GLY-1102 Lecture Notes - Lecture 13: Bryophyte, Melastomataceae, Ascidiacea
17 Sep 2018
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First could have been simple shelled organisms, quickly diversified. Could control internal buoyancy by filling shell with air. Notochord specialized can become essentially a backbone. Pikaia many features of vertebrate, v shape muscle attachments, ancient vertebrate ancestor. Amphioxis (branchiostoma or lancelet) still alive today, has all primitive chordate features. Gills supported by bone structures, low amounts of oxygen may have led to the need of more gill slits. Older theory states that it was formed by modifications of gill arches. Newer theory proposes that jaw evolved from velum (respiratory and feeding structure) Theory is that over time, evolution favored gill arches that were slanted forward, bottom of arch acted as a hinge. Osteichthyes are what we think of as modern fish, 99% of all living vertebrates come from them. Earlier fish and even fish today can use gill muscles to essentially chew prey with their throat. Spores in ordovician rocks earliest fossil evidence for land plants.
