'We're Pretty Sure It's Not a Bird'

The earliest known fossils attributed to ancestors of modern birds date to around 160 million years ago, which is why birdlike tracks discovered in southern Africa and dated to tens of millions of years earlier have become a fascinating topic of discussion for paleontologists. In reviewing 163 tracks found across four sites in what is now Lesotho, experts have identified an unknown reptile with "distinctly birdlike" feet, per New Scientist. (You can see the images at that link.) There are three toes with "a big wide splay in the outer digits, like a waterbird," Miengah Abrahams, a sedimentologist at South Africa's University of Cape Town, tells the outlet. The toes are slender with a central digit "not really projecting far forward," as with modern birds.

The research team identified the fossils as Trisauropodiscus, a genus based solely on fossilized impressions, per CNN. Not all Trisauropodiscus prints resemble bird prints. But in reviewing available casts, historical photographs, and field material at the Maphutseng site in Lesotho, researchers were able to divide the genus into two groups: the non-avian Morphotype I and the avian-like Morphotype II. The prints from this latter group, dated to the Late Triassic and Early Jurassic periods (roughly 240 million to 175 million years ago), were shorter, wider, and less robust than the others and closely resembled prints left by a wading bird that existed during the Cretaceous period (145 million to 66 million years ago). "We knew we needed to investigate them further," Abrahams tells CNN.

The evidence "firmly shows that the origin of birdlike foot morphology is at least ~210 million years old," according to the resulting study, published Wednesday in PLOS One. It notes the prints "could represent a missing clue about avian evolution, or they could belong to reptiles that aren't close to the avian lineage but independently evolved birdlike feet," CNN reports, noting they date to a time when "evolutionary adaptations were booming in archosaurs—the ancient reptile group that includes dinosaurs, pterosaurs, and crocodilians." "We're pretty sure it's not a bird, and it's most likely a dinosaur, but what dinosaur I'm not really sure," Abrahams tells New Scientist. "We have nothing in our local fossil record that's comparable." (More paleontology stories.)