ZOO 2090 Lecture Notes - Lecture 2: Symmetry In Biology, Amnion, Organogenesis

• School: University of Guelph
• Department: Zoology
• Course: ZOO 2090
• Professor: Jinzhong Fu

Document Summary

The origin of vertebrates can be studied by: Fossil record: most direct, but never complete: phylogenetic approach: using shared derived characters to determine common ancestry. Candidate fossil chordates(cid:198)there are very few: pikaia of the burgess shale (from the middle of the cambrian ~520 mya, vetulicolians of chengjiang (from the early cambrian ~540 mya) Early cambrian in chengjiang: haikouella (or yunnanzoon) This may actually be a non-vertebrate basal deuterostome: haikouichthys, rudimentary vertebrae surrounding a strengthened notochord, eyes might be present. Early cambrian of north america burgess shale, marble canyon: metaspriggina shows a notochord, pairs of camera eyes and nasal sacs, fish-like myomeres and tail as well as bipartite branchial bars associated with external gills. Scenarios for the making of vertebrates: abstract: over the past 200 years, almost every invertebrate phylum has been proposed as a starting point for evolving vertebrates. Most of these scenarios are outdates, but several are still seriously considered.