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Chapter 15 . Life of the Mesozoic Era. Mesozoic Life Fascinates . Ever since Sir Richard Owen first used the term dinosaur in 1842, these animals have been the objects of intense curiosity Current interest in dinosaurs was fueled by the movies Jurassic Park and its sequels
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Chapter 15 Life of the Mesozoic Era
Mesozoic Life Fascinates • Ever since Sir Richard Owen • first used the term dinosaur in 1842, • these animals have been the objects of intense curiosity • Current interest in dinosaurs • was fueled by the movies Jurassic Park and its sequels • No other group of animals • has so thoroughly captured the public imagination, • but dinosaurs were only one type of Mesozoic reptile
Cretaceous Scence • In this scene from the Late Cretaceous, • Ankylosaurus is defending itself • from the large predator Tyrannosaurus.
The Age of Reptiles • Other Mesozoic reptiles include • flying reptiles • marine reptiles, • as well as turtles, crocodiles, lizards, and snakes • Geologists informally call the Mesozoic • "The Age of Reptiles," • although there were far more species of insects • and fishes at this time
The Age of Reptiles • The Mesozoic was in important time • in the evolution of reptiles. • Recent discoveries have added much to our knowledge: • Remarkable discoveries of feathered dinosaurs • in China • have important implications • about the warm-blooded-cold-blooded dinosaur debate, • and the relationships of dinosaurs to birds.
Birds & Mammals • Birds first appeared • during the Jurassic, • probably having evolved • from small carnivorous dinosaurs • Mammals evolved • from mammal-like reptiles • during the Triassic • Mammals and dinosaurs were contemporaries • but mammals were not nearly as diverse • and all were small
Land Plants & Invertebrates • Important changes took place • in Cretaceous land plant communities • when flowering plants evolved • and soon became the most numerous • and diverse of all land plants • The invertebrate animals that survived • the Paleozoic mass extinctions • diversified during the Triassic • and repopulated the seas.
Mesozoic Extinction • Biotic diversity once again increased • in all realms of the organic world, • only to decrease again • at the end of the Mesozoic. • The Mesozoic extinction was second • in magnitude • to the one at the end of the Paleozoic, • but it is more widely known.
Systems Approach • We continue to emphasize • the systems approach to Earth and life history • The distribution of land and sea • profoundly influences oceanic circulation, • which in turn partly controls climate • The proximity of continents • partly determines the geographic distribution of organisms
Isolation • Pangaea began fragmenting • during the Triassic and continues to do so • Intercontinental interchange among faunas • became increasingly difficult • for most organisms • In fact, South America and Australia • were isolated continents • and their faunas evolving in isolation • became increasingly different from those elsewhere
Marine Invertebrates and Phytoplankton • Following the Paleozoic mass extinctions, • the Mesozoic was a time • when marine invertebrates repopulated the seas • The Early Triassic invertebrate fauna • was not very diverse, • but by the Late Triassic the seas • were once again swarming with invertebrates • from planktonic foraminifera • to cephalopods
Brachiopods Never Fully Recover • The brachiopods, • that had been so abundant during the Paleozoic, • never completely recovered from • their near extinction • Although brachiopods still exist • the bivalves • have largely taken over their ecological niche
Mollusks • Mollusks such as • cephalopods, bivalves, and gastropods • were the most important elements • in the Mesozoic marine invertebrate fauna • Their rapid evolution • and the fact that many cephalopods were nektonic • make them excellent guide fossils
Ammonoidea • The Ammonoidea, • cephalopods with wrinkled sutures, • constitute three groups: • the goniatites, ceratites, and ammonites • Ammonites, while present during the entire Mesozoic, • were most prolific during the Jurassic and Cretaceous • Most ammonites were coiled, • some attaining diameters of 2 m, • whereas others were uncoiled • and led a nearly benthonic existence
Cephalopods • Cephalopods • such as the Late Cretaceous ammonoids Baculites • and Helioceros • were important predators • and excellent guide fossils
Surviving Cephalopods • Ammonites went extinct • at the end of the Cretaceous, • but two related groups of cephalopods • survived into the Cenozoic • the nautiloids, • including the living pearly nautilus, • and the coleoids, represented by extinct belemnoids • which are good Jurassic and Cretaceous guide fossils • as well as by the living squid and octopus
Belemnoids • These extinct squidlike cephalopods • were abundant during the Cretaceous • and are excellent guide fossils • for the Jurassic and Cretaceous
Mesozoic Bivalves • Mesozoic bivalves diversified • to inhabit many epifaunal and infaunal niches • Oysters and clams • epifaunal suspension feeders • became particularly diverse and abundant • and despite a reduction in diversity • at the end of the Cretaceous, • remain important animals in the marine fauna today
Cretaceous Bivalves • Bivalves were particularly diverse and abundant during the Mesozoic • Even today they remain important elements in the marine invertebrate fauna
Mesozoic Reef-Builders • Where shallow marine waters were warm and clear, coral reefs proliferated • Reefs did not rebound from the Permian extinctions • until the Middle Triassic
Mesozoic Reef-Builders • An important reef-builder • throughout the Mesozoic • was a group of bivalves known as rudists • Rudists are important • because they displaced corals • as the main reef-builders during the later Mesozoic • and are excellent guide fossils for the Late Jurassic and Cretaceous
Familiar Coral • A new and familiar type of coral • also appeared during the Triassic, • the scleractinians • Whether scleractinians evolved from rugose corals • or from an as yet unknown soft-bodied ancestor • with no known fossil record • is still unresolved
Echinoids • Another invertebrate group • that prospered during the Mesozoic • was the echinoids • Echinoids were exclusively epifaunal • during the Paleozoic, • but branched out into the infaunal habitat • during the Mesozoic • Both groups began a major adaptive radiation • during the Late Triassic • that continued throughout the remainder • of the Mesozoic and Cenozoic
Burrowing Organisms • A major difference between Paleozoic and Mesozoic marine invertebrate faunas • was the increased abundance and diversity • of burrowing organisms. • With few exceptions, Paleozoic burrowers • were soft-bodied animals such as worms. • The bivalves and echinoids • evolved various means of entering infaunal habitats • This may have been an adaptive response • to increasing predation • from the rapidly evolving cephalopods
Foraminifera • The foraminifera • single-celled consumers • diversified rapidly during the Jurassic and Cretaceous • They are still diverse and abundant today • The planktonic forms in particular • diversified rapidly, • but most genera • became extinct at the end of the Cretaceous • The planktonic foraminifera • are excellent guide fossils for the Cretaceous
Planktonic Foraminifera • Many planktonic foraminifera • are excellent guide fossils for the Cretaceous, • such as species of the genus Globotruncana, • which is restricted to the Upper Cretaceous.
Mesozoic Primary Producers • The primary producers in the Mesozoic seas • were various types of microorganisms • Coccolithophores are an important group • of calcareous phytoplankton • that first evolved during the Jurassic • and became extremely common during the Cretaceous
Coccolithophores • Coccolithophores from the Gulf of Mexico • of Miocene age • of Miocene-Pliocene age
Diatoms • Diatoms • which build their skeletons of silica, • made their appearance during the Cretaceous, • but they are more important • as primary producers during the Cenozoic • Diatoms are presently most abundant • in cooler oceanic waters • and some species inhabit freshwater lakes
Diatoms • Diatoms from Upper Miocene rocks in Java
Dinoflagellates • Dinoflagellates • Which are organic-walled phytoplankton, • were common during the Mesozoic and today are the major primary producers in warm water • An Eocene dinoflagellate from Alabama • A Miocene-Piocene dinoflagellate from the Gulf of Mexico
Increasing Complexity • The Mesozoic was a time of • generally increasing complexity • of the marine invertebrate fauna • At the beginning of the Triassic, • diversity was low and food chains were short • Near the end of the Cretaceous, though, • the marine invertebrate fauna was highly complex • with interrelated food chains • This evolutionary history • reflects changing geologic conditions • influenced by plate tectonic activity
Fish • Today, Earth’s oceans, lakes, and rivers are populated by about 24,000 species of bony fish • whereas only 930 species of cartilaginous fish exist • all of them confined to the seas • Sharks and the other cartilaginous fishes • became more abundant during the Mesozoic, • but even so they never came close • to matching the diversity of the bony fishes • Sharks, an evolutionarily conservative group, • were and remain important in marine fauna as predators
Lungfishes and Crossopterygians • Few species of lungfishes and crossopterygians • persisted into the Mesozoic, • and the latter declined • and was nearly extinct by the end of the era • Only one crossopterygian species exists now • and the group has no known Cenozoic fossil record
Living Fossil • Latimeria • belongs to a group of fish known as coelacanths thought to have gone extinct at the end of the Mesozoic Era • A specimen was caught off the coast of East Africa in 1938 • Since then many more have been captured
Bony Fish • All bony fish, • except lungfishes and crossopterygians, • belong to 3 groups, which for convenience we call • primitive, intermediate, and advanced • Superficially they resemble each other • but important changes took place • as one group replaced another • The internal skeleton of the primitive and intermediate varieties • was partly cartilaginous • but in the advanced group it was completely bony
Advanced Bony Fish • The primitive bony fishes • existed mostly during the Paleozoic, • but by Middle Mesozoic time, • the intermediate group predominated • The advanced group, • more formally known as teleosts, • became the most diverse of all bony fishes by Cretaceous time • in both fresh and saltwater environments • and now are the most varied • and numerous of all vertebrate animals
Mesozoic Fish • Mesozoic fish Leedsichthys and the short-necked plesiosaur Liopluerodon • The fish (background), from the intermediate group • was one of the largest ever • It was probably a plankton feeder
Labyrinthodont Amphibians • The labyrinthodont amphibians • were common during the latter part of the Paleozoic, • but the few surviving Mesozoic species died out • by the end of the Triassic • Since their greatest abundance • during the Pennsylvanian Period, • amphibians have made up • only a small part of the total vertebrate fauna • Frogs and salamanders diverged • during the Late Permian or Early Triassic • but both have poor fossil records
Plants—Primary Producers on Land • Just as during the Late Paleozoic, • seedless vascular plants and gymnosperms • dominated Triassic and Jurassic land plant communities, • and, in fact, representatives of both groups • are still common • Among the gymnosperms, • the large seed ferns became extinct • by the end of the Triassic, • but ginkgos remained abundant • and still exist in isolated regions
Ginkgos • These fan-shaped leaves • from a present-day gingko tree • look much like those • of their ancient ancestors
Gymnosperms • Conifers continued to diversify • and are now widespread in some terrestrial habitats, • particularly at high elevations and high latitudes • A new group of gymnosperms • known as cycads made its appearance • during the Triassic • These palm-like plants • became widespread • and now exist in tropical • and semi-tropical areas
Mesozoic Plants • The Jurassic landscape was dominated by • seedless vascular plants, • especially ferns, • as well as gymnosperms • including conifers • and cycads
Cycads • These living cycads look much like the vegetation of the Jurassic
Angiosperms • The long dominance of seedless plants and gymnosperms • ended during the Early Cretaceous, • perhaps the Late Jurassic, • when many were replaced • by angiosperms, • or flowering plants • The fossil record of the earliest angiosperms is sparse • so their precise ancestors remain obscure • Nevertheless, studies of living plants and the fossils • indicate close relationships with the gymnosperms.
Fossil Angiosperms • Archaefructus sinensis • from Lower Cretaceous rocks in China • is among the oldest known angiosperms
Fossil Angiosperms • Restoration of Archaefructus sinensis
Angiosperms Evolved and Adapted • Since they evolved, angiosperms have adapted • to nearly every terrestrial habitat • from mountains to deserts • and some have even adapted • to shallow coastal waters • Several factors account for their phenomenal success, • including enclosed seeds • and above all the origin of flowers • which attract animal pollinators • especially insects
More Than 90% • The interrelationships among flowering plants and insects are so close • that biologists refer to changes in one induced by the other • as coevolution • The 250,000 to 300,000 species of angiosperms that now exist • account for more than 90% of all land plant species. • They inhabit some habitats • hostile to other plants, a testimony to their success • Nevertheless, seedless vascular plants and gymnosperms • remain important in the world’s flora