A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): implications for body size evolution amongst the earliest diving birds

Abstract

Despite extensive discoveries across the globe over the past two centuries, little phylogenetic work has been done on the Hesperornithiformes. Spanning the late Early to Late Cretaceous, hesperornithiforms are one of the most diverse groups of Mesozoic birds in terms of both their geographical distribution and the wide differences in body size and diving specializations. This study presents the first phylogenetic analysis of the Hesperornithiformes that includes a majority of the described taxa, enabling the first detailed look at evolutionary relationships within the clade. The results of this study support the monophyly of the Hesperornithiformes, which is recovered as the sister clade to the avian crown group, Neornithes. Within the Hesperornithiformes, the Brodavidae and Hesperornithidae are monophyletic while the Baptornithidae are polyphyletic. Little evidence of species-level taxonomic differentiation is found within Hesperornis, with many species indistinguishable from Hesperornis regalis. Evolution within the Hesperornithiformes provides a fascinating example of progressive development of specialized diving adaptations in birds. The acquisition of these diving specializations appears to be uncorrelated to the independent evolution of multiple large increases in body size.

Keywords:

• Aves
• evolution
• palaeontology
• diving birds
• body size

Acknowledgements

The authors would like to thank the following institutions for their assistance in facilitating access to specimens: American Museum of Natural History; Natural History Museum, London; Field Museum of Natural History; Lund University; Sternberg Museum of Natural History; Smithsonian Institution; South Dakota School of Mines Museum of Geology; University of Kansas Museum of Paleontology; University of Nebraska State Museum; and the Yale Peabody Museum. We would like to thank Larry Martin, Mike Everhart, Carl Mehling, Walter Joyce, Garreth Dyke and Daniel Brinkman for assistance in viewing specimens or photographs of specimens.

Supplemental data

Supplemental material for this article can be accessed here: http://dx.doi.org/10.1080/14772019.2015.1036141