Chapter 26. Cenozoic Life GUIDED STUDY. Life on Land (pp ) Cenozoic Marine Life (pp )

Transcription

1 236 Chapter 26 Cenozoic Life GUIDED STUDY The text chapter should be studied one section at a time. Before you read, preview each section by skimming it, noting headings and boldface items. Then read the appropriate section objectives from the following outline. Keep these objectives in mind and, as you read the chapter section, search for the information that will enable you to meet each objective. Once you have finished a section, write out answers for its objectives. Life on Land (pp ) 5. Describe the adaptations of grasses and herbaceous plants that caused their spectacular radiation in the Cenozoic. Cenozoic Marine Life (pp ) 1. List examples of major invertebrate groups that were missing from Cenozoic seas. 6. Discuss the diversification of birds in the Cenozoic, and the dominant roles they played. 2. Describe the diversification of foraminifera during the early Cenozoic. 7. Marsupial mammals developed in both South America and Australia. Why did those in South America suffer greatly from extinction in the Pliocene Epoch, but those in Australia have survived untouched until modern times? 3. Which marine invertebrates seemed little affected by the Cretaceous-Tertiary extinction event? 4. Describe the various forms that led to the evolution of whales from original land-based predators. 8. Describe the different stages in the development of the modern horse. What features underwent the most change, and why?

2 237 Quaternary Extinctions (pp ) 9. Describe the kinds of animals, both mammal and bird, that were lost in the late Quaternary extinction event. CHAPTER REVIEW When you have finished reading the chapter, work through the material that follows to review it. Complete the sentences. As you proceed, evaluate your performance for each section by consulting the answers on page 245. Do not continue with the next section until you understand each answer. If you need to, review or reread the appropriate section in the textbook before continuing. 10. Describe how an abrupt climate change at the end of the Pleistocene could have been fatal to the large animal population at that time. Human Origins (pp ) 11. Describe the features that characterize primates. What advantages do these features offer? 12. List several differences between the two major groups of primates. 13. Describe the fundamental structural differences between modern humans and apes. 14. What are the most significant features of the recently discovered Australopithecus garhi? Introduction (p. 549) 1. Fossils of creatures that lived in and around large lakes in what is now Utah, Wyoming, and Colorado during the Eocene Epoch are preserved in rocks of the. 2. The warm, tropical climate of the region was indicated by the presence of fossilized trees and ferns. 3. The abundance of fossil skeletons in these layers indicate a poisonous overturning of oxygenrich surface waters with oxygen-poor bottom waters, causing massive kills. Cenozoic Marine Life (pp ) 4. The mass extinctions at the end of the Era included all of the large marine, and the ammonoid cephalopods and rudistid bivalves. 5. diversified quite rapidly in the early Cenozoic, with forms reaching the size of a five-cent piece. 6. seemed to have flourished with the increase of volcanism during the Miocene Epoch, when increased volcanism loaded the waters with silica from which their tests were built. 7. With the extinction of the reef-building rudistid bivalves, the reclaimed their role by the Oligocene Epoch.

3 were little affected by the Cretaceous-Tertiary event, and are a main component of temperate-water reefs today. 9. and quickly reestablished their dominance in the shallow marine environment, with the rapid appearance of many modern forms. 10. Their chief new adaptation was to inhabit the shallow marine environments. 11. The cephalopods were severely impacted by extinctions, with only a single genus of surviving. 12. Echinoids such as the familiar, evolved to take advantage of the sandy, shallow marine environment. 13. The ammonoid predators of the Mesozoic were replaced in the Cenozoic by modern fish called, which have symmetrical fins, round scales, and short jaws. 14. Larger marine predators such as evolved during the Tertiary Period, with one form reaching nearly 40 feet in length. 15. The largest marine predators of the Cenozoic were the, as they are today. They seem to have evolved from wolf-sized, hoofed ancestors that were adapted to an aquatic environment. 16. The earliest whale ancestors had functional hind limbs and have been found in, but later forms retain only of these limbs, and appear to be adapted to a fully aquatic existence. 17. Most whales today are forms, but by the Miocene, the larger whales appeared, which include today the largest animals that have ever lived on Earth. Life on Land (pp ) 18. The evolution of on land far outdistanced diversification in the oceans. 19. The demise of the opened the way for rapid diversification of both mammals and in the Cenozoic. 20. Despite the prominence of gymnosperms and many seedless vascular plants in some environments today, it is the continued expansion of the that highlights Cenozoic plant evolution. 21. The cooler and drier climate of the Miocene Epoch favored the expansion of, which had adapted to the grazing habits of mammals. The physical toughness of these plants comes from their incorporation of into the cell structure. 22. Colonization of spaces made vacant by flood or fire was a special adaptation of the plants, which also underwent a spectacular radiation in the later Cenozoic. 23. Today, the surviving reptiles are mostly, which include crocodiles, lizards, and snakes. The only other surviving reptile group was the. 24. By the end of the Mesozoic, the modern design of birds with a beak, hollow, and the absence of a reptilian tail was established. 25. In the Early Tertiary Period, scavenging birds such as vultures and large forms appeared. Some of the later carnivorous forms stood 2 meters tall and were probably the dominant of the time. 26. In isolated locations such as Madagascar and New Zealand, giant flightless birds survived until the Pleistocene, when with mammals and hunting by humans them to extinction. 27. Because of the long presence of the dinosaurs, of mammals was relatively slow before the start of the Cenozoic Era. 28. In the early Paleocene Epoch, only about a families of mammals existed. By the early Eocene epoch, there were already families present.

4 The early mammals were very small and their fossils are quite scarce. Fortunately, their and structures are very distinctive, and can be used for identification. 30. There are five subclasses of mammals. One of the two subclasses that arose in the Mesozoic and became extinct in the early Cenozoic was the. 31. The most primitive of the three mammal subclasses present today are the, which lay eggs and nurse their young. They can be traced back to Cretaceous fossils. 32. The group of mammals in which the embryo hatches in the uterus and continues its development there are called. 33. has been a factor in the evolution of this mammalian group, for in areas such as South America, where landbridges suddenly forced these animals into direct competition with more advanced mammal groups, they eventually became. In areas such as Australia, they have flourished in the absence of outside competition, until only recently. 34. mammals have the most advanced system of reproduction. They evolved from marsupial ancestors during the Cretaceous Period and quickly became widespread. 35. The first mammals of this most advanced group were the, and all other groups probably evolved from them. Diversification of placental mammal orders occurred in the Paleocene, Eocene, and later Miocene or Pliocene epochs. 36. Placental mammals with few or no teeth are the, and are represented today by tree sloths, anteaters and. 37. The are the most successful of all mammal orders, and account for 40% of all living mammal species. 38. Flesh-eating placental mammals are called. They form the most diverse and complex of all mammalian orders, and are characterized by specialized teeth, and keen senses of sight and. These mammals can be divided into three groups or superfamilies 39. The group containing cats, civets, and hyenas is called the. Dogs, bears, racoons, and weasels belong to the group. The marine group is called the, and includes seals, sea lions, and walruses. 40. Mammals having hoofed feet are called. Horses, rhinoceroses, and tapirs are classified as being, or perissodactyls. Deer, giraffes, bison, pigs, and hippopotamuses as are classified as being, or artiodactyls. 41. The competitive success of the artiodactyls against their perissodactyl neighbors may have come by their development of a multi-chambered stomach, which gave these an advantage in more efficient digestion. 42. The largest land animals alive today evolved from hoofed ancestors, and are recognized by their long trunks or modified noses. These gave rise to the mammoths, mastodons, and modern elephants. Quaternary Extinctions (pp ) 43. Only 12,000 years ago, an astoundingly diverse large mammal fauna inhabited the northern hemisphere, including both grazing and carnivorous mammals. Between and years ago, nearly all of these large animals disappeared Extinction rates of large mammals were greatest in North and South America, where and of the genera were lost. In Europe and Asia, extinction rates were much less at this time, at about 30% and 5%.

5 One hypothesis for the large mammal extinctions suggests that a sudden change was responsible. 46. The blames hunting by humans for the loss of species. Spear points found with the bones of these giant mammals have been dated at about the same age as their extinctions, and at about the same time as the widespread appearance of people in this region. A of both hypotheses may have ultimately caused the large mammal extinctions. Human Origins (pp ) 47. Humans belong to the mammal order called. These history of these mammals is difficult to study, because their remains were never large or abundant. 48. Important characteristics of members of this order include fingers and toes, opposable digits that are adapted to, and front-set eyes that create overlapping fields of. 49. This order can be divided into two main groups. The tree shrews, lemurs, tarsiers, and lorises are. They have toes and snouts that represent a lack of evolutionary advancement. 50. The more advanced forms such as the Old World monkeys, New World monkeys, and hominoids are. They have a more upright, and flatter. 51. Hominoids can be divided into the lesser apes, the great apes, and the. 52. Purgatorius may have been the earliest primate, having lived during the Late Age. 53. Early prosimian remains have been found in the Paleocene and Eocene of North America and Asia, but the North American stock was by Oligocene climate change. The Middle Eocene fossil had both prosimian and anthropoid characteristics, putting it at the base of the anthropoid family tree. 54. Aegyptopithecus was an anthropoid primate that may have been an ancestor to the. Their descendants at some time migrated to South America and radiated independently to give rise to the. 55. The that lived in the cooler, drier Miocene climates of Africa had a long torso and limbs that were, but a skull, jaws, and teeth that were. These features suggest that these forms were ancestral to both the great apes and the hominids 56. The skeletal differences between apes and humans include a shorter, shorter limbs, and a skull that houses a. 57. The human skull differs from that of the ape in its flattened, smaller, and reduced canine teeth. 58. The pathway leading from the ape-like Miocene families to the hominids disappears for lack of remains. 59. Discoveries of early hominid fossils as old as 4.4 million years have come from sediments of the. 60. Ardipithecus ramidus fossil remains show a of human and apelike features. 61. Slightly younger hominid fossil remains have been collectively termed. Although their faces were apelike, their pelvis indicates that they clearly walked. 62. Up to seven species of Australopithecus have been assigned, including both and forms. A. garhi is the most exciting find of al, for with its bones were found and animal bones with cut marks on them. 63. A recent Kenyan find, Kenyanthropus platyops, is dated at 3.5 million years ago. Its strong resemblance to members of the much younger genus Homo may remove the australopithecines as the of modern humans. 64. The disappearance of forests in East Africa caused by the onset of glaciation in the Late Pliocene may have caused early humans to travel greater distances in search of food. Evidence of this can be seen in the leg bones and changes in the. 65. The first species of the genus Homo was named habilis because of its ability to use. It was no larger than its contemporary australopithecines, but it had a bigger. 66. was the first hominid to appear on other continents. This form had better developed stone tools, and may have used fire.

6 Between 200,000 and 30, 000 years ago, larger, more muscular forms occurred in Europe and the Near East called. DNA studies of their remains suggest they are a separate species of humans from modern peoples. 68. The origin of our own species,, has been explained by two different theories. The theory suggests that modern humans arose from ancestral stocks present in several regions simultaneously, such as from the widespread species Homo erectus. 69. The hypothesis proposes that migrations of modern people from Africa populated the entire world. This idea is supported by studies of DNA. 70. The European newcomers were a nomadic people with a distinctive culture, termed, which was characterized by the manufacture of elaborate tools, decorative arts, musical instruments, and even elegant paintings of large mammals now. 71. The presence of humans in southeast Asia and Australia 35,000 to 40,000 years ago suggests that the development of technology had already occurred. As a result, settlement of the Americas by humans could have occurred long before the opening of the near the end of the Pleistocene allowed land passage between Asia and North America. 72. The greatest threats to modern humans come today from, exhaustion of natural resources, and human-induced. PRACTICE TESTS After you thoroughly understand the correct answers of the Chapter Review, answer the following questions and check them with the answers on page If your answer is incorrect, consult the appropriate pages of the text. Multiple Choice Questions Circle your answers to the following questions. 1. The numerous fish fossils found in the Early Tertiary Green River Formation were killed by: a. overturn of lake waters. c. submarine landslide. b. volcanic eruptions. d. None of the above. 2. The Earth today is populated by the descendants of animals that restocked the land after the mass extinction at the Mesozoic-Cenozoic boundary by: a. the evolution of many new, bizarre animals and plants. b. convergent evolution. c. parallel evolution. d. the adaptive radiation of the surviving plants and animals. 3. Marine life at the beginning of the Tertiary Period was completely devoid of: a. brachiopods. b. cephalopods. c. large marine reptiles. d. teleost fishes. 4. Tertiary bivalves occupied additional niches, such as the: a. shifting shoreline sands. b. waters of salt lakes. c. land surface. d. seasonal mud flats. 5. Most modern fishes are: a. sharks. b. teleosts. c. placoderms. d. lobe-fins. 6. The largest marine predators of the Cenozoic were: a. mosasaurs. b. giant sharks. c. baleen whales. d. toothed whales. 7. The herbaceous plants flourished in: a. jungles. b. grasslands. c. spaces opened by fire or flood. d. deep forests. 8. Modern birds are characterized by: a. a toothless beak. b. hollow bones. c. a short, non-reptilian tail. d. all of the above. 9. Giant flightless birds survived until the Pleistocene in: a. South America. b. Australia. c. North America. d. Africa. 10. Mesozoic mammals that became extinct in the Early Tertiary Period were called: a. multituberculates. b. monotremes. c. marsupials. d. placentals. 11. The first placental mammals to appear were Cretaceous:

7 242 a. edentates. b. carnivores. c. primates. d. insectivores. 12. Armadillos are: a. marsupials that migrated north from South America. b. placentals that migrated South from North America. c. placentals that migrated north from South America. d. marsupials that migrated south from North America. 13. The most successful of mammals are the: a. edentates. b. rodents. c. carnivores. d. ungulates. 14. The largest odd-toed ungulates were : a. horses. b. chalicotheres. c. rhinoceroses. d. brontotheres. 15. The origin of camels occurred in: a. Africa. b. Asia. c. Australia. d. North America. 16. Elephants obtain food with their: a. trunk. b. teeth. c. tusks. d. front legs. 17. The Paleocene origin of horses occurred in: a. North America. c. Africa. b. Asia. d. Europe. 18. Until 12,000 years ago, large mammals roamed: a. Asia. b. Europe. c. North America. d. South America. 19. Mammoths on Wrangel Island were small because of: a. the extreme cold. b. a limited food supply. c. the thin ice surrounding the island. d. the large forests on the island. 20. The large mammal extinctions at the end of the Pleistocene were probably caused by: a. climate change. b. overhunting by humans. c. a combination of a. and b.. d. None of the above. 21. Primate hands are adapted for: a. grasping. b. tearing. c. digging. d. running. 22. The early Tertiary primates, which had long snouts and clawed fingers were: a. anthropoids. b. prosimians. c. hominids. d. hominoids. 23. The lesser apes, great apes, and humans are: a. anthropoids. b. prosimians. c. hominids. d. hominoids. 24. Australopithecus and Homo are: a. anthropoids. b. prosimians. c. hominids. d. hominoids. 25. The australopithecine species found with stone tools and scraped animal bone was: a. A. afarensis. b. A. garhi. c. A. robustus. d. A. africanus. 26. Australopithecines coexisted with: a. Homo habilis. b. Homo sapiens. c. Homo erectus. d.. Kenyanthropus platyops. 27. Modern humans are assigned to: a. Homo habilis. b. Homo sapiens. c. Homo erectus. d.. Kenyanthropus platyops. True or False Items Write true or false on the line in front of each statement. 1. The Green River Formation represents an Eocene lake deposit. 2. Sharks were the most common marine predators of the Early Cenozoic Era. 3. Planktonic foraminifera evolved rapidly, and are excellent index fossils for much of the Cenozoic Era.

8 Bivalves and gastropods were devastated by the Cretaceous-Tertiary mass extinctions. 5. Toothed whales are the largest animals that ever lived. 6. Grasses and herbaceous plants were angiosperms that expanded their range in the Cenozoic. 7. The remaining Cenozoic reptiles were primarily synapsids. 8. Marsupial mammals rear their young in an external pouch. 9. Armadillo fossil remains can be found as far back as the Cretaceous. 10. The carnivores are the most successful of all the mammal orders. 11. Dogs, bears, and racoons are canids. 12. Brontotheres and chalicotheres are extinct odd-toed ungulates. 13. Camels originated in Asia. 14. Mammoths and Mastodons are extinct proboscideans. 15. The large mammal fauna became extinct last in Asia. 16. Primates have five fingers with opposable digits. 17. Kenyanthropus may actually be the direct ancestor of humans. 18. Different species of humans have not coexisted in time. Essay Questions Write a brief essay on a separate sheet of paper answering each of the following questions. 1. Discuss the evolutionary record of the whales. 2. Explain the adaptations of grasses that made them so successful. 3. What two hypotheses seek to explain the extinction of the Late Pleistocene large mammal fauna? 4. Why is the search for human ancestry so full of complications and controversy? CHALLENGE TEST Answer these questions the day before an exam as a final check on your understanding of the chapter s terms and concepts. Check your responses with the answers on pages 247. If your answer is incorrect, consult the appropriate pages of the text. Completion Fill in the correct answers. 1. The sediments of the Green River Formation were deposited in exceptionally. 2. The limestone blocks comprising the pyramids of Egypt contains fossils of the large benthic foaraminifers called. 3. With the extinction of the, the scleractinian corals returned as the prominent marine reef-builders. 4. The teleost fishes took over the marine predatory role previously occupied by the. 5. The largest Cenozoic marine predators were. 6. The Cenozoic Era could be described as the Age of Mammals or the Age of. 7. Grasses were favored by the cooler, drier climates of the. 8. The large, flightless birds of the early Tertiary Period have been interpreted as both carnivores and. 9. The most primitive living group of mammals are the monotremes, which lay, but nurse their young. 10. In marsupials, the egg hatches in the uterus, and the embryo continues development in a modified, external. 11. Placental mammals have the most advanced system of. 12. The oldest mammal order is the insectivores, which is represented by shrews,, and hedgehogs. 13. Rodents number over of all living mammal species. 14. Flesh-eating placental mammals include cats, dogs, and. 15. Ungulate mammals are divided on the basis of the number of their. 16. Quaternary large-mammal extinctions are commonly attributed to the activities of humans. 17. Humans belong to the division of anthropoids. 18. Humans belong to the family of hominoids.

9 Humans belong to the genus of hominids. 20. The use of tools was once thought to distinguish early humans from their neighbors. Multiple-Choice Questions Circle the correct answer. 1. The largest Cenozoic protozoans were: a. planktonic foraminifers. b. benthic foraminifers. c. planktonic fusulinids. d. benthic fusulinids. 2. Later Cenozoic corals were important reef-builders, supplemented in temperate waters by colonies of: a. belemnites. c. rudists. b. brachiopods. d. bryozoans. 3. Whales evolved from: a. fishes c. sharks. b. marine reptiles. d. land mammals. 4. The largest animals that ever lived were: a. dinosaurs c. baleen whales. b. giant sharks. d. pliosaurs. 5. The grasses were most successful in which climate? a. warm, dry. c. cool, dry. b. warm, wet. d. cool, wet. 6. The early Tertiary multituberculate mammals were eventually outcompeted by: a. placental rodents. c. marsupials. b. placental primates. d. monotremes. 7. The monotremes are characterized by: a. pouches. c. a placenta. b. egg-laying ability. d. multi-cusped teeth. 8. The only marsupial native to North America is the: a. opossum. b. kangaroo. c. koala. d. wombat. 9. Carnivores are flesh-eating: a. therapsids b. momotremes c. placentals d. marsupials 10. Felid carnivores include the famous a. cave bear. b. saber-tooth cat. c. dire wolf. d. chalicothere. 11. Seals, sea lions, and walruses are: a. felids. b. canids. c. pinnipeds. d. toothed whales. 12. Horses are: a. odd-toed ungulates. b. even-toed ungulates. c. odd-toed ruminants. d. even-toed ruminants. 13. Even-toed ungulates were successful because of: a. fast hooves. b. better eyesight. c. lightweight design. d. a multichambered stomach. 14. Large mammal extinctions in North America followed the arrival of: a. mammoths c. humans. b. mastodons. d. horses. 15. Humans belong to the: a. rodents. b. primates. c. insectivores. d. edentates. 16. Old world monkeys, New world monkeys, and apes are: a. anthropoids. b. prosimians. c. hominids. d. hominoids. 17. The actual ancestor of humans may be: a. Australopithecus afaresis. b. Australopithecus robustus. c. Australopithecus africanus. d. Kenyanthropus platyops. 18. The earliest hominid to be found outside of Africa was : a. Homo habilis. b. Homo sapiens. c. Homo erectus. d.. Kenyanthropus platyops. True or False Items Write true or false on the line in front of each statement. 1. The fossilized fish skeletons in the Green River Formation were killed by a nearby volcanic eruption.

10 Early Tertiary planktonic foraminifers reached the size of a five-cent piece. 3. Bivalves became established in the environment of shifting shoreline sands. 4. Toothed whales were the largest marine predators of the Tertiary Period. 5. Large flightless birds such as Diatryma were herbivorous. 6. Multituberculate mammals survived into the Eocene Epoch. 7. Monotremes are the most advanced of today s remaining mammal groups. 8. Insectivores are the earliest of the placental mammals. 9. Cats, civets and hyenas are pinniped mammals. 10. Odd-toed ungulates were once called perissodactyls. 11. Horses are even-toed ungulates. 12. The multichambered stomach gave ruminants a selective advantage in the digestion of coarse plant material. 13. The Overkill hypothesis suggests that overhunting by humans brought the large Pleistocene mammals to extinction. 14. Anthropoids have primitive features such as clawed fingers and elongate snouts. 15. Hominoids include monkeys and apes. 16. Ardipithecus ramidis is the oldest hominid. 17. Humans of today continue to evolve rapidly. ANSWERS CHAPTER REVIEW 1. Green River Formation 2. palm 3. fish 4. Mesozoic; reptiles 5. Foraminifera; benthic 6. Diatoms 7. scleractinian corals 8. Bryozoans 9. Bivalves; gastropods 10. high-energy 11. nautiloid 12. sand dollar 13. teleosts 14. sharks 15. whales 16. river sediments; vestiges 17. toothed; baleen 18. mammals 19. dinosaurs; birds 20. angiosperms 21. grasses; silica 22. herbaceous 23. diapsids; turtles 24. toothless; bones 25. flightless; predators 26. competition; drove 27. diversification 28. dozen; tooth; jaw 30. multituberculates 31. monotremes 32. marsupials 33. Tectonics; extinct 34. Placental 35. insectivores 36. edentates; armadillos 37. rodents 38. carnivores; smell 39. felids; canids; pinnipeds 40. ungulates; odd-toed; even-toed 41. ruminants 42. proboscideans ,000; 8, %; 80% 45. climate 46. Overkill hypothesis; combination 47. primates 48. five; grasping; vision 49. prosimians; clawed; elongated 50. anthropoids; posture; face 51. hominids 52. Cretaceous 53. eliminated; Eosimias 54. Old World monkeys; New World monkeys 55. dryomorphs; monkey-like; ape-like 56. pelvis; large brain 57. face; jaw 58. fossil 59. East African Rift 60. mix 61. australopithecines; upright 62. robust; gracile; stone tools 63. true ancestors 64. longer; pelvic 65. tools; brain 66. Homo erectus 67. Neanderthals 68. Homo sapiens; multiregional origin 69. out of Africa; mitochondrial 70. Cro-magnon 71. sea-faring; Bering landbridge 72. pollution; climate change PRACTICE TESTS Multiple-Choice Questions 1. a 2. d 3. c 4. a

11 b 6. d 7. c 8. d 9. b 10. a 11. d 12. c 13. b 14. c 15. d 16. a 17. b 18. c 19. b 20. c 21. a 22. b 23. d 24. c 25. b 26. a 27. b True or False Items 1. True. 2. False. Teleost fishes were the most common marine predators of the Cenozoic Era. 3. True. 4. False. Mollusks were impacted little by the Cretaceous Tertiary extinction event. 5. False. Baleen whales are the largest animals that have ever lived on Earth. 6. True. 7. False. The remaining reptiles were primarily diapsids. 8. True. 9. False. Armadillo fossils have been found in Paleocene rocks. 10. False. Rodents are the most successful of all the mammal orders. 11. True. 12. True. 13. False. Camels originated in North America during the Oligocene, and then migrated into Asia before their American forms became extinct. 14. True. 15. False. The large mammal fauna became extinct last in North America, at about 8,000 years ago. 16. True. 17. True. 18. False. Homo sapiens probably coexisted with H. erectus in southeast Asia, and with Neanderthals in Europe. Essay Questions 1. The origin of whales can be traced through several intermediate forms which show similar but modified features relating to the limbs of the animals: a. The earliest whales from the early Eocene Epoch were quite small, with hind limbs that were functional for swimming and modest locomotion on land. These remains were found in river sediments, indicating an aquatic environment. b. The Middle Eocene Pakicetus and Protocetus lost their functional hind legs, leaving behind only small, vestigal limb bones. c. At the end of the Eocene Epoch, Basilosaurus reached lengths comparable to modern whales. d. In the Miocene Epoch, baleen whales diverged from toothed whales, and later in the Pliocene Epoch, the smaller toothed whales appeared. 2. The success of the grasses was due in part to their adaptation to a cooler, drier climate, and also their ability to spread while the upper part of the plant is constantly being chewed off. The durability of the grasses was due to their incorporation of minute silica particles into their cell structures, and the challenge that grazing mammals had to overcome to withstand the constant abrasion. Even today, the teeth of grazing animals eventually wear out from the abrasive grasses. 3. The extinction of the large mammal fauna at the end of the Pleistocene specifically targeted mammals of large size. These mammals had been through several cycles of glaciation before, and had suffered no ill effects. What was different about this last retreat of the glaciers? The Climate Change hypothesis has a difficult time explaining how this change could cause extinctions, as the animals should be able to outrun the severe conditions to locate more favorable ones. The Overkill hypothesis may explain what really happened better. Everywhere humans had been, the large mammals had already disappeared, whether in Asia, Europe, or even Australia. The fact that the large mammals of North America were the last to disappear has to do with the late arrival of humans into this region, and with the spear points that were left behind in the bones of these animals. Some mammoths remained on Wrangel Island in Siberia until only 3500 years ago, primarily because humans were unable to get there until then. Humans probably did overkill their large mammal contemporaries in a matter of 4,000 years or so, and the large mammals such as buffalo that did survive were present in sufficient numbers to survive until this last century. 4. Investigations into the origin of humans are fraught with many problems, such as a lack of wellpreserved fossils, a lack of established nearby

12 247 volcanic ash beds for radiometric age dates, a very incomplete fossil record, and a more limited set of depositional environments that are capable of preserving human remains. It is also difficult to establish whether scattered bones belong to one or many different individuals, whether they were contemporary of lived hundreds of years apart, and also what kind of differences should separate the sexes, different species, and even different genera of humans. Human populations also probably evolved at different rates in response to different environmental stresses, and as a result, some populations may have changed rapidly, whereas others may have changed very little. Interactions between populations of early humans and predators, early humans and australopithecines, populations of modern humans with Homo erectus populations, or populations of modern humans with Neanderthal peoples may also represent disaster for the less well-adapted group. All of these considerations make the interpretation of human remains a difficult and challenging study. What was once considered a very straightforward evolutionary tree has become a very thorny bush indeed. CHALLENGE TEST Completion 1. large lakes 2. nummulitids 3. rudistid bivalves 4. ammonites 5. toothed whales 6. Birds 7. Miocene Epoch 8. scavengers 9. eggs 10. pouch 11. reproduction 12. moles % 14. seals 15. toes 16. hunting 17. hominoid 18. hominid 19. Homo 20. australopithecine 6. a 7. b 8. a 9. c 10. b 11. c 12. a 13. d 14. c 15. b 16. a 17. d 18. c True or False Items 1. False. The fossilized fish of the Green River Formation were probably killed by the poisonous turnover of stratified lake waters. 2. False. Planktonic foraminifera were small. Benthic foraminifera grew to the size of a five-cent piece. 3. True. 4. True. 5. False. Diatryma was either a predator or a scavenger. 6. True. 7. False. Monotremes are the most primitive of today s remaining mammal groups. 8. True. 9. False. Cats, civets, and hyenas are felid mammals. 10. True. 11. False Horses are odd-toed ungulates. 12. True. 13. True. 14. False. Prosimians have primitive features such as clawed fingers and elongated snouts. 15. False. Hominoids include the lesser apes, great apes, and humans. 16. True. 17. False. Humans today are so well connected by transportation rates that potential differences could not accumulate. New human species therefore would not form. Multiple-Choice Questions 1. b 2. d 3. d 4. c 5. d