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Mammals: Major Groups and Evolutionary Traits

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Terms in this set (20)

  • What are the two main clades of mammals?
    Monotremes (egg-laying) and Non-monotremes (live birth, includes marsupials and placentals).
  • How do monotremes reproduce?
    Monotremes lay eggs instead of giving live birth.
  • What distinguishes marsupials from placentals in reproduction?
    Marsupials have short pregnancies and most development occurs in a pouch; placentals have long pregnancies with a placenta for nutrient exchange.
  • Name the six most diverse groups of placental mammals.
    Rodents, bats, moles & shrews, primates, even-toed hoofed mammals, and carnivores.
  • Why are monotremes and marsupials often mistakenly called primitive?
    Because they have fewer species and unique reproductive traits, but they are equally evolved and adapted as placentals.
  • What are two shared derived characteristics that unite all mammals?
    Milk production (mammary glands) and hair.
  • What is the evolutionary origin of mammals?
    Mammals evolved from extinct mammal-reptile ancestors called synapsids.
  • How many extant species of monotremes exist and what are examples?
    Five species including the duck-billed platypus and four echidnas.
  • What is the formal name for non-monotreme mammals?
    Theria, which includes marsupials (Metatherians) and placentals (Eutherians).
  • When did monotremes split from other mammals?
    Approximately 170 million years ago.
  • When did marsupials and placentals diverge?
    Around 160 million years ago.
  • What major event occurred 66 million years ago affecting mammals?
    The extinction of non-avian dinosaurs, leading to an adaptive radiation of mammals.
  • What is adaptive radiation in the context of mammals?
    A rapid burst of speciation creating many diverse mammal lineages after dinosaur extinction.
  • Why is it misleading to call marsupials primitive?
    Their reproductive strategy is adaptive and successful in uncertain habitats, not a sign of being less evolved.
  • What ancestral traits do echidnas retain?
    Egg-laying and lack of nipples, but they have rapid growth rates and other derived traits.
  • What unique defense does the male platypus have?
    It can inject venom into rivals.
  • What is the problem with traditional taxonomic ranks in mammals?
    Ranks like order or family are not equivalent across groups, making comparisons misleading.
  • How many major clades of placental mammals evolved in the adaptive radiation?
    About 16 major clades.
  • Give examples of smaller placental mammal groups.
    Odd-toed hoofed mammals, sloths, elephants, manatees, rabbits, and cetaceans.
  • Are any extant mammals truly primitive?
    No, all living mammals have evolved and adapted; none represent ancestral primitive forms.