Plastremys lata

Scheyer, T. M., Pérez-García, A. & Murelaga, X., 2015, Shell bone histology of solemydid turtles (stem Testudines): palaeoecological implications, Organisms Diversity & Evolution (New York, N. Y.) 15 (1), pp. 199-212 : 206-208

Plastremys lata from the Early Cretaceous of the UK

The costal fragment showed a compact diploe structure and well developed internal and external cortices of similar thickness ( Fig. 6a ).

External cortex—Due to preservational bias, the external-most part of the cortex does not show any microstructural details. Only the presence of former vascular spaces can be discerned within the completely altered bone matrix. Towards the cancellous interior, there appears a wavy border, internal to which the fossil bone matrix is still pristine and its microstructure is well discernible. Here the cortex reveals a meshwork of ISF. The cortex is vascularized by scattered primary osteons. There is no clear transitional zone to the cancellous bone as evidenced by large scattered secondary osteons and erosion cavities lined with lamellar bone ( Fig. 6b ). Whether the external-most ornamental part of the of shell bone consisted of the same ISF matrix as the more internal part cannot be elucidated ( Fig. 6c ).

Cancellous bone—The vascular spaces in the interior area of the bone are small, round to oval-shaped, mostly lined with lamellar bone, and separated by interstitial primary bone. Only a few small trabeculae formed between adjacent vascular spaces, but those are not secondarily remodelled.

Internal cortex—The cortex is mainly composed of parallel-fibered bone, vascularized by few scattered simple primary vascular canals and primary osteons. Most of the fibres in the bone matrix are transversely sectioned; however, a few well delineated, transversely sectioned fibre bundles are visible as well ( Fig. 6d ).

Figures

Fig. 6 Thin-sections of Plastremys lata. Images in a and d are in normal transmitted, b and c in cross-polarised light. a Costal fragment (NHMUK R 2251). b Close-up of the central part of the section.Note well preserved interior bone tissue. c Close-up of the external cortex showing a clear front of bone tissue alteration (upper part of image). d Close-up of the internal cortex, consisting of parallel-fibred bone. Abbreviations: CB cancellous bone; ECO external cortex; ICO internal cortex; ISF interwoven structural fibres; LB lamellar bone; PFB parallel-fibred bone; trFB transversally sectioned fibre bundles