TAILIEUCHUNG - Linzey - Vertebrate Biology - Chapter 8

C H A P T E R 8 Reptiles: Morphology, Reproduction, and Development Reptiles, comprising over 16,150 of the 53,000; species of vertebrates, include turtles (230 species), tuataras (2 species), lizards (3,900 species), snakes (2,400 species), crocodilians (21 species), and birds (9,600 species). | Linzey Vertebrate Biology 8. Reptiles Morphology Reproduction and Development Text The McGraw-Hill Companies 2003 CHAPTER 8 Reptiles Morphology Reproduction and Development INTRODUCTION Reptiles comprising over 16 150 of the 53 000 species of vertebrates include turtles 230 species tuataras 2 species lizards 3 900 species snakes 2 400 species crocodilians 21 species and birds 9 600 species . With the evolution of internal fertilization and the amniote egg reptiles became the first fully terrestrial vertebrates. Turtles Tuataras Lizards and Snakes Testudomorpha AND LEPIDOSAUROMORPHA MORPHOLOGY Integumentary System Turtles and lepidosaurs possess scales that unlike those of fishes are formed mainly from epidermal layers. The dry scaly epidermis which may be six or more layers in thickness serves primarily for protection and to reduce water loss. Some snakes utilize the broad flat scales known as scutes on the undersides of their bellies to aid in locomotion. In turtles the shell of dermal plates Fig. b is covered by horny keratinized scales also known as shields or scutes Fig. d . The embryonic origin and morphology of the integument in reptiles is discussed by Maderson 1985 . In squamates snakes and lizards the epidermis consists of a stratum corneum outer tissue layer and a stratum intermedium middle tissue layer above the stratum basale basal cell layer Fig. b . In most lizards and snakes a continual body covering of scales develops from the stratum corneum with each scale projecting backward to overlap part of the one behind. In turtles however each epidermal scale develops separately so that the scales do not form a solid sheet. The number and arrangement of epidermal scales on the body is usually species-specific and is used extensively in classification. The stratum corneum is sloughed and replaced either a few cells at a time or in patches or it is shed at intervals in FIGURE Nuchal a Bones of carapace Entoplastron Epiplastron Hypoplastron