Vertebrate Paleontology

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Angdredd
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271383
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Vertebrate Paleontology
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2014-04-22 16:02:26
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Mammals part 2
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    • Horse Evolution
    • Increase in body size
    • Reduction of toes
    • Increases in crown height of teeth for grazing
    • Early Horses small - 3-5 toes
    • Teeth low crowned for browsing
    • Teeth became high crowned for grazing (food far more gritty)
    • Mesohippus
    • A larger browsing horse that appeared before Miocene grasslands developed
    • Greyhound-sized - three toes
    • Common in Oligocene Badlands sediments
  1. Horses
    • Modern Equus, expanded on prairies of North America and invaded South America and Asia.
    • Extinct in Americas 10k ybp - repopulated by Spaniards in 1500s
  2. Rhinoceroses
    • Heavy-bodied Perissodactyls
    • Begain in North America
    • Begain small and grew through time much like horses
    • Many Teleoceras skeletons preserved at Ashfall Fossil Bed in Nebraska
    • Paraceratherium (rhinoceraoses)
    • largest land mammal ever
    • 7m tall
    • 10m long
    • Hornless
    • Asia
  3. Perissodactyls and Artiodactyls
    • Perissodactyls declined in the late Cenozoic as artiodactyls diversified.
    • Artiodactyls - heels less likely to dislocate because of double-pulley astragalus.
    • Bovids (most diverse artiodactyls) also have bacteria-driven digestive system better able to break down cellulose, helped by chewing their cud.
  4. Artiodactyls
    • Paraxonic feet
    • Axis between toes 3 and 4
    • Toe reduction from 5 to 4 to 2
    • Metapodials 3 and 4 commonly fuse to form cannon bone
    • Early artiodactyls
    • Basal rabbit-sized artiodactyls Diacodexis
    • -Early Eocene of North America, Europe, Asia
    • -Walked on 4 main toes
    • -Double-pulley astragalus
    • Oligocene entelodont
    • -Archaeotherium in Badlands
    • Skull of Oligocene Peccary.
  5. Artiodactyls
    • Suiformes - pigs and hippos (no longer used); body form convergence only
    • -Bulbous cusps on molars - omnivorous diet
    • -Tusks with triangular cross section
    • NOW: Cetioartiodactyla
    • -Cetaceans and artiodactyla
    • Selenodonta - camels, cattle, sheep, deer
    • -Selenodont molars - rectangualr with paired crescent-shaped ridges
    • -Upper incisors reduced or missing (replaced with pad for plucking plant food against lower incisors)
    • -Procumbent, spatulate lower incisors
    • -Tend to reduce the number of toes to two

    • Even number of toes (2 or 4)
    • Successful in survival, variety, and abundance
    • Pigs, deer, hippos, sheep, goats, cattle (ruminants)
    • Oreodont: extinct sheep-sized grazer in grasslands, common in Badlands National Park, burrowers.
    • Selenodonts: Tylopods
    • Camels undergo size increase in parallel with horses.
    • Oreodonts superficially pig-like
  6. Selenodonts: Ruminants
    • Lose upper incisors in favor of a pad
    • Cud chewers with multi-chambered stomach
    • -regurgitate and rechew
    • Irish Elk: a deer
  7. Runimants
    • Giraffids - bony skin-covered horn cores (sometimes forked)
    • -Giraffes and okapis
    • Cervids - forked bony structures (antlers) - shed annually (grow under a skin that is shed)
    • -Deer, elk, Moose
    • Antilocaprids - bony core covered by keratin sheath shed annually (both may be forked)
    • -Pronghorns (American "antelope") formerly more diverse
    • Bovids - true horns (bony core covered by permanent unforked keratin sheath)
    • -Sheep, goats, cattle, muskoxen, bison, antelopes
  8. Cetaceans
    • Related to hippos
    • Arose in Eocene
    • Early whales could walk on land
    • Piscivorous
    • Mysticetes evolve plankton feeders by Miocene
  9. Baleen Whales
    feeding with a strainer
  10. Whale sizes
    • Blue whale = largest animal of all time.
    • All baleen whales = "great whales."
    • ONly "great whale" toothed whales = sperm whale=deep diver for giant squid.
    • Dolphins and porpoises = smalles cetaceans.
  11. South American Ungulates
    • Evolved in parallel with horses, hippos, and tapirs
    • Arose from North America immigrants and underwent their own radiation.
    • Rodents were their only large competitors
  12. Afrotheria
    • Diverged early from other lineages
    • Early Cretaceous in Gondwannaland
    • Or arose in Eurasia - reached Africa in late Cretaceous
    • First to diverge: aardvark, tenrec, golden mole and elephant shrew - all are insectivorous and restricted to Africa.
    • Includes elephants and their relatives, hyraxes, and sirenians (sea cows and dugongs).
  13. Aardvark
    nocturnal, burrowing anteater with a big snout and long ears.
  14. Tenrecs
    • diverse
    • resemble hedgehogs, shrews, opossums, mice and even otters in environments including aquatic, arboreal, terrestrial and fossorial.
  15. Golden moles
    live underground and have short limbs, non-functional eyes covered by skin and hair. Can lower body temperature to conserve energy, some never drink.
  16. elephant shrews
    • named for long "trunk-like" nose
    • diverse but uncommon in many many environments in africa. Not closely related to shrews, so the native name sengis has been proposed.
  17. Paenungulata
    • Proboscideans, Hyraxes, and Sirenians
    • Share posterior extension of jugal to front margin jaw and serial arrangement of wrist bones
    • Old Theory-Paenungulates related to Perissodactyls, now ruled out by morphological and DNA evidence.
    • New Theory-Part of Afrotheria, with aardvarks, tenrecs, golden moles, and elephant shrews, based on DNA evidence.

    • Hyraxes rabbit-sized herbivores - Africa and Middle East - 4-toed  forefeet, 3-toed hindfeet, large bacterial chamber digestion poor thermoregulation.
    • Sirenians (manatees sea cows, dugongs) fully aquatic herbivores that give birth in water. Docile - poor cold tolerance - low metabolism, living in warm coastal waters worldwide.
  18. sirenia
    • Dugongs and sea cows
    • arose in early Eocene 
    • sea grass eaters
    • Fully aquatic, but stay in shallow water
  19. Proboscidea
    • Reduced jugal, orbit opens in maxilla, enlarged second incisor (become tusks), lower canines and first premolars absent, large molar teeth with multiple ridges, limbs adapted for supporting weight
    • originated in early Eocene in Africa 
    • split into two groups in later Eocene 
    • -deinotheres-lower disks curl under chin
    • -elephantiforms- split into paleomastodontids (simpler teeth) and elephantoids (cheek teeth erupt serially from front to rear)
  20. Elephantids
    • As heads enlarged and necks shortened, elephants developed longer trunks to reach the ground.
    • teeth deepened and evolved up to 30 enamel loops for grinding tough vegetation.
    • Northern elephants evolved thick fur and long tusks for digging in snow during the Ice Age, thus becoming mammoths.
    • Several species of mammoths, as well as more primitive mastodonts, invaded North America.
  21. Proboscideans
    • Trunk for breathing, drinking, washing and food gathering
    • tusks for combat and browsing for food
    • Mastodonts retain elongate but otherwise primitive teeth.
    • Elephants and mammoths develop deep ridged teeth with serial eruption for grazing tough plant foods.
  22. Gomphotherium pic
    • Gomphotherium arrived in North America via Bering land bridge in Miocene.
    • Reached South America via Isthmus of Panama in Pliocene.
  23. Mammoths
    • Furry ice age elephants
    • went extinct 8000 years ago - from hunting?
    • african and Indian elephants are all that remain
  24. Tundra adapted mammals
    • Wooly mammoths, wooly rhinos, musk oxen, etc.
    • Faunal communities migrated toward poles during interglacials, toward equator during glacial advances
  25. Rodents
    • Gnaw and dibble (elongate ever-growing incisors)
    • diastema (loss of some incisors, canines, premolars)
    • primitive body behind the head
    • huge range and adaptations: arctic to tropics to deserts
    • Advantages: rapid breeding rate, small size
  26. Rodent teeth
    • Continuous tooth growth for eating abrasive foods
    • splitting of masseter allows for precise tooth movements - occurs differently in rodent groups:
    • protrogomorph
    • hystricomorph
    • sciuromorph
    • myomorph
  27. Rodent groups
    • Sciurognaths
    • -sciuromoropha-squirrels and bevers
    •   -Eocene origin, most primitive surviving rodents
    • -myomorpha - hamsters, mice, rats, voles
    •   -Voles most advanced - ever-growing cheek teeth. Huge Pleistocene radiation.
    • Hystricognaths
    • -Hystricomorpha - porcupines
    •   -African origin in Oligocene, since spread across northern continents
    • -Caviamorpha - guinea pigs, capybaras, chinchillas
    •   -South American rodents (probably arrived from Africa)
  28. Worlds largest rodent
    • Rous's
    • uruguay fossil of biggest rodent, lived in wooded areas of south America about 4mya, when the continent was not connected to North America.
    • Herbivorous - may=contemporary & ?=prey, of sabertoothed cats. Skull - more than 20 inches long - animal more than 8' long - weighs 1700-3000 pounds.
  29. Lagomorphs
    • Rabbits, hares, pikas
    • grouped with rodents under the name glires
    • burrowing leaf eaters with great profundity?
    • traits:
    • -Fenestrated maxilla
    • -Second incisor behind first
    • -1 layer of enamel on incisors
    • -P2/1 M3/3
    • -Transverse grinding
    • -Short tail
    • -Generalists, low diversity
  30. Continental connections
    • eocene - India collided with Asia forming Himalayas - terrestrial faunas dispersed in both directions
    • miocene - Africa joined southern Eurasia, creating the Mediterranean, Black, and Caspian Seas allowing some afrotherians to spread to Eurasia.
    • Pliocene - Isthmus of Panama formed, joining North and South America - allowing Great American Interchange.
  31. South American mammals
    • Marsupials - arrived from North America by late Cretaceous 
    • South American ungulates and edentates - arrived from North America in early Paleogene.
    • New world monkeys and hystricomorph rodents arrived from Africa in Oligocene (by rafting?)
    • Cats, camels, and many other North American placental mammals - arrived from North America in Pliocene via Isthmus of Panama.
  32. South American mammals map
    • Pliocene: isthmus of panama formed
    • -marsupials, porcupines, xenarthrans spread north
    • -carnivores and other placentals spread south
    • -marsupials initially flourished, then declined.
  33. Great American interchange
    • Populations expanded in both directions, and diversity increased.
    • Most extinctions occurred long after the interchange.
  34. Cenozoic cooling trend
    • Cooling began - end of Cretaceous and continued through Cenozoic 
    • glaciation began in Antarctica when with cooling of South Pole in Oligocene.
  35. North America during the Pleistocene
    • Northern hemisphere 21,000 bp - laurentide and cordilleran ice sheets covered 16 million square kilomemters - ~2/3 of North America.
    • Ice mass reduced sea level, allowing land bridge to span the Bering Straight from Alaska to Asia.
  36. What did north america look like during the last ice age?
    • River drainage in glaciated areas (Canada, northern U.S.) much different than today.  Mississippi Drainage Basin much smaller (didn't include South Dakota!)
  37. Cycles of glaciation
    • Glaciers expanded and retreated many times during the Ice Age.
    • May have been caused by variations in Earth's orbit - Milankovich Cycles.
  38. Ice age mammal migration
    • Widespread interchange in animals across Bering land bridge
    • Among migrants out of America: Horses and camels
    • Immigrants into North America, Bison, mastodons, wolly mammoths, brown bears, and humans.
  39. Late Pleistocene extinctions
    • being in Australia >20,000 bp
    • other continents 10-12,000 bp
    • many loses in Americas:
    • -mammoths and mastodons
    • -horses and tapirs
    • -Camels, some deer, some pronghorns
    • -Saber-tooth cats and giant lions
    • -Dire wolves and short-faced bears
    • -Ground sloths and glyptodonts
    • -South American ungulates
    • Mostly large species were affected (73% lost)
    • Extinctions in other glacial cycles had more even affect on large and small species.
  40. Climatic change theory
    • Drying conditions at end of Ice Age led to huge range changes and many extinctions.
    • Why were large species selected for extinction while most small species thrived?
  41. Human overkill theory
    • Extinctions coincide with expanding human population, so humans hunted the large animals to extinction.
    • but bison is the only animal with widespread evidence of human hunting, and it survived.
  42. Paul Martin overkill model
    • Now proven to be unlikely
    • Humans entered America 11,000 years ago - found populations unaccustomed to humans.
    • Human population expanded exponentially in because of so much food.
    • Humans moved in a wave across the continent, forcing remaining animals into smaller and smaller land area.
    • Wave of hunting over a few hundered years, leaving little evidence.
    • Population crash once food source gone.
  43. Mixed model of climate change and human hunting
    • Both extinctions and Clovis points progress south-north. Follows glacial retreat rather than human entry into Americas from Bering Strait.
    • Consistent with human hunting pressures if populations already strained.
    • Mammal phylogeny, including relative Abundance
    • Later standardization, variation on themes, competition among groups.
    • Huge adaptive radiation following dinosaur extinction.
    • Early experimentation in body plans.

    Rodents especially voles, corssed into North America in great numbers when the land bridge was open.
  44. Late Pleistocene Extinctions
    • Extinctions over several glacial cycles show differences in the effects on large and small species.
    • Note the number of surviving species in each category to figure the percentages of extinction.

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