New PDF release: Guide to Living Reptiles

By J. E. Webb, J. A. Wallwork, J. H. Elgood (auth.)

ISBN-10: 0333256530

ISBN-13: 9780333256534

ISBN-10: 1349042889

ISBN-13: 9781349042883

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There seems little doubt that the Chelonia arose from the cotylosaurs at an early date, although fossil chelonians have not been found in rocks earlier than the Triassic. Triassic turtles differ from their modern counterparts in minor respects only and had already evolved the anatomical peculiarities characteristic of the group. The most striking of these are in the skeleton which has become profoundly modified by the existence of the shell, although the shell has been reduced in some recent forms such as Dermochelys.

The earliest reptiles, such as the cotylosaur Limnoscelis fronl the lower Permian period, had a skull in which there were no temporal openings (see page J). The chelonian skull also lacks true temporal fossae, that is, i t is of the primitive anapsid type. There seems little doubt that the Chelonia arose from the cotylosaurs at an early date, although fossil chelonians have not been found in rocks earlier than the Triassic. Triassic turtles differ from their modern counterparts in minor respects only and had already evolved the anatomical peculiarities characteristic of the group.

The neck can be retracted completely "ithin the shell. • ( 47) 2. The nasal bones are absent. 3· They are omnivorous freshwater animals. 4- Their distribution is discontinuous. Pelomedusa and Pelusios are African and Podocnemis o ccurs in Ma d a g ascar and South America. There are 3 genera and about 15 species. Examples:- Pelomedusa, Pelusios, Podocnemis. distribution of the Pelomedusidae the giant Ama£onian turtle - Podocnemis 48 T0 R T0 I S E S A N D T U R T L ES Family Chelidae - the Matamata and Snake-necked turtles Pleurodira in which:1.

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Guide to Living Reptiles by J. E. Webb, J. A. Wallwork, J. H. Elgood (auth.)


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