Card Set Information
Mammals part 2
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
Begain in North America
Begain small and grew through time much like horses
Many Teleoceras skeletons preserved at Ashfall Fossil Bed in Nebraska
largest land mammal ever
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.
Axis between toes 3 and 4
Toe reduction from 5 to 4 to 2
Metapodials 3 and 4 commonly fuse to form cannon bone
Basal rabbit-sized artiodactyls Diacodexis
-Early Eocene of North America, Europe, Asia
-Walked on 4 main toes
-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
-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)
: extinct sheep-sized grazer in grasslands, common in Badlands National Park, burrowers.
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
: 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
: 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?
-Second incisor behind first
-1 layer of enamel on incisors
-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
: 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.