Hesperornithiformes: the Origin and Evolution of the Cretaceous Diving Birds

Abstract

Hesperornithiformes were toothed, foot-propelled diving birds and among the most widely distributed groups of birds in the Cretaceous (Late Albian to Maastrichtian) in the Northern Hemisphere. The first species of this group, Hesperornis regalis was discovered from the Niobrara Formation (Upper Santonian) in Kansas in 1871. H. regalis had extremely reduced forelimbs, powerful hind limbs, and a non-keeled sternum. Taking into consideration the osteological features mentions above, this huge diving bird was obviously a flightless foot-propelled diver. Currently, Cretaceous Hesperornithiformes are recognized as the oldest diving birds in the avian evolutionary history. Thirty-one species and at least fifteen genera have been named so far. Most of the known hesperornithiform remains have been recovered from the marine deposits of the Western Interior Seaway in North America, especially from Kansas and South Dakota in USA and Manitoba and Saskatchewan in Canada. In Europe, some hesperornithiform remains have been found from the Cretaceous deposits of the Turgai Strait (Russia and Kazakhstan), but Hesperornithiformes are extremely rare in Asia where they are only known from three remains from Mongolia and Japan. Current phylogenetic analyses of Mesozoic birds suggest that these diving birds are one of the closest relatives of the Neornithes (modern birds). In this article, we review the current knowledge of the origin of the Neornithes, the phylogeny of Mesozoic birds, and hesperornithiform osteology and paleoecology. We also discuss future prospects for research into these oldest diving birds.