Amniote Relationships. Reptilian Ancestor. Reptilia. Mesosuarus freshwater dwelling reptile

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1 Amniote Relationships mammals Synapsida turtles lizards,? Anapsida snakes, birds, crocs Diapsida Reptilia Amniota Reptilian Ancestor Mesosuarus freshwater dwelling reptile Reptilia General characteristics of reptiles (not all of these are shared derived characters) amniotic egg internal fertilization pulmonary respiration single occipital condyle* two sacral vertebrae with ribs epidermal scales * knob of bone at back of skull that articulates with the first vertebrae 1

2 Modern 7,500 species About 6,800 of these are lizards and snakes All continents except Antarctica Amniote Relationships mammals Synapsida turtles lizards, Anapsida snakes, birds, crocs Diapsida Reptilia Amniota Reptile Relationships Class Reptilia - turtles Subclass Diapsida - diapsids Superorder Lepidosauria - lepidosaurs Order Rhyncocephalia - tuataras Order Squamata - lizards and snakes Superorder Archosauria - ruling reptiles Order Crocodylia - crocodilians 2

3 of Modern Reptiles snakes and lizards? crocodilians turtles Relationships Among Modern Reptiles turtles snakes, lizards crocs All reptiles have internal fertilization. Why? Male turtles and crocodilans have a penis that lies in the floor of the cloaca Tuataras lack an intromittent organ. How is fertilization achieved? Snakes and lizards paired hemipenes that are formed from the rear of the cloaca snake hemipenes 3

4 Retention of eggs and live birth Most reptiles are oviparous and lecithotrophic There are a few viviparous lecithotrophic snakes/lizards and even fewer viviparous placentotrophic snakes/lizards Six families of snakes/lizards are entirely oviparous Seven families of snakes/lizards are entirely viviparous Fifteen have both All turtles and crocodilians are oviparous Costs of viviparity: production limited to one clutch per season clutch size is lower because of space limitations gravid (pregnant) females are more vulnerable to predators Viviparity may have evolved in association with cold climates because embryos retained in a thermoregulating female are warmer and develop faster than embryos developing in nests on the ground. This results in earlier hatching which has obvious benefits in cold climates with a short summer. 4

5 Parental Care absent in turtles found in all crocodilians with both parents involved. Takes three forms: defense of nest (females), opening nest and aiding young in hatching, transporting young to water. approximately 100 species of squamates (=snakes & lizards) have parental care. Takes three forms: egg brooding, defense of nest site, and egg brooding with thermogenesis. Sex Determination In most animals the sex of offspring is determined by which sex chromosomes they inherit. This is known as genotypic sex determination (GSD). All amphibians, snakes, and some lizards have GSD. X Y Sex Determination However, the sex of some lizards, most turtles, and all crocs and tuataras is determined by the incubation temperature of the nest. This is called temperature dependent sex determination (TSD). There are three major patterns of TSD. A. Males at high temps B. Males at low temps C. Males at intermediate temps 5

6 Asexuality Parthenogenesis is the only form of asexuality known in reptiles. It has been reported in 30 species of squamates, mostly geckos, lacertids, and teiids (all lizards) and blind snakes (a group of small, sightless, primitive snakes). The Shell Of all living reptiles, turtles are most recognizable because of the shell. The turtle shell is made up of the carapace (top) and the plastron (bottom). Both are bone covered with keratinized scutes or leathery skin. The Shell The CARAPACE is composed of 10 trunk vertebrae and the associated, widened ribs. Dermal bone fills in the spaces between the ribs. The extent of this filling, and thus the completeness of the shell varies among families. 6

7 The Shell The PLASTRON is composed of unique abdominal ribs and the expanded pectoral girdle. This results in a unique situation in which the ribs are external to the girdles (pelvic and pectoral) as opposed to almost all other tetrapods in which the opposite spatial arrangement is true. Shared Derived Characters shell no teeth skull with large otic notch to support tympanum presence of trochlea, a ridge of bone over which the jaw adductor muscles pass loss of pineal foramen Size Range: 10 cm 2.5 m and 1,000 kg 7

8 Systematics and Classification Order Testudinata - living turtles Suborder Pleurodira - side-neck turtles Suborder Pleurodira - side-neck turtles 3 families about 75 species southern hemisphere Podocnemis unifilis Chelodina mccordi 10 families about 200 species worldwide snapping and big-head turtles Macrochelys temminckii Platysternon megacephalum 8

9 sea turtles Dermochelys coriacea Eretmochelys imbricata pond turtles Clemmys guttata Rhinoclemmys punctularia tortoises Testudo sp. Geochelone radiata 9

10 softshells Apalone spinifera Cycloderma frenatum pignose turtle Central American river turtle Carettochelys insculpta Dermatemys mawii mud and musk turtles Kinosternon carinatum Staurotypus salvinii 10

11 Evolutionary Trends aquatic habit (esp. locomotion) e.g. sea turtles terrestrial habit e.g. tortoises bottom dwelling e.g. softshells 11