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Early Vertebrates (Oxford Monographs on Geology and Geophysics)

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Although this reference is a very detailed treatise on early vertebrate fossils, it may prove useful to the general reader trying to make sense of early vertebrate evolution because it does not reproduce photographs of the early fossils, but instead takes artistic license to illustrate them in reconstructed forms. The earliest known fossil vertebrate is Sacabambaspis/Arandaspis found in Bolivia/Australia and 470 million years old - head armor, jawless, mouth containing bony parts for scraping the seabottom, lateral eyes, two pineal eyes, gill openings, and only a median and caudal fins. At the end of Ordovician there was a period of glaciation, and then afterwards in the early Silurian there is a large appearance of both jawless and jawed fossil vertebrates - heterostracans (cephalaspids), galeaspids, thelodonts, acanthodians, shark relatives (chondrichthyans), placoderms (jawed & armored), and possibly bony fishes (osteichthyans). In the mid-Silurian tectonic plate movement created mountain ranges that subsequently eroded what became a red sandstone in many areas that were favorable to vertebrate life. In the Devonian fossils are found showing fish evolving into groups that would survive to the present, as well as tetrapods. In the Carboniferous it is found that the cartilaginous fishes and the ray-finned fishes greatly diversify, as well ferns and club-mosses are found around bays and lakes. After the Permian ended, the 'modern' vertebrate world appears in the Triassic and Jurassic - sharks, teleosts, modern amphibians, modern reptiles, birds and mammals. Lampreys, hagfishes, chimaeras, some ray-finned fish, coelacanths and lungfishes survive relatively unchanged from the emergence of the vertebrates in the Late Palaeozoic. The early vertebrate fossils, along with comparisons of extant vertebrates, are considered in detail. Origins of the vertebrate head and the tetrapod limb are then considered, followed by broader topics in evolution.