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Tetrapod four-legged vertebrate Reptile tetrapod with scaly skin that reproduces with an amniotic egg Thus can lay eggs on land More solid vertebrate and more powerful limbs than amphibians Biggest difference from amphibians is mode of reproduction First reptile appeared in the Carboniferous Environment of the First Reptiles Near to water Warm, humid tropical regions Large variations in temp, rainfall and food supply Amniote Eggs Amniote Egg an egg that provides the embryo with: 1) a yolk for nutrition; 2) two sacs, one that holds the embryo (amnion) and one that holds waste products; 3) durable outer shell Allowed vertebrates, for the first time, to live and reproduce away from water Reptiles also evolved advanced jaw structure permitting heavy pressure with sharp teeth for puncturing and ripping food apart Amniotic egg probably evolved from laying eggs in humid air rather than in water 3
Reptile Phylogeny 3 reptilian groups evolved by the Late Carboniferous and Early Permian 1) Anapsid skulls with no openings behind the eyes 2) Synapsids - skulls with one opening behind the eyes includes mammal-like reptiles Pelycosaurs Therapsids Mammals 3) Diapsids - skulls with two openings behind the eyes First diapsid was the Late Carboniferous Petrolacosaurus Dinosaurs Pterosaurs All later amniotes EXCEPT mammals a. Anapsid b. Diapsid c. Synopsid 4
Pelycosaurs Heavy-boned fore-limbs supported body weight Strong muscular hind-limbs provided thrust and maneuvering 1) Carnivorous Pelycosaurs Ophiacodonts long snouts with many teeth Archaeothyris 50 cm-long lizard-like Sphenacodonts powerful jaws with differentiated teeth sail-backed Permian Dimetrodon (>50% Penn reptiles; >70% of Permian reptiles) vertebrate extended into spines 2) Herbivorous Pelycosaurs Caseids 3 m, 300 kg Edaphorsaurs ancestors were carnivores, vertebrate fused into spines Tetrapod Herbivory Possible Evolutionary Pathways 1) Start with small-body animals selective in attaining high-calorie food 2) Start with large-body animals with rapid indiscriminate feeding 3) Feeding strategy changes with growth (early small carnivore later large herbivore?) 5
Diapsid Petrolacosaurus Tetrapod Thermoregulation Functional enzymes are sensitive to temperature cold blooded = takes on temperature of the surrounding environment Early reptiles were small in body size Small body size easier for thermoregulation (heat exchange, refugia) Terrestrial environments were rich in food sources (trees, insects) Exothermic cold-blooded, rest frequently to absorb heat from the environment Endothermic generate your own heat Shut off blood at night to preserve heat Probably thermoregulation even in pelycosaurs without spines 6
Thus, reptiles probably first evolved on forest floors, river banks, or tree canopies thermoregulation animals ability to keep body temp in optimal range small body = larger (surface area/body mass) large body = smaller (surface are/body mass) Dimetrodon (carnivorous predator) and Edaphosaurus (herbivorous) 1) Both were large bodied (> 3m) 2) Large vertical spines on vertebrate covered with tissue, used for thermoregulation 3) Solar heat supplied to blood in the tissue (perpendicular = heating; parallel = cooling) Permian Dimetrodon 7
Eryops, a 2 m-long amphibian Pelycosaurs (Dimetrodon far right) 8
Therapsid Dinocephalian Moschops Therapsid Dinocephalian Estemmenosuchus 9
Therapsids - evolved from Pelycosaurs powerful jaws legs positioned more vertically differentiated teeth Had hair endothermic (maintained body temperature at constant level, but not as constant as mammals) enhanced predators capability to sustain activity Therapsids (Jonkeria center) 10