The Long-Ignored Reptile Rewriting the Prologue to the Dinosaur Story

After 84 years, scientists have finally unravelled the mystery of an early dino-cousin.

A rendering of Teleocrater (Mark Witton / Natural History Museum, London)

The creature known as Teleocrater has been described as one of the most notorious fossils in paleontology. Pieces of its limbs, spine, and tail were excavated from Tanzania in 1933, and the British paleontologist Alan Charig discussed it 23 years later in his Ph.D. thesis. But even though Charig talked about the animal, and wrote about it in his popular children’s books, he never formally published its name or description in an academic journal. Perhaps that was because the creature had such a strange mix of features that Charig couldn’t tell what it was. A dinosaur? An early crocodile? Some other kind of ancient reptile?

While he procrastinated, “the fossils were off the table,” says Sterling Nesbitt, a paleontologist at Virginia Tech University. “I don’t think he allowed anyone to see them unless he knew them very well.” By the time Charig died in 1997, Teleocrater was still as mysterious as the day it was unearthed. “For 60 years, [the specimens] existed in suspended animation—like Schrödinger’s fossils,” says Stephen Brusatte, from the University of Edinburgh. “They were there, we knew they existed, but we didn’t really know what they were.”

Well, not anymore. In the summer of 2015, Nesbitt and his colleagues returned to the same spot where Charig’s fossils were found, and dug up three more specimens of Teleocrater. And they’ve finally published a formal description—enshrining its name, and depicting its body.

Physically, Teleocrater isn’t spectacular. It was a labrador-sized animal, six feet from nose to tail, with a long neck, a slender build, a four-legged stride, and the sharp teeth of a meat-eater. “A monitor lizard is probably the closest comparison you can make—but less sprawling,” says Michelle Stocker, who was part of Nesbitt’s expedition.

But evolutionarily, Teleocrater turns out to be pivotal. It’s one of the earliest offshoots of the lineage that eventually led to dinosaurs and birds, and provides important clues about their evolution. It’s not the ancestor of dinosaurs, but its physique “gives a glimpse at what that ancestor might have looked like, what it ate, and how it would have moved and behaved,” says Brusatte, who wasn’t involved in the new study. “Simply put, Teleocrater helps tell us where dinosaurs come from.”

Teleocrater (Courtesy of Martin D. Ezcurra)

In the early Triassic period, around 250 million years ago, a group of ancient reptiles split into two mighty lineages. The first—the pseudosuchians (SOO-doh-SOO-key-erns)—gave rise to living crocodiles and their extinct kin, including a bizarre menagerie of bipedal, stilt-legged, hoof-toed, cat-toothed, duck-billed, armadillo-armored, pig-snouted oddities. The second—the avimetatarsalians (AY-vee-MEH-tuh-tar-SAY-lee-erns)—gave rise to the dinosaurs and their bird descendants, the winged pterosaurs, and other dinosaur-ish groups. For millions of years, these two lineages—the croc branch, and the dino/bird branch—ruled the planet. (Note that lizards belong to a very different group of reptiles altogether, so while Teleocrater looks superficially like a monitor, it definitely wasn’t one.)

The early split between these two groups, and the nature of their first members, has long been a mystery. There just aren’t that many good fossils from the early and mid-Triassic, and the earliest members of both lineages already look very different from each other. That’s why Teleocrater is so important. It sits on the dino/bird branch of the family tree, but very close to the split with the croc branch. Its body reveals what these animals were like just after they started diverging from each other.

Consider its ankles. In crocodiles, the two major ankle bones can rotate against each other, creating a flexible arrangement that’s suitable for both sprawling and erect gaits. In dinosaurs and birds, those two bones are stuck together and move as one, so these animals can only walk erect. Scientists had assumed that these two ankle types had evolved on their respective branches. But surprise! Teleocrater had the flexible, croc-like ankle, which is probably what the common ancestor of the croc and dinosaur lineages had. “It clearly demonstrates that the first forms on the bird lineage were much more similar to pseudosuchians than we previously thought,” says Randall Irmis, from the Natural History Museum of Utah.

Likewise, until now, the earliest known members of the dinosaur/bird branch were small, lithe, two-legged runners. But Teleocrater suggests that these animals were very specialized, and the group’s first representatives were slower, and moved on four legs.

From left to right: Christian Sidor, Sterling Nesbitt, Michelle Stocker, and Kenneth Angielczyk excavating Teleocrater. (Courtesy of Roger Smith)

This kind of information “will allow us to get at the really interesting questions, such as what features evolved in pterosaurs and dinosaurs that allowed them become successful,” says Irmis. “When did these features evolve, and did it have anything to do with the environments they lived in after the end-Permian mass extinction?” He’s talking about the greatest catastrophe in Earth’s history—the prolonged event that took place just before the Triassic period, which wiped out the vast majority of life on the planet.

The split between the croc lineage and dinosaur lineage happened shortly after, and the story has long been that the former dominated first. They were more widespread, richer in species, and more diverse in their body shapes. Indeed, the Triassic has been described as the “age of crocodilians.” The dinosaurs and pterosaurs had evolved, but they stuck to the sidelines, only taking center stage when another extinction event marked the end of the Triassic. But Nesbitt’s team thinks otherwise.

Their new discovery allowed them to reevaluate several other enigmatic Triassic weirdos, known from partial and piecemeal fossil remains. On their own, their bones provided few clues. But each is similar enough to a piece of Teleocrater that Nesbitt could confidently unite them into a single family—the aphanosaurs. They were clearly very widespread. Teleocrater lived in what is now Tanzania, Yarasuchus in India, Dongusuchus in Russia, and Spondylosoma in Brazil. “These things were probably everywhere,” says Nesbitt.

Other scientists have found similar patterns for several early dinosaur-adjacent groups, like the silesaurs and lagerpetids. “All these side-branches—these dinosaur relatives—were doing all the same things that dinosaurs eventually did. Again and again, they radiated and spread out across the world. The more we look in the Triassic sediments, the more we find them.”

This clearly shows that during the supposed “age of crocodilians,” the early members of the dinosaur bird lineage were also physically diverse, widespread, and successful. “It’s not that the dinosaurs suddenly took over,” says Stocker. “They and the croc lineage are both living together in the Triassic, and represent the same range of forms.”

Just last month, I wrote about another big paper that also relied on Triassic fossils. It showed that the first big fork in the dinosaur family tree, which has been the stuff of textbooks and museum exhibits for 130 years, might be wrong. As Lindsay Zanno, from the North Carolina Museum of Natural Sciences, told me, “If confirmed by independent studies, the changes will shake dinosaur paleontology to its core.”

Combined, the two studies are a “one-two punch,” says Nesbitt. “They say: Hey, we didn’t have the whole story of early dinosaur evolution figured out. There’s been so much new information.”

But Brusatte notes that with many of these studies, there’s a lot of uncertainty. “It might only take one new fossil, or the reinterpretation of a trait or two, to swing the results and make Teleocrater and other aphanosaurs members of the crocodile side of the family tree,” he says. “There have been so many genealogical studies of early dinosaurs and their close relatives lately, and they all find slightly different results. It wouldn't surprise me if the family tree changes with the next discovery or next analysis from a different research group.”