More interesting than whether the whole mammalian class has some gender-based size bias (honestly, who cares) is how such common knowledge is, as frequently, wrong. Well, most likely wrong. I would have liked more on the #statistics.
An analysis of 429 mammalian species published in Nature Communications reveals that just 45 percent feature males that are larger than females. Nearly an equal number of species, 39 percent, have sexes that are about the same size. And in 16 percent of species, females are larger than males.
Most past studies that compared male and female size, Tombak found, only considered the average body mass for each of the sexes. The authors then drew conclusions based on whatever cutoff they set for determining if there was a difference. “It was just arbitrary,” Tombak says. Virtually all of these papers reinforced Darwin’s view that males are larger than females in mammalian species.
Tombak and her colleagues started filling in the gaps by conducting a thorough literature review, oftentimes turning to “obscure” papers published decades ago, she says. They were looking for not just averages pertaining to the sexes’ sizes but also measures of variance around the mean so they could apply statistical tests to determine whether a species truly seemed to be dimorphic.
https://www.scientificamerican.com/article/males-arent-larger-than-females-in-most-mammal-species/
