Chordates: We’re All Family


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Amphioxus, a worm like animal, is our ancestor with numerous common features including the precursor to the vertebrate backbone. Some chordates like tunicates, salps and larvaceans, have remained simple creatures without backbones.  But others like the vertebrates have four times as many genes as their simple chordate ancestors which allowed an explosion of new forms.  Fish evolved skulls and jaws and dominated the seas. Some fish evolved limb-like fins and crawled out onto land. Reptiles (lizards, snakes) and dinosaurs flourished on land. When the dinosaurs went extinct 65 million years ago, mammals inherited the land. Humans are most closely related to the great apes.

Next Generation Science Standards for this Video

The internal skeleton of vertebrates provides support for a large body and allows for a diversity of movements from walking to swimming to flying.

The body plan animation visualizes the complex chordate structures and how they function:

  • Notochord
  • Nerve cord
  • Gill slits
  • Segmented muscles


When the dinosaurs went extinct after an asteroid hit the earth, mammalian species diversity exploded into the unfilled niches.