A comparative histological study of the osteoderms in the lizards Heloderma suspectum (Squamata: Helodermatidae) and Varanus komodoensis (Squamata: Varanidae).

Alexander Kirby,Matthew Vickaryous,Alessandro Olivo,Sergio Bertazzo,Alan Boyde,Susan Evans,Mehran Moazen

doi:10.1111/joa.13156

Alexander Kirby, Matthew Vickaryous + Show 5 more

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https://doi.org/10.1111/joa.13156

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Abstract

We describe the histological appearance of the osteoderms (ODs) of Heloderma suspectum and Varanus komodoensis using multiple staining and microscopy techniques to yield information about their morphology and development. Histological analysis showed that the ODs of H. suspectum are composed of three main tissue types, a superficial layer, herein identified as osteodermine, capping a base composed of Sharpey‐fibre bone and lamellar bone rich in secondary osteons (Haversian bone tissue). In contrast, ODs in V. komodoensis are composed of a core of woven bone surrounded by parallel‐fibred bone without a capping tissue. Thus, in these two species, ODs differ both in terms of their structural composition and in details of their skeletogenesis. The histology of the mineralised tissues observed in these two reptile taxa provides insights into the mechanism of formation of lizard ODs and presents a direct comparison of the histological properties between the ODs of the two species. These data allow greater understanding of the comparative histological appearance of the dermal bones of lizards and highlight their structural diversity.

Highlights

Osteoderms (ODs), a term which literally means 'bone in the skin', are hard tissue organs embedded into the dermis of vertebrates (Moss, 1972), forming part of the dermal skeleton of tetrapods (Vickaryous and Sire, 2009)
Capping each H. suspectum OD residing in the non-mineralised stratum superficiale (SS) was an unusual tissue, identified as osteodermine (Fig. 1A,D,G)
The second objective was to characterise the histological appearance of osteodermine and to confirm its presence in H. suspectum ODs

Summary

| INTRODUCTION

Osteoderms (ODs), a term which literally means 'bone in the skin', are hard tissue organs embedded into the dermis of vertebrates (Moss, 1972), forming part of the dermal (integumentary) skeleton of tetrapods (Vickaryous and Sire, 2009). A recently discovered highly mineralised OD component, osteodermine, was first named in a fossil squamate (Glyptosaurinae) from the late Cretaceous (de Buffrénil et al 2011) Since this material has been observed on the superficial surface of extant Tarentola annularis (Geoffroy Saint-Hilaire, 1827; Vickaryous et al 2015) and Tarentola mauritanica ODs (Linnaeus, 1758; Levrat-Calviac and Zylberberg, 1986). To provide a detailed histological characterisation of ODs from the anguimorphs H. suspectum and V. komodoensis and, secondly, to characterise the unknown capping tissue in H. suspectum to test if it is osteodermine and to determine whether it is present in the ODs of V. komodoensis, the histology of which is currently undescribed

| METHODOLOGY

Findings

| DISCUSSION