Evolution and systematics

The Echimyidae is one of the families of rodents with an evolutionary center in South America, and members of the family are still actively speciating in several genera (especially Proechimys). Four genera formerly present in the West Indies became extinct by the nineteenth century. The family shows remarkable convergent evolution with other rodent lineages, including a giant spiny rat (Chaetomys) that so closely resembles a porcupine that zoologists classified it with porcupines for many years until its true affinities were recognized. One of the most abundant and successful families of Neotropical mammals, virtually every type of lowland habitat has at least one echimyid species in it, and many have more than six. Though the least specialized echimyid genera (such as Proechimys and Hoplomys) have spines, the evolutionary trend within this family is to lose these. Thus, the more advanced and specialized genera lack spines in their fur. Fossil echimyids are known from the late Oligocene to Miocene and Pleistocene to recent. Several fossil forms reached considerable size. The family is closely related to the Capromyidae (Hutias) by the now-extinct Heteropsomyinids, the Caribbean spiny rats.

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