Table 2.

Shared reproductive features of menstruating mammals

Group	Spontaneous decidualization?	Type of placentation	Timing of mating	Ovulation (spontaneous or induced?)	Offspring
Higher primates (monkeys, apes, and humans)	Yes	Invasive (hemochorial), more so than in non-menstruating primates	Extended mating, not restricted to periovulatory period	Spontaneous	Usually 1 well-developed offspring/pregnancy
Bats (4 species)	Yes, at least 1 of 4 species	Invasive (hemochorial)	At least 1 species has extended mating, not restricted to periovulatory period	Spontaneous	Usually 1 well-developed offspring/pregnancy
Elephant shrew	Yes	Invasive (hemochorial)	Mating occurs over an extended period because ovulation lasts many days with over 100 eggs released	Spontaneous	Usually 2 well-developed offspring/pregnancy; only 3 pregnancies/lifetime