The vertebrates are the most advanced of all chordates. They are
characterized by a skull and a bony or cartilaginous _internal
skeleton_, with a _vertebral column_ of bone or cartilage. This
subphylum is commonly divided into two superclasses, the Pisces (the
fishes and their relatives) and the Tetrapoda (the four-footed animals).
As mentioned earlier, most amateur collectors collect very few
vertebrate remains, and for this reason this group is not discussed in
detail. However, the more important vertebrate classes are briefly
reviewed to enable the reader to have some understanding of this
important group of animals. This part of the handbook will also serve as
an introduction to some of the interesting and unusual, but now extinct,
animals that have inhabited Texas in the geologic past. Among these
animals are giant fishes, primitive amphibians, and many different types
of dinosaurs. Included also are such unusual mammals as the giant ground
sloths, saber-tooth cats, mammoths, and mastodons, all of which are now
extinct. The remains of these, and many other interesting extinct
vertebrates, may be seen in the geological collections of the Texas
Memorial Museum at Austin. Many of these displays are accompanied by
drawings which depict the scientific restoration of the animal’s soft
parts and show how the animal may have appeared in life.