Invertebrate Mesozoic fauna Microfossils • Coccolithophoroids – extremely small single-shelled algea – produced tiny plates called coccoliths – fell to bottom and produced great chalk deposits • Foraminifera continued to thrive – globigerinids built shells of bubble-shaped chambers Marine vertebrates • Early Mesozoic had primitive bony fish • Modern teleost fishes – developed by late Jurassic – highly mobile jaws and swim bladder • Marine reptiles (not dinosaurs) – plesiosaurs (long necked fish-catchers) – icthyosaurs (fish-lizards, dolphin-like reptiles) – mosasaurs (related to monitor lizards) Terrestrial flora Gymnosperms (seed-bearing plants) • dominated most of Mesozoic • modern conifers are members of this class • Angiosperms (flowering plants) – began to dominate in Late Cretaceous • flowers to attract pollinating birds and insects • fruit eaten by animals to help spread seeds • generally grew, regenerated, and reproduced faster • better adapted for surviving grazing by dinosaurs Mammals • Developed from latest Late Triassic synapsids – remained mouse-sized – did not compete with dinosaurs in their niches • developed mammary glands • endothermic and homothermic--required high food intake • jaw muscles and teeth well adapted for catching prey • soft palate to separate breathing from eating passages – mid-Cretaceous divergence into two groups • placentals (young carried in uterus until ready for birth) • marsupials (pouched mammals) – young crawl to pouch to finish development » oppossum, kangaroo, koala, etc. Dinosaur groups • Two major groups based on pelvis shape – Saurischian (lizard-hipped) • sauropods (brontosaurus, etc.) • theropods (two-legged carnivores) • birds eventually developed from this line – Ornithiscian (bird-hipped) • all herbivorous – Anklyosaurs – Stegosaurs – Hadrosaurs, Pachycephalosaurs – Iguanodonts – Ceratopsids Oldest flowering plant fossil Reptiles and Birds • Relationships among fossil and living reptiles and birds Euryapsid Marine reptiles 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 Who were the Theropods • Contained all of the meat eating dinosaurs of the Mesozoic • Also contained some plant eaters having primitive characteristics Typical Coelurosauria: Saltopus Coeleurosaurs • Very successful in Mesozoic • Coelurosauria Velociraptor (Jurassic Park) Archaeopteryx Where are Archaeopteryx found? And T-Rex Tyrannosaurides (T-Rex) Prosauropoda Plateosaurus (flat-lizard) Prosauropoda (Plateosaurus) Plateosaurus (small head) Sauropods Who were the Sauropods? Who were the Sauropods The Ornithischians (bird-hip structure) - Phytodinosauria 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 Stegosauria Iguanodonts Hadrosaurs Types of Hadrosaurs Ceratopsia Ceratopsia Types of Ceratopsia Types of Ceratopsia Types of Ceratopsia Types of Ceratopsia Warm Blooded Dinosaurs, Reptile Biology, Archosaurs vs. Reptiles The Warm Blooded Dinosaurs 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 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 Superiority of predators • Mammals generally superior to reptiles 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!) 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. Geographic Distribution 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 Archaic Mammals of the Jurassic Mammalian radiation of the early Jurassic • Tricondodontia (3 cusps in a row) large (750 g), predaceous mammals of early Triassic • Monotremata: A living example of Mesozoic mammals Fossil record is poor, beginning in early Cretaceous Thought have diverged in Jurassic • Multituberculata: herbivorous, molars w/ multiple cusps Highly successful: from Jurassic to Oligocene (100 m yr) • Zatheria: includes Aegialodon (with tribospenic molar) & ancestor of therian mammals (Eutheria & Metatheria) K/T Boundary • Cretaceous-Tertiary (K/T) boundary (~65 Ma) • Second largest mass extinction in Earth’s history • Half of life on Earth died out (3/4 species) Mass Extinctions — Crises in the History of Life • Greatest mass extinction took place at the end of the Paleozoic Era • K/T extinction has attracted more attention because it affected dinosaurs K/T Boundary Extinction • Tropical groups suffered most • Seawater cooling, global regression • Mammals, birds, turtles, crocodiles, lizards, snakes and amphibians unaffected Meteorite Impact Crater • Proposed meteorite impact crater • Centered on Chicxulub on the Yucatán Peninsula of Mexico • Discovered in 1950’s, interpreted to be volcanic Chicxulub Crater What happened? Acid Rain • With sunlight greatly diminished, Earth's surface temperatures were drastically reduced, adding to the biologic stress • Another proposed consequence of an impact is that sulfuric acid (H[2]SO[4]) and nitric acid (HNO[3]) resulted from vaporized rock and atmospheric gases • Both would have contributed to strongly acid rain that might have had devastating effects on vegetation and marine organisms According to the impact hypothesis • 60 times the mass of the meteorite was blasted from the crust high into the atmosphere • heat generated at impact started raging forest fires that added more particulate matter to the atmosphere • Sunlight was blocked for several months – caused a temporary cessation of photosynthesis – food chains collapsed and extinctions followed Fruit fossil Oldest flowering plant fossil 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