Chapter 34 - Vertebrates
Chapter 34 Vertebrates
Overview: Half a Billion Years of Backbones
Vertebrates are named for vertebrae, the series of bones that make up the vertebral
column or backbone.
There are about 52,000 species of vertebrates, far fewer than the 1 million insect species
Plant-eating dinosaurs, at 40,000 kg, were the heaviest animals to walk on land.
The biggest animal that ever existed is the blue whale, at 100,000 kg.
Humans and our closest relatives are vertebrates.
This group includes other mammals, birds, lizards, snakes, turtles, amphibians, and the
various classes of fishes.
Concept 34.1 Chordates have a notochord and a dorsal, hollow nerve cord
The vertebrates belong to one of the two major phyla in the Deuterostomia, the chordates.
Chordates are bilaterian animals, belonging to the Deuterostomia.
The phylum Chordata includes three subphyla, the vertebrates and two phyla of
invertebrates—the urochordates and the cephalochordates.
Four derived characters define the phylum Chordata.
Although chordates vary widely in appearance, all share the presence of four anatomical
structures at some point in their lifetime.
These chordate characteristics are a notochord; a dorsal, hollow nerve cord; pharyngeal
slits; and a muscular, post-anal tail.
The notochord, present in all chordate embryos, is a longitudinal, flexible rod located
between the digestive tube and the nerve cord.
It is composed of large, fluid-filled cells encased in fairly stiff, fibrous tissue.
It provides skeletal support throughout most of the length of the animal.
While the notochord persists in the adult stage of some invertebrate chordates and
primitive vertebrates, it remains only as a remnant in vertebrates with a more
complex, jointed skeleton.
For example, it is the gelatinous material of the disks between vertebrae in
The dorsal, hollow nerve cord of a chordate embryo develops from a plate of
ectoderm that rolls into a tube dorsal to the notochord.
Other animal phyla have solid nerve cords, usually located ventrally.
The nerve cord of the chordate embryo develops into the central nervous system:
the brain and spinal cord.