BIOL 3114 Lecture 16: Ch 18, 20, 21

• School: OSU
• Department: Biological Science
• Course: BIOL 3114
• Professor: Karen Mc Bee

Document Summary

First appeared in fossil record ~300 mya (carboniferous period of paleozoic) Most important terrestrial vertebrates from late carboniferous to early triassic. Non-mammalian synapsids declined during permian-triassic extinctions and early. Last non-mammalian forms extinct by early cretaceous. Mammals relatively minor part of fauna until cenozoic. Check out section 18. 3 evolutionary trends in synapsids especially numbered points. Clearly mammalian by late triassic, early jurassic (~195 mya) Limbs under body: deeper acetabulum, pelvis and pectoral girdle changes. Shorter feet: point forward, enlarged calcaneum. Larger jaw muscles: masseter, zygomatic arch. Reduction of lower jaw bones to just 1 dentary. Ancestral tetrapod lower jaw included several bones: dentary bears teeth, articular forms joint with quadrate on base of skull, angular forms angle at back of lower jaw. May have had tympanic-like structure in synapsids: quadrate articulates with stapes (columella, they vibrate! Stronger jaw needed for more active feeding may have interfered with flexibility needed for hearing.