Review of Mesozoic Earth History Main Happenings in

Review of Mesozoic Earth History • Main Happenings in Mesozoic – Breakup of Pangaea – Lots of mountain-building in western North America – Appearance + extinction of dinosaurs – More detail in the geologic record • More climate information!

The hydrologic cycle and climate

Water moves heat around the planet; tectonics determines how effectively this heat can move • Mountains and continental shape/size determine whether the hydrologic cycle can transport heat effectively – – – Mountains can block rainfall Massive continents tend to have dry interiors Coastal regions benefit from water cycle climate controls Circumpolar currents cut off polar access to warm waters N/S currents & waterways moderate polar climate

End Permian land oceans • Pangaea was shaped like a ‘C’ • Inside ocean: Tethys Sea • Outside ocean: Panthalassa Tethys sea

Breakup of Pangea 1: Triple Junctions • Seafloor spreading creates a triple junction: a point where 3 tectonic plates diverge • North America split off from S America and Africa

Seafloor spreading raises sea level • Seafloor spreading causes bulges in ocean basins • Big enough bulges and/or lots of them lowers the ocean volume • This can cause flooding of the continents.

Western Interior Seaway www. isgs. uiuc. edu/dinos/westernseaway. gif

Cordillera Orogenies • General term refering to complex period of mountainbuilding Jurassic-Cenozoic • Farallon plate goes below N American plate – Nevadan orogeny – Late Jurassic/Early Cretaceous • Orogeny near the current W coast • Slope of subducting Farallon plate decreased -> – Sevier orogeny – Late Cretaceous • Further east (Utah) – Laramide orogeny – Late Cretaceous/Cenozoic • Even FURTHER east! Rockies

Triassic • Arid, red beds • Lots of fern prairies – no grasses yet • Dinosaurs first appear

Triassic • Dinosaurs evolved from reptiles • Special hips and ankles that allow them to stand on 2 feet • Speed, agility and less need for water gives them edge

Jurassic • Pangaea is breaking up – causes SL to rise

Jurassic • Climate wetter than Triassic • Forests replace deserts, still fern prairies • Dinosaurs diverse and abundant • Giant marine reptiles

Cretaceous • SL still rising as breakup of Pangaea continues • Atlantic only about 300 km wide

Cretaceous • Abundant flying reptiles • First flowers • Birds with feathers

Isolation • Pangaea began fragmenting – during the Triassic and continues to do so • Organisms had increasing difficulty – migrating between continents as a result • In fact, South America and Australia – became isolated island continents – their faunas evolving in isolation – became quite different from those elsewhere

Mesozoic Marine Revolution • Many predators in ocean – Marine reptiles – Fish, sharks – Crabs, lobsters – could crush shells

Mesozoic Marine Revolution • Many predators in ocean – Marine reptiles – Fish, sharks – Crabs, lobsters – could crush shells • Marine animals had to adapt: – Burrow/hide (eg. clams, gastropods) – Thick shells – Swim

Echinoderms • Metazoans (animals) but not vertebrates or even chordates • 5 -fold symmetry www. humboldt. edu/~natmus/Exhibits/Life_time/Cretaceous. web/327. jpg

Marine Vertebrates • Numerous bony fish • Cephalopods most common swimming animals – Squids, octopus, ammonites • Marine reptiles – not dinosaurs, not fish! Ichthyosaurs – Plesiosaurs – Mosasaurs

Ichthyosaurs • The streamlined, rather porpoiselike ichthyosaurs – varied from species measuring only 0. 7 m long – to 15 -m-long giants • Evolved from small animals

Ichthyosaurs • fully aquatic animals • evolved from land-dwelling ancestors

Ichthyosaurs evolved from reptiles http: //www. ucmp. berkeley. edu/people/motani/ichthyo/intro. html

Plesiosaurs • The plesiosaurs, • Mesozoic marine reptiles, – belonged to one of two subgroups: – short necked and long-necked • Most were modest sized animals 3. 6 to 6 m long, – one species found in Antarctica measures 15 m

Plesiosaurs • Although the plesiosaurs – were aquatic animals, • their fipperlike forelimbs – probably allowed them to come out onto land

Mosasaurs • Mosasaurs were Late Cretaceous marine lizards – related to the present-day – Komodo dragon or monitor lizard • Some species measured no more than 2. 5 m long, – but a few such as Tylosaurus were large, – measuring up to 9 m • Mosasaur limbs resemble paddles – and were used mostly for maneuvering – whereas the long tail provided propulsion

Tylosaurus • Tylosaurus was – a large, – Late Cretaceous – mosasaur – It measured up to 9 m long

Mosasaur Skull • Mosasaur skull on display – in the Museum of Geology and Paleontology, – University of Florence, Italy

Mosasaurs Were Predators • All mosasaurs were predators, – and preserved stomach contents indicate – that they ate fish, birds, smaller mosasaurs, – and a variety of invertebrates – including ammonoids

And on land…

Land Plants • Important changes took place – in land plant communities – flowering plants evolved during the Cretaceous – soon became widespread and numerous • The major groups of Paleozoic land plants persisted, – but now they constitute less than 10% of all species

Seedless Vascular Plants and Gymnosperms • Seedless vascular plants and gymnosperms – were prolific • until angiosperms – replaced many of them during the Mesozoic

Angiosperms • The long dominance of seedless plants and gymnosperms – ended during the Early Cretaceous/Late Jurassic, – many were replaced by angiosperms, or flowering plants • Angiosperms probably evolved – from specialized gymnosperms

Fossil Angiosperms • From the lower Cretaceous – Potomac Group – of the eastern United States • Sapindopsis, – Cecil County, Maryland

The Diversification of Reptiles • Reptile diversification began – during the Mississippian Period – with the evolution of the first animals to lay amniotic eggs • From this basic stock of so-called stem reptiles – all other reptiles, as well as birds and mammals, evolved

Reptiles and Birds • Relationships among fossil and living reptiles and birds

First Dinosaurs • Evolved from archosaurs (reptiles) • Late Triassic • Small, only 3 ft long • Major characteristics – Can walk fully upright - bipedal – Special hip and ankle structure

Archosaurs and the Origin of Dinosaurs • Reptiles known as archosaurs • archo meaning "ruling" and sauros meaning "lizard” – include crocodiles, pterosaurs (flying reptiles), dinosaurs, and the ancestors of birds • Including such diverse animals – in a single group implies – that they share a common ancestor – and indeed they possess several characteristics that unite them

Dinosaurs Orders • All dinosaurs possess – a number of shared characteristics, – yet differ enough for us to recognize two distinct orders • the Saurischia • and Ornithischia • A distinctive pelvic structure characterizes each order – 3 bones in pelvis: illium, ischium, and pubis – Saurischian: pubis points down – Orinischian: pubis points back

Distinctive Pelvic Structure • Saurischian dinosaurs – have a 1 izardlike pelvis – and are thus called lizard-hipped dinosaurs • Ornithischians – have a birdlike pelvis – and are called bird-hipped dinosaurs • Convergent evolution – ‘birdlike’ pelvic structure reinvented in Saurischian descendents (avian dinosaurs = birds)

Saurischians www. enchantedlearning. com/subjects/dinosaurs/dinoclassification/Saurischian. html

Saurischian Dinosaurs • The saurischians, – include two distinct groups – known as theropods and sauropods • All theropods – were carnivorous bipeds – ranging in size from tiny Compsognathus – to giants such as Tyrannosaurus • and similar species • that might have weighed • as much as 7 or 8 metric tons

Dinosaur Cladogram