180mya Monotremes

PLATYPUS, ECHIDNA.

The monotremes are one of the three main mammalian groups along with placentals (Eutheria) and marsupials (Metatheria). They consititute only a few genera: Platypus, Short-beaked Echidna and Long-beaked echidna. They are mammals and have typical mammalian features such as warm-bloodedness, hair and milk production. But they resemble reptiles and birds in their possession of the cloaca and their egg-laying mode of reproduction.  The name monotreme derives from the Greek words monós ('single') and trêma ('hole'), referring to the cloaca.

Monotremes are typified by structural differences in their brains, jaws, digestive tract, reproductive tract, and other body parts compared to the more common mammalian types. In addition, they lay eggs rather than bearing live young, but, like all mammals, the female monotremes nurse their young with milk.

The platypus has exactly the same time to evolve as the rest of mammals. In fact, it has evolved a highly developed form of electroreception served by 40,000 electric sensors, and 60,000 mechanical push rods, both on its large bill to aid it in search of crustaceans in the mud. In human, the brain dedicates disproportionally large amount of cells to the two hands as illustrated by the Penfield brain map, or Penfield homunculus. When the same somatotopic map is drawn for platypus brain, the bill is served by equally prominent percentage of the brain.