BIOC50H3 Lecture Notes - Lecture 6: Heterostraci, Invertebrate, Myllokunmingia
23 Oct 2015
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Document Summary
Notochord stiff, rod-shaped body found in embryos of all chordates primitive axis of embryo; persists in some as main axis. Cephalochordates notochord important in the adult stages primitive brain of sensory organs. Several adaptations over time (eyes, head -2 , skull -3, spine -4, first bone-like elements. 5, paired fins, cellular bone -6, jaws, pelvic fins -7, bony exoskeleton disappears -8, endoskeleton of bone -9, lungs (homologous) -10) Precursors to early craniates - haikouichthys and myllokunmingia (distinct head with small eyes), craniates are defined by having a skull (either bone or cartilage) (hagfish), lamprey, Heterostracans (lacked endoskeleton), osteostracans (paired fins), gnathostomes (jawed vertebrates) Placoderms carnivorous; extensive armor plating on head and neck. Early devonian to present lacked bony exoskeleton, endoskeleton of cartilage. Diversified so rapidly in late silurian and early devonian that we have very few fossils of the earliest forms.
