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Mammal Ancestors

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Laying An Egg
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Laying An Egg

This is a member of the mammalian order Monotremata, the smallest order of mammals with only 5 species. It's an Echidna commonly known as a spiny ant eater.

You're A Mammal That Lays Eggs?

If comedians have a favorite animal, it is quite likely the platypus (Ornithorhynchus anatinus). Playtpus are mammals that lay eggs, have a duck-like bill and fight with poisonous barbs. That's a lot of material for a comedian to work with! For scientists, the platypus represents a bit more than foil for a comedic schtick. They represent an opportunity to observe an adaptive path that most mammals did not take, and as such represent a valuable comparison point for theories about how mammals developed into large organisms which dominate the planet in many ways. They are also members of the smallest mammalian order (Monotremata) which has only 5 species and 3 genera, the platypus and 4 species of Echidna in two genera. Find out here about how scientists are studying the population structure of the platypus, and why we may be on the road to having more species of monotremes.

Extension Investigation

Use the resources below to answer the following questions:

  1. Where are platypuses (Ornithorhynchus anatinus) found? Be as specific as you can. What sorts of biomes do they occupy?
  2. What physical factors may be leading to speciation in the platypus? What pattern of physical differences do you see in the platypus throughout its range?
  3. Does this difference support the idea that allele (different versions of genes) frequency is changing within the playpus's range?
  4. What danger can playpuses present to humans? Are they unique among mammals in this trait?
  5. What part of the playpus do scientists collect DNA from? Do you think this is harmful to the animals? Why do you think scientists chose this technique?
  6. What is unique about platypuses sex chromosomes? Can you think of any situation where this would be beneficial to the platypuses?
  7. Where are monotremes found other than Australia?

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