BISC 120Lg Lecture Notes - Lecture 15: Dorsal Nerve Cord, Agnatha, Devonian
Document Summary
Bisc 120: general biology: organismal and evolutionary biology- lecture 15: We can date chordates back all the way to the burgess shale. Pikaia is the first organism with evidence of a backbone--ancestor of all humans. In basic chordates, its just a grizzly rod between the tube and nerve cord. Very rudimentary but gives basic shape and structure to body. Layer of ectoderm that pinches off w/ surrounding neural crest cells (certain type of stem cells) Neural crest drives the invagination of the ectoderm that will form the nerve cord. Openings from the exterior of the organism into the mouth. Pharyngeal pouches ear, head, and neck (eustachian tube, Muscular post-anal tail middle ear, tonsils, etc ) As a very early embryo, even humans have post-anal tail, but is lost during development. This is present in chordates, arthropods, and mammals. Lancelet-- has all the classic features of a simple chordate. Only living species that looks like early chordates.
