Biogeographic problem-solving reveals the Late Pleistocene translocation of a short-faced bear to the California Channel Islands

Alexis M Mychajliw,Courtney A Hofman,Nihan D Dagtas,Brendan J Culleton,Torben C Rick,Douglas J Kennett,Michael Buckley,Jon M Erlandson

doi:10.1038/s41598-020-71572-z

Abstract

An accurate understanding of biodiversity of the past is critical for contextualizing biodiversity patterns and trends in the present. Emerging techniques are refining our ability to decipher otherwise cryptic human-mediated species translocations across the Quaternary, yet these techniques are often used in isolation, rather than part of an interdisciplinary hypothesis-testing toolkit, limiting their scope and application. Here we illustrate the use of such an integrative approach and report the occurrence of North America’s largest terrestrial mammalian carnivore, the short-faced bear, Arctodus simus, from Daisy Cave (CA-SMI-261), an important early human occupation site on the California Channel Islands. We identified the specimen by corroborating morphological, protein, and mitogenomic lines of evidence, and evaluated the potential natural and anthropogenic mechanisms of its transport and deposition. While representing just a single specimen, our combination of techniques opened a window into the behavior of an enigmatic species, suggesting that A. simus was a wide-ranging scavenger utilizing terrestrial and marine carcasses. This discovery highlights the utility of bridging archaeological and paleontological datasets to disentangle complex biogeographic scenarios and reveal unexpected biodiversity for island systems worldwide.

Highlights

Islands have long been important places for evaluating fundamental ecological and evolutionary processes and are areas of significant conservation c oncern[1]
We report a new addition to the biodiversity register of Daisy Cave: a large metapodial recovered during excavations in 1993 (Fig. 2), which we identify as the short-faced bear, Arctodus simus (Carnivora: Ursidae: Tremarctinae14), based on morphology, ancient DNA, and collagen fingerprinting
We present four hypotheses to explain the presence of this megafaunal carnivore on the California’s Channel Islands (CCI) by either pre or post-mortem transport: (1) a population of A. simus existed on the CCI following dispersals during glacial lowstands; (2) a single A. simus individual dispersed to the CCI; (3) humans or 4) a bird of prey carried the metapodial from the mainland and deposited it in Daisy Cave

Summary

Introduction

Islands have long been important places for evaluating fundamental ecological and evolutionary processes and are areas of significant conservation c oncern[1]. Distinct geologic histories: the northern islands (Santa Rosa, San Miguel, Santa Cruz, Anacapa) were joined as a single superisland, Santarosae, as recently as 10,000 years ago, whereas the southern islands have always been more isolated[5,6] (Fig. 1) Given these dispersal filters and fluctuations in sea level, the CCI terrestrial faunal communities are depauperate compared to the nearby mainland, with a total of just 10 known extinct and extant terrestrial mammals[7]. We report a new addition to the biodiversity register of Daisy Cave: a large metapodial recovered during excavations in 1993 (Fig. 2), which we identify as the short-faced bear, Arctodus simus (Carnivora: Ursidae: Tremarctinae14), based on morphology, ancient DNA, and collagen fingerprinting (zooarchaeological mass spectrometry, ZooMS15) These data help address longstanding questions about the ecology and biogeography of this enigmatic carnivore south of Canada. We provide the first collagen stable isotope values for this

Methods

Discussion

Conclusion