The erethizontid fossil from the Uquia formation of Argentina should not be referred to the genus Erethizon

In 2007, Reguero et al. described a 2.5 Ma erethizontid dentary from the Uquia Formation in Argentina (MACN5376) and referred it to the genus Erethizon, a genus found at present only in North America. They based their generic identification on the presence in the fossil of a markedly inflected angular process. I argue in this commentary that this single trait (the angular process) in a single incomplete fossil is insufficient evidence for the Erethizon attribution, for the following reasons: 1. The trait (the inflected angular process) is variable in modern South and North American porcupines and observer bias and/or allometry may be responsible for observed differences; 2. Among fossil South American porcupines, the inflected angular process is not unique to the Uquian fossil: 3. The fossil possesses other traits (including one trait newly described in this paper) associated with modern South American (Coendou) porcupines and not modern Erethizon; and 4. The traits by which we recognize modern Erethizon, primarily related to the genus's ability to survive severe winters, are most readily explained by evolution driven by the South American porcupine immigrants' exposure in North America to that severe weather. The Uquian fossil is not Erethizon and should be attributed for the present to the genus Coendou. (C) 2011 Elsevier Ltd. All rights reserved.