FIG. 71 in Model-based analysis of postcranial osteology of marsupials from the Palaeocene of Itaboraí (Brazil) and the phylogenetics and biogeography of Metatheria

FIG. 71. — Comparisons of several stages of monotreme and therian astragalocalcaneal patterns and articular relationships. For each of the six taxa the dorsal and distal views are shown in articulation above, and the lower ankle joint surfaces for the two left bones are shown below. In the metatherians the movement of the tarsus on the crus has one degree of freedom in rotation and another in translation, whereas in eutherians the stabilized upper ankle joint usually only allows one degree of freedom in rotation. Arrows on the tibial facet of the astragalus show rotational (and translational) freedom in the upper ankle joint, whereas the slimmer arrow on the astragalar fibular facet shows rotation of the calcaneus under the astragalus (i.e. movement in the lower ankle joint). Abbreviations: AFi, astragalofibular facet; ampt, astragalar medial plantar tuberosity; AN, astragalonavicular facet; ATil, lateral astragalotibial facet; ATim, medial astragalotibial facet; CaA, calcaneoastragalar facet; CaCu, calcaneocuboid facet; CaCua, auxiliary calcaneocuboid facet (australidelphian) CaCud, distal calcaneocuboid facet (didelphid); CaCul, lateral calcaneocuboid facet (australidelphian) CaCum, medial calcaneocuboid facet (australidelphian); CaCup, proximal calcaneocuboid facet (didelphid); CaFi, calcaneofibular facet; cpp, calcaneal peroneal process; ct, calcaneal tuber; Su, sustentacular facet.