Bird tracks from Liaoning Province, China: New insights into avian evolution during the Jurassic-Cretaceous transition

Tracks of shorebird-like species from a small outcrop in the upper part of the Tuchengzi Formation at Kangjiatun, in the Beipiao area, Liaoning Province, may be the oldest bird tracks known from China. Formerly considered Late Jurassic in age, new fission track dates give an age of 145.9 Ma for ash beds associated with dinosaur track-bearing beds from the middle part of the Tuchengzi Formation outcrops at a nearby locality. Thus, the age appears to be close to the Jurassic-Cretaceous (Tithonian-Berriasian) boundary. The precise age of the bird track-bearing beds has not been determined, but is unlikely to be younger than about 139 Ma, based on dates for the upper part of the Tuchengzi Formation. Thus, the bird tracks, like the Tuchengzi ichnofauna in general, predate the famous Yixian Formation, which has produced a different avifauna. st distinctive tracks are here named Pullornipes aureus ichnosp. nov. and are tentatively assigned to the ichnofamily Koreanornipodidae. Other tracks from the same site appear to represent different ichnotaxa and therefore indicate the potential to find diverse avian ichnofaunas at this time. This record supports the evidence that East Asian avian ichnofaunas are the most diverse known during the Early Cretaceous.