Picture an ostrich-mimic dinosaur: long legs, a light frame, a toothless beak, and arms shrunk down to almost nothing. Now imagine finding an animal with that body plan in rock about 212 million years old. It seems wildly out of place. The dinosaurs best known for that shape would not appear until many tens of millions of years later. And yet paleontologists in New Mexico dug up a creature with a remarkably similar build. The twist: it was not a dinosaur at all. The animal, Labrujasuchus expectatus, sits on the branch of the reptile family tree that leads to modern crocodiles. That gap between what it looked like and what it actually was makes it one of the more interesting Triassic finds I have read about lately.

The claim: this looked remarkably like a later dinosaur

If you handed the skeleton to someone and asked them to guess, “small ostrich-mimic dinosaur” would be a reasonable answer. It walked upright on two legs, had greatly reduced forelimbs, and had a toothless mouth tipped with a beak. Its overall shape closely resembles the ostrich-mimic dinosaurs scientists call ornithomimosaurs. The team behind the description leans into that comparison. They describe shuvosaurs as “gracile, bipedal, and edentulous,” and generally convergent with ornithomimid theropod dinosaurs from the Cretaceous period. In plain words: slender, two-legged, and toothless, with a body plan strikingly similar to dinosaurs that would not appear until much later.

Why it was not one, and what it actually was

The reptiles of the Triassic had split into two major branches. One would eventually produce dinosaurs and birds. The other would lead to crocodiles and alligators. Labrujasuchus belongs firmly to that second branch, as part of a family of crocodile-line reptiles that independently evolved a dinosaur-like build. Its toothless, beaked mouth and upright stance were not inherited from an ostrich-mimic dinosaur ancestor. Similar features evolved separately on the crocodile side of the archosaur family tree. Labrujasuchus is only the fifth formally identified shuvosaur species, which is part of why it matters. The name carries a joke, too. It nods to “Ranchos de los Brujos,” an old Spanish name associated with the Ghost Ranch area, paired with a Greek-derived word for crocodile. Hence the nickname going around: “witch croc.”

How convergent evolution pulled off the trick

Convergent evolution is the process by which distantly related animals independently arrive at similar solutions to similar problems. Bats and birds both evolved wings without inheriting them from a shared winged ancestor. Sharks and dolphins both evolved sleek, streamlined bodies. In the Triassic, a crocodile relative evolved an ostrich-mimic-like shape long before the Cretaceous dinosaurs it would later resemble. Alan H. Turner, the paleontologist who led the study at Stony Brook University, sees the two-legged posture as the surprising part. “Bipedalism is certainly a unique path for crocodile relatives to take, but it’s a path well-trod by dinosaurs and later birds. It obviously worked for these animals,” he said. Walking on two legs was an unusual route for the crocodile line, even if it became familiar elsewhere. Turner also reads these animals as early examples of evolutionary strategies that would appear again in later groups. “We see a lot of the successful strategies for modern animals and non-avian dinosaurs first arise in the Triassic, and shuvosaurs are a great example of that convergent evolution,” he said. That is a broad interpretation of the period rather than a final verdict, but the specific case in front of him is difficult to dispute.

What it tells us about reading the fossil record

The species name, “expectatus,” means expected or awaited, and it points to the gap Labrujasuchus helps fill. In time, it sits between an earlier relative, Shuvosaurus inexpectatus from Texas, and a later one, Effigia okeeffeae, which was also found at Ghost Ranch. Co-author Nate Smith, of the Natural History Museum of Los Angeles County, put the logic plainly. “We also wanted to highlight how the fossil record works — finding one shuvosaur from earlier in the Triassic and one from later meant that we paleontologists knew there were probably more from in-between waiting to be discovered and described,” he said. The known fossils implied that intermediate shuvosaurs should have existed, and Labrujasuchus helps fill that interval. What I take from all this is a small correction to a common mental picture. We tend to file the crocodile line under “ancient, sprawling, lurking in swamps,” and the dinosaur line under “upright, fast, endlessly inventive.” Labrujasuchus complicates that. One side branch of the crocodile line evolved an ostrich-mimic-like combination of bipedality, reduced forelimbs and a toothless beak long before the Cretaceous dinosaurs it would later resemble. Shuvosaurs maintained versions of that body plan through a substantial part of the Late Triassic. The family tree that leads to today’s crocodiles was far stranger and more varied than the animals sunning themselves on riverbanks would suggest.