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

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

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qualitative debate over arctometatarsus shape concentrateci on its antenor<br />

outline, l apply morphometdc analysis of theropod metatarsi in antenor view in an<br />

attempt to uncover potential patterns of systematic and functional diversity.<br />

Promisingly, clustering of elements by planar outline has elucidated questions<br />

of both function and phylogeny in extant taxa. Lombard et al. (1 986)<br />

quantitatively assigned the ectopterygoids of colubroid snakes to shape classes.<br />

Their classification of ectopterygoid morphology corresponded with differences in<br />

feeding mechanics specific to colubmid subtaxa. The shape of the ectopterygoid<br />

informs the function and ontogeny of the articulating maxilla and pterygoid in<br />

snakes; al1 three bones form an integrated anatomical system (Lombard et al.<br />

1986). The ectopterygoid is especially enlightening in this regard, because it<br />

functions as the central element in the system, and influences both neighboring<br />

bones and the elements they contact. This neontological precedent reinforces<br />

the utility of the theropod third metatarsal in explicating pedal morphology in a<br />

diversity of taxa.<br />

To quantitatively sort snake ectopterygoids by shape, Lombard et al. (1 986)<br />

employed Principal Components Analysis (PCA; see Appendix 1 for the rationale<br />

and methodology behind PCA). Often applied in ecology to determine<br />

community structure (Pielou 1984), researchers have also used PCA to cluster<br />

modem and extinct taxa according to morphological variables (Cundall and<br />

Rossman 1984, Lombard et al. 1986, Weishampel and Chapman 1990, Forster<br />

1995, Smith 1998, Carrano 1999). Mer methods of visual data dustering, such<br />

as bivariate plots (Hoitz 1994) and temary diagrams (Gatesey and Middleton

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