Backbone vs tail in mammals?

Factual Questions
1

Are humans the only mammals who do not have a tail? It seems to me just about every other animal on this planet has one, big or small.

Why do we not have tails?

2

Off the top of my head:

  • apes
  • bats
  • koalas (ok, they have one, but it’s nearly invisible)
  • echidnas
  • cetceans (dolphin and whale “tails” are modified feet)
  • manx cats
  • tenrecs
3

Bats,koalas,echidnas,cetceans, tenrecs,and even some manx cats have tails.

4

For the record, a “tail” is any extension of the vertebral column past the anus. Just in case anyone ever wondered about that.

Also, the tail is one of four unifying characters for all chordates. Which means, of course, that all vertebrates have one. In most cases, the loss of a tail (as in humans) is the the result of developmental changes, not genetics (that is, we still possess the genes to make tails, but their expression is controlled during development; indeed, at some point during development, human embryos have a very definite tail).

And, of course, we do still have “tail bones” - the coccyx - which is the remaining portion of that aspect of our chordate heritage.

5

Human beings also have a vestigial tail. You just don’t see it. Ever hear of the coccyx? It’s the part of the spine that extends beyond the sacrum.

6

Correction: the tail is an elongation of the body which extends past the anus. Seeing as how early chordates didn’t have vertebral columns, and all.