Comment on ‘Two new compsognathid-like theropods show diversified predation strategies of theropod dinosaurs’ by Qiu et al.

Abstract

Frozen in time by multiple volcanic eruptions, the exquisitely preserved (Lagerstätte) fossils from the Barremian (Lower Cre- taceous) Yixian Formation of western Liaoning offer a remark- able glimpse into an incredibly rich ecosystem that thrived in what is now northeastern China ∼125 mi l lion years ago [1 ]. Together with fossils from the Huajiying and Jiufotang forma- tions, they form an assemblage that comprises > 60 species of plants, thousands of species of invertebrates and > 90 species of vertebrates known as the Jehol Biota. One of the most famous species from the Jehol Biota is Sinosauropteryx prima , which pro- vided the first evidence of protofeathers in a non-avian dinosaur (i.e. dinosaurs w ithout their av ian descendants, the birds) in 1996 [2 ]. Named by Qiang Ji and Shu’an Ji [3 ], Sinosauropteryx was initially thought to be the earliest fossil bird and the first representative of the new family “Sinosauropterygidae.”Itwas, however, reclassified as a member of the Compsognathidae—a small radiation of basally branching coelurosaur theropods en- compassing small-bodied ( < 3 m in length) bipedal dinosaurs that mainly inhabited Eurasia during the Late Jurassic and the Early Cretaceous [4 ]. The feeding ecology of compsognathids is among the best documented in non-avian theropod dinosaurs, with most species preserving stomach content and, in one ex- ceptional case, ingested skeletal remains within extraordinarily preserved internal organs [5 ]. Direct evidence of their diet re- vealed that these small dinosaurs were opportunistic carnivores that fed on a wide array of prey items such as fish, lizards, birds and mammals [6 ]. The classification of compsognathids, how- ever, is more obscure, with a recent study suggesting that they probably form an artificial grouping of immature individuals that belong to other theropod clades [7 ]. Compsognathid species in- deed appear to be mostly, if not exclusively, represented by skele- tally immature specimens that, other than their small size, show several traits that are seen in juvenile theropods such as unser- rated teeth [7 ].