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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)
- A larger browsing horse that appeared before Miocene grasslands developed
- Greyhound-sized - three toes
- Common in Oligocene Badlands sediments
- Modern Equus, expanded on prairies of North America and invaded South America and Asia.
- Extinct in Americas 10k ybp - repopulated by Spaniards in 1500s
- 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
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.
- 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.
- 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
- Lose upper incisors in favor of a pad
- Cud chewers with multi-chambered stomach
- -regurgitate and rechew
- Irish Elk: a deer
- 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
- Related to hippos
- Arose in Eocene
- Early whales could walk on land
- Mysticetes evolve plankton feeders by Miocene
feeding with a strainer
- 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.
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
- 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).
nocturnal, burrowing anteater with a big snout and long ears.
- resemble hedgehogs, shrews, opossums, mice and even otters in environments including aquatic, arboreal, terrestrial and fossorial.
live underground and have short limbs, non-functional eyes covered by skin and hair. Can lower body temperature to conserve energy, some never drink.
- 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.
- 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.
- Dugongs and sea cows
- arose in early Eocene
- sea grass eaters
- Fully aquatic, but stay in shallow water
- 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)
- 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.
- 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.
- Gomphotherium arrived in North America via Bering land bridge in Miocene.
- Reached South America via Isthmus of Panama in Pliocene.
- Furry ice age elephants
- went extinct 8000 years ago - from hunting?
- african and Indian elephants are all that remain
Tundra adapted mammals
- Wooly mammoths, wooly rhinos, musk oxen, etc.
- Faunal communities migrated toward poles during interglacials, toward equator during glacial advances
- 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
- Continuous tooth growth for eating abrasive foods
- splitting of masseter allows for precise tooth movements - occurs differently in rodent groups:
- -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.
- -Hystricomorpha - porcupines
- -African origin in Oligocene, since spread across northern continents
- -Caviamorpha - guinea pigs, capybaras, chinchillas
- -South American rodents (probably arrived from Africa)
Worlds largest rodent
- 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.
- Rabbits, hares, pikas
- grouped with rodents under the name glires
- burrowing leaf eaters with great profundity?
- -Fenestrated maxilla
- -Second incisor behind first
- -1 layer of enamel on incisors
- -P2/1 M3/3
- -Transverse grinding
- -Short tail
- -Generalists, low diversity
- 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.
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.
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.
Great American interchange
- Populations expanded in both directions, and diversity increased.
- Most extinctions occurred long after the interchange.
Cenozoic cooling trend
- Cooling began - end of Cretaceous and continued through Cenozoic
- glaciation began in Antarctica when with cooling of South Pole in Oligocene.
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.
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!)
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.
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.
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.
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?
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.
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.
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.
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.