BIOL 305 Lecture Notes - Lecture 23: Therapsid, Skull, Cynodont
7 Jun 2019
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Document Summary
Synapsids have a single temporal fenestra, distinguishing them from other tetrapods. Evolution of synapsids: branched into 2 groups: pelycosaurs and therapisids, both considered to be extinct but cynodonts are where mammals arose. Pelycosauria: arise in mis-carbonigerous, extensive radiation during the early permian: 50% of all amniote genera, some herbivorous, most carnivorous, some had a sail: flap of skin supported by projection o the vertebrae, extinct by end permian. Therapsida: flourished during early triassic, diversity of body design, differentiated teeth, legs more directly positioned under the body (more efficient and active locomotion) Therapsida: cynodontia: advanced therapsids, arose in late permian and survived the mass extinction, ancestral stock from which modern mammals arose, have mammalian characteristics. Mammalian characteristics: traits not exclusive to mammals but very common, endothermy, 4-chambered heart, single bone in lower jaw, 3 bones in middle ear, 1 time tooth replacement, hair, mammary glands, diaphragms.
