Pequeninos

Pequeninos are a small pig-like people, they are often simply referred to as Piggies by humans. They have complex biology that has caused some conflict with the human race.

Reproduction and Sexual Dimorphism
The piggies' life cycle and reproduction is strange enough that it really deserves to be explained in full detail. Both sexes start out small and grublike, but the dimorphism starts quickly. The males develop into the pig-like form that the humans in the story first assume were the only form, but will develop into enormous trees upon death and retain their sentience upon  being ritually vivisected.

The females, on the other hand, almost all stay small and grublike, and after a certain time are carried by the pig-like males to the trees, and are  impregnated by said trees  via pollen. Then, when the young they're carrying are ready to be born, they  eat their way out of their mother. In addition, the occasional female will develop into a pig-like form like the males to serve as a matriarch, and eventually also be vivisected to become a "mothertree", which holds all the young and nourishes them with its sap. "Bizarre sexual dimophism" doesn't even  begin  to cover it.