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

Figure 1.1 shows a phylogeny of theropods, based on dadograms in Holtz
(1 996) and Cume and Padian (1997). AI1 theropods with an arctometatarsus are
within the ciade Coelurosautia. The most famous coelurosaurs are the
Tyrannosauridae, including the familiar Tyrannosaurus ex. Tyrannosaurids and
some but not al1 other coelurosaurian clades with an arctometatarsus comprise
the Arctametatarsalia (sensu Holtz 1996).
Tyrannosaurids, other arctometatarsalians (in the phylogenetic sense), and
other taxa on the phylogeny are now introduced to place the arctometatarsus in a
phenotypic context. Entnes in Weishampel et al. (1990) and Cume and Padian
(1 997) provide more extensive treatment. Figures 1.2 through 1.4 show skeletat
outlines of some members of these taxa.
1. Tyrannosauridae (Figure 1.2): Tyrannosaurids were large to giant
arctometatarsalians, ofkn exceeding two tonnes in mass. Tyrannosaurids
had relatively long hind limbs, extensive attachent sites for jaw musculature,
and a broad muzzle and rob& teeth, but had short forelimbs with only two
functional fingers. Tyrannosaurid tooth marks on fossil bones (Ryan 1992,
Erickson et al. 1996) and coprolitic evidence (Chin et al. 1998) indicate a
macrocarnivorous diet, consisting of other large dinosaurs.
2. Omithomimidae (Figure 1.2): These were ostrich-like arctometatarsalians,
whose hind Iimb iength and element proportions indicate that they were
among the fastest dinosaurs. Ornithomirnids were toothless, and evidence of
gastroliths and other stomach contents indicates they may have been
herbivorous (Kobayashi et al. 1999).