“…Among gnathostomes (jawed vertebrates), the structural organization of the integumentary skeleton continues to vary taxonomically: the skull and integumentary elements of placoderms (Silurian to late Devonian, ~435-360 Ma) are characterized by cellular bone covered by a cellular dentine with polarized cell processes (semidentine), whereas the scalation of chondrichthyans [= odontodes (placoid scales)] consists of a superficial layer of enameloid, capping an orthodentine crown, attached to the dermis by bone of attachment (Goodrich, 1907;Miyake et al 1999; Ărvig, 1957;Jarvik, 1980;Dias & Richter, 2002 Anura osteoderm mostly dorsal body surface; usually multiple small polygonal elements creating a juxtaposed mosaic but sometimes larger plates fused to neural spines cellular bone (parallel-fibred and/or lamellar bone) non-stratified compact bone uncertain: hypothesized to include bone metaplasia Ruibal & Shoemaker, 1984 lamina calcarea distributed across body as a thin intradermal layer; sometimes segmented to form granular bodies known as dermolita acellular, non-collagenous matrix that contains proteoglycans (including glycosaminoglycans) and hydroxyapatite-like crystals homogeneous tissue uncertain: hypothesized to be deposited by fibroblasts Muzzi, 1968;Elkan, 1976;Sampson et al 1987;Toledo & Jared, 1993;Katchburian et al 2001;Schwinger et al 2001 Schmidt, 1914;Moss, 1969;Scheyer & Sander, 2004;Main et al 2005;Vickaryous & Hall, 2008 Lepidosauria osteoderm variable distribution: often restricted to head and/or dorsal body surface but may encase the entire body; highly polymorphic: granular, bead-like, vermiform, compound and imbricating scalelike shapes cellular bone (woven-fibred, parallelfibred, lamellar); calcified and unmineralized fibrous connective tissue; and (in some taxa) an enigmatic collagen-poor capping tissue often stratified into two distinct layers of which the basal portion is always bone (parallel-fibred or lamellar); superficial layer is variable and may consist of woven-fibred bone or an enigmatic collagenpoor tissue uncertain: evidence suggests both bone metaplasia and intramembranous ossification Moss, 1969;Zylberberg & Castanet, 1985;Levrat-Calviac et al 1986;Levrat-Calviac & Zylberberg, 1986 Testudines carapace skeletal complex consisting of multiple tightly articulating and fused bony elements enclosing the dorsal body surface (trunk), including the pectoral apparatus cellular bone (lamellar); plywood-like arrangement of collagen fibres in the external cortex of some trionychids trilaminar org...…”