Eodicynodon

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 : 349

EODICYNODON

Two femora and two tibiae were thin sectioned for the bone histological analysis of Eodicynodon . The cortex of all the elements studied is relatively thick, with an average femoral cortical thickness of 37% and 41% for tibia NMQR2996b ( Table 2). All the elements have free medullary cavities although a few bony trabeculae have invaded the medullary cavity of tibia NMQR3153b. A thick layer of endosteal circumferential bone surrounds the medullary cavity in femur NMQR3153a. Several large resorption cavities surround the medullary cavities of all specimens. The thin sections from the femur and tibia of specimen NMQR2996 are extremely dark and the preservation of these elements is such that any further grinding destroys the sections entirely. Thus, few histological data could be collected from NMQR2996. However, certain details are clear. For example, both elements are moderately vascularized (10% average) and show numerous enlarged channels arranged in longitudinal radial rows throughout their cortices ( Fig. 2B ). Femur NMQR3153a is the best-preserved Eodicynodon element studied and reveals moderately vascularized (11.5%) uninterrupted fibrolamellar bone tissue ( Fig. 2C ). The channels are enlarged in the perimedullary and midcortical regions. Tibia NMQR3153b exhibits similar bone tissue. In both these elements, the vascular canals are arranged in circumferential rows near the medullary cavity and radial rows towards the midcortex and periphery.

Figures

Figure 2. Permian dicynodont bone histology. A, adult Galeops humerus SAM-PK-12261a; B, early subadult Eodicynodon femur NMQR2996a; C, late subadult Eodicynodon femur NMQR3153a; D, late subadult Diictodon SAM-PK-K7725; E, subadult Endothiodon tibia SAM-PK-5605c; F, adult Endothiodon humerus SAM-PK-K6618a. Arrows indicate enlarged midcortical channels. Enlarged channels are absent in Galeops, Diictodon, and Endothiodon. However, subadult Endothiodon reveals rapid, sustained growth with an average channel area of 13%. Scale bars: B, C = 500 mm; A, D, E, F = 413 mm.