. The dinosaur book : the ruling reptiles and their relatives. Dinosaurs; Reptiles, Fossil. ft Ancestors of the Dinosaurs THE REIGN OF THE DINOSAURS Was founded some 200 million years ago in Triassic times, the first division of the Mesozoic era. The last of the laby- rinthodont amphibians were seeking refuge in such streams and ponds as they could find, primitive turtles were continuing the history of the ancestral, roofed-skull rep- tiles, and the active, mammal-like reptiles were ranging across the land in search of their food. At that time the dinosaurs made their earliest appearance on th
. The dinosaur book : the ruling reptiles and their relatives. Dinosaurs; Reptiles, Fossil. ft Ancestors of the Dinosaurs THE REIGN OF THE DINOSAURS Was founded some 200 million years ago in Triassic times, the first division of the Mesozoic era. The last of the laby- rinthodont amphibians were seeking refuge in such streams and ponds as they could find, primitive turtles were continuing the history of the ancestral, roofed-skull rep- tiles, and the active, mammal-like reptiles were ranging across the land in search of their food. At that time the dinosaurs made their earliest appearance on the earth. Yet even though the lines of dinosaurian radia- tion became established in the Triassic pe- riod, the story of these great reptiles begins still further back in geologic time, in the distant days of the Permian, when the first diapsid reptiles made their debut on the stage of Earth History. The 225-million-year-old records of Permian diapsids are rather Per- haps the best evidence as to the nature of these forerunners of a great line of evolu- tionary development is to be found in the little reptile, Youtigina (young-EYE-na) or its close relative, Youngoides (young-OY-deez) from the upper Permian rocks of South Africa. Yotingina was small, and generally lizard- like in appearance. (Please remember that this is a comparison, and is not intended to suggest any relationships with the lizards, which appeared at a much later stage of geologic history.) Youngina had a long bodv and slender limbs. The head was J pointed and the jaws were armed with sharp, needle-like teeth. The key to the rela- tionships of this animal is, of course, in the back portion of the skull, which had two temporal openings, an upper one and a lower one, separated each from the other by bars of postorbital and squamosal bones. From an ancestry typified by reptiles such as Youngina the diapsids evolved in vari- ous directions during Mesozoic times, to become the dominant land animals of that g
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Keywords: ., bookauthoramericanmu, bookcentury1900, booksubjectreptilesfossil
