Category: Mammals
Dogs have been domesticated by man longer than other species: genetic evidence tells us that the modern domesticated dog diverged from its extinct Eurasian ancestor around 40,000 years ago! Over this large swath of time, dogs have arrived in their myriad modern forms through a combination of natural selection in feral populations and selective breeding by humans for a vast spectrum of physical, behavioral, and sensory traits. This variety of purpose and temperament can be observed in the multitude of “jobs” and roles dogs fill in human lives, from guardian and helper to guide for the blind – we have shaped their evolution and they have shaped ours.
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A 200 Million Year-old Iconoclast
If a defining trait of mammals is that they give live birth to their young, how do you explain monotremes? Monotremes are mammals that lay eggs like a reptile, rather than giving birth to live young. Living examples of these unusual animals can only be found in Australia and New Guinea today, though they used to be more widespread. A monotreme egg has less yolk for supplying nutrients than a reptile egg, and when a young echidna or platypus hatches, it is very tiny and less developed than its reptile counterpart. But monotreme babies are able to grow and thrive because their mothers stay with them, lactating to supply vital nutrients for their growth - just like other mammals!
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Discover Animals is a web-based educational resource offered by the NAIA
