Complex sentence: Cimolestans had a wide variety of body shapes, dentition and livestyles, though the majority of them were small to medium sized general mammals that bore superficial resemblances to rodents, weasels or opossums.
Split into simpler sentences: Cimolestans had a wide variety of body shapes, dentition and livestyles. The majority of them bore superficial resemblances to rodents, weasels or opossums.