They frequently live in large agrigations in close proximity, solitary ways of life are asociated with speciesliving in arid grasslands and desert areas. Rodent behavior is as highly adapable as their evolutionary genetics. At low populations individuals may be solitary with territories, but at high frequency they may fall into a socialistic hierarchy. Dominant individaual show confidence and are usually the oldest males inthe group. Higher ranking individauls in the hierarchy have higher testoseterone levels.
Visual cues play a large role in courtship in many species.
Although presently there are large numbers of living rodent individuals, there is only a sparse fossil record of the order. Rodent reamains as old as 58 million years have been found. Between 54 and 38 million years ago the rodents greatly diversified and leaping, running and burrowing forms arose. About 38 million years ago many of the families that live today bcame recognizabe. Two and a half MYA the Muidae family was the first and only family of the order to invade Austrailia.