First report of bird tracks (Aquatilavipes) from the Cedar Mountain Formation (Lower Cretaceous), eastern Utah

• First report of bird tracks from the Lower Cretaceous Cedar Mountain Formation, Utah
• First bivariate and multivariate analysis of multiple Cretaceous avian ichnotaxa
• Statistical support for validity of most well-known Cretaceous avian ichnotaxa
• Oldest evidence of birds from Cretaceous of USA

More than 130 footprints representing ~ 43 trackways of birds (avian theropods) and two non-avian theropods occur as seven separate assemblages on loose blocks recovered from the Poison Strip Member of the Cedar Mountain Formation, near the Stikes Quarry locality in eastern Utah. Six of assemblages, four with bird tracks and two with small non avian theropod tracks, are inferred to originate from the same stratigraphic horizon, and can therefore be considered part of the same ichnofauna. The seventh assemblage comes from a different horizon a few meters above that yielding the other six assemblages. The bird tracks are all attributed to the ichnogenus Aquatilavipes, a track type morphologically similar to those of modern shorebirds. The ichnogenus is also known from broadly coeval ichnofaunas from South Dakota and Canada, and the identification is confirmed by detailed comparative analysis of available Aquatilavipes samples using bivariate and multivariate analyses. This is the first definitive report of bird tracks from the Cedar Mountain Formation and the first evidence of birds from this otherwise richly fossiliferous unit. The ichnofauna is therefore quite unique in comparison with others from this same formation.