. The dinosaur book : the ruling reptiles and their relatives. Dinosaurs; Reptiles, Fossil. that it is an example of heredity "gone ; The ophiacodonts, for instance, had rather tall spines on the vertebrae, spines that served for the attachment of strong muscles to help hold up and stiffen the back. It may be that there was some sort of a hereditary upset, so that the spines elongated much faster than the animal grew, and since this strange adaptation was not particularly deleterious, the animal survived in spite of it. We frequently see such developments in nature. For instance
. The dinosaur book : the ruling reptiles and their relatives. Dinosaurs; Reptiles, Fossil. that it is an example of heredity "gone ; The ophiacodonts, for instance, had rather tall spines on the vertebrae, spines that served for the attachment of strong muscles to help hold up and stiffen the back. It may be that there was some sort of a hereditary upset, so that the spines elongated much faster than the animal grew, and since this strange adaptation was not particularly deleterious, the animal survived in spite of it. We frequently see such developments in nature. For instance, there was a herbivorous pelycosaur, known as ^daphostuirus (e-DAF- o-sawr-us), in which the spines were not only elongated but equipped with numer- ous transverse processes, like the yardarms of an old square-rigger. It is certainly diffi- cult to assign any functional purpose to such a development. It is much more logical to assume that this peculiar growth was merely a case of a hereditary maladjust- ment. The pelycosaurs are extraordinarily in- teresting to us, not only because of the bizarre adaptations shown by some of them, but also because some of these animals, particularly the sphenacodont-like forms, were the ancestors of those synapsidre^p- tiles known as therapsids. The therapsids were the "mammal-like reptiles," a descrip- tive term that delineates not only their general appearance but also their morpho- logical relationships, for these were the reptiles that were in part actually the direct ancestors of the Mammalia, that division of the animal kingdom of which we are members. The therapsids are found in many locali- ties in the several continental areas, but it is in South Africa and in Russia that our evidence for the past history of these ani- mals is especially complete. 56 The mammal-like reptiles had their be- ginnings in small synapsids known as dromasaurs, from which they radiated throughlater Permian and Triassic times along two general lines
Size: 1621px × 1541px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthoramericanmu, bookcentury1900, booksubjectreptilesfossil
