The Cretaceous World - 144 - 65 MY: a period of dramatic changes and a transition towards the modern world - Jarðsaga 1 - Saga Lífs og Lands – Ólafur Ingólfsson Late Jurassic-Early Cretaceous: Pangea is ripping apart, creating new landscapes and habitats and changing evolutionary conditions Continental drift and Ocean spreading causes transgressions in N America and Europe Turonian Stage Texas (93.5-88.5 million years ago) Large scale trans- gression from both north and south connects Arctic to Gulf region, dividing North America into two landmasses. Europe undergoes a series of transgression- regression events Climate and landscapes during the early Cretaceous No major mountain- building episode for 100 MY. Erosion and deposition prevailed. Widespread plains and lowlands, deltas, swamps and warm, shallow seas. There were no glaciers anywhere on Earth, and global sea level was 60m + Early Cretaceous: A world steaming under near-tropical conditions... (cool temperate climates at very high latitudes, >70oN and S) ... with incredible diversity of both fauna and flora, as well as optimal conditions for evolution and occupation of new evolutionary niches... Oceanic circulation The fossil story reflecting warm conditions Finds of Cretaceous fossil tree-trunks The fossil story reflecting warm conditions Cretaceous vs modern temperatures http://www.clas.ufl.edu/users/emartin/GLY3074S01/figures/cretgradient.htm Laterite and Laterite Bauxite Bauxite Thick, red, greatly The chief ore of Residual deposits formed weathered and aluminium, under tropical climate altered strata of consisting of conditions, where sili- tropical ground. hydrous aluminium cate-rich rocks are Laterites are red oxides and leched during a wet because silicates aluminous laterite. season and subject to have been leached It is a claylike strong evaporation during out, and iron and amorphous dry season... aluminium salts now material formed predominate. by the weathering Horizons are unclear of silicate rocks and the nutrient under tropical status of the soil is conditions. The low. Laterite is soft chief producers but hardens rapidly are Australia, when to the air until Guinea, Jamaica, it has a brick-like Russia, Brazil, and hardness. Surinam. Deltas and swamps... Crocodile-like animals appeared in the Late Triassic, and true croc´s in Jurassic times. Some Cretaceous crocodiles were awesome: the giant Deionsuchus ('terrible crocodile') was 12-14 m long and had a skull 1.8 m long Sarcosuchus The crocodile is believed to have reached 14 m in length. The animal lived about 110 million years ago in what is now the windswept Ténéré Desert in central Niger. The snout and > 100 teeth were designed for grabbing prey–fish, turtles and dinosaurs that strayed too close. This enormous reptile would have made Africa’s ancient riverbanks a dangerous place, even for a Fossil remains of one of the largest crocodilian species dinosaur. The fossils belong to an ever to live have been extinct creature named found in the Sahara by a Sarcosuchus imperator ("flesh team led by Paul Sereno (University of Chicago). crocodile emperor") Metriorhynchus – purely aquatic crocodile Metriorhynchus was ca. 3 m long. It was a highly modi- fied aquatic predator which had evolved from its cousins, the land living crocodiles. Apart from its long snout,it bears little resemblance to Metriorhyncus probably moved the conventional crocodile by sideways beatings of its tail shape. Metriorhynchus was and it had evolved to be more flexible and mobile than its land- specially adapted to an living relatives, making it faster aquatic way of life with in water. Its skin was also less flippers to replace the legs scaly and more flexible than that of the land-crocodiles, reducing and a vertical fin at the end its resistance through the water. of its tail to help it swim. Snakes and lizzards Snakes are uncommon as fossils: They have lightly constructed skeletons and skulls comprised of separate moveable sections and so are generally too fragile to preserve well. The more They were the last major group of specialised reptiles to appear in the fossil record. poisonous snakes One of the earliest known forms was are not thought Dinilysia, meaning 'terrible destroyer', to have evolved which lived in the Early Cretaceous until the middle period. It seems likely that snakes of the Tertiary evolved from aquatic lizards, although period, perhaps most have now returned to life on land. 30 MY ago. And then there were the dinosaurs... Cretaceous dinosaurs lived on all Gondwana-Laurentia continents, except Antarctica Development towards heavier herbivorae armour and more vicious predators The break-up of Pangea affected dinosaur evolution Dinosaurian paleobiogeography: Temporally calibrated areagram showing the breakup of Pangaea into 10 major land areas by the end of the Cretaceous. Checkered bars indicate high-latitude con- nections that may have persisted into the Late Cretaceous. Five paleogeographic reconstructions divide continental areas into dry land (black) and shallow (epieric) seas (unshaded). Different lines of evolution among the allosaurs Dinosaurian paleobiogeography. Acrocanthosaurus, Giganotosaurus, and Carcharodontosaurus, living on N America, S America, and Africa, respectively, approximately 90-110 MY. Dino´s walked across existing land bridges... The geographic distribution of ceratops and some other groups during Late Cretaceous can only be explained by dispersal across Beringia. The Dino´s... The dinosaurs came in all varieties including carnivores (meat-eaters), herbivores (plant eaters) and omnivores (all-eaters). Some were small as a chicken and others as big as a house, some of them flew like birds. They occupied almost every nisch... Within the last decaded there has been a transformation in our under- standing of dinosaur paleobiology. They now are regarded as active, agile, and adaptable, as opposed to huge, awkward, lumbering versions of large reptiles. HERBIVORES: Plant-eating dinosaurs were the most common large animals in the Cretaceous ecosystems A group of Omeisaurus, medium-sized sauropods, are reconstructed browsing in a conifer forest. Their physology is poorly understood, and some aspects are widely debated: • Biomechanical problems. Some paleobiologists argue that the mechanics of muscle and tendon attachment would not permit these animals to raise their long necks that far above the horizontal. • Blood pressure. It is difficult to imagine how sufficient blood could have been provided to the head at extreme elevation to avoid unconsciousness when the head was held up for any extended period. The huge sauropods, so typical for Late Jurassic dinosaurs, continued to live in Gondwana, but died out in Laurassia Paralititan stromeri, a Titanosauria, Madagaskar new, giant sauropod dinosaur from Upper Cretaceous mangrove deposits in Egypt. Laurassic herbivores relatively small and heavily armed Ankylosaurs: They were relatively small, heavily armored Cretaceous herbivores. Their ecology is poorly understood, but their build suggests that they fed primarily on vegetation at ground level. Hadrosaurs: A small group of Telmatosaurus, hadrosaurs from the Upper Cretaceous of central Europe. Hadrosaurs were a very diverse group of bipedal herbivores and were the most important herbivore group during the Cretaceous. Ceratopsians The most widely recognized ceratopsian dinosaur is Triceratops, but this was a very diverse group of Creta- ceous herbivores and the only group that may have been adaptively radiating near the end of the period. No armour, quick and agile: an alternative strategy... Curiously, the most abundant and diverse of the Cretaceous herbivores were the unarmoured ornithopod dinosaurs, specifically the hypsilophodontids and iguanodontian lines, all of which achieved cosmopolitan distribution. Dinosaur Carnivores Given the relatively large size of most dinosaur carnivores, they would have required significant numbers of large prey animals to sustain their populations. Carnivores would thus be much less numerous than herbivores in any Mesozoic ecosystem. An Ornithomimus, Cretaceous, USA. These animals were probably very quick and agile and may have preyed largely on the eggs of other dinosaurs. The Therapods The theropod (meaning "beast-footed") dinosaurs are a diverse group of bipedal saurischian dinosaurs. They include the largest terrestrial carnivores ever. Birds are the descendants of small nonflying theropods. http://www.ucmp.berkeley.edu/diapsids/saurischia/theropoda.html T-Rex and friends... Tyrannosaurus rex was a huge (12 m long, about 6 m tall, 5-7 tons) meat-eating dinosaur that lived during the late Cretaceous, 85-65 MY ago. T. rex lived in a humid, semi-tropical environment, in open forests with nearby rivers and in coastal forested swamps. Until recently, Tyrannosaurus rex was the biggest known carnivorous dinosaur; Gigan- otosaurus and Carcharodontosaurus were slightly bigger. How fast did the dinosaurs move: There is a general relationship between speed and stride length in living animals. This can be used to estimate how fast the dinosaurs were: • Sauropods and ankylosaurs were slowest, ~ 3-5 km/hr • Most ornithopods were faster, ~ 5-7 km/hr • Theropod predators were fastest, ~ 10 km/hr, bursts up to 40-50 km/hr Velociraptor ("Speedy Thief“) Velociraptor was a fast- running, two-legged dinosaur. This meat-eater had about 80 very sharp, curved teeth in a long, flat snout; some of the teeth were over 2.5 cm long. This predator had an s-shaped neck, arms with three-fingered