Reptilia A Very Brief History

Reptiles: What are they? n Possess an amniotic /cleidoic egg. –Amnion –Chorion –Allantois –Yolk sack –Reptilian/Monotreme vs. eutherian placentas. n Cleidoic eggs. –Leathery egg which is often pervious to water. –Egg becomes calcified and impervious to water. –Necessitates internal fertilization.

Reptiles: What are they? n Possess an intromittent organ. –All sauria and serpentes have hemipenes. –Other groups (Chelonians, Crocodylians, and Sphenodon) have a different structure. –Intromittent organ increases chance of fertilization. –Reduces sperm loss. –Increases probability of reproductive success. –Increases cost of reproduction for female.

Reptiles: What are they? n Pulmonary respiration. –Increased surface area in lungs. –Changes in circulation: 3.5 chamber heart. –Increased rigidity of ribs? n One occipital condyle! –(amphibians have 2). –Atlas and axis, with organization of centra. –Pleurocentra instead of intercentra. –Maintain osseous strength while enhancing cranial mobility

Reptiles: What are they? n 2 sacral vertebrae. n Epidermal scales –Arise as dermal evaginations. –Contain both alpha and beta keratin. Beta keratin is found only in reptiles. n Nerve endings in epidermis are expanded at tips, not tapered as in all other vertebrates.

Reptiles: What are they? n Nictitating membranes over eyes. n Intraocular muscles of iris are striated, not smooth. n Tabular bone of skull is separated from opisthotic. n Suborbital fenestra n Posttemporal fenestra

Reptiles: What are they? n Absence of anterior coronoid bone in lower jaw. n Cervical vertebrae have midventral keels. n In adults, second intercentrum fuses to the axis. n Evolution within the skull.

What are the consequences of a reptilian mode? n Divorce from water. –Increased foraging options. –Increased exposure to thermal variation. –Higher operating temperatures. –Increased metabolic efficiency.

Radiation of Early Amniotes n Earliest fossils come from mid- Pennsylvanian of Nova Scotia. –Includes relatively small aminals: Pelycosaurs (Archaeothyris) and romeriids (Hylonomus and Paleothryis). n Pelycosaurs became important in the Permian: This is the lineage that ultimately leads to the therapsida, and then the mammals.

Westlothiana lizziae: E. Carboniferous of Scotland - earliest known sistertaxon to amniotes.

Radiation of Early Amniotes n The Synapsida: –These pelycosaurs were very successful in the Permian. There were 6 families. Initially they were small, but later became much larger (c. 3m+). Included good carnivores and herbivores as well. Initially, very lizard-like. Included Ophiacodon and Dimetrodon.

Radiation of Early Amniotes n The Synapsida: –Some Pelycosaurs (Ophiacodon, Dimetrodon, and Edaphosaurus) were sail backed. The sails were supplied with blood, as evidenced by grooves on neural arches – presumably for blood vessels. How would the sails have worked as thermoregulatory structures? What are the other hypotheses (since not all large pelycosaurs had sails)?

Radiation of Early Amniotes n The Synapsida: –Pelycosaurs died out at the end of the Permian, at the same time that the Therapsids had an adaptive radiation.

Characters n 1) Sacrum w/ more than 1 vertebra

Radiation of Early Amniotes n Paleozoic Reptiles: –The anapsida are the first offshoots of the reptilia that we understand (Parareptiles fit in somewhere, but where?). –Anapsida includes the turtles and the Captorhinids. We have an extremely limited fossil record of the turtles. We know that the Testudines must have been present, but we have no fossils. This may be related to their habits, and consequently poor chance of fossilization.

Radiation of Early Amniotes n Cont: –Captorhinids are lizard-like, they are not turtles. They had relatively big heads, and they had teeth. Turtles do not have teeth. Is it possible that ‘turtleness’ had not yet evolved? What would be required for a turtle to evolve its shell?

n Pre-diapsid Romeriids: –Petrolacosaurus (Araeoscelida). Lizard- like. Probable good carnivore. Fore and rear limbs of near equal size. Dissapear in early Permian. Diapsid radiation really takes off in the Triassic. Radiation of Early Amniotes

n Parareptiles: –Origin is uncertain. This seems to be a garbage group. It is possible that all forms represent independent origins for the Romeriids. –Lumped with Sauropteryginas and Ichthyosaurs. –Adaptive radiation off all parareptiles occusrs in the Mesozoic.

Radiation of Early Amniotes n Parareptiles: –Mesosaurs are from the early Permian. Marine, gharial-like, with a length of about 1m. Undulatory swimmers with laterally compressed tails. (Think about how to swim with a reptilian body plan). –Millerosaurs are from the late Permian. Lizard-like, small, similar to modern Iguanids.

Radiation of Early Amniotes n Parareptiles: –Pareiasaurs and Procolophonoids. Pareiasaurs are from the mid to late Permian, while the Procolophonoids are from the late Permian through the late Triassic. –Pareiasaurs were up to 3m, columnar limbs, robust bodies. Laterally compressed, closely spaced teeth with leaf shaped crowns. Probable herbivores. –Procolophonoids were smaller and lizard- like, similar to Sauromalus in appearance. Widely spaced crushing teeth.

Quadrupedal Ornithischians

Bipedal Ornithischians

Saurischian Theropods

Saurischian Sauropodomorphs