Osteoderms are a bony deposit forming a scale, plate, or other structure in the dermal layers of the skin. Osteoderms are found in many groups of extant and extinct reptiles, including lizards, various groups of dinosaurs (most notably ankylosaurs and stegosaurus), crocodylians, phytosaurs, aetosaurs, placodonts, and Nanchangosaurus (a marine reptile with possible ichthyosaur affinities). Osteoderms are uncommon in mammals, but do occur in most edentates (glyptodonts, armadillos, pangolins, ground sloths). Osteoderms have clearly evolved independantly in many different lineages, and these varied structures should be thought of anatomical analogues, not homologues, and do not necessarily indicate monophyly. In many cases osteoderms may function as defensive armor. This article needs to be cleaned up to conform to a higher standard of quality. ... A section of Human Skin In zootomy and dermatology, skin is an organ of the integumentary system made up of a layer of tissues that guard underlying muscles and organs. ... The opposite of extinct. ... In biology and ecology, extinction is the ceasing of existence of a species or group of species. ... Orders  Crocodilia - Crocodilians scary crocodiles. ... This page is about Lizards, the order of reptile. ... Orders Saurischia    Sauropodomorpha    Theropoda Ornithischia Dinosaurs are giant reptiles that dominated the terrestrial ecosystem for most of their 165-million year existence. ... Subfamilies Family Crocodylidae    Crocodylinae    Alligatorinae    Gavialinae Crocodylia is an order of large reptiles that scientists believe branched off from class Reptilia about 220 million years ago. ... Phytosaurs - family Phytosauridae or Parasuchidae - were a group of large (2 to 12 meters long - average size 3 to 4 meters) semi-aquatic predatory thecodonts that flourished during the Late Triassic period. ... Genera Aetosaurus Coahomasuchus Desmatosuchus Longosuchus Neoaetosauroides Paratypothorax Redondasuchus Stagonolepis Typothorax The Aetosaurs (family Stagonolepididae or Aetosauridae) are an extinct clade of heavily armoured, medium to large sized, Late Triassic herbivorous archosaurs. ... Placodonts were a group of marine reptiles that lived during the Triassic period, becoming extinct at the end of the period. ... Taxonomy See text Ichthyosaurs (Greek for fish lizards) were giant marine reptiles that resembled fish and dolphins (see convergent evolution). ... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... Families Myrmecophagidae Megalonychidae Bradypodidae Dasypodidae The order Xenarthra is a group of placental mammals, extant today only in the Americas. ... Glyptodon (Greek for grooved or carved tooth) was a relative of the armadillo that lived during the Pleistocene Epoch. ... Genera Chlamyphorus Cabassous Chaetophractus Dasypus Euphractus Priodontes Tolypeutes Zaedyus Armadillos are any of several small mammals of the family Dasypodidae, mostly known for having a bony armor shell. ... Species Manis culionensis Manis gigantea Manis temmincki Manis tricuspis Manis tetradactyla Manis crassicaudata Manis pentadactyla Manis javanica Pangolins or scaly anteaters are mammals in the Pholidota order. ... Families Rathymotheriidae Scelidotheriidae Mylodontidae Orophodontidae Megalonychidae Megatheriidae Ground sloths are extinct edentate (Order Xenarthra) mammals that are believed to be relatives of tree sloths and three-toed sloths. ... In phylogenetics, a group is monophyletic (Greek: of one stem) if all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group. ...

References

Carroll, R. L. 1988. Vertebrate Paleontology and Evolution. W. H. Freeman and Company.