Unknown animals left birdlike footprints lengthy earlier than birds existed

Footprints preserved in stone in Lesotho appear to have been made by animals that walked on birdlike feet around 215 million years ago, long before the earliest known birds.

The earliest fossils recognised as ancestors of modern birds, including the famous Archaeopteryx, date back 150 million to 160 million years.

Miengah Abrahams and Emese Bordy, both at the University of Cape Town, South Africa, studied an 80-metre-long stretch of footprints at a site called Maphutseng, as well as casts and sketches made by previous researchers at four other sites in Lesotho.

Like the other sites, Maphutseng preserves diverse footprints. The researchers focused on Trisauropodiscus, a name given to distinctively-shaped three-toed footprints left by animals whose exact identities remain a mystery.

They found the footprints could be separated into two main groups based on their shape, one of them distinctly birdlike.

“Our birdlike ones have a big wide splay in the outer digits, like a waterbird, and the toes were incredibly slender, with the central toe not really projecting far forward,” says Abrahams.

The general shape of the footprint is very comparable to other fossil bird tracks and also modern bird tracks, she says.

The second group of footprints had more rounded, robust and elongated toes that were less splayed out. They resembled another type of footprint, known collectively as Anomoepus, which are attributed to dinosaurs with birdlike hips.

The discovery of two distinct groups of Trisauropodiscus suggests that birdlike feet evolved much earlier than the first birds, and may have evolved independently in other animal groups.

But it remains unclear what the animal that made the footprints looked like. “We’re pretty sure it’s not a bird, and it’s most likely a dinosaur, but what dinosaur I’m not really sure,” says Abrahams. “We have nothing in our local fossil record that’s comparable.”