Mammals

Ceratotherium simum simum or Southern White Rhino

At the Phoenix zoo

Asian elephant or Elephas Maximus

At the Phoenix zoo

Possibly Papio hamadryas or Baboon female

Phoenix zoo

Possibly Papio hamadryas or Baboon female

It used to be theorized that female Baboons with bigger redder bottoms was a signal for mating. However new findings suggests that bottom swelling isn't a reliable indicator of evolutionary fitness, the researchers said.

The bigger-bottomed baboons didn't attract more males, either, the researchers report in the June issue of the journal Animal Behaviour. Rather, males really seemed to go for females that had gone through more ovulatory cycles since their last pregnancy. Like humans, baboons are not as fertile while nursing infants, so it might behoove males to wait a few cycles to mate.