THE UNIVERSITY OF CALGARY Eric Snively A ... - Ohio University

CHAPTER 2: Descriptive and quantitative morphology of the arctometatarsalian
third metatarsal
INTRODUCTION
As explained in Chapter 1, HoItz (1 994a,b) investigated the phylogenetic and
functional implications of the proximal constriction of the third metatarsal (MT III)
in several clades of Cretaceous coelurosaurs. He designated the
arctometatarsus, in which MT 111 is proximally pinctied, as a character state
present in taxa that also display relatively long lower limb elements (see Figures
1.1, 1.2, and 1.5, Chapter 1). Those taxa that Holtz qualitatively assessed to
have a full arctometatarsus are the Tyrannosauridae, Omithomimidae,
Troodontidae, and Elmisauridae (Hoitz 1994a). This chapter explores qualitative
differences between the third metatarsals of these taxa, to extend Holtz's work
on pedal variation within "arctometatarsalian" clades. Building upon this
qualitative framework, a Principal Cornponents shape analysis statistically
crystallizes divisions between theropod metatarsal morphologies. l then
synthesize and discuss statistical and qualitative data for resultant subgroupings
of metatarsal shape. Once the comparative morphology of the tyrannosaurid
arctometatarsus has been estabtished observationally and statistically, the thesis
logically proceeds into detaited questions of its function and evolution (Chapters
3-4 and Chapter 5, respectively).
Conceptions of arctometatarsus morphology
The terni arctometatarsus has been used imprecisely in the literature and in
public scientific discourse. This confusion anses primarily because Holtz (1994b)