therapsid


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Related to therapsid: Pelycosauria, synapsid, Enterozoa
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Synonyms for therapsid

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Among the reptiles, a group of therapsids called "mammaloids" developed and are considered to be the predecessors of mammals.
The abundant vegetation covering the region during the Permian sustained the lives of numerous herbivorous therapsids, which were unable to subsist when the climate changed and the vegetation became impoverished; they were substituted by Lystrosaurus, which was more resistant and had a curious nasal appendage, which is believed helped them to unearth the rhizomes typical of arid vegetation.
In the mammalian lineage, these structures most likely evolved in concert with the development of enhanced aerobic capacity and endothermy among the ancestors of mammals, the mammallike reptiles or therapsids (Hillenius 1992).
In this paper, I review the relationships between mammalian nasal turbinates and endothermy, as well as the presence of turbinates in the fossil record of early mammals and therapsids. Several newly prepared fossil specimens are described, which suggest that respiratory turbinals did, in fact, occur among therocephalians and cynodonts, two groups of advanced therapsids.
Among primitive therapsids, Orlov (1958) described longitudinal ridges on the ventral surface of the nasal and frontal bones of the Late Permian dinocephalian Titanophoneus, but interpreted these as marking the lateral edges of the nasal septum.
In both Lystrosaurus and Pristerodon the ridges are paired and closely resemble the nasoturbinal ridges of other therapsids. Furthermore, in Pristerodon a short ridge is present in a preorbital recess of the nasal cavity, lateral to the nasoturbinal ridges (pers.
Dicynodonts are the first group of therapsids to develop a secondary palate.
The nasal cavity of gorgonopsians is much larger than in dicynodonts, but like pelycosaurs and other primitive therapsids, they lack a bony secondary palate.
Lead author Dr Marcello Ruta of the University of Lincoln of the study, said that mass extinctions are seen as entirely negative but in this case, cynodont therapsids, which included a very small number of species before the extinction, really took off afterwards and was able to adapt to fill many very different niches in the Triassic - from carnivores to herbivores.
The most common tetrapod fossils are teeth referable to small ornithischians and possible theropods, followed by bones and osteoderms of Protosuchus, and bones of cynodont therapsids including a tritylodontid dentary and limb bones.
(2011) argued for strong provinciality in the moist equatorial Pangaean region; there, traversodontid cynodonts are abundant, whereas remains of these therapsids are rare or absent and procolophonid reptiles are abundant in the Northern Hemisphere subtropics (as, for example, in the Evangeline Member of the Wolfville Formation).