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 extant organisms, especially reptiles.
[1] This structure is commonly called "dermal armor" and serves to protect the organism, while also helping with temperature regulation.
Osteoderms represent hard tissue components of the integument, making them easy to identify in fossil examination.
Some early amphibians have this armor, but it is lost in modern species with the exception a ventral plate, called the gastralia.
[3][4] Osteoderm demonstrates a slightly delayed development compared with the rest of the skeleton, as it does not appear until after hatching has occurred.
On the other hand, in common geckos, the bony osteoderm plates are much smaller than the scales and appear to be independently organized.
Scutes are made of keratin, a protein which also makes up human fingernails, along with the horns and claws of some animals.
Evolution of predator and prey has played a role in encouraging the development and shaping of body armor.
They increased in size, decreasing the applied jaw forces, but their larger structure also made them more difficult to remove from rocks and other burrows.
For example, if the habitat decreases their ability to hide in their surroundings, they need to move at increased speeds which occurs at the expense of the body armor.
The food the species eats can affect mineral deposit and re-uptake levels and that would influence the amount of osteoderm present.
When small osteoderms are found, they include compact structures, low remodeling and poor growth lines which suggests early development.
Advanced and final stages of development are characterized by keeled elements with protuberances and an axis longer than 15 centimeters.
[12] The most modern species are not heavily armored but they have many smaller ossicles, or small bones, found in the dermis.
[14] Since crocodiles submerge completely underwater for long periods of time, the osteoderms release neutralizing ions into the bloodstream that buffer the accumulating carbon dioxide and prevent acidosis.
[16] Lizards have wide spread forms of osteoderms, especially on the skull roof which fuses with the present dermal bone.
Over time, horizontal rows develop under the body that include small lateral plates that can connect the ventral and dorsal osteoderms.
In extant armadillo species, their osteoderms are physically linked to their nerves, muscles, glands, and connective tissues, creating a very sensitive, dynamic integument system.
[18] The carapace of an armadillo consists of a thin layer of keratin over the top of a compacted matrix of bony osteoderm tiles that are connected via collagen fibers.
[19] Armadillos are the only living mammals with an outer carapace shell that consists of ossified dermal tissue.