Geology Reference
In-Depth Information
Figure 19-4:
A
straight-shelled
nautiloid from the
Paleozoic.
Spinal Tapping: Animals with Backbones
While the early Paleozoic was ruled by invertebrates, the development of skeletal fea-
tures had also begun. The evolutionary story of
chordates
— animals with a nerve chord
(which later includes animals with a backbone, or
vertebrates
) — is missing its earliest
chapters in the fossil record because there were no hard skeletal parts to preserve.
