Wright, J., Kirkland, J. Foster, J., Deblieux, D. & Gaston, R. (2006) Earliest known bird tracks from the Cedar Mountain Formation, Utah. JVP 26(3) Abstracts pp. 141

The earliest known bird, Archaeopteryx, is known from the Upper Jurassic deposits of Solnhofen in Germany but all other fossil bird remains are Early Cretaceous or younger. Similarly, the oldest known fossil bird tracks are Early Cretaceous in age, with the possible exception of some bird-like tracks reported from the Triassic of South America. The Cedar Mountain Formation of western Colorado and eastern Utah is renowned for producing diverse Early Cretaceous terrestrial fossils, and several tracksites have also been reported. However, these are the first bird tracks reported from the Cedar Mountain Formation. The tracks are preserved in the Yellow Cat Member, which is probably Barremian in age.

These bird tracks were discovered in summer 2005 by JRF and RG on a fallen sandstone block. Further investigation of the site turned up two further blocks, found by JIK and JLW respectively. Aripple-marked fourth slab preserves two small theropod tracks. All the tracks are preserved in concave epirelief on a thin medium-grained sandstone layer at the top of a meter thick erosional-based coarser sandstone with a rippled top surface, which may be of crevasse splay origin. This lithology is very distinctive and it was therefore possible to definitively locate it in the measured cliff section, although no tracks were found in situ.

The tracks are 35-45mm in length and have pace lengths of 130-150mm. Some preserve faint phalangeal pads and small claw marks but there are no traces of interdigital webbing. Several preserve a hallux impression. The divarication angle of digits II-IV is 105-115 degrees. The tracks are toed-in about 15 degrees. Approximately 50 tracks are preserved on the three slabs and there are several short trackways. We believe these to be the earliest known bird tracks in the world.

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