33.2 What
Are the Major Groups of Echinoderms
and Hemichordates? 718
Echinoderms have a water vascular
system 719
Hemichordates have a three-part body
plan 721
33.3
What New Features Evolved in the Chordates?
722
Adults of most urochordates and cephalochordates
are sessile 722
A new dorsal supporting structure
replaces the notochord in vertebrates
723
The vertebrate body plan can support
large animals 724
Fins and swim bladders improved stability
and control over locomotion 725
33.4 How
Did Vertebrates Colonize the Land?
728
Jointed fins enhanced support for
fishes 728
Amphibians adapted to life on land
728
Amniotes colonized dry environments
730
Reptiles adapted to life in many habitats
731
Crocodilians and birds share their
ancestry with the dinosaurs 731
The evolution of feathers allowed
birds to fly 733
Mammals radiated after the extinction
of dinosaurs 734
Most mammals are therians 735
33.5 What
Traits Characterize the Primates?
737
Human ancestors evolved bipedal locomotion
738
Human brains became larger as jaws
became smaller 740
Humans developed complex language
and culture 741
