Relationships of <i>Megaoryzomys curioi</i>, an Extinct Cricetine Rodent (Muroidea: Muridae) from the Galápagos Islands, Ecuador

Abstract

<i>Megaoryzomys curioi</i> is a thomasomyine, not an oryzomyine as previously believed. This rodent was originally described, from three bony fragments found in a cave on Isla Santa Cruz, Galápagos, as a new species of the Antillean oryzomyine genus <i>Megalomys</i>. The genus <i>Megaoryzomys</i> was named recently for this species, based on new material from Isla Santa Cruz. Our study of additional material indicates that <i>Megaoryzomys curioi</i> is not closely related to <i>Oryzomys</i> but is most similar to large species of <i>Thomasomys</i>, a genus confined to mainland South America. The Galápagos have been colonized by cricetine rodents at least three times, once by a thomasomyine and twice by oryzomyines. Of these colonists, <i>Megaoryzomys curioi</i> is the most divergent from mainland relatives and thus is probably derived from the earliest immigrant. Although the time of extinction of <i>Megaoryzomys curioi</i> has not been determined, and it has never been recorded from life, it probably survived into historic time.