See in 3D

Fossilized remains of several species of birds have been found in the Green River Formation. Birds also left traces of their activity in the form of fossil tracks. Lockley et al. (2021) give a comprehensive overview of the known Green River bird tracks, which, like this specimen, are found in the Uinta basin of Utah, from two separate intervals. An interesting conclusion of their study is that the Uinta basin “shorebird” track assemblages do not correspond to the avian body fossil from the larger Green River basins.

This specimen contains at least two intersecting trackways, each consisting of at lest two tracks showing inward rotation and the presence of a hallux. The tracks have not been formally studied, but based on their small size they could possibly be identified as cf. Avipeda phoenix (see Lockley et al., 2021). However, distinct hallux traces and a small proximal web trace between digits III and IV (seen in in one of the tracks; see close-up) are described by Lockley et al. (2021) as typical of the ichnospecies Quadridigitus semimembranus.

Detail of bird tracks, showing the clear impression of a hallux (center left) and a hint of a proximal web trace between digits III and IV (center right).

Reference:

Lockley, M., Kim, K.S., Lim, J.D. and Romilio, A., 2021. Bird tracks from the Green River Formation (Eocene) of Utah: ichnotaxonomy, diversity, community structure and convergence. Historical Biology, 33(10), pp. 2085-2102. doi:10.1080/08912963.2020.1771559.