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

Probable fundion of the tyrannosaurid arctometatarsus
The preceding chapters offer observational and biomechanical support for the
energy transference (Holtz 1994a) and tensional keystone hypotheses of
tyrannosaurid metatarsus function. These may be surnmarized as follows:
1)
When the tyrannosaurid pes contacted the substrate at an acute angle,
distal intermetatarsal Iigaments prevented the greater torque on MT III from
displacing it anterodorsally relative to MT II and MT IV. Instead, the plantar
angulation of the metatarsals and orientation of ligaments drew MT II and MT IV
towards the plantar midline of MT III (Figure 3.12), although the displacement
was slight. This caused the metatarsus to be loaded as a unit during the push off
phase of the step cycle, and lateral and medial angulation of the metatarsus did
not disproportionately load MT II or MT IV.
2)
When the animal imposed torsion on its foot, the plantar angulation of
metatarsals translated this force into compression on adjacent elernents across
their articular surfaces, andfor into modest tension on intermetatarsal ligaments
(Figure 3.1 4).
3)
When compression was channeled along the long axis of the metatarsus
(either at midpoint in the linear step cycle or when the animal was decelerating),
loading on MT III was transferred to the outer metatarsals (Wilson and Curn'e
1985, Holb 1994a) via tension on intermetatarsal ligaments (Figure 3.13). MT II
was the primary recipient of these loadings, because its articular surface with MT
III has a more acute angle to the substrate than the corresponding surface of MT
IV.