Question

Complete the following table comparing reproduction in different mammal groups

Trait     Prototherians    Metatherians Eutherians

example/representative

reproductive mode

length of gestation vs lactation

Answer 1

Complete table comparing reproduction in different mammal groups:

Trait

Prototherians

Example/representative Reproductive mode Length of gestation vs lactation

Monotremes (Prototheria) Platypus (subclass Prototheria) Echidna (subclass Prototheria) Example: Tachyglossus (spiny ant-eater), Ornithorthynchus (duckbill mole) Platypus possess 1-2 eggs Echidna possess 1 egg Egg-laying mammals Young’s are left in their pouches also called, abdominal groove No nipples No placenta present Monotremes have a cloaca Monotreme egg = 4 mm diameter Example: Platypus a. lays 1-2 eggs b. Incubation time ~ 12 days the egg remains in uterus for about 28 days development proceeds shell formed external incubation time ~10 days short gestation period For example in echidna, Gestation is about 22 to 23 days Lactation time ~ 3-4 months

    

Trait

Metatherians

Example/ representative Reproductive mode Length of gestation vs lactation

Marsupials Three American orders (Didelphimorphia, Paucituberculata, and Microbiotheria) Four Australasian orders (Notoryctemorphia, Dasyuromorphia, Peramelemorphia, and Diprotodontia) Example: kangaroos, wallabies, koalas Reproduce and give birth to live Partially developed youngs are reproduced Young possess nipples Young’s present in the pouch altricial young Marsupial egg size ~ 0.12 – 0.28 mm Extremely small sized young The simple placenta is present Short gestation (11 – 30 days) period of lactation (2–12 months)

Trait

Eutherians

Example/representative Reproductive mode Length of gestation vs lactation

Eutherian (Placental) Atlantogenata and Boreoeutheria (Magnorder) Examples: rodents (hamster, Mus), some carnivores Viviparous mammals young are reproduced are well developed young’s are not usually attached with nipples Placental egg = 0.07 – 0.15 mm Possess complex placenta Precocial and altricial young’s are produced Period of gestation varies among eutherians Depending on the size of the animal and conditions present during the birth The gestation period of the animals: golden hamster ~ 2 weeks blue whale ~ 11 months African elephant ~21 to 22 months Eutherians have relatively shortest period of lactation than all due to the fact that the young ones produced get fully developed inside the uterus