The largest among the smallest: the body mass of the giant rodent Josephoartigasia monesi

摘要

Body mass in extant rodents covers more than four orders of magnitude, from a few grams up to 40 kg on average in the capybara (Hydrochaeris hydrochaeris; Silva & Downing 1995). However, rodents have been much bigger in the past. The South American fossil rodent, Phoberomys pattersoni (Sanchez-Villagra et al. 2003), found in northwestern Venezuela (Mones 1980; Horovitz et al. 2006) had an estimated body mass of 436–741 kg (Sanchez-Villagra et al. 2003). Most recently, Rinderknecht & Blanco (2008, hereafter R&B 2008) described a giant fossil rodent from the Plio–Pleistocene of Uruguay. The new species Josephoartigasia monesi was estimated to have weighed 1211 kg on average, and perhaps as much as 2584 kg; a value well outside the range of size of any previously described rodent. However, a closer examination of R&B’s (2008) methods suggests that the body mass of J. monesi may have been overestimated.