Some female mammals are larger than males, challenging the belief that male mammals are typically bigger. A study of over 400 mammalian species found that in 45% of species, males outweigh females, while in 39% both sexes are the same mass, and in 16% females are heavier. The findings suggest that assumptions about male size in mammals may be influenced by biases in scientific literature. The study highlights the need for more research into mating systems, reproductive strategies, and evolutionary forces shaping mammals. The findings are based on 5% of mammalian species and are not conclusive, but they demonstrate the significant variation in animal sizes.