Estimating Flight Style of Early Eocene Stem Palaeognath Bird Calciavis grandei (Lithornithidae)

Lithornithids are volant stem palaeognaths from the Paleocene-Eocene. Except for these taxa and the extant neotropical tinamous, all other known extinct and extant palaeognaths are flightless. Investigation of properties of the lithornithid wing and its implications for inference of flight style informs understood locomotor diversity within Palaeognathae and may have implications for estimation of ancestral traits in the clade. Qualitative comparisons with their closest extant volant relatives, the burst-flying tinamous, previously revealed skeletal differences suggesting lithornithids were capable of sustained flight, but quantitative work on wing morphology have been lacking. Until comparatively recently, specimens of lithornithids preserving wing feather remains have been limited. Here, we reconstruct the wing of an exceptionally preserved specimen of the Early Eocene lithornithid Calciavis grandei and estimate body mass, wing surface area, and wing span. We then estimate flight parameters and compare our estimates with representatives from across Aves in a statistical framework. We predict that flight in C. grandei was likely marked by continuous flapping, and that lithornithids were capable of sustained flight and migratory behavior. Our results are consistent with previous hypotheses that the ancestor of extant Palaeognathae may also have been capable of sustained flight. Anat Rec, 303:1035-1042, 2020. © 2019 Wiley Periodicals, Inc.