BLG 144 Lecture Notes - Lecture 9: Gnathostomata, Amniote, Yolk Sac
Document Summary
Chapter 34 deuterostomes selection for bulk feeding predation modification of support structures into jaw more powerful muscles no bony endoskeleton but early fishes with bony exoskeleton teeth but no jaws. Vertebrate evolution recall: early vertebrates with cartilaginous armed fishes notochord for structural support (still in some living lineages) You can"t bite without jaws! early vertebrates limited to filter/deposit-feeding. So where did jaws come from? strong support for gill-arch hypothesisy cartilaginous support structure later taken over by bony endoskeleton bone also allows greater support in appendages (fins) but mainly rays. Very elaborate in one fish lineage bony elements enlarged & more complex in lobe-finned fishes fleshy fins support more body weight. So now you want to be a terrestrial vertebrate greater structural support larger embryos nutrition via yolk sac external fertilization, embryos do seen in reptilia & mammalia creates amniote lineage modification in mammals. 1st cartilaginous, brain elaboration embryo develops inside uterus nutrition via placenta modification in mammalian lineage.
