BLUEPRINT FOR BACKBONES

The image below is a photo of the exhibit panel. Following it is a transcript of the panel.

Photo of the panel from the exhibit.

Animals with backbones share an ancestor with modern seastars, acorn worms, and sea squirts.

The fossil record does not document the origin of vertebrates. To determine how they evolved, we look to their ancestors.

Echinoderms (such as seastars and sea urchins) and chordate relatives (such as acorn worms and sea squirts) don't look alike as adults, but their embryos share a unique pattern of development, inherited from their last common ancestor.

deuterostomes ( DOO -ter-o-stomes): animals with a mouth that developed secondarily, including echinoderms and chordates

New features:

  • body cavities form from outpocketings of the embryonic gut
  • three pairs of body cavities in larvae

chordates ( KOR -dates): animals with a dorsal support rod at some stage of their development, including sea squirts, amphioxus, and craniates

New features:

  • notochord a cartilaginous rod supports muscles and organs
  • hollow nerve tube runs down the back, along the notochord, contains nerves that synchronize body muscles
  • gill slits behind the mouth filter food from sea water
  • segmented body muscles
  • muscular tail extends behind gut cavity

When? 530 million years ago to present

craniates ( KRAY -nee-ates): chordates with a well-developed head, including lampreys, hags, and vertebrates

New features:

  • distinct head with sensory structures, such as eyes, ears, and nose

When? 510 million years ago to present

PICTURE CAPTIONS:

  • seastar adult
  • seastar embryo
  • acorn worm adult
  • acorn worm embryo
  • acorn worm larva
  • amphioxus adult
  • lamprey larvae
  • Diagram showing common ancestry and evolution of seastars, amphioxus, and lampreys from organisms with three embryonic body cavities. Evolution of amphioxus and lampreys is where notochord and hollow nerve tube branch off.