Endothiodon, Owen, 1876

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 : 349-351

ENDOTHIODON

The humeri, radii, and tibiae of specimens SAM-PK- 5605 and SAM-PK-K6618 were available for thin sectioning. The cortical thickness values of the

Values of the Diictodon elements were taken from Ray & Chinsamy (2004), and those of L. declivis SAM-PK-11184 and SAM-PK-K8013, and L. murrayi SAM-PK-K8 were taken from Ray et al. (2005). Juvenile = 0–30% adult, subadult = 30–80% adult, adult = 80–100% adult.

elements from SAM-PK-5605 all exceed 30%, with the tibia having the greatest value (48%; Table 2). The bone tissue of the elements from this specimen consists of highly vascularized (14% for the humerus) uninterrupted fibrolamellar bone ( Fig. 2E ). The vascular canals form a mixture of longitudinal primary osteons and a subreticular network, and there is no decrease in vascularization towards the periphery in any of these elements. Enlarged channels, however, such as those seen in Eodicynodon , are not observed. The humerus, radius, and tibia of SAM-PK-K6618 also consist of fibrolamellar bone, but annuli (sometimes multiple) interrupt the bone tissue in all elements ( Fig. 2F ). The vascular canals are arranged as longitudinal primary osteons, with short anastomoses. The canals are smaller and less dense compared to the elements belonging to SAM-PK-5605. There is a decrease in vascularization and parallelfibred bone appears towards the periphery of the humerus (SAM-PK-K6618a). Prominent Sharpey’s fibres were observed in radius SAM-PK-K6618b.

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.