GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 38-15
Presentation Time: 9:00 AM-5:30 PM


NORIEGA, Nicolas L.1, PITCHER, Ellie1, COHEN, Joshua E.2, MORADO, Melissa2, YAGER, Anna2, LINDSEY, Emily3, MEACHEN, Julie4, O'KEEFE, F. Robin5, DESANTIS, Larisa R.G.6 and BINDER, Wendy J.2, (1)Biology Department, Loyola Marymount University, 1 LMU Drive, Los Angeles, CA 90045, (2)Department of Biology, Loyola Marymount University, 1 Loyola Maryomount University Dr, Los Angeles, CA 90045, (3)La Brea Tar Pits and Museum, 5801 Wilshire Blvd., Los Angeles, CA 90036, (4)Anatomy Department, Des Moines University, Des Moines, IA 50312, (5)Department of Biology, Marshall University, Huntington, WV 25755, (6)Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235

Rancho La Brea (RLB) is an asphaltic fossil site and represents a unique window into the latest Pleistocene and megafauna extinction in North America. In order to understand the dynamics of the extinction, the taphonomic history of RLB must be understood. However, this history has only been described from one deposit: Pit 91. Pit 91 is one of the oldest deposits at RLB, approximately 45–26 Ka during the last glacial period, leaving a key gap in our knowledge of RLB through the interglacial transition into the Holocene. Here, we quantified taphonomic variables for mammalian megafauna between four deposits - pits 91, 13, 3, and 61/67 - ranging in age from approximately 45–11 Ka. Taphonomic variables included: minimum number of individuals (MNI), ontogeny, pit wear (a taphonomic feature caused by bone on bone contact in asphalt deposits), weathering, and abrasion. Relative abundance (MNI) of megafauna varied between Pit 13 and all other pits with relatively greater proportions of canids in Pit 13. Proportion of juveniles varied by taxa, with herbivores 43–75% juveniles and carnivores 18–25% juveniles. The amount of juveniles at RLB reflects modern carnivore and ungulate mortality rates due to the attritional nature of these deposits. Pit wear frequencies varied substantially by pit with 68% of specimens in Pit 13 exhibiting pit wear, 22% in Pit 3 and less than 10% in pits 61/67 and 91. The high frequency of pit wear in Pit 13 may be due to the dense concentration of the deposit. Pits 13, 3, and 61/67 followed similar distributions for both weathering and abrasion stages, in which the majority of specimens exhibited little to no weathering and abrasion. In contrast, a greater percentage of specimens from Pit 91 exhibited some weathering, which indicates slower burial. Additionally, Pit 91 specimens were more heavily abraded, suggesting increased fluvial action compared to the other pits. Overall, pits 13, 3, and 61/67 were similar in weathering and abrasion, while pits 91, 3, and 61/67 had similar relative abundances. Despite these similarities, the taphonomic history of Pit 91 is not representative of all pits at RLB, suggesting that analysis of multiple pits is necessary to better understand the transition into the Holocene at RLB.