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Closeup of a helodermatid's skin, revealing the osteodermsArmadillo skeleton, with shell made of osteoderms (displayed at the Museum of Osteology)
Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amphibians), various groups of dinosaurs (most notably ankylosaurs and stegosaurians), phytosaurs, aetosaurs, placodonts, and hupehsuchians (marine reptiles with possible ichthyosaur affinities).
Osteoderms are uncommon in mammals, although they have occurred in many xenarthrans (armadillos and the extinct glyptodonts and mylodontid ground sloths). The heavy, bony osteoderms have evolved independently in many different lineages.[1] The armadillo osteoderm is believed to develop in subcutaneous dermal tissues.[2] These varied structures should be thought of as anatomical analogues, not homologues, and do not necessarily indicate monophyly. The structures are however derived from scutes, common to all classes of amniotes and are an example of what has been termed deep homology.[3] In many cases, osteoderms may function as defensive armor. Osteoderms are composed of bone tissue, and are derived from a scleroblast neural crest cell population during embryonic development of the organism. The scleroblastic neural crest cell population shares some homologous characteristics associated with the dermis.[4] Neural crest cells, through epithelial-to-mesenchymal transition, are thought to contribute to osteoderm development.[2]
The osteoderms of modern crocodilians are heavily vascularized,[5] and can function as both armor and as heat-exchangers,[6] allowing these large reptiles to rapidly raise or lower their temperature. Another function is to neutralize acidosis, caused by being submerged under water for longer periods of time and leading to the accumulation of carbon dioxide in the blood.[7] The calcium and magnesium in the dermal bone will release alkaline ions into the bloodstream, acting as a buffer against acidification of the body fluids.[8]
^Hill, R.V. (December 2006). "Comparative anatomy and histology of xenarthran osteoderms". Journal of Morphology. 267 (12): 1441–1460. doi:10.1002/jmor.10490. PMID 17103396. S2CID 22294139.
^ abNasoori, Alireza (2020). "Formation, structure, and function of extra‐skeletal bones in mammals". Biological Reviews. 95 (4): 986–1019. doi:10.1111/brv.12597. PMID 32338826. S2CID 216556342.
^Vickaryous, M.K.; Hall, B.K. (April 2008). "Development of the dermal skeleton in Alligator mississippiensis (Archosauria, Crocodylia) with comments on the homology of osteoderms". Journal of Morphology. 269 (4): 398–422. doi:10.1002/jmor.10575. PMID 17960802. S2CID 5927674.
^Vickaryous, Matthew K.; Sire, Jean-Yves (2009-04-01). "The integumentary skeleton of tetrapods: origin, evolution, and development". Journal of Anatomy. 214 (4): 441–464. doi:10.1111/j.1469-7580.2008.01043.x. ISSN 1469-7580. PMC 2736118. PMID 19422424.
^Clarac, F.; Buffrénil, V; Cubo, J; Quilhac, A (2018). "Vascularization in ornamented osteoderms: Physiological implications in ectothermy and amphibious lifestyle in the crocodylomorphs?". Anatomical Record. 301 (1): 175–183. doi:10.1002/ar.23695. PMID 29024422.
^Clarac, F.; Quilhac, A. (2019). "The crocodylian skull and osteoderms: A functional exaptation to ectothermy?" (PDF). Zoology. 132: 31–40. doi:10.1016/j.zool.2018.12.001. PMID 30736927. S2CID 73427451.
^Jackson, DC.; Andrade, D.; Abe, AS. (2003). "Lactate sequestration by osteoderms of the broad-nose caiman, Caiman latirostris, following capture and forced submergence". Journal of Experimental Biology. 206 (Pt 20): 3601–3606. doi:10.1242/jeb.00611. PMID 12966051.
^"Antacid armour key to tetrapod survival". ABC Science. 2012-04-24. Retrieved 6 March 2017.
Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct...
Osteoderms are dermal bone structures that support the upper layer of skin and serve as protection against the elements in a large variety of extinct and...
of a dorsal rib, complete or partial identifiable osteoderms, and fragments of additional osteoderms. Two other specimens were referred to Invictarx: UMNH...
collected 77 osteoderms while excavating a Tyrannosaurus specimen in the Lance Formation of Wyoming in 1900. He mentioned these osteoderms (specimen AMNH...
muelleri. Garzapelta is known primarily from an associated collection of osteoderms, although some other bones such as ribs are also known. The anatomy of...
deposited in the Federal University of Rio de Janeiro. An isolated titanosaur osteoderm described in 2018, specimen UFRJ-DG 549-R, was tentatively suggested to...
armored carapaces (top shell) that were made of hundreds of interconnected osteoderms (structures in dermis composed of bone). Other pieces of armor covered...
single carapace osteoderm that had been collected from the Lower Pleistocene "Equus Beds" of Nueces County, Texas. Cope named his osteoderm Glyptodon peltaliferus...
the basis of a series of associated osteoderms that formed the paramedian and lateral armour. Based on the osteoderms the carapace of Venkatasuchus was...
from very fragmentary fossils, elements of the skull, dentary, teeth and osteoderm. Remains of a mesocrocodylian were found in Portugal, it was named Iberosuchus...
snouts, erect limbs, and a body ornamented with four rows of plate-like osteoderms (bony scutes). Aetosaur fossil remains are known from Europe, North and...
attenuation as bone, and concluded that this suggested the presence of osteoderm as well. They noted that, like in Schmidt's illustrations, a zone toward...
far recovered from North America. The specimen also preserved in situ osteoderms, keratin, and skin remains. In 2014, Theropoda Expeditions LLC was excavating...
built for crushing, and its back was covered with thick hemispherical osteoderms. One study indicated Deinosuchus may have lived for up to 50 years, growing...
skin is embedded with bony particles (scutes) (i.e., osteoderms) . Dubbed “armored skin”, osteoderms are composed of hydroxyapatite and collagen, the same...
alongside the modern nine-banded armadillo. The only known fossil is a single osteoderm, though it has been lost, that was found in the Late Miocene strata of...
dinosaurs closer to living birds than to Tyrannosaurus rex. The loss of osteoderms otherwise common in archosaurs and acquisition of primitive feathers might...
and/or dorsal vertebrae fragments, complete and fragmentary thoracic osteoderms, and other unidentifiable postcranial fragments. The holotype specimen...
certain tissues such as in horns of cattle and rhinos, and armadillos' osteoderm. The only other biological matter known to approximate the toughness of...
cattle) and rhinos, cervids' antlers, giraffids' ossicones, armadillos' osteoderm, and os penis/os clitoris. All mammals have some hair on their skin, even...
Norian stage of the Late Triassic. Scutarx are “medium sized” paramedian osteoderms belonging to the clade Aetosauria, a heavily armored and more herbivorous...
includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful...
is far more likely to be an osteoderm indicating that Dasygnathoides had skin armour. It resembles the elongated osteoderms of Ornithosuchus. Paleontology...
represents part of the skull roof and associated osteoderms of the frontal region. Due to the overlying osteoderms that are fused to the skull roof, the frontals...
relationship to other members of that subfamily are uncertain. It had osteoderms embedded within its skin, like some other mylodontids. It was likely a...
and produce dermal armour. Scutes with a bony base are properly called osteoderms. Dermal scutes are also found in the feet of birds and tails of some mammals...
the fact that many known lithostrotians are preserved with osteoderms. However, osteoderms are not a distinguishing feature of the group, as the two noted...
currently only known from four isolated and incomplete dorsal osteoderms. Regardless, said osteoderms show a clear mix of features that does not match any other...
from deposits that are Anisian-Ladinian in age. Long known mostly from osteoderms, vertebrae, and fragments of the skull, specimens described in 2017 provided...
which contain tiny bones called osteoderms that function as a sort of natural chain-mail. The only areas lacking osteoderms on the head of the adult Komodo...
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