Aulacephalodon, Seeley, 1898

Botha-Brink, Jennifer & Angielczyk, Kenneth D., 2010, Do extraordinarily high growth rates in Permo-Triassic dicynodonts (Therapsida, Anomodontia) explain their success before and after the end-Permian extinction?, Zoological Journal of the Linnean Society 160 (2), pp. 341-365 : 352

AULACEPHALODON

Only two elements were available for thin sectioning, a radius (SAM-PK-8789) and a femur (NMQR3016). The radius has a thick cortex and a tiny free medullary cavity (although the cortical thickness could not be calculated as the bone is incomplete). A large region of secondary remodelling surrounds the medullary cavity. The primary bone tissue consists of moderate to highly vascularized fibrolamellar bone and is interrupted by at least four annuli and/or LAGs. The vascular canals are arranged as longitudinal primary osteons either evenly distributed throughout the cortex or in radial rows. The femur contains a completely infilled medullary cavity. It also consists of fibrolamellar bone, interrupted by at least two annuli. Prominent enlarged channels ( Fig. 3F ), in circumferential rows, surround the medullary cavity and extend into the midcortex, from where the vascular canals narrow and form a laminar network up to the periphery of the bone. There is no decrease in vascularization at the periphery of either element.

Figures

Figure 3. Permo-Triassic dicynodont bone histology. A, subadult Cistecephalus ulna NMQR1465b; B, early subadult Dicynodontoides tibia NMQR479a; C, adult Rhachiocephalus ulna SAM-PK-3714a; D, subadult Tropidostoma tibia SAM-PK-K9960c; E, adult Oudenodon femur SAM-PK-K4807a; F, adult Aulacephalodon femur NMQR3016. Arrows indicate enlarged midcortical channels in Rhachiocephalus and Aulacephalodon. Scale bars: A, D, E = 500 mm; B, C, F = 413 mm.