A new tuskless walrus from the Miocene of Orange County, California, with comments on the diversity and taxonomy of odobenids

Isaac Magallanes; James F Parham; Gabriel-Philip Santos; Jorge Velez-Juarbe

doi:10.7717/peerj.5708

A new tuskless walrus from the Miocene of Orange County, California, with comments on the diversity and taxonomy of odobenids

PeerJ. 2018 Oct 12:6:e5708. doi: 10.7717/peerj.5708. eCollection 2018.

Authors

Isaac Magallanes^#^{1

2}, James F Parham^#¹, Gabriel-Philip Santos³, Jorge Velez-Juarbe^{4

5}

Affiliations

¹ Department of Geological Sciences, California State University, Fullerton, Fullerton, CA, USA.
² Department of Geological Sciences, University of Florida, Gainesville, FL, USA.
³ Raymond M. Alf Museum of Paleontology, Claremont, CA, USA.
⁴ Department of Mammalogy, Natural History Museum of Los Angeles County, Los Angeles, CA, USA.
⁵ Department of Paleobiology, National Museum of Natural History, Washington, DC, USA.

^# Contributed equally.

Abstract

We describe Titanotaria orangensis (gen. et. sp. nov.), a new species of walrus (odobenid) from the upper Miocene Oso Member of the Capistrano Formation of Orange County, California. This species is important because: (1) It is one of the best-known and latest-surviving tuskless walruses; (2) It raises the number of reported odobenid taxa from the Oso Member to four species making it one of the richest walrus assemblages known (along with the basal Purisima of Northern California); (3) It is just the second record of a tuskless walrus from the same unit as a tusked taxon. Our phylogenetic analysis places T. orangensis as sister to a clade that includes Imagotaria downsi, Pontolis magnus, Dusignathus spp., Gomphotaria pugnax, and Odobeninae. We propose new branch-based phylogenetic definitions for Odobenidae, Odobeninae, and a new node-based name (Neodobenia) for the clade that includes Dusignathus spp., G. pugnax, and Odobeninae. A richness analysis at the 0.1 Ma level that incorporates stratigraphic uncertainty and ghost lineages demonstrates maximum peaks of richness (up to eight or nine coeval lineages) near the base of Odobenidae, Neodobenia, and Odobenini. A more conservative minimum curve demonstrates that standing richness may have been much lower than the maximum lineage richness estimates that are biased by stratigraphic uncertainty. Overall the odobenid fossil record is uneven, with large time slices of the record missing on either side of the Pacific Ocean at some times and biases from the preserved depositional environments at other times. We recognize a provisional timescale for the transition of East Pacific odobenid assemblages that include "basal odobenids" (stem neodobenians) from the Empire and older formations (>7 Ma), to a mixture of basal odobenids and neodobenians from the Capistrano and basal Purisima (7-5 Ma), and then just neodobenians from all younger units (<5 Ma). The large amount of undescribed material will add new taxa and range extensions for existing taxa, which will likely change some of the patterns we describe.

Keywords: Capistrano formation; Diversity; Miocene; Neodobenia; Odobenidae; Oso member; Pacific; Phylogeny; Tusks; Walrus.

Grants and funding

The Louis Stokes Alliance for Minority Participation (LSAMP) NSF Grant: HRD-0802628 provided crucial funding to the lead author (Magallanes) during the completion of his undergraduate research, making this study possible. This work was facilitated by a National Science Foundation grant for Collections in Support of Biological Research (NSF grant #CSBR-1349430, Parham PI). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.