21 minutes

Phylum Chordata evolved in ancient seas over 530 million years ago as shown by fossils (Pikaia) discovered in the Burgess Shales. The unique features of this group: a supporting rod, a hollow dorsal nerve cord, post-anal tail, and pharyngeal gills are investigated in modern animals - tunicates, lancelets (Branchiostoma or Amphioxus), hagfish, cartilaginous fish and the other groups of vertebrates. Key adaptations leading to the diversification and proliferation of the modern vertebrate groups, from fish to mammals, are explored through fossil evidence, living examples and animation. (2006).