A high latitude hesperornithiform (Aves) from Devon Island: palaeobiogeography and size distribution of North American hesperornithiforms

Abstract

A new hesperornithiform bird specimen from Devon Island in the Canadian High Arctic is represented by three cervical vertebrae and is assigned to Canadaga arctica. The new specimen is only the second occurrence of C. arctica and corresponds in morphology and size to the type specimen from Bylot Island, also in the High Arctic. This new fossil adds to the record of North American hesperornithiforms, which had a well-documented Arctic presence. Body size comparisons of all North American specimens from the Campanian reveal that the largest known hesperornithiforms were from high latitudes, but otherwise no clear correlation between body size and latitude is apparent. The largest hesperornithiforms (Canadaga arctica and Heperornis regalis) are found at the highest latitudes, while the smallest forms (Baptornis advenus and Parahesperornis alexi) are found at the southern extent of the birds’ range. Coniornis (a medium body-sized genus) is only found in the middle of the range. No size trends are discernable within the genus Hesperornis or within the species H. regalis. The presence of large hesperornithiforms at high latitudes may indicate that either strong seasonal distribution of resources contributed to larger body sizes at higher latitudes, or Campanian thermal gradients along the Western Interior Seaway were significant enough to affect body size for thermoregulatory reasons (sensu Bergmann's rule). The absence of body size trends within mid-latitude Hesperornis specimens suggests that the climatic gradient in the southern portion of the Seaway was not strong enough to force morphological evolutionary responses, or that character displacement, migration and/or other factors affected body size. Sample size and the inherent problems of an incomplete fossil record must also be considered.

Keywords:

• Bergmann's rule
• character displacement
• body size
• palaeobiogeography
• fossil bird
• Mesozoic

Acknowledgements

We would like to thank Walter Joyce (now at the University of Tübingen, Germany) and Dan Brinkman of the Yale Peabody Museum, Larry Martin of the University of Kansas Museum of Natural History, Kieran Shepherd, Margaret Currie and Joseph Sanchez of the Canadian Museum of Nature, Pat Holroyd of the University of Californian Museum of Paleontology, and Jessica Kotierk and Julie Ross of the Nunavut Government Department of Culture, Language, Elders and Youth for access to collections, loans, and/or help with data acquisition. Specimen NUVF 284 was collected under NSF Polar Programs Award no. 0241002 to KC; museum travel was funded in part by a Beverly Sears Graduate Student Grant from the University of Colorado to LEW. We would like to thank Larry Martin and an anonymous reviewer for helpful comments on this manuscript. LEW also thanks Alex Dutchak and Wendy Schultz (University of Colorado, Boulder) for conversations helpful in developing this project.