Elephants have the longest gestation period of any mammal, lasting a staggering 22 months. Most mammals have 1 corpus luteum, a temporary endocrine structure that serves to regulate hormone levels during pregnancy. Elephants, on the other hand, can have as many as 11. From Science Mag:
In most mammals, one corpus luteum forms from a single egg follicle in the ovary during each menstrual cycle. The temporary gland produces progesterone, which in turn promotes thickening of the endometrium and, if an egg is fertilized, maintains the correct balance of hormones throughout a pregnancy to ensure that a female’s body remains geared toward supporting her growing baby. If fertilization doesn’t occur, the corpus luteum dies, only to reform during the next reproductive cycle. From dissected animals, scientists have known for more than 50 years that elephant ovaries contain multiple corpora lutea. But they didn’t know how these structures formed or what roles they played in elephant pregnancies. And they’d never studied the corpus lutea in real-time during an elephant’s life or pregnancy.
Researchers have now discovered that these remarkable creatures form, on average, 5 corpora lutea per menstrual cycle: one derived from an egg generating follicle (as was expected) and the rest forming from separate follicles throughout the menstrual cycle. While pregnancy in elephants is still not fully understood, scientists now theorize that by increasing the number of corpus lutea during pregnancy helps maintain hormone levels, allowing for the complex brain of an elephant to fully form during gestation.