Jumbled bones show birds on the menu

An unusual fossil found in Spain is providing the oldest evidence of birds serving as food.

The mass of bones, jumbled together in an area less than 4 square inches, turned up in a layer of fossil-riddled sediments where the other specimens remain complete, intact, and isolated from one another. Analysis shows that the mixed bones came from four baby or juvenile birds of three different species, says José L. Sanz, a paleontologist at the Universidad Autónoma de Madrid.

A still body of water formed the fine-grained sediments encasing the fossil, Sanz and his colleagues report in the Feb. 22 Nature. Therefore, it’s unlikely that four immature birds would have washed into the lake and been buried together in a single mass.

Sanz and his colleagues discount the idea that the birds came from a single nest, because ancient birds aren’t known to have laid eggs in other birds’ nests.

The disjointed bones show pitting and other signs of partial digestion, providing the earliest evidence that ancient birds were a meal component, says Sanz.

Most coprolites–fossilized fecal matter–contain small bone fragments, but the bones in Sanz’ fossil are nearly intact and aren’t surrounded by mineralized feces. The researchers say this suggests the small wad of bones is actually a regurgitated pellet of undigested portions of prey, similar to those coughed up by modern owls.

Various predators, including large fish, early mammals, lizards, or other birds, could have produced such a pellet. However, Sanz and his colleagues say that the size of this pellet suggests that a small theropod dinosaur or a pterosaur, an ancient flying reptile, had dined on the young birds.