A newly discovered enantiornithine foot preserved in mid-Cretaceous Burmese amber

Recent discoveries of enantiornithine remains in Burmese amber have provided a wealth of paleobiological data on this extinct clade of Mesozoic birds. Amber, as a unique medium of fossilization, preserves in three dimensions structures with details unmatched elsewhere in the fossil record. This provides the opportunity to combine osteological information with more detailed information on integumentary structures, including soft tissues and the plumage of the specimens. Herein, we describe an isolated bird foot, DIP-V-19354, consisting of complete metatarsals and digits, including the claws. Placement among the Enantiornithes is supported by the presence of a metatarsal IV with a trochlea formed by a single condyle and the large size and curvature of the claws. The bones of the right foot are preserved fully encased in soft tissue. Scutellae scale filaments (SSFs) are present along the metatarsals and digits, and are similar to those previously described in other enantiornithines. The distribution and relative size of the SSFs on the longest digit support the hypothesis of a mechanosensory tactile role of these structures: this may implicate the digit in the feeding strategy of the animal, as has been suggested for Elektorornis. Unlike many of the previously described enantiornithine remains from this deposit, the taphonomic history of DIP-V-19354 suggests that the foot was trapped in resin flows above the forest floor, likely on the trunk of a tree, after the bird had died.