This chapter discusses early vertebrates. These were more complex and more active animals than the nonvertebrate chordates. Novel vertebrate anatomical features included a tripartite brain enclosed by a cranium, and a muscular pharynx for using the gills for respiration rather than for filter feeding. The chapter mentions gnathostomes, jawed vertebrates which represent an increase in complexity in the vertebrate body plan and reflects the vertebrate mode of life as an active predator. Soft-bodied vertebrates were known to derive from the early Cambrian and the earliest known vertebrates with bone or ostracoderms from the Late Ordovician. The chapter looks at the earliest evidence of bone in vertebrates. This is covered in the odontodes of the dermal head shield of ostracoderms and their bony tissues included bone, dentine, and enamaloid.
