Life of the Mesozoic Era

1. Chapter 15 Life of the Mesozoic Era

2. 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

3. Cretaceous Scence • In this scene from the Late Cretaceous, • Ankylosaurus is defending itself • from the large predator Tyrannosaurus.

4. 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

5. 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.

6. 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

7. 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.

8. 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.

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. Cephalopods • Cephalopods • such as the Late Cretaceous ammonoids Baculites • and Helioceros • were important predators • and excellent guide fossils

16. 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

17. Belemnoids • These extinct squidlike cephalopods • were abundant during the Cretaceous • and are excellent guide fossils • for the Jurassic and Cretaceous

18. 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

19. Cretaceous Bivalves • Bivalves were particularly diverse and abundant during the Mesozoic • Even today they remain important elements in the marine invertebrate fauna

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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.

27. 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

28. Coccolithophores • Coccolithophores from the Gulf of Mexico • of Miocene age • of Miocene-Pliocene age

29. 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

30. Diatoms • Diatoms from Upper Miocene rocks in Java

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. 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

41. Ginkgos • These fan-shaped leaves • from a present-day gingko tree • look much like those • of their ancient ancestors

42. 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

43. Mesozoic Plants • The Jurassic landscape was dominated by • seedless vascular plants, • especially ferns, • as well as gymnosperms • including conifers • and cycads

44. Cycads • These living cycads look much like the vegetation of the Jurassic

45. 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.

46. Fossil Angiosperms • Archaefructus sinensis • from Lower Cretaceous rocks in China • is among the oldest known angiosperms

47. Fossil Angiosperms • Restoration of Archaefructus sinensis

48. 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

49. Reproductive Cycle of Angiosperms

50. 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