Here’s a handy rule of thumb: the more teats, the bigger the litter.
And thus began one of my weirder journeys on the internet, all because the Britannica said this regarding the Bandicoot rat of India and Sri Lanka: “The litter size is probably large, since the female has 12 teats.”
Sadly, there are people who actually research this stuff (I mean, besides me). According to the scientist Avery Nelson Gilbert (http://bit.ly/1UQExYr), Aristotle first suggested this relationship between the mammary number and litter size. However, it has not been proven and is somewhat controversial among evolutionary biologists.
After studying rats, mice and squirrels, Gilbert’s conclusion? “Mean litter size is typically one-half the number of available mammaries, while maximum litter size approximates mammary number….Mammary number may have operated as a selective constraint on litter size over evolutionary time.”
To save you the embarrassment of examining your own pets, here are the numbers:
Teats Litter sizes
dogs, 8-12 2-8 (varies widely, with bigger dogs having bigger litters)
cats, 8 3-5.
Photo credit (from the actual photographer–check out his site!):