Introduction 1 Late Mesozoic Cretaceous Period a Transition i Some sed lithified some not ii Continents began attaining a position that is close to their modern locations iii Biota some with archaic features some modern b End of an era i In famous ME of the dinosaurs and other life forms such as c Life was a mix of biota some now extinct and some still in existence the ammonites i Extinct forms 1 Dinosaurs 2 Ammonites 3 Belemnites 4 Marine reptiles ii Extant forms 1 Flowering plants 2 Modern fish 3 Cruaceans 4 Modern types of bivalves and gastropods Life in the Sea 1 Pelagic life a Two new marine plankton i Diatoms 1 Plant like protists ii Plantonic foraminifera 1 Animal like protists 2 Pelagic sediments a Contributions by plantonic forams and calcerous nannoplankton b Calcareous nannoplankton extremely abundant in warm Cretaceous seas c Cretaceous creta chalk 3 White chalk deposits above the coastline of SE England to form the famous White Cliffs of Dover 4 Extremely high SL a Same layer is found in Normandy France a 100 250 m higher than present b Due to very large MOR c Flooding much of Europe d High rates of carbonate accumulation 5 Large MOR a High Ca2 Mg2 ratios b High productivity of nannoplankton 6 Pelagic swimming predators ammonoids and belemnoids remain 7 New group of fish appeared the teleost a Index fossils a Dominate today b c Bony fish with Include marine and freshwater varieties salmon sunfish carp eel etc i Symmetric tail specialized fins short jaws overlapping scales 8 Top of food chain a Plesiosaurs some 10 m b Mosasaurs up to 15 m in length c Hesperornis common flightless diving bird d Archelon giant 4 m long marine turtle 9 Benthic life was modernized a Forams b Bryozoans c Burrowing bivalves d Sea urchins e Hexacorals f Advanced predators lead to the decline of stalked crinoids and brachiopods i Crabs 1 Pinching predator ii Carnivorous gastropod mollusks 1 Drill holes through shells g Only those species that could swim or burrow actively and those with defensive spines or very heavy shells could survive Cretaceous predation Life on Land 1 Although gymnosperms dominated 2 1st appearance of angiosperms Flowering plant a b Enclosure of the fertilized egg in a seed fruit i Create a fertilized seed and food supply for embryo c Included i Flowering plants conspicuous flowers ii Hardwood trees maple oaks inconspicuous flowers iii Grasses 3 Earliest angiosperm floras a Advanced reproductive mode allows for seed growth and release over the course of just a few weeks b Evolution at equator and spread pole ward c Diversity and complexity increase rapidly i Known from fossil pollen and leaves 4 Apparently due to a patchy fossil record early Cretaceous vertebrate fauna aren t well known a Scientists say it was closely related to its slightly larger relative T Rex b But lived earlier making it the largest living land predator of its time a But well preserved fossils of Late Cretaceous 5 Age of large Dinosaurs crocodiles and tiny mammals 6 Communities likely analogous to modern African savannah 7 Duck billed dinos like antelopes and zebras a Large herd travelers b Communicators c Tended young after birth d Likely grass eaters 8 Horned dinos a Like rhinos 9 Tyrannosaurus a Like lions b Largest carnivores ever 10 King of Gore Lythronax argestes 11 Flying vertebrates a Reptiles pterosaurs i Like vultures b Birds water birds feathered wings i Like herons and cranes c Terrestrial crocodiles i Length of head alone human ii Like modern crocs alligators 12 Small mammals a Small populations b Evolved 13 Two groups of Cretaceous mammals a Placentals b Marsupials c Purgatorious i Placental mammal ii Size of a cat iii Ancestral to modern primates iv Survives KT extinction i Pointed more specialized teeth ii Enlarged brain iii Advanced differentiation between jaw and ear bones iv Likely nocturnal 1 Most mammals evolved from this and similar early mammal groups Paleogeography 1 Recall Jurassic position of the continents 2 Cretaceous continents continue to move apart a Major continents were fragmented and isolated except Australia Antarctica b Opening new seas 3 As a consequence of large rapidly spreading MOR the SL was very high a Estimates between 100 250 m higher than today 4 High sea level Stagnant deep ocean and climate warming a Extensive marine deposits blanketed most continents b Large MOR displaced water c Interesting lack of magnetic reversals 5 Cretaceous greenhouse climate a Average surface temperature was very warm due to high CO2 in the atmosphere b High CO2 cause i Reduced mountain building ii Subduction related melting of calcareous planktonic ooze released CO2 iii Biotic evidence for Cretaceous warmth 1 Fossil leaves of warm loving tropical plants at the poles low stomatal density 6 Cretaceous climatic warmth shut down thermohaline circulation a Low atmospheric temperatures gradients less wind less upwelling from wave production b Organic rich black shales accumulated on continents and continental i Rich in petroleum due to anoxic conditions a Forced subduction an eastward shift in igneous activity fold thrust i Low angle subduction lead to broad orogenic belt ii Foreland basin east of orogeny 8 Foreland basin east of igneous arc and Sevier Orogeny fold and thrust belt a Arctic waters spread southward forming the Mowry Sea i The Mowry Formation consists primarily of oil shale 9 Transgression connected a seaway from the Arctic to the Gulf of Mexico to form the Cretaceous Interior Seaway a Bound by barrier islands b Created inland lagoons swamps c Lowlands gave way to alluvial fans d Lots of sediment input e Late Cretaceous fossil record of dinosaurs is rich 10 Stratigraphy within the foreland basin Cretaceous Interior Seaway recorded many cycles of transgression and regression a Sediment supple and subsidence rates 11 Eastern margin of NA was a carbonate platform 12 Late Cretaceous modern siliclastic continental shelf began forming 7 Sevier Orogeny shelves belts was flooded a Triassic fault block basins b Overlain by Jurassic carbonates evaporates and siliclastics c Additional carbonates deposit during warm Cretaceous d Late Cretaceous siliclastics took over marked the beginning of the modern shelf Earth System Shift 1 65 6 Ma many life forms that were dominant during late Mesozoic came to an abrupt end a Marked by the K T Boundary 2 Mesozoic groups that went extinct a Dinosaurs b Ammonoids c Many plants d All marine reptiles e 90 of calcareous nannoplankton plantonic