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Mammals: Major Groups and Evolutionary Traits

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Termini in questo insieme (20)

  • What are the two main clades of mammals?

    Monotremes (egg-laying mammals) and Non-monotremes (live-bearing mammals, also called Theria).

  • What reproductive methods distinguish monotremes, marsupials, and placentals?

    Monotremes lay eggs; marsupials have short pregnancies and develop young in a pouch; placentals have long pregnancies with a placenta for nutrient exchange.

  • How many extant species of monotremes exist and where are they found?

    There are 5 extant species of monotremes, including the platypus and 4 echidna species, found in Australia and New Guinea.

  • Why are monotremes and marsupials often mistakenly called primitive mammals?

    Because they have fewer species and retain some ancestral traits, but they have been evolving separately for over 100 million years and are not primitive.

  • Name the six most diverse groups of placental mammals.

    Rodents, bats, moles & shrews, primates, even-toed hoofed mammals, and carnivores.

  • What are the two shared derived characteristics that unite all mammals?

    Milk production (mammary glands) and hair.

  • What is the significance of the placenta in placental mammals?

    The placenta allows diffusion of materials from the mother's blood to the embryo's blood, enabling longer development inside the uterus.

  • What is the evolutionary relationship between marsupials and placentals?

    They split from a common ancestor about 160 million years ago and have been evolving separately since then.

  • What is an example of a retained ancestral characteristic in echidnas?

    Echidnas retain egg-laying, an ancestral trait shared with early mammals.

  • Why do platypus and echidnas not represent primitive ancestral mammals?

    They have many recently derived traits and have evolved uniquely for their environments despite retaining some ancestral features.

  • What is the approximate time of divergence between monotremes and other mammals?

    About 170 million years ago.

  • What is the term for the group that includes marsupials and placentals?

    Theria, the non-monotreme live-bearing mammals.

  • How many species are in the marsupial group approximately?

    About 350 species including kangaroos, koalas, and opossums.

  • What is the adaptive significance of marsupial development in a pouch?

    It may be adaptive in uncertain habitats, allowing flexible development outside the uterus.

  • What is a unique defense trait of the male platypus?

    Male platypuses can inject rivals with venom.

  • What is the problem with traditional taxonomic ranks like 'order' when applied to mammals?

    Ranks are not equivalent across groups; for example, monotremes as an order are not equivalent to the many orders within non-monotremes.

  • List some smaller groups of placental mammals besides the six major ones.

    Odd-toed hoofed mammals, sloths, elephants, manatees, rabbits, and cetaceans (whales and dolphins).

  • What is the significance of the extinction event 66 million years ago for mammals?

    The extinction of non-avian dinosaurs allowed a burst of mammal speciation and adaptive radiation.

  • Are humans considered primitive mammals?

    No, humans are placental mammals and not the pinnacle or primitive form of evolution.

  • How many groups of primates are listed on the board in the study materials?

    Four groups: Old World monkeys, apes, New World monkeys, and lemurs.