Isaac Magallanes

Hello everyone! For this forum post I wanted to discuss a recent paper by Isaac Magallanes (myself), James F. Parham, Gabriel-Philip Santos, and Jorge Velez-Juarbe (2018), published in the open access journal PeerJ.

The paper “A new tuskless walrus from the Miocene of Orange County, California, with comments on the diversity and taxonomy of odobenids” describes the new fossil walrus from Southern California. This specimen represents the most complete fossil walrus known to date and provides insights on the evolution of this enigmatic group.

If you don’t have time to read the full paper, here are the key details:

Who: Researchers from Cal State Fullerton, Los Angeles Museum of Natural History, and the Raymond M. Alf museum.

What: Description of a nearly complete male tusk-less fossil walrus

Where: Collected in Orange County, Southern California.

When: Late Miocene (6.6-5.8 Ma)

Why: Modern walruses are the sole extant member of a once more diverse lineage, the Southern California specimen offers an opportunity to better understand their evolution, diversity, and geographic distribution.

 You can also read the abstract provided by the authors:

“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.”

Open access link to paper:

https://peerj.com/articles/5708/

Article summary:

http://news.fullerton.edu/2018fa/walrus-fossil-research.aspx

Questions for discussions:

• What morphological similarities/differences between the modern walrus and fossil walruses were most interesting?
• The specimen described showed evidence of a healed injury on the left side of the skull. How do you think this could have happened?
• Stratigraphic uncertainty and a large amount of undescribed material play a significant role in reporting diversity and taxonomic richness. How do you think this problem affects not only this report but paleontology as a whole?