2015, when a multi-institution team of researchers recovered additional bones of Teleocrater from Tanzania’s Manda Beds, that researchers began a new analysis of the ancient enigma.

While significant, Parrington’s Teleocrater find was relatively meager. “The original material consists of limb elements and some vertebrae,” Stocker says, “but no skull material.” This left Stocker and colleagues eager to find more bones during their field expeditions to Tanzania; their 2015 jackpot added more elements of the hips, limbs, spine and skull of the animal. The new collection brought Teleocrater into finer focus: This 10-foot-long reptile walked on all fours, and its curved, serrated teeth hint that Teleocrater used its long neck to strike at protomammals and other small prey of its time.

But the most impressive thing about Teleocrater, Stocker and colleagues highlight, is its pedigree. Teleocrater was a very early predecessor of Mesozoic superstars like dinosaurs and the flying pterosaurs. The evolutionary arrangement goes like this.

Among the archosaurs, or “ruling reptiles,” there are two major groups: the crocodiles and their relatives on one side, and the dinosaurs and their relatives on the other. The dinosaur and pterosaur side is called the Avemetatarsalia, or “bird feet.” Early on, it seemed impossible for scientists to tell which side of the split Teleocrater sat on, as the crucial bones were missing. But the new analysis places Teleocrater definitively near the base of the Avemetatarsalia—the line that includes dinosaurs and their closest relatives.

It’s important to note that doesn’t necessarily mean that Teleocrater was a direct dinosaur ancestor; direct ancestry is almost always impossible to discern in the fossil record. Instead, Teleocrater and related reptiles from Triassic rocks act as stand-ins that show paleontologists the general form and nature of dinosaur ancestors. In this case, that the earliest members of the dinosaur branch of the archosaur family tree were four-legged meat-eaters that still shared some features in common with their more distant crocodile cousins.

The characteristics that place Teleocrater as being just that much closer to dinosaurs than crocodiles are subtle: a depression on a bone at the back of the skull; the length of the neck vertebrae; articulations on the spine; and muscle attachment points on the arms and legs. Taken together, Stocker says, these qualities all pin Teleocrater as being an early member of the Avemetatarsalia line that would later spin off the dinosaurs.

Paleontologists can still see Teleocrater as an animal in transition. Dinosaurs and their close relatives are often characterized by a simple hinge-like ankle joint, while crocodiles and their kin have a more complex arrangement of bones. Yet despite being on the dinosaur side, the ankle of Teleocrater resembles that of a crocodile. This came as a surprise, Stocker says, and indicates that the more complex, crocodile-type ankle shape was ancestral for archosaurs.

It was the combination of continued fieldwork and previously collected specimens that allowed paleontologists to reconcile the identity of Teleocrater, Stocker says. Beyond Teleocrater, researchers are also beginning to identify other mystery animals from India and Russia as early members of the line that would give rise to dinosaurs and their kin that would go on to rule the world for well over 100 million years. Once the puzzle of Teleocrater was solved, the identity of other mysterious fossil reptiles snapped into focus.

These kinds of finds are changing what paleontologists had come to expect of the earliest dinosaurs. “For a long time we thought that the ancestral body plan of dinosaurs was small and bipedal,” Stocker says, “but Teleocrater instead shows us that those small bipedal forms were unique and on their own evolutionary path.”

At the time Teleocrater prowled along the ancient river system it called home, dinosaurian dominance was still a long way off. It would take another mass extinction to give dinosaurs the edge they needed to step out of the shadow of the more numerous crocodile cousins that dominated the Triassic. But from our modern perspective, we can see in Teleocrater the glimmerings of what was to come: a whisper of when dinosaurs would come to rule the Earth.

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.