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 II-MT 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.
1996. The evolution of locomotor morphology in the genus Rhoptropus (Squamata: Gekkonidae). Afr. 1. Herpetol. 45(1): 8-30.Reduced major axis regressions of limb skeletal element length against occiput-vent length (OVL) indicate that there are significant differences in the scaling relationships among the five Namibian species ofthe genus Rhoptropus. R. afer differs from all other taxa in y-intercept and size ofordinate variable at smallest common OVL for almost all regressions. The proportional differences in limb morphology for this species are most notable for the metapodial elements and proximal phalanges. Distal phalanges do not show this pattern, perhaps reflecting functional constraint imposed by the hyperextensive scansorial system of the toes. Rhoptropus afer also typically has one fewer presacral verlebra than its congeners. There is no evidence that these features ofR. afer are shared by its sister taxon, R. bradfieldi. It therefore seems likely that R. afer has evolved these locomotor characteristics, along with many other autapomorphies. since the divergence ofthe two taxa. The shorler body and longer limbs ofR. afer are adaptations for locomotion on horizontal substrates.
Tyrannosaurid necks were strong and powerful instruments for wielding the jaws during feeding. Hypotheses of tyrannosaurid neck function are here grounded by observations of neck morphology and function in extant archosaurs. Respectively derived morphologies in birds, crocodilians and tyrannosaurids compromise inferences for some muscles. However, alternate reconstructions indicate that tyrannosaurid neck muscles combined the robustness of crocodilian musculature with the functional regionalization seen in birds. Alternate hypothesized attachments of an avian‐style muscle, the M. complexus, indicate different capacities for head dorsiflexion and lateroflexion. Electromyography of the M. complexus in chickens strengthens inferences about its function in both dorsiflexion and lateroflexion in extinct dinosaurs, and further suggests that it imparted roll about the longitudinal axis in concert with the actions of contralateral ventroflexors. Videography of extant raptors reveals the involvement of the neck when striking at prey and tearing flesh, and reconstructed tyrannosaurid musculature indicates capacity for similar neck function during the feeding cycle. As for birds, muscles originating in the anterior region of the neck likely stabilized the head by isometric or eccentric contraction as tyrannosaurids (and other large theropods) tore flesh by rearing back the body through extension of their hind limbs.
With a carefully designed rating instrument and simulation operation, the manikin-based simulation examination was shown to be reliable and valid. However, a further refinement of the test instrument will be required for higher stake examinations.
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