EARTH 7 Lecture Notes - Lecture 7: Chinle Formation, Saurischia, Herrerasaurus
Document Summary
Can"t be explained by typical background extinction. Landmark study that first gave us an indication of significant, focused extinction events. 96% of all marine species went extinct. 70% of all terrestrial vertebrate species went extinct. Formation of pangea: severe decrease in extent of shallow marine environments, new competition from invaders, lowering of sea level, alteration of oceanic circulation and atmospheric weather patterns. Volcanic eruptions: huge dust and clouds would have blocked sunlight, released catastrophic a(cid:373)ou(cid:374)ts of co a(cid:374)d so , acidification/anoxia in the oceans. Synapsids were dominant, but entire ecosystem failed around them. There are reasons to suspect archosaurs were better adapted to arid environments. Archosaurs evolved a more erect stance before synapsids. Erect posture + narrow tracked gait: upright posture convergent in dinosaurs and mammals, efficient locomotion. Keep body off ground with minimal energy. Easier to breathe and run at same time. Opening in hip socket bordered by bony upper ridge.
