Date of Award
Master of Science (MS)
Dr. Laura Wilson
Hesperornithiformes (Aves: Ornithurae) were flightless foot-propelled diving birds that lived during the Late Cretaceous and have a good fossil record compared to most Mesozoic birds. Extinct taxa are often identified using fragmentary or isolated specimens, and several species of Hesperornis have been named from the morphology of the tarsometatarsus, often relying on size for taxonomic differentiation. However, little has been done to examine intraspecific variation in this bone and evaluate its use for taxonomic identification. To test for intraspecific and interspecific variation in the tarsometatarsus of hesperornithiforms, variation in extant members of the foot-propelled diving Gaviidae (loons) and Podicipedidae (grebes) was considered. Loons and grebes are morphologically similar to extinct hesperornithiforms, making them appropriate analogues. Only adult female specimens were chosen for analysis to eliminate the possibility of sexual dimorphism or ontogenetic differences. Landmark-based Geometric Morphometrics was performed on 3D scans of specimens from three species per family, totaling 22 modern specimens. Five species of Hesperornis were scanned and analyzed, totaling 13 individuals. Separate analyses were performed on the shape of the full bone, the shape of the distal end, and the shape of the proximal end for each clade (Gaviidae, Podicipedidae, and Hesperornis). In nearly every Principal Component (PC) morphospace analysis of extant and extinct groups, individuals did not group by species, and any grouping that did occur was poorly defined. These results indicate that there is too much intraspecific variation and too little interspecific variation to confidently identify a species using only the tarsometatarsus in foot-propelled divers. Consequently, fossil hesperornithiform taxa described based on the tarsometatarsus alone may not be valid and require reevaluation.
Copyright 2015 Mackenzie E. Kirchner-Smith
Kirchner-Smith, Mackenzie E., "3D Geometric Morphometrics In Modern And Extinct Foot-Propelled Diving Birds: An Evaluation Of The Tarsometatarsus For Species Identification" (2015). Master's Theses. 48.