Abstract
The Smoky Hill Member of the Niobrara Chalk in Kansas (USA) has yielded the remains of numerous members of the Hesperornithiformes, toothed diving birds from the late Early to Late Cretaceous. This study presents a new taxon of hesperornithiform from the Smoky Hill Member, Fumicollis hoffmani, the holotype of which is among the more complete hesperornithiform skeletons. Fumicollis has a unique combination of primitive (e.g. proximal and distal ends of femur not expanded, elongate pre-acetabular ilium, small and pyramidal patella) and derived (e.g. dorsal ridge on metatarsal IV, plantarly-projected curve in the distal shaft of phalanx III:1) hesperornithiform characters, suggesting it was more specialized than small hesperornithiforms like Baptornis advenus but not as highly derived as the larger Hesperornis regalis. The identification of Fumicollis highlights once again the significant diversity of hesperornithiforms that existed in the Late Cretaceous Western Interior Seaway. This diversity points to the existence of a complex ecosystem, perhaps with a high degree of niche partitioning, as indicated by the varying degrees of diving specializations among these birds.
Highlights
The Cretaceous Hesperornithiformes were one of the first lineages of Mesozoic birds discovered [1]
B. advenus, H. regalis, P. alexi, and F. hoffmani are all known from the upper portion of the Late Cretaceous Smoky Hill Member of the Niobrara Chalk in Logan County (Kansas), strata that only spans around five million years of depositional history [16], yet contains the highest known taxonomic diversity of hesperornithiforms (Fig 2)
UNSM 20030 provides us with a novel hesperornithiform, Fumicollis hoffmani, that is morphologically transitional between the smaller, more primitive Baptornis advenus and the larger, more derived Hesperornis regalis and Parahesperornis alexi
Summary
The Cretaceous Hesperornithiformes were one of the first lineages of Mesozoic birds discovered [1]. The shaft expands at the distal end, with the medial side more expanded than the lateral, giving the distal end the appearance of flaring or angling medially in cranial view This is observed in B. advenus and to a greater degree in H. regalis and P. alexi (Fig 18a). The shaft of the tarsometatarsus of B. advenus and B. varneri is only slightly twisted, while that of UNSM 20030, P. alexi, and H. regalis is more dramatically twisted This twist combined with the shingling of the metatarsals gives the tarsometatarsus a very narrow, straight appearance when the distal end is in dorsal view (Fig 20c) and a much broader, curvy appearance when the proximal end is in dorsal view (Fig 20a). The uncinate processes appear to be unfused from the ribs, as in other hesperornithiforms
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