Figure 5: Right astragali and left calcanei of Cambaytherium and comparative taxa.
From: Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India
(a–c) astragali in posterior view (above, dorsal at top) and dorsal view; (d–f) calcanei in dorsal and lateral views. (a,d) Phenacodus primaevus (USGS 7146). (b,e) Cambaytherium thewissi (b, GU 780; e, WIF/A-1190). (c,f) cf. Arenahippus sp. (c, USGS 25157; f, USGS 38039). Each series scaled to same length; scale bars, 1 cm. Cambaytherium shares several primitive traits with Phenacodus (not found in primitive perissodactyls), including a dorsal astragalar foramen, wide astragalar trochlea and longer neck, robust calcaneus with wider ectal and sustentacular facets and a rounded ectal facet. Derived traits shared with perissodactyls include a deeper astragalar trochlea and concave navicular facet, though the latter is shallower than in perissodactyls. AF, astragalar foramen; NF, navicular facet; PAA, posterior astragalar articulation; SF, sustentacular facet; TR, trochlea.
