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RE: New tyrannosaur articles

Andrew A. Farke wrote:

Evolutionary morphology of the coelurosaurian arctometatarsus:
descriptive, morphometric and phylogenetic approaches
the Linnean Society; Volume 142, Issue 4, Page 525

Descriptive, principal component (PCA), and thin-plate spline (TPS) analyses of theropod third metatarsals (MT III) definitively segregate the arctometatarsus from other theropod pedal morphologies and reveal variation within phylogenetic and functional subgroups of metatarsi. PCA indicates that the arctometatarsalian MT III differs in shape from the nonarctometatarsalian condition independently of size, indicating that allometric differences among taxa produced this divergence in MT III shape. TPS indicates substantial transfer of footfall force from MT II to MT III in ornithomimids and tyrannosaurids and from MT IV to MT III in troodontids. The study suggests different modes of ligament-damped sagittal rotation of MT III in tyrannosaurids, ornithomimids, and troodontids. Deinonychus had a large MT IIMT III articulation consistent with resisting forces of predatory strikes, while MT III of some large carnosaurs are less robust than expected. Phylogenetic bracketing suggests that proximal intermetatarsal ligaments in theropods were a key innovation preceding arctometatarsus evolution. A Bayesian phylogenetic analysis indicates that an arctometatarsus evolved in the common ancestor of the Tyrannosauridae + (Ornithomimosauria + Troodontidae) clade, but other optimizations are plausible. The most likely selective benefit of the structure was increased agility; if so, homoplasy indicates multiple exaptive and adaptive pathways towards predation and escape roles.

I found this especially interesting (from the paper): "Because coelurosaurs and so many successive outgroups display adaptations for carnivory (Currie, 1997), it is reasonable to infer carnivory in the common ancestor of forms with the potential for the arctometatarsus. Carnivory is indisputable in tyrannosaurids (Erickson et al., 1996; Ryan et al., 2001), and healed tooth marks record predatory activity by T. rex (Carpenter, 2000; P. Larsson, pers. comm. 2002). Carnivory occurred in troodontids (Ryan et al., 2000), although Holtz, Brinkman & Chandler (2000) present evidence for troodontid omnivory. Phylogenetic correlation of tyrannosaurid and troodontid arctometatarsi with carnivory suggests the morphology was a predatory aptation in these clades. Under Holtz's (2000) phylogenetic hypotheses and the Bayesian inference results of this study, the structure would be considered primarily adapted for predation, with this biological role lost in ornithomimids. Toothlessness and other factors (Currie, 1997) indicate a shift from a flesh-based diet in ornithomimids, caenagnathids, and alvarezsaurids. Gastroliths associated with skeletons in an ornithomimid bone bed (Kobayashi et al., 1999) provide evidence of their herbivory. This indicates that the ornithomimid arctometatarsus was exapted for the primary function of escape (Holtz, 2001) or evolved neomorphically for this function (Clark et al., 2002). Caenagnathids and their oviraptorid relatives, while toothless, had raptorial hands similar to those of dromaeosaurids, with acute recurved claws and joints suggestive of grasping ability. Neonate theropod remains have been found in the nest of an oviraptorid (Clark, Norell & Chiappe, 1999). Predation is therefore a possibility in caenagnathids. If so, agility enhanced by the arctometatarsus may have been beneficial in acquiring prey, although the evidence is sparse and indirect."