New perspectives on lagomorph and rodent biochronology in the Anza-Borrego Desert of southern California, USA
Faunal compilations and biochronologies of the late Pliocene to early Pleistocene often include some or all of the Anza-Borrego Desert records of Lepus, Microtus with five closed triangles, Microtus meadensis, and Lasiopodomys, especially because they are among the oldest, if not the oldest, reported records for those taxa in North America. The purported Lepus specimens are represented by three partial dentaries with incomplete dentitions, each retaining the third premolar, one of which is incomplete. The arvicoline specimens include one edentulous dentary and three isolated lower first molars, one of which is incomplete. We provide a detailed review of background documentation and identify inaccuracies in taxonomic assignment, stratigraphic origin, and general curatorial documentation that affect the identity and reliability of the individual specimens and have important ramifications for Pliocene-Pleistocene biochronology. As a result of our review, we reassign all Lepus records to Leporinae, genus and species indeterminate. The specimen of Microtus with five closed triangles cannot be placed in a reliable stratigraphic context, and the edentulous jaw is diagnosable only to Arvicolinae, genus and species indeterminate. The locality that produced the Microtus meadensis specimen is stratigraphically higher and in a different section of the Anza-Borrego Desert than previously reported, lowering the age of the specimen by nearly a million years. We retain the Lasiopodomys designation although we are hesitant to accept 'Lasiopodomys' as a higher order taxon; the specimen is from reversed polarity sediments dating to between 1.77 and 1.07 Ma, making it the oldest reported specimen of the Lasiopodomys morphotype.
KEY WORDS: Vallecito Creek - Fish Creek; Microtus californicus?; Microtus (= Terricola) meadensis; Lasiopodomys morphotype; Lepus cf. callotis
PE Article Number:
Copyright: Society of
Vertebrate Paleontology November 2011
Submission: 15 June 2007. Acceptance: 27 March 2011