Glanosuchus macrops
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Glanosuchus Temporal range: Late Permian |
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| Illustration of the skull of Glanosuchus macrops, 1904 | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Order: | Therapsida |
| Suborder: | †Therocephalia |
| Family: | †Scylacosauridae |
| Genus: |
†Glanosuchus Broom, 1904 |
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Glanosuchus is a genus of scylacosaurid therocephalian from the Late Permian of South Africa. The type species G. macrops was named by Robert Broom in 1904. Glanosuchus had a middle ear structure that was intermediate between that of early therapsids and mammals. Ridges in the nasal cavity of Glanosuchus suggest it had an at least partially endothermic metabolism similar to modern mammals.
Glanosuchus macrops was first described in 1904 by South African paleontologist Robert Broom, who named the genus and species on the basis of a nearly complete holotype skull. The skull has been distorted during fossilization and the bone is indistinguishable from the surrounding matrix in some parts. In illustrating the holotype, Broom chose to reconstruct the skull of the species rather than draw the actual specimen.
The skull of Glanosuchus is about 12 inches (30 cm) long.Glanosuchus probably grew to around 6 feet (1.8 m) in length. Like other early therocephalians, Glanosuchus had a long, deep snout and large canine teeth. The incisor teeth at the front of the upper jaw are also large and blade-like. There are six incisors on either side of the upper jaw, the furthest one being noticeably smaller than the rest. Five small pointed teeth are located behind each canine. The snout is wider in the front than it is behind, a usual feature among therapsids but present in several other related therocephalians. The nostrils are positioned at the tip of the snout and directed forward.
Glanosuchus represents an early stage in the development of the mammalian middle ear. Modern mammals have three bones in the middle ear (the malleus, incus, and stapes) that transfer sound energy from the eardrum to the fluid of the inner ear. The malleus and incus of mammals developed from the articular and quadrate of early therapsids. Studies of the bones of Glanosuchus show that it had a very thin plate of bone that acted as an eardrum, receiving sounds and transferring them to a small air-filled cavity. The stapes and vestibular foramen (the hole that connects the middle and inner ears) are preserved in one specimen of Glanosuchus that was examined by grinding away cross sections of the skull. The anular ligament, a ring-like structure that forms a seal between the end of the stapes and the rim of the vestibular foramen, was probably held in place by cartilage. The transfer of sound between the thin bony plate and the vestibular foramen in Glanosuchus was not as effective as it is in mammals, meaning that the animal had a less acute sense of hearing.
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