REVISITING IRVINGTON, TYPE FAUNA OF THE IRVINGTONIAN NORTH AMERICAN LAND MAMMAL AGE

Although it is the type fauna of the Irvingtonian North American Land Mammal Age (NALMA), Irvington is not well documented in the peer-reviewed literature. Vertebrate remains discovered in fluvial deposits of gravel quarries at three locations in the Irvington District of Fremont, California were brought to the attention of the University of California Museum of Paleontology (UCMP) in 1936. Stirton (1939) reported five taxa from UCMP localities V3602, V3604, V3605, including a new antilocaprid (Tetrameryx irvingtonensis). Following additional fossil collecting at Irvington by teacher Wes Gordon and his band of “Boy Paleontologists”, Savage (1951) provided what remains the most thorough published account of the fauna, reporting 24 taxa (2 fish, 2 amphibians, 1 reptile, 1 bird, 18 mammals). Based on the fauna, Savage (1951) established the Irvingtonian NALMA. Further excavations during the 1950s and 1960s yielded significant remains which Firby (1968) described for her thesis, but never published. Firby (1968) more than doubled the Irvington fauna reported by Savage (1951), recognizing 54 taxa (5 mollusks, 4 fish, 4 amphibians, 3 reptiles, 8 birds, 30 mammals). Major excavations at Irvington ended in the 1960s following construction of State Route 680 through the gravel quarries. Age of the Irvington fauna and associated “Irvington Gravels” is not well constrained. Lindsay et al. (1975) determined that the fossil bearing strata are reversely magnetized. Coupled with biostratigraphy, the age of Irvington is typically inferred to be within the upper Matuyama magnetic polarity chron (i.e. greater than .78 Ma), however, maximum age of the fauna is unresolved. Bell and Bever (2006) note that consideration also must be given to the possibility that the fauna may be older than 1.21 Ma. Lack of fine-grained sedimentary exposures in the area at present prevents further evaluation of the site magnetostratigraphy. Apart from a paper by Rich (1977) reporting Neophrontops americanus from the site and a study of Microtus by Bell and Bever (2006), Irvington has received little attention from researchers in recent decades. In addition to the unpublished portion of the Irvington collection at the UCMP, the Math/Science Nucleus and Ohlone College in Fremont, California also have unstudied collections of Irvington specimens.