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

hypothesis. Fossil evidence of basal tyrannoraptorans (sensu Sereno 1999) will
potentially corroborate or falsify the proposal of a single arctometatarsus origin.
Overall, the distribution mapped onto Holtz's topology (Holtz 2000; Figure 5.3)
is more parsimonious, as it requires only tfiree gains in one scenano, or one gain
and three losses, of this complex kinctional suite. More crucially, however, both
phylogenies indicate multiple independent ongins andlor losses. The implications
of this convergence must be discussed in the context of selective pressures
leading to fixation of the arctometatarsus once it emerged. The following section
explores this selective aspect of arctometatarsus evolution
What selective factors contributed to arctometatarsus evolution?
The hypothesis tested here is that the arctometatarsus was an innovation
initially involved in prey capture. The long legs of theropods have been
considered adaptations enhanang predatory behavior (Gauthier 1986), and with
equal validity as an adaptation associateci with increases in home range size
(Carrano 1998). Tensile keystone dynamics imply the capacity for increased
agility in arctometatarsalians, as presented abuve in Chapter 3. Modem animals
employ agility in order to procure prey or to estxtpe predators, and also for
intraspecific combat. Potential modem behavioral analogs suggest parallel
hypotheses of biological role in theropods.
Although observational corroboration is impossible, hypotheses of the
biological role of potential agility are subject ta testing by falsification. We can
falsify the prey capture hypothesis if herbivory was the primary habit of