The structure of the osteoderms in the gekko: Tarentola mauritanica

Abstract

Histological and cytological analysis reveals that the osteoderms of Tarentola mauritanica are composed of an outer part superimposed on a basal region. The structure of both parts can be related to that of the surrounding dermis. The basal part of the osteoderms, inserted in the dense dermis, is made up of abundant closely packed collagen fibrils that orient the mineral deposit. The outer part, located in the superficial loose dermis, is crossed by few bundles of mineralized collagen fibrils arising from the basal part. These bundles connect the osteoderm to the overlying loose dermis. The outer superficial part is characterized by the presence of mineralized globules surrounding the mineralized collagen bundles. In these globules, the crystals are deposited on a microfibrillar matrix rich in acidic mucosubstances and composed of radially oriented, tangled microfilaments that lie among the collagen bundles. The two different mineralizing systems in the osteoderms of Tarentola mauritanica may reflect two different organic matrices. The mineral is deposited in a preexisting dermal tissue, as a "metaplastic ossification," and is another expression of the potential retained by the reptilian dermis to form mineralized structures.

Development of the dermal skeleton in Alligator mississippiensis (Archosauria, Crocodylia) with comments on the homology of osteoderms

“…The pattern of osteoderm formation observed in Alligator mississippiensis is consistent with previous studies on structural-grade lizards (Moss, 1969;Zylberberg and Castanet, 1985;Levrat-Calviac and Zylberberg, 1986) and armadillos (Vickaryous and Hall, 2006b). Osteoderms develop late during ontogeny, and are generally among the last skeletal elements to form.…”

“…In Dasypus novemcinctus, the adult element includes a combination of woven, lamellar, and Sharpey fiber bone (Vickaryous and Hall, 2006b). In the structural-grade lizard Tarentola mauritanica, osteoderms are composed of two discrete horizons; a superficial horizon of heavily mineralized, collagenpoor tissue underpinned by deeper layer of bone (Levrat-Calviac and Zylberberg, 1986). For Alligator mississippiensis, osteoderms demonstrate a broad spectrum of tissues, including woven and lamellar bone, and calcified and uncalcified dense irregular connective tissue (Fig.…”

Sauropod dinosaur osteoderms from the Late Cretaceous of Madagascar

“…The shape and surface texture of Rapetosaurus osteoderms indicates that these elements were low in relief and embedded in the integument as in other vertebrates [1][2][3]14,16 . As evidenced from extant taxa, all osteoderms form and reside within the dermis, either adjacent to the interface between the strata superficiale and compactum, or exclusively within the stratum superficiale, and are overlain by the epidermis [1][2][3][14][15][16][17] . The surface texture of Rapetosaurus osteoderms is consistent with the hypothesis that, as in crown group archosaurs, these structures were overlain by epidermal scales [1][2][3] .…”

The histological structure of glyptosaurine osteoderms (Squamata: Anguidae), and the problem of osteoderm development in squamates

“…This process would consist in the mineralization of the dense and loose dermal strata, and their direct transformation into bone tissue in the absence of osteoblasts (Haines and Mohuiddin, 1968). Although a possible contribution of osteoblasts has been considered in some lepidosaurian taxa, it remains a controversial issue (Zylberberg and Castanet, 1985;Levrat-Calviac, 1986;Vickaryous and Hall, 2008;Vickaryous and Sire, 2009).…”