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Effects of substrate diameter on locomotor biodynamics were studied in the gray short-tailed opossum (Monodelphis domestica). Two horizontal substrates were used: a flat 'terrestrial' trackway with a force platform integrated into the surface and a cylindrical 'arboreal' trackway (20.3·mm diameter) with a force-transducer instrumented region. On both terrestrial and arboreal substrates, fore limbs exhibited higher vertical impulse and peak vertical force than hind limbs. Although vertical limb impulses were lower on the terrestrial substrate than on the arboreal support, this was probably due to speed effects because the opossums refused to move as quickly on the arboreal trackway. Vertical impulse decreased significantly faster with speed on the arboreal substrate because most of these trials were relatively slow, and stance duration decreased with speed more rapidly at these lower speeds. While braking and propulsive roles were more segregated between limbs on the terrestrial trackway, fore limbs were dominant both in braking and in propulsion on the arboreal trackway. Both fore and hind limbs exerted equivalently strong, medially directed limb forces on the arboreal trackway and laterally directed limb forces on the terrestrial trackway. We propose that the modifications in substrate reaction force on the arboreal trackway are due to the differential placement of the limbs about the dorsolateral aspect of the branch. Specifically, the pes typically made contact with the branch lower and more laterally than the manus, which may explain the significantly lower required coefficient of friction in the fore limbs relative to the hind limbs.

Assuming some optimization of bone structure to applied mechanical loadings in vivo, different killing and feeding behaviours in carnivores should be reflected in observed differences in cross‐sectional shape of their mandibular corpora. Section moduli are used to gauge the magnitudes of bending moments in the mandibular corpus and, when dentary length is controlled, the magnitudes of forces applied to the corpus. Comparisons are made of section moduli at the P3P4 and P4M1 interdental gaps among canids, felids and hyaenids; in canids only, the M1M2 interdental gap was also studied. Local variations in loadings are identified by comparing the section moduli at adjacent loci along the corpus within each family. The findings of this study show that the precarnassial corpora of canids and hyaenids have greater strength in bending than the corpora of felids of similar body weight. This is taken to reflect relatively greater bending moments under loading in the corpora of canids and hyaenids due, in part, to their elongate dentaries (relative to body weight). Relative to dentary length, however, the precarnassial corpora of felids and hyaenids have much greater strength in bending than the corpora of canids. These scaling relationships appear to reflect the high customary forces (i.e. not moments) applied to the precarnassial corpora of felids and hyaenids with sustained canine killing bites and with bone ingestion using the premolars, respectively. An increase in bending strength of the corpus caudal to the camassial blade in canids is interpreted to be an adaptation for bone‐crushing with the postcarnassial molars.

An ecomorphological study of extant small carnivorans demonstrates that dietary groups can be distinguished using quantitative morphological characters. Small (o10 kg) modern carnivorans were divided into three dietary classes: carnivores, insectivores and omnivores/hard-object feeders. Statistical analyses revealed differences between these classes including longer carnassial blades in carnivorans, as opposed to larger molar grinding areas, larger post-canine dentitions, and wider fourth premolars in omnivores/hard-object feeders. Insectivores are not consistently distinguished from other dietary types, although they do tend to have weaker dentaries and shorter temporalis muscle moment arms. These trends can be used to help interpret morphologies of taxa of uncertain ecologies, including fossil taxa.

reaction forces of the whole body were used to assess how well Alligator was able to utilize mechanical energy-saving mechanisms (inverse pendulum or mass-spring). A highwalking Alligator recovers, on average, about 20% of its mechanical energy by inverse pendulum mechanics. These modest energy recovery levels are likely to be due to a combination of factors that may include low locomotor speed, imprecise coordination of contralateral limbs in the trot, frequent dragging of feet of protracting limbs during swing phase and, possibly, tail dragging.

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SUMMARY Small terrestrial animals continually encounter sloped substrates when moving about their habitat; therefore, it is important to understand the mechanics and kinematics of locomotion on non-horizontal substrates as well as on level terrain. To this end, we trained gray short-tailed opossums(Monodelphis domestica) to move along level, 30° inclined, and 30° declined trackways instrumented with a force platform. Vertical,craniocaudal and mediolateral impulses, peak vertical forces, and required coefficient of friction (μreq) of individual limbs were calculated. Two high speed video cameras were used to simultaneously capture whole limb craniocaudal and mediolateral angles at limb touchdown, midstance and lift-off. Patterns on the level terrain were typical for non-primate quadrupeds: the forelimbs supported the majority of the body weight, forelimbs were net braking and hindlimbs net propulsive, and both limb pairs exerted small laterally directed impulses. M. domestica moved more slowly on sloped substrates in comparison to level locomotion, and exhibited a greaterμ req. On inclines, both limb pairs were more protracted at touchdown and more retracted at lift-off, fore- and hindlimbs had equal roles in body weight support, forelimbs exerted greater propulsive impulse than hindlimbs, and μreq was greater in the forelimbs than in hindlimbs. On declines, only the forelimbs were more protracted at touchdown;forelimbs supported the great majority of body weight while they generated nearly all of the braking impulse and, despite the disparity in fore-vs hindlimb function on the decline, μreq was not significantly different between limbs. These differences on the inclined and declined surfaces most likely result from (1) the location of the opossums'center of mass, which is closer to the forelimbs than to the hindlimbs, and(2) the greater functional range of the forelimbs versus the hindlimbs.