Osteoderm

Osteoderms are bony deposits forming scales, plates, or other structures based in the <a href="/facts/Dermis/WAm7Fd6P">dermis</a>. Osteoderms are found in many groups of <a href="/facts/Extant_taxon/YK8uj7qU">extant</a> and <a href="/facts/Extinct/24p5NP2q">extinct</a> <a href="/facts/Reptile/04n1uKf1">reptiles</a> and <a href="/facts/Amphibian/r2BleD2W">amphibians</a>, including <a href="/facts/Lizard/VPCpCwjT">lizards</a>, <a href="/facts/Crocodilia/G4LbxJs6">crocodilians</a>, <a href="/facts/Frog/IxYhbeda">frogs</a>, <a href="/facts/Temnospondyli/lEoAzjJe">temnospondyls</a> (extinct amphibians), various groups of <a href="/facts/Dinosaur/JRdMqBnq">dinosaurs</a> (most notably <a href="/facts/Ankylosaur/lXPkLf0e">ankylosaurs</a> and <a href="/facts/Stegosauria/vLTt2MS1">stegosaurians</a>), <a href="/facts/Phytosaur/BUUoxqhm">phytosaurs</a>, <a href="/facts/Aetosaur/TlmQTyeg">aetosaurs</a>, <a href="/facts/Placodont/Nzp2JXJg">placodonts</a>, and <a href="/facts/Hupehsuchia/fVeC2b8V">hupehsuchians</a> (marine reptiles with possible <a href="/facts/Ichthyosaur/fBNIIJaJ">ichthyosaur</a> affinities). 
Osteoderms are uncommon in <a href="/facts/Mammal/phSwTzBo">mammals</a>, although they have occurred in many <a href="/facts/Xenarthra/jEr4EcPD">xenarthrans</a> (<a href="/facts/Armadillo/4acbwyFn">armadillos</a> and the extinct <a href="/facts/Glyptodont/7Dhw5RAA">glyptodonts</a> and <a href="/facts/Mylodontidae/CeAf4Trj">mylodontid</a> <a href="/facts/Ground_sloth/x7vVYmBo">ground sloths</a>). The heavy, bony osteoderms have evolved independently in many different lineages. The armadillo osteoderm is believed to develop in subcutaneous dermal tissues. These varied structures should be thought of as anatomical analogues, not <a href="/facts/Homology_(biology)/muctKlyT">homologues</a>, and do not necessarily indicate <a href="/facts/Monophyly/pD8Yrrn6">monophyly</a>. The structures are however derived from <a href="/facts/Scute/IeqbYure">scutes</a>, common to all classes of <a href="/facts/Amniotes/TeLtDTrJ">amniotes</a> and are an example of what has been termed <a href="/facts/Deep_homology/QPxNmKFR">deep homology</a>. In many cases, osteoderms may function as defensive <a href="/facts/Armour_(zoology)/BYvjkjtz">armor</a>. Osteoderms are composed of <a href="/facts/Bone_tissue/pCU37jBe">bone tissue</a>, and are derived from a scleroblast <a href="/facts/Neural_crest_cell/SgvAz0Ww">neural crest cell</a> population during embryonic development of the organism. The scleroblastic neural crest cell population shares some homologous characteristics associated with the <a href="/facts/Dermis/WAm7Fd6P">dermis</a>. Neural crest cells, through epithelial-to-mesenchymal transition, are thought to contribute to <a href="/facts/Osteoderm_development/bFRSxQKW">osteoderm development</a>.
The osteoderms of modern crocodilians are heavily vascularized, and can function as both armor and as heat-exchangers, allowing them to rapidly raise or lower their temperature. Another function is to neutralize <a href="/facts/Acidosis/hmfAo1uR">acidosis</a>, caused by being submerged under water for longer periods of time and leading to the accumulation of carbon dioxide in the blood. The calcium and magnesium in the dermal bone will release alkaline ions into the bloodstream, acting as a <a href="/facts/Buffering_agent/zrLz9eaa">buffer</a> against acidification of the body fluids.

Osteoderm open-in-new

Osteoderm