A couple of new publications concerning mammoths in National Park Service units have crossed my desk recently, so it seemed like a good opportunity to say a few further words on behalf of extinct proboscideans in the National Parks. I present to you first the finely wrought map below, which shows the various parks where body fossils of mammoths, mastodons, and their friends have been reported. At press time, there were 37 parks, monuments, and so forth with confirmed records, and another six with possible records (cases where the locality is not clear). This map has the novelty of differently colored and shaped symbols, which aside from providing a splash of color, show a preponderance of mastodons in the northeast and mammoths in the southwest. I've relied on the literature and such, so there's definitely the chance that some of the "mammoths" are mastodons, and vice-versa. Most of these records are from the Pleistocene, but there are a few that are older; notably, John Day Fossil Beds National Monument and Niobrara National Scenic River have both gomphotheres and mastodons of pre-Pleistocene age. The great majority of the mammoth reports in the lower 48 are likely Columbian mammoths, Mammuthus columbi (M. exilis of Channel Islands National Park being a notable exception), but given the ambiguities in North American mammoth taxonomy, I figured it wasn't worth the time to try to split them up.
Item 1: Pigati et al. (in press) on Channel Islands National Park mammoths
When we last checked in on the pygmy mammoths, Muhs et al. (2015) had just published on the oldest reliably dated example, a tusk from Santa Rosa Island belonging to an animal that lived about 80,000 years ago. In a complementary vein, Pigati et al. (in press) have written on the importance of rigorous collection of geologic data in regard to dating and interpreting Channel Islands mammoth fossils, using two examples from San Miguel Island. The major issue is that although there is a large sample of mammoth bones from the islands, and close to three dozen radiocarbon dates on specimens in the literature, there is virtually nothing on the geologic context of these specimens. Muhs et al. (2015) is a notable exception, although uranium-thorium series dates on corals were used rather than radiocarbon due to age (radiocarbon as a system is only good for a few tens of thousands of
years, whereas U-Th is good for a few hundred thousand years). This lack of data presents a problem if you want to say anything about your fossils other than you found them. Pigati et al. use their San Miguel Island specimens as case studies for reporting geologic context. Speaking of context and interpretation...
Item 2. Wiest et al. (2016) on the taphonomy of Waco Mammoth National Monument
As discussed in my introductory post, the classic interpretation of the Waco Mammoth Site is as a mass death from flooding. Wiest et al. (2016) challenge this interpretation on the grounds of trace fossils. Specifically, they found diverse traces on numerous bones representing the activities of beetles, rodents, carnivores, and roots. The presence of these traces implies that dead mammoths were exposed for some significant amount of time, as opposed to live mammoths being overtaken in a flash flood and quickly buried. Wiest et al. propose that the main accumulation of bones resulted from a group of mammoths dying around a shrinking water hole during a drought. The presence of articulated specimens is explained as there simply being too many dead mammoths for scavengers to destroy them all. The authors propose further testing of their interpretation using isotopes in the mammoths' teeth: evaporation concentrates certain isotopes in water, which should in turn show up in the teeth. If Wiest et al. are correct, the mammoths have "traded" a quick death from flooding for a slow death from drought.
Muhs, D. R., K. R. Simmons, L. T. Groves, J. P. McGeehin, R. R.
Schumann, and L. D. Agenbroad. 2015. Late Quaternary sea-level history
and the antiquity of mammoths (Mammuthus exilis and Mammuthus columbi), Channel Islands National Park, California, USA. Quaternary Research 83(3):502–521.
Pigati, J. S., D. R. Muhs, and J. P. McGeehin. In press. On the importance of stratigraphic control for vertebrate fossil sites in Channel Islands National Park, California, USA: examples from new Mammuthus finds on San Miguel Island. Quaternary International in press.
Wiest, L. A., D. Esker, and S. G. Driese. 2016. The Waco Mammoth National Monument may represent a diminished watering-hole scenario based on preliminary evidence of post-mortem scavenging. Palaios 31:592–606.