CLASS Reptilia

• SUBCLASS Anapsida
  • ORDER Cotylosauria: Ancient and extinct stem reptiles
  • ORDER Testudinata: Turtles and tortoises
    • FAMILY Chelydridae: Snapping turtles
    • FAMILY Emydidae: Common freshwater turtles
    • FAMILY Testudinidae: Land tortoises
    • FAMILY Dermochelidae: Leatherback sea turtles
    • FAMILY Cheloniidae: True sea turtles.
• SUBCLASS Synapsida: Extinct mammal-like reptiles
  • ORDER Pelycosauria: Primative synapsids. Carboniferous to Permian
  • ORDER Therapsida: Advanced synapsids. Permian to early Jurassic.
• SUBCLASS Diapsida
  • INFRACLASS Ichthyopterygia: Ichthyosaurs: Extinct dolphin-like reptiles.
  • INFRACLASS Lepidosauromorpha: Diapsid reptiles lacking bipedal specializations.
    • ORDER Squamata: Lizards and snakes
      • SUBORDER Lacertila (Sauria): Lizards
        • FAMILY Gekkonidae: Gekkos
        • FAMILY Chamelionidae: Chameleons
        • FAMILY Iguanidae: Iguanas
        • FAMILY Scincidae: Skinks
        • FAMILY Helodermatidae: Gila monsters
        • FAMILY Varanidae: Monitors
      • SUBORDER Serpentes (Ophidia): Snakes
        • FAMILY Boidae: Boas
        • FAMILY Pythonidae: Pythons
        • FAMILY Hydrophidae: Sea snakes
        • FAMILY Viperidae: true vipers
        • FAMILY Crotalidae: Pit vipers
  • INFRACLASS Archosauromorpha
    • ORDER Thecondontia: Extinct (Triassic)
    • ORDER Crocodilia
      • FAMILY Crocodylidae: Crocodiles
      • FAMILY Alligatoridae: Alligators
    • ORDER Pterosauria: Flying reptiles. Extinct (Jurassic and Cretaceous)
    • ORDER Saurisichia: Reptile-like dinosaurs. Extinct diapsid bipedal toothed dinosaurs. Front limbs usually reduced. Pelvis triradiate. Triassic to Cretaceous.
      • SUBORDER Thecodonta: ancestors of mammals.
    • ORDER Ornithischia: Birdlike dinosaurs. Extinct diapsid largely quadrupedal dinosaurs lacking teeth and possessing a tetrraradiate pelvis (due to two-pronged pubis). Triassic to Cretaceous.

Synopsis of Reptiles

General: Estimated 6000 species of living reptiles. Most important advance over amphibians is cleidoic egg and amnion, which allow exploitation of terrestrial environments close to amphibians. Reptiles are ectothermic, although endothermy has been proposed for some dinosaurs based on bone structure, stride length, predator-prey ratios, and other factors.

Skeleton: more ossified than in amphibians. Skull arched more than flattened as in amphibians; may have no temporal openings (anapsid: seen in turtles), a single supratemporal fenestra (euryapsid: seen in plesiosaurs), a single infratemporal fenestra (synapsid: seen in extinct mammal-like reptiles of the Permian to Jurassic), or both infratemporal and supratemporal openings (diapsid: seen in most living reptiles except for turtles, and also in ruling dinosaurs of Mesozoic). Beginnings of a bony secondary palate are seen in most, as is an interorbital septum. Vertebral column (except in snakes and other limbless reptiles) is differentiated into cervical, thoracic, lumbar, sacral, and caudal regions.

Circulation: No functional gills. Atria completely separated. In some forms sinus venosus is incorporated into the wall of the right atrium (pacemaker). Ventricle is divided by septum (incomplete in most reptiles, complete in alligators and crocodiles). Conus arteriosus divides embryologically into three vessels: one leaves right side of ventricle and goes to lung; second leaves left side of ventricle and goes to aorta; third leaves right side of ventricle and connects to aorta through foramen of Panizzae where it picks up some oxygenated blood. Thereafter most of the blood in this vessel goes to the left subclavian and coeliac arteries, but a branch joins with the aorta to form the dorsal aorta. Kidneys are supplied in part through the dorsal aorta, reducing the importance of the renal portal system.

Kidneys: Metanephric as in mammals.

Respiration: Use expansion of body cavity to ventilate lungs. Anatomically lungs are quite mammal-like with cartilagenous tracheae and bronchi, and divisions into lobes.

Salt glands: Possessed by some marine reptiles.

Brain: Marked increase in cerebrum, marking a shift from midbrain to forebrain emphasis.

Sense organs: Lateral line lacking as in all amniotes. Some pit vipers possess infrared detecting organs. Middle ear shows much variability from amphibian-like to nearly mammal-like. Pineal eye reduced in all but a few lizards, but still involved in regulation of diurnal rhythms.

Integument: Scaly and impermeable to water.