MULTITUBERCULATE

any member of an extinct group of small, superficially rodentlike mammals that existed from the Late Jurassic Epoch (about 163 to 144 million years ago) of the Mesozoic Era through the early part of the Cenozoic Era (the last 66.4 million years of Earth history). During most of this span, they were by far the most abundant mammals, but relatively little evolutionary diversification occurred throughout their long history. These herbivores were usually the size of mice, though the largest approached beaver size. The distinguishing fossil characteristic of multituberculates was their molar teeth, which had 2 or 3 longitudinal rows of cusps, 5 or 6 cusps in primitive forms, and up to 30 in advanced genera. They had a single pair of long lower incisors and possibly one to three pairs of upper incisors. In most genera the anterior lower premolars were large shearing teeth. The multituberculates are not closely related to any other mammals. They apparently arose from the mammallike reptiles and did not give rise to any other types.