SINOCALLIOPTERYX

Although giant for a compsognathid, Sinocalliopteryx was a mere 2.5 meters in length and far from the big league of predatory dinosaurs. But we know it was plenty big enough to swallow the lower leg of a meter-long raptor—tentatively identified as Sinornithosaurus, toes, claws and all, because palaeontologists found one in its stomach cavity. They also found four large gastroliths: stones that are frequently found within herbivores who swallow them to pulverize plant matter. But stones aren't particularly fussy, and they'll happily grind meat and bone, too.

In 2012, a second specimen showed that Sinocalliopteryx liked a more varied diet as its stomach preserved the remains of at least two birds called Confuciornis as well as the shoulder blade of an ornithischian dinosaur. There were no gastroliths, though, which prompted experts to backtrack and conclude that the first specimen swallowed the stones accidentally. Bearing in mind only two specimens have been found so far, it's just as plausible that the second had passed its gastroliths during a toilet break and was so busy gorging itself on rich pickings that it simply forgot or didn't have room to swallow more.

Sinocalliopteryx is very similar to the same area's smaller-but-still-large-for-a-compsognathid Huaxiagnathus, though its hands were longer in relation to its arms, and its arms were longer in relation to most other compsognathids. Like many theropods from the Yixian Formation, the well-preserved fossils of Sinocalliopteryx showed imprints of bristly, Sinosauropteryx-like "protofeathers", which were longest over its hips, tail base and back of the thighs. Even its feet were proto-feathered, which came as something of a shock: hitherto, evidence was lacking to suggest that fuzzy feet existed outside of the advanced theropod dinosaurs known as maniraptorans.