Skull roof in the context of "Synapsids"

A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification forming components of the vertebrate skeleton, including much of the skull, jaws, gill covers, shoulder girdle, fin rays (lepidotrichia), and the shells of turtles and armadillos. In contrast to endochondral bone, dermal bone does not have a cartilage precursor, and it is often ornamented. Dermal bone is formed within the dermis and grows by accretion only – the outer portion of the bone is deposited by osteoblasts.

The function of some dermal bone is conserved throughout vertebrates, although there is variation in shape and in the number of bones in the skull roof and postcranial structures. In bony fish, dermal bone is found in the fin rays and scales. A special example of dermal bone is the clavicle. Some of the dermal bone functions regard biomechanical aspects such as protection against predators. The dermal bones are also argued to be involved in ecophysiological implications such as the heat transfers between the body and the surrounding environment when basking (seen in crocodilians) as well as in bone respiratory acidosis buffering during prolonged apnea (seen in both crocodilians and turtles). These ecophysiological functions rely on the set-up of a blood vessel network within and straight above the dermal bones.

Glyptotherium (from Ancient Greek for 'grooved or carved beast') is a genus of glyptodont (an extinct group of large, herbivorous armadillos) in the family Chlamyphoridae that lived from the Early Pliocene, about 3.9 million years ago, to the Late Pleistocene, around 15,000 years ago. It was widely distributed, living in the United States, Mexico, Guatemala, Costa Rica, Honduras, El Salvador, Panama, Venezuela, Colombia, and Brazil. Fossils that had been found in the Pliocene Blancan Beds in Llano Estacado, Texas were named Glyptotherium texanum by American paleontologist Henry Fairfield Osborn in 1903. Another species, G. cylindricum, was named in 1912 by fossil hunter Barnum Brown on the basis of a partial skeleton that had been unearthed from the Pleistocene deposits in Jalisco, Mexico. The two species differ in several aspects, including age: G. texanum is from the older Early Pliocene to Early Pleistocene strata, whereas G. cylindricum is exclusive to the Late Pleistocene.

Glyptotherium was a large, four-legged (quadrupedal), herbivorous armadillo with an armored top shell (carapace) that was made of hundreds of interconnected osteoderms (structures in dermis composed of bone). Other pieces of armor covered the tail and cranium roof, while small pebbly pieces of armor were in the skin. Glyptotherium grew up to 2 meters (6.56 feet) in length and 400 kilograms (880 pounds), making it one of the largest glyptodonts known. Glyptotherium is morphologically most similar to Glyptodon: though they differ in several ways. Glyptotherium is smaller on average, with a shorter carapace, a longer tail, and had a different distribution.

Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant reptiles and, therefore, birds). Unlike other amniotes, synapsids have a single temporal fenestra, an opening low in the skull roof behind each eye socket, leaving a bony arch beneath each; this accounts for the name "synapsid". The distinctive temporal fenestra developed about 318 million years ago during the Late Carboniferous period, when synapsids and sauropsids diverged, but was subsequently merged with the orbit in early mammals.

The basal amniotes (reptiliomorphs) from which synapsids evolved were historically simply called "reptiles". Therefore, stem group synapsids were then described as mammal-like reptiles in classical systematics, and non-therapsid synapsids were also referred to as pelycosaurs or pelycosaur-grade synapsids. These paraphyletic terms have now fallen out of favor and are only used informally (if at all) in modern literature, as it is now known that all extant reptiles are more closely related to each other and birds than to synapsids, so the word "reptile" has been re-defined to mean only members of Sauropsida or even just an under-clade thereof. In a cladistic sense, synapsids are in fact a monophyletic sister taxon of sauropsids, rather than a part of the sauropsid lineage. Therefore, calling synapsids "mammal-like reptiles" is incorrect under the new definition of "reptile", so they are now referred to as stem mammals, proto-mammals, paramammals or pan-mammals. Most lineages of pelycosaur-grade synapsids were replaced by the more advanced therapsids, which evolved from sphenacodontoid pelycosaurs, at the end of the Early Permian during the so-called Olson's Extinction.

The calvaria is the top part of the skull. It is the superior part of the neurocranium and covers the cranial cavity containing the brain. It forms the main component of the skull roof.

The calvaria is made up of the superior portions of the frontal bone, occipital bone, and parietal bones. In the human skull, the sutures between the bones normally remain flexible during the first few years of postnatal development, and fontanelles are palpable. Premature complete ossification of these sutures is called craniosynostosis.

"Labyrinthodontia" (Greek, 'maze-toothed') is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras (about 390 to 150 million years ago). Traditionally considered a subclass of the class Amphibia, modern classification systems recognize that labyrinthodonts are not a formal natural group (clade) exclusive of other tetrapods. Instead, they consistute an evolutionary grade (a paraphyletic group), ancestral to living tetrapods such as lissamphibians (modern amphibians) and amniotes (reptiles, mammals, and kin). "Labyrinthodont"-grade vertebrates evolved from lobe-finned fishes in the Devonian, though a formal boundary between fish and amphibian is difficult to define at this point in time.

"Labyrinthodont" generally refers to extinct four-limbed tetrapods with a large body size and a crocodile-like lifestyle. The name describes the pattern of infolding of the dentin and enamel of the teeth, which are often the only part of the creatures that fossilize. They are also distinguished by a broad, strongly-built skull roof composed of many small heavily-textured skull bones. "Labyrinthodonts" generally have complex multi-part vertebrae, and several classification schemes have utilized vertebrae to define subgroups.