CENOZOIC LIFE - OVERVIEW

1. GRASSES EVOLVED IN THE OLIGOCENE & EXPANDED DURING THE MIOCENE
   • Response to cooler & drier climate as Antarctica becomes glaciated
2. MAMMALS DIVERSIFIED & IMPORTANT GROUPS DEVELOPED
   • Grazing mammals diversify in response to evolution & diversification of grasses
   • Primates (evolved in Late Cretaceous) diversify
3. MASS EXTINCTIONS
   • End of the Eocene & End of the Pleistocene

CENOZOIC PLANTS

1. MARINE PLANTS
   • Phytoplankton recovered from terminal Cretaceous mass extinction
     • Peaks in diversity in the Eocene & Miocene
2. TERRESTRIAL PLANTS
   • Angiosperms continued to diversify at expense of Gymnosperms
   • Grasses evolved in the Oligocene & became widespread in the Miocene
     • Forests decreased in size; grassy steppes & savannahs developed
     • Evolution of grasses (tough, abrasive & coated with dust) & development of open grassland had a profound effect on grazing mammals
       • Evolution of high-crowned teeth with folded enamel that continued to grow at the roots & elongation of face to hold bigger teeth; 4-chambered stomach; Elongation of limb & toe bones, elevation of ankle & reduction in number of toes, & evolution of hoofs
       • Carnivorous mammals also evolved & diversified in response

CENOZOIC INVERTEBRATES

1. PROTOZOANS
   • Foramifera & radiolarians recovered from terminal Cretaceous mass extinction
     • Maxima & minima in diversity similar to phytoplankton
     • Evolution of large (up to 2 cm) benthonic foraminifera (used to build pyramids)
2. COELENTERATES - Corals remain major reef builders
3. BRYOZOANS - Very successful, particulary in the Eocene
4. MOLLUSKS
   • Shell-less cephalopods (octopi, squid, cuttlefish) are abundant
   • Pelecypods & gastropods diversify
5. ECHINODERMS - Sand-dollars evolved during the Tertiary

CENOZOIC VERTEBRATES

1. BIRDS
   • Very successful in fully exploiting the aerial hibitat
   • Many large, flightless predatory birds evolved in the Cenozoic
     • Modern large, flightless birds (ostrich) are herbivorous
2. MAMMALS

• Fossil mammals are distinguished from fossil reptiles by differences in skull structure

Skull Structure	Reptiles	Mammals
Lower jaw	several bones	single bone
Jaw-skull joint	articular-quadrate	dentary-squamosal
Middle-ear bones	stapes only	stapes, incus, malleus
Teeth	no differentiation	fully differentiated
Secondary palate	absent	well-developed

• Mammalian orders are distinguished by molars
• Mesozoic Mammals
  • Evolved from Cynodont Therapsids during the Triassic
  • Mesozoic mammals were mostly small, shrew-like insectivores
  • Five orders (docodonts, tricodonts, symmetrodonts, eupanthotheres, & multituberculates) of small, nocturnal insectivores during Triassic & Jurassic
    • Eupantotherians - gave rise to Marsupial & Placental (insectivore) mammals in the Late Cretaceous
• Decimation of reptile faunas at the end of the Mesozoic opened up new habitat, & a vigorous mammalian adaptive radiation followed in the early Cenozoic
  • The Cenozoic is often referred to as the "Age of Mammals"
  • 7-8 orders of mammals in Cretaceous, 16-19 in Paleocene, and 24-27 in Eocene
    • Throughout the Early Tertiary, new groups appeared & old groups disappeared
    • A general decline in the number of mammal orders during the later Cenozoic (24-25 orders in Oligocene, 22 in Miocene, 20 in Pliocene & Pleistocene, and 18 at present)
    • There have been more than 30 orders of mammals during the Mesozoic & Cenozoic
• Monotremes (3 species) & Marsupials (~250 species)
  • Monotremes are primitive mammals that still lay eggs,but have primitive mammae
    • Fossil record is poor until the Pleistocene
    • Only 3 species remain (duck-billed platypus [Australia & Tasmania] & 2 echidna species [New Guinea, Australia, & New Zealand])
  • Marsupials are pouched mammals that developed extensively in Australia & South America during the Tertiary
    • The Australian marsupials have survived intact
    • The S. American marsupials fared well until the Pliocene - N. American placentals decimated these marsupials (as well as the native S. American placentals) after uplift of the Isthmus of Panama
    • Opossum is only remnant of S. American marsupial fauna north of Mexico
    • Like placental faunas, marsupials exhibit a wide array of modifications for various habitats & life styles
• Placental Mammals
  • MAJOR ORDERS:
    1. ORDER RODENTIA (~1700 species)
       • Rodents include a diversified group of burrowing, aquatic, & arboreal animals; Probably the most successful mammal order (>40% of mammals)
    2. ORDER CHIROPTERA (~875 species)
       • Bats, the only truly flying mammals, comprise the order Chiroptera; Probably the second most successful mammal order (>20% of mammals)
    3. ORDER INSECTIVORA (~400 species)
       • Insectivores are the oldest placental mammals & gave rise to many other placental orders; ~10% of mammal species
    4. ORDERS CREODONTA & CARNIVORA (~275 species)
       • Creodonts are extinct (in the Pliocene) carnivorous mammals similar to weasels
         • Creodonts were the dominant carnivores during the Paleocene & Eocene
       • Carnivores evolved from creodonts in the Paleocene
         • 2 suborders - Fissipeds ( bear, raccoon, weasel, hyena, dog & cat ); & Pinnipeds ( seal, sea lion & walrus)
    5. ORDERS CONDYLARTHA, ARTIODACTYLA (~180 species), PERISSODACTYLA (~16 species) & PROBOSCIDEA (~2 species) - Ungulate (hoofedherbivores) Orders
       • Condylarths are the earliest ungulates; became extinct in the Eocene
         • Condylarth gave rise during the Early Cenozoic to the other ungulate orders
       • Perissodactlys are odd-toed ungulates (include horses, rhinoceri & tapirs)
         • extinct families are chalicotheres (have claws instead of hoofs) & titanotheres
         • horses evolved from smaller forms by progressive increases in body, tooth & brain size & leg length during the Eocene through the Oligocene, as did rhinoceri, chalicotheres & titanotheres
         • with the diversification of grasses in the Miocene, horse evolution becomes more complicated
         • the largest land mammal ever, 5 m tall at the shoulder, was the Oligocene to early Miocene hornless rhinoceros Baluchitherium
         • Perissodactyls were the dominant ungulates during the Eocene
       • Artiodactyls are even-toed ungulates (include pigs, hippos, deer, goats, sheep, cows & camels)
         • artiodactyls are divided into 3 major suborders - Suina which includes pigs & hippos; Tylopoda which includes camels; & Ruminantia which includes deer, giraffes, sheep & cows
         • Artiodactyls have been the dominant ungulates since the Oligocene
       • Proboscideans are ungulates with trunks (include elephants & extinct mastadons & mammoths)
    6. ORDER PRIMATES (~175 species) - see below
    7. ORDER CETACEA (~80 species)
       • Cetaceans include whales & porpoises
    8. ORDER LAGOMORPHA (~65 species)
       • Lagomorphs include rabbits & hares
  • MINOR ORDERS:
    1. ORDER EDENTATA (~30 species)
       • Edentates include armadillos, anteaters & tree sloths
         • extinct forms are glyptodonts & ground sloths (skeleton in Science Library)
    2. ORDERS DERMOPTERA (flying lemurs), PHOLIDOTA (scaly anteaters), TUBULIDENTATA (Aardvarks), SIRENIA (Manatees), HYRACOIDEA (Hyrax)
  • ORDER PRIMATES (~175 species)
    • Primates include humans, as well as apes, monkeys, tarsiers, lorises & lemurs
    • Primates are divided into 2 suborders - Prosimii which includes tarsiers, lorises & lemurs; & Anthropoidea which includes humans, apes & monkeys
    • Prosimians dominated the Early Cenozoic (Paleocene & Eocene)
      • formerly widespread, now found only in tropical regions surrounding Indian Ocean
    • Anthropoids dominated the Late Cenozoic (Oligocene & Neogene)
      • response to cooler & drierr climate as Antarcticaa becomes glaciated
      • new World monkeys (Family Ceboidea) are found in Central & South America
      • old World monkeys (Family Cercopithecoidea) are found in Africa, India & Asia
      • apes (Superfamily Hominoidea, Family Pongidae) are found in Africa (chimpanzee, gorilla) & Southeast Asia (orangutan, gibbon)
    • Humans (Superfamily Hominoidea, Family Hominidae) are the most numerous & widespread primate
      • hominids evolved from ape-like ancestors in Africa about 5 my ago (following the drying out of the Mediterrranean)
      • 2 genera (Australopithecus, Homo) & 7 species (A. ramidus, A. afarensis, A. africanus, A. robustus, H. habilis, H. erectus & H. sapiens) of hominids have existed, with archaic H. sapiens (specifically H. sapiens neanderthalensis) evolving ~300,000 years ago & modern H. sapiens (H. sapiens sapiens) evolving ~50,000 years ago

CENOZOIC MASS EXTINCTIONS

1. TWO CENOZOIC MASS EXTINCTIONS
   • Eocene
     • Marked by a decrease in diversity of marine plankton & Oligocene-Miocene adaptive radiations of mammals
   • Pleistocene
     • Marked by EXTINCTION OF LARGE MAMMALS
2. CAUSES
   • Eocene
     • climate change
       • First glacial ice in Antarctica
       • Sealevel low
       • Drier & colder conditions
     • extraterrestrial - Planet X & the Companion Star Nemesis
   • Pleistocene
     • climate change
       • Climate warmed as ice melted; Problem is that it had done this many times before
     • human overkill
     • probably a combination

    

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