Topic 32 Clade Reptiles Clade Reptiles The reptile clade diapsids includes the tuataras lizards snakes turtles crocodilians birds and some extinct groups like the dinosaurs Early taxonomists excluded birds class Aves from the classification of class Reptilia Fig 34 26 A phylogeny of amniotes Characteristics of non avian reptiles Skin protection and shedding Reptile skin is protected by thick dry keratinous scales that create a waterproof barrier Reptilian skin can be shed in sections as observed in turtles or all at once as seen in snakes and lizards Reproductive adaptations Most reptiles lay shelled eggs which protect them against desiccation Most bury their eggs on land A few species are viviparous where extra embryonic membranes function as a simple placenta Parental care of eggs or juveniles is typically minimal Except in crocodilians Characteristics of non avian reptiles Most reptiles have three chambered hearts similar to amphibians Most reptiles are ectothermic absorbing external heat as the main source of body heat Ectotherms regulate their body temperature through behavioural adaptations Compared to similarly sized mammals reptiles have a lower metabolic rate and significantly reduced food and energy requirements Sunbathing monitor lizard The Origin and Evolutionary Radiation of Reptiles Fossil evidence indicates that the earliest reptiles lived about 310 million years ago during the Carboniferous period These early reptiles were diapsids like all reptiles today Permian diversification The collapse of Carboniferous rainforests created a cooler arid climate in the Permian driving reptile diversification as they adapted to new terrestrial habitats Permian mass extinction and reptile adaptive radiation The end Permian extinction 252 mya eliminated most animal species including many dominant synapsids This mass extinction opened ecological niches allowing reptiles to rapidly evolve and dominate terrestrial ecosystems during the Mesozoic era Fig 25 18 Mass extinction and the diversity of life during Phanerozoic Eon The Origin and Evolutionary Radiation of Reptiles Diapsids consist of two main lineages the lepidosaurs and the archosaurs 12k species Lepidosaurs include tuataras lizards snakes and extinct mososaurs Archosaur lineage produced the crocodilians pterosaurs and dinosaurs Pterosaurs were the first tetrapods to exhibit flight Dinosaurs diversified into a vast range of shapes and sizes Included bipedal carnivores theropods from which birds evolved Fig 34 26 A phylogeny of amniotes Turtles tortoises Until recently it was not clear whether turtles like all other living reptiles should be classified within the diapsid clade Anapsid skulls without large openings behind the eyes but descended from diapsid ancestors Freshwater terrestrial and marine reptiles 360 extant species some highly endangered e g many sea turtles are endangered Dietary habits include herbivory and carnivory many sea turtles eat jellyfish All turtles have a boxlike shell made of upper and lower shields that are fused to the vertebrae clavicles and ribs The shell consists of both skeletal and dermal bones Order Testudines test shell armour Teeth lost replaced by toothless beaks Males have a single intromittent organ Green sea turtle WC Lepidosaurs Lepidosaurs are reptiles characterized by teeth fused to their jaws and bodies covered in overlapping scales Scales are derived from the epidermis and are shed collectively moulted Male lepidosaurs have a hemipenis paired reproductive organ This contrasts with the single penis found in turtles crocodilians birds and mammals Surviving lineage of lepidosaurs is represented by two species of lizard like reptiles called tuatara Fig 34 30a and lizards and snakes or squamates Burmese python hemipenis Fig 34 26 A phylogeny of amniotes Lepidosaurs Tuataras Tuataras remnants of an ancient lineage of lepidosaurs were once widespread and diverse 100 220 mya Two remaining species of tuataras are restricted to small islands off the coast of New Zealand Although tuataras resemble lizards they do not possess the modified jaw structure or male genitalia characteristic of squamates They undergo internal fertilization through copulation but lack an intromittent organ however they do have structural precursors for a hemipenis Tuataras are endemic to New Zealand where they are listed as endangered Lepidosaurs Squamates Squamates are the dominant extant lineage of lepidosaurs comprising lizards and snakes The most numerous and diverse group of extant non avian reptiles 12k species squam scaly Squamate characteristics Loosely jointed jaws and skulls This allows for significant flexibility and the ability to consume large prey Hemipenis in males paired reproductive organs Periodic moulting Squamates shed their skin periodically Fig 34 30 Lizards External ears Lizards have visible external ear openings unlike snakes Well developed limbs Leglessness has evolved independently in various families e g legless lizards Diet Primarily insectivorous but some species like iguanas are herbivorous Marine iguana grazing Burton s legless lizard WC https scubaboard com community media marine iguana feeding 174967 Lepidosaurs Squamates A snake s skull consists of multiple unfused bones connected by flexible ligaments allowing it to stretch its jaw widely in various directions Snakes Snakes are a monophyletic group of legless lepidosaurs https skfb ly 6swHJ that evolved from burrowing lizards Snakes lack external limbs but some species retain vestigial pelvic girdles Feeding behaviour and diet Snakes are carnivorous and have adaptations to aid in capture and consumption of prey including Fig 34 30 Chemical sensors Heat detecting organs Venom Loosely articulated jawbones and elastic skin Most snakes eat vertebrates but some consume invertebrates Python swallowing a wallaby Archosaurs Order Crocodilia Nile crocodile swimming Archosaurs are reptiles characterized by socketed teeth which are not fused to the jaw In some lineages such as birds teeth are lost and replaced by a horny beak or bill The two extant archosaur lineages are crocodilians and birds Crocodilians alligators and crocodiles belong to an archosaur lineage that dates back to the Late Triassic Freshwater and marine 26 species restricted to warm regions lifestyle Many crocodilians are adapted to a semi aquatic Clockwise from top left WC saltwater crocodile Crocodylus porosus American alligator Alligator mississippiensis and gharial