Class Reptilia – Amniote Origins and Nonavian Reptiles

1. Class Reptilia – Amniote Origins and Nonavian Reptiles • With the reptile group(s) we see better adaptation to a terrestrial existence. • 1) shelled amniotic egg • 2) tough, dry and scaly skin • 3) efficient jaws for crushing and gripping prey • 4) efficient circulatory system with a higher blood pressure • 5) internal fertilization using some form of copulatory organ • 6) better developed lungs • 7) better body support; more efficient limbs • 8) more complex nervous systems

3. The Amniotic Egg • The liquid environment needed for the eggs/embryo of amphibians has been enclosed within the amniotic egg • No longer a necessity to breed in water • Amniotic egg consists of 4 extraembryonic membranes; the amnion, yolk sac, allantois, and the chorion all surrounded by a protective, porous shell. • Ancestral reptiles gave rise to the monophyletic group of the Amniota which include modern reptiles, birds, and mammals

6. Figure 18_04

7. Skull Structures of Reptilian Groups • Evolutionary development within the late Carboniferous gave rise to 3 major groups of amniotes based upon skull structure • Anapsids – no temporal opening behind orbits; gave rise to turtles • Diapsids – 2 temporal openings behind orbit; gave rise to modern reptilian groups and birds • Synapsids – 1 temporal opening behind orbit; gave rise to modern mammals

9. Paraphyly of Reptilians • Class Reptilia is a paraphyletic group; does not include birds (Aves) within the clade of Reptilia although birds are the direct descendants of reptiles • Crocodilians and birds share a more recent common ancestor (along with dinosaurs) and represent the Archosauria • Lepidosauria represents the snakes, lizards, tuataras, and worm lizards

10. Figure 18_01

12. Order Testudines - turtles • Anapsid group having diverged early in the evolutionary history of the reptilian group • Possess distinctive shells • Long-lived adapted to terrestrial (tortoises typically), semi-aquatic, aquatic, and marine existence (sea turtles) • Lack teeth • All are oviparous and bury eggs on land (including aquatic and sea turtles • No specific distinction between the words turtle, tortoise, and terrapin; tortoise and terrapin generally refers to terrestrial types and turtles to aquatic types

18. Diapsid groups – Lizards (Order Squamata) • Highly diversified and successfully adapted for walking, running, climbing, swimming, and burrowing; common groups are geckos, iguanas, skinks, monitors, and chameleons • Differentiated from snakes by: • 2 pair of legs (although a few are legless) • Fused lower jaw halves • Movable eyelids • External ears • Absense of fangs • The Amphisbaenia are the worm lizards well adapted for burrowing

25. Diapsid groups - Snakes • Completely legless (python and boa groups possess vestigial limbs) and elongated • Kinetic skull allowing for swallowing of prey whole • Many possess Jacobson’s organs to detect prey • Pit vipers possess infrared sensors • Some venomous and with fangs (rear-fanged vs. front-fanged types)

32. Diapsid groups – Tuataras Order Sphenodonta • Ancient, relic lizard like species found in New Zealand • Possess diapsid skull like that of ancient ancestors and a median parietal “third eye”

34. Diapsid groups – Order Crocodilia • Only extant reptilian representatives of the archosauria that gave rise to dinosaurs and birds • Large skulls with powerful jaws • Secondary palate • Most complex social behavior of any reptilians (mating and reproductive behavior) • High nest temps produce males, low temps produce females (opposite in turtles) • Alligator common to Florida; North American crocodile in South Florida also