. Athlon : essays on palaeontology in honour of Loris Shano Russell. Paleontology. 104 HYPSILOPHODONT DINOSAURS tion of a shallow pit on the lateral surface of the tibia into which the calcaneum would have fitted. This arrangement is very similar to that of IT. garbanii. Gilmore (1924) figured the tibia and fibula of the pachycephalosaurid Stego- ceras (Fig. 3f). Unfortunately the astragalus and calcaneum were not reported and the fibula is poorly preserved. However, the slenderness of the distal end of the fibula and the relatively broad tibia suggest that the proximal tarso-meta- tarsal join
. Athlon : essays on palaeontology in honour of Loris Shano Russell. Paleontology. 104 HYPSILOPHODONT DINOSAURS tion of a shallow pit on the lateral surface of the tibia into which the calcaneum would have fitted. This arrangement is very similar to that of IT. garbanii. Gilmore (1924) figured the tibia and fibula of the pachycephalosaurid Stego- ceras (Fig. 3f). Unfortunately the astragalus and calcaneum were not reported and the fibula is poorly preserved. However, the slenderness of the distal end of the fibula and the relatively broad tibia suggest that the proximal tarso-meta- tarsal joint is very like that of IT. garbanii. H. Osmolska (1973, pers. comm.), after correspondence concerning this similarity between Stegoceras and IT. gar- banii, sent me photographs of the Mongolian pachycephalosaurid Homalocephale calathoceras. Although the skull is very similar to Stegoceras, the excellent photo- graphs show that the proximal tarso-metatarsal joint of the pes is not at all like that of IT. garbanii or, for that matter, T. edmontonensis. Furthermore the pelvis of H. calathoceras is very different from that described for Thescelosaurus. The pes of ?T. garbanii was found articulated (Fig. 3b, c). In Fig. 3d, e, f, the elements have been oriented, as indicated by the curvature of the particular facets, to portray positions during maximum protraction and retraction. The geometrical possibilities suggest that IT. garbanii may have been digitigrade during the power stroke with the phalanges pressed against the ground and the metatarsus nearly vertical. I suggest that a similar situation occurs in the power stroke of both the emu and cassowary. The firm union of the astragalus and tibia in IT. garbanii sug- gests a modification, similar to that in carnosaurs, in which stress is transmitted from the lower foot to the tibia by the broadly expanded astragalus. This modifi-. .^^agpsr •.; r3cr Fig. 4 Axis of T. neglectus (lacm 33543). Note preservation of two well-preser
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