. The dinosaur book : the ruling reptiles and their relatives. Dinosaurs; Reptiles, Fossil. The First Land Animals I e do not know when life began \A/ on the earth, and it seems likely P that the answer to this question will remain forever hidden from us. What we do know is that it was some 500 million years ago when the plants and animals of early geologic history had reached a stage of development where they produced hard parts capable of being preserved as fossils. At that distant date there seemingly was no land life; all life was in the sea. More- over, there were no vertebrates, or back-
. The dinosaur book : the ruling reptiles and their relatives. Dinosaurs; Reptiles, Fossil. The First Land Animals I e do not know when life began \A/ on the earth, and it seems likely P that the answer to this question will remain forever hidden from us. What we do know is that it was some 500 million years ago when the plants and animals of early geologic history had reached a stage of development where they produced hard parts capable of being preserved as fossils. At that distant date there seemingly was no land life; all life was in the sea. More- over, there were no vertebrates, or back- boned animals, living—at least none of suf- ficient complexity that they left hard struc- tures to be preserved in the form of fossils. According to the fossil record, the animals of that time were mostly various types of sea-shells and crablike forms. It is probable, however, that even by the beginnings of Cambrian times, about 540 million years ago, the basic patterns for the backboned animals had been established, for it was at an early stage in the Paleozoic era that the first vertebrates appeared. These were primitive, fishlike forms. The fishes rose and evolved at a rapid rate, so that by middle Paleozoic times, in the Dey^maji_p_eriod (340-275 million years ago), they were abundajit_anjiafgnuiiiurf in the waters of the earth. There were many kinds of Devonian fishes, some large, some small, some fast-swimming and predaceous hunters, others flattened burrowers and grovelers in the muds of shallow bottoms. Among the Devonian fishes there were cer- tain ones, belonging to a group known as the crossopteri/gian (cross-op-ter-ij-e-yan) or lobe-finned fishes, which were destined to play a very important role in the history of evolution, for these were the immediate, direct ancestors of the first land-living vertebrates. The lobe-finned or crossoptervgian fishes were of medium size and were covered by a heavy armor of scales. Some of the signifi- cant structures characterizin
Size: 3646px × 685px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthoramericanmu, bookcentury1900, booksubjectreptilesfossil
