Mammals

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Biological diversity - mammals

  • subphylum Vertebrata: class Mammalia
  • provide young - milk via mammary glands
  • mammal skin = highly glandular
  • mammary glands - simple secretory glands - monotreme mammary patch - more complex breasts
  • presence - monotremes - early evolution 
  • skin covered - hair/fur
  • hairs = multiple intertwined filaments - keratin
  • hair keratin unique - mammals (recently found - Anole lizard claws)
  • endothermy
  • importance - insulating layer - naked mole rat = moderate body temperature via behavioural regulation+microhabitiat selection (inefficient endotherms not ectotherms)
  • proportionally larger brains
  • increased metabolic rates, better memory, social behaviour
  • modifications - skull structure
  • bony palate
  • inner ear bones
  • subphylum Vertebrata: class Synapsida
  • mammalian origins. divergence - modern mammals early - amniotes. 320 mya
  • classified - synapsid skull
  • early synapsid pelycosaurs (+Dimetrodon)
  • mammal like reptiles: the Therapsids (lion/dog size carnivores) - derived palate, ear bones+heterodonty
  • class Synapsidae: order Therapsidae
  • mammalian origins - late Permian (260 mya): diverse Cynodonts - fossil record 
  • derived palate, ear bones, heterodonty, structures skull - endothermy (blood vessel density+turbinal bones)
  • laid eggs - burrows
  • subphylum Vertebrata: class Mammalia
  • 1st true mammals - generic, small shrew like creatures - survived age - dinosaurs - nocturnal
  • ACTUALLY great diversity concurrent - dinosaurs
  • 2 subclasses, 6000 species 
  • Prototheria (Monotremes: echidna+platypus, 5 species)
  • Theria (2 infraclasses)
    • Metatheria (Marsupials, 300 species, 7 orders) - koalas, kangaroos, quolls, wombats, numbat
  • characterised - maintaining offspring - pouch (born very early stages - development) (decreased gestation, increased lactation)
  • 2 subclasses, 6000 species 
    • Prototheria (Monotremes: echidna+platypus, 6 species)
    • Theria (2 infraclasses)
      • Metatheria (Marsupials, 300 species, 7 orders)
      • Eutheria (Placentals, 5000+ species, 26 orders)
  • class Mammalia: infraclass Eutheria
  • 4 superorders
    • Xenarthia (anteaters, sloths, armadillos)
    • Afrotheria (tenrecs, elephant shrews, hyraxes, elephants)
    • Laurasiatheria (shrews, bats, ungulates, carnivores)
    • Euarchontoglires (rodents, lagomorphs, tree shrews, primates)
  • placental mammals
  • diverse - share reproductive strategies: long internal gestation period vs lactation 
  • embryo retained - uterus
  • external shape = lost+embryo maintained - amniotic sac, nourished via elaborated extra embryonic membranes (placenta)
  • marsupials vs placentals
  • Eutherian diversity outstrips marsupial diversity. not - marsupials don't compete well - same resources
  • Australia - occupy similar range - ecological niches - placentals not highly specialised 
  • constraints - reproductive mode - marsupials
  • modern phylogeny 
  • taxonomy - placentals - long been contentious
  • convergent evolution - distantly related groups leads - similar body forms
  • morphology grouped shrews+elephant shrews - class…

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