Aplacentals

Aplacentals are a infraclass of placental mammals that are characterized by the absence of a placenta during gestation. This group includes a diverse range of mammals, such as marsupials and monotremes, which reproduce differently than other placental mammals. Marsupials, like kangaroos and koalas, give birth to underdeveloped young that complete their development in a pouch. Monotremes, like the platypus and echidna, are even more distinct as they lay eggs.

The evolutionary history of aplacentals is significant, as they represent an earlier divergence within the mammalian lineage compared to the eutherians, which possess a true placenta. This fundamental difference in reproductive strategy has led to unique adaptations in their physiology and life cycles. While they share many mammalian traits like fur, milk production, and being warm-blooded, their reproductive methods set them apart as a distinct infraclass. Studying aplacentals provides valuable insights into the early evolution of mammals and the diversity of reproductive strategies that have arisen within the class. Their phylogenetic position helps scientists understand the relationships between different mammal groups and the evolutionary pressures that have shaped mammalian diversity.