(class Mammalia, subclass Prototheria)
An extinct order of primitive mammals, known only from teeth found in Late Jurassic rocks. Their brains may have been larger than those of reptiles; probably their young were fed with milk; possibly they were homoiotherms; and perhaps they were insectivorous, arboreal, and nocturnal. They were about the size of, and must have resembled, shrews.
Subjects: Zoology and Animal Sciences.