Australia: The Land Where Time Began

A biography of the Australian continent 

Earliest Vertebrates

According to Benton, the earliest known vertebrates are fish from the Cambrian, recognised as ancestral vertebrates only from the appearance and microstructure of their hard tissues, the remains that have been found of these organisms show only part of their overall shape and anatomy. Beginning in the Ordovician, continuing in the Silurian and Devonian, the fossils of fish are often complete and well preserved, displaying a large amount anatomical detail. From these period it has been possible to identify 9 or 10 major lineages of fish, most of which appear very different from modern fish, though some look familiar.

The Ordovician and Silurian, 443-417 million years ago, is believed to be the time when the key episodes in fish evolution occurred, all the major groups appearing, though it was only in the Devonian, 417-354 million years ago, that specimens are abundant. Prior to this time marine and fresh waters were dominated by heavily armoured forms, and during this period the sharks and bony fishes gained dominance of the seas and fresh water, eventually giving rise to terrestrial vertebrates, the tetrapods. As they exclude the tetrapods, terms such as fish, and the various lines of fish, all refer to prophylactic groups.

According to Long the oldest known vertebrates arose in China in the Early Cambrian.

Sources & Further reading

1. Benton, Michael J., 2005, Vertebrate Palaeontology, 3rd Ed. , Blackwell Science.
2. Long, John A., 2011, The Rise of Fishes - 500 Million years of Evolution, 2nd ed, University of New South Wales Press.