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The quadrate bone is a skull bone in most tetrapods, including amphibians, sauropsids (reptiles, birds), and early synapsids. In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms upper part of the jaw joint. The lower jaw articulates at the articular bone, located at the rear end of the ...
It usually fuses with the equally small quadrate to form the quadrate-quadratojugal complex. [15] Oddly enough, the cynodont Thrinaxodon retains a separate quadratojugal. In other cynodonts such as Cynognathus , the quadrate-quadratojugal complex remains hidden within the skull, obscured from the side by the large squamosal bone which loosely ...
The bones of the pelvis and hind limb are very robust compared to other dicynodonts due to the massive size of the animal (e.g. the largest known femur is 80 centimetres (31 in) long), but are otherwise similar to those of other stahleckeriids. Like other stahleckeriids, the hind legs were also held upright beneath the body.
Figure 1:In mammals, the quadrate and articular bones are small and part of the middle ear; the lower jaw consists only of dentary bone.. While living mammal species can be identified by the presence of milk-producing mammary glands in the females, other features are required when classifying fossils, because mammary glands and other soft-tissue features are not visible in fossils.
The skull of a snake differs from a lizards in several ways. Snakes have more flexible jaws, that is, instead of a juncture at the upper and lower jaw, the snake's jaws are connected by a bone hinge that is called the quadrate bone. Between the two halves of the lower jaw at the chin there is an elastic ligament that allows for a separation.
Some of the bones were lost, but the quadrate, the articular, and the angular bones became free-floating and associated with the stapes. This occurred at least twice in the mammaliformes. The multituberculates had jaw joints that consisted of only the dentary and squamosal bones, and the quadrate and articular bones were part of the middle ear ...
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The tuatara and some extinct rhynchocephalians have a more rigid skull with a complete lower temporal bar closing the lower temporal fenestra formed by the fusion of the jugal and quadrate/quadratojugal bones, similar to the condition found in primitive diapsids. However early rhynchocephalians and lepidosauromorphs had an open lower temporal ...