When did dinosaurs live? What are dinosaurs? • Technically: no such thing as dinosaurs • Classification: – Class – Reptilia (reptiles) – Order – Archosauria – Suborders • Saurrischia – lizard hips • Ornithischia – bird hips Order Saurischia • Characterized by 3 part hip structure similar to that of lizards Order Saurischia Characterized by 3 part hip structure similar to that of lizards Who were the Theropods Earliest forms of Coelurosauria of Triassic Typical Coelurosauria: Saltopus Archaeopteryx Where are Archaeopteryx found? Cretaceous Coelurosaurs • Some species became very specialized Velociraptor (Jurassic Park) 2^nd Theropod Group • Flesh-like spectacular forms • Famous because of their starring role in Japanese movies Teratosaurus Earliest species – Triassic, 6 m Teratosaurs Tyrannosaurides (T-Rex) And T-Rex Sauropodomorpha Prosauropoda Prosauropoda (Plateosaurus) Plateosaurus (small head) Sauropoda Who were the Sauropods? Who were the Sauropods Who were the Sauropods? The Ornithischians (bird-hip structure) There were five basic kinds of ornithischians • (1) stegosaurs • (2) ankylosaurs • (3) ornithopods • (4) pachycephalosaurs • (5) ceratopsians • Each group included many different species. Entirely vegetarians • Exploited vegetation low to the ground Pelvis characteristics (1) stegosaurs Stegosaurus Ankylosaurs Iguanodonts Hadrosaurs Types of Hadrosaurs Ceratopsia Types of Ceratopsia Types of Ceratopsia Types of Ceratopsia Geographic Distribution Pterosaur Timeline Two Major Bird Lineages • Enantiornithes – Fusion of tarsometatarsus in opposite order – Most Diverse avian group in Cretaceous • Neornithes True Birds (Aves) • Archaeopteryx long thought to be a bird ancestor • Still hotly debated • Ground-Up vs. Trees-Down models of flight • This one is Trees-Down Archaeopteryx Archaeopteryx with no artist’s interpretation - (note the feathers!) Feathers • Feathers are obviously good for flight • Feathers are also good insulators • It’s not clear which property was the impetus for their evolution - Archaeopteryx might well have just been trying to keep warm. Timing of Birds • Birds don’t fossilize well - they have weak, light bones that are often hollow. • From 1990-1995, the number of known bird fossils doubled. • When did they start? • Archaeopteryx is from Late Jurassic • There were lots of birds, flying and flightless, by the end of the Cretaceous, including members of modern groups Timing of Birds • Lots of bird diversification in the Cenozoic, although most fossils are incomplete. • By the Early Oligocene (35 Ma), most modern bird groups had arrived. • There were unusual forms, e.g. phororhachids from South America - present for much of Cenozoic Timing of Birds • Controversy -Protoavis from Late Triassic • This would move back bird evolution about 80 million years to the earlier parts of the Mesozoic • Not everybody thinks this is a real bird, although its discoverer (Chaterjee) claims it is closer to modern birds than Archaeopteryx is • Birds have lots of fans - creates interest ProtoAvis Warm Blooded Dinosaurs, Reptile Biology, Archosaurs vs. Reptiles The Warm Blooded Dinosaurs Bone structure • Haversian Canals • Most cold blooded animals lack this bone structure. Predator-Prey Ratios: ectothermic? • Require far less food/energy than warm blooded animals Dinosaur Communities Size of dinosaurs Superiority of predators • Mammals generally superior to reptiles Warm blooded vs. Cold blooded Dinosaurs... Definitions • Endothermic: creates heat from inside • Ectothermic: absorbs heat from outside • Homeothermic: maintains a constant internal temperature • Poikilothermic: temperature fluctuates depending on outside conditions Evidence for endothermic dinosaurs • Fast things need to have heat available. Many dinosaurs appear to be fast-moving. • Today, endotherms normally outcompete ectotherms. Since dinosaurs coexisted with known endotherms, they must also have been endothermic. • Dinosaurs were upright walkers with legs below their bodies - typical of endotherms Evidence for endothermic dinosaurs • Dinosaurs had big brains, and endotherms tend to have big brains (but not always, and brain size is correlated with other things, too). • Ectotherms aren’t usually found at high latitudes, and dinosaurs were (but it was warmer) • Endotherm predator/prey ratio is usually low, and dinosaur ratios match mammals Evidence for endothermic dinosaurs • Dinosaurs were big and had large, complex hearts. Complex heart matches modern endotherms. • Dinosaurs were ancestral to birds, and birds are endotherms. • Endotherms tend to grow fast, and dinosaurs were big (but who knows how long they lived? • Dinosaur bone structure matches modern endotherms better than modern ectotherms Evidence for ectothermic dinosaurs • Dinosaurs were huge - could have been effectively homeothermic w/o endothermy • Dinosaurs were huge - couldn’t possibly have been endothermic because they’d burn up. • Mesozoic was warm - dinosaurs didn’t need to be endothermic • Ectotherms tend to be scaly, and dinosaurs were (but so are birds!) Evidence for ectothermic dinosaurs • Some dinosaurs show lines of arrested growth (LAGs) in bones. Modern endotherms don’t have LAGs (unless stressed), but modern ectotherms do. • Dinosaurs didn’t have respiratory turbinates - bony structures at front of nasal cavity which are covered in mucus, which modern endotherms have. Five current thermal hypotheses (from UCMP) • Dinosaurs were complete endotherms, just like birds, their descendants. • Some or all dinosaurs had some intermediate type of physiology between endothermy and ectothermy. • We know too little about dinosaurs to hazard a guess at what their physiology was like. • Dinosaurs were mostly inertial homeotherms; they were ectothermic but maintained a constant body temperature by growing large. Small dinosaurs were typical ectotherms, maybe with a slightly elevated metabolic rate. • All dinosaurs were simple ectotherms, enjoying the warm Mesozoic climate. But that's okay; many ectotherms are quite active, so dinosaurs could be active, too.