An update on the pygmy mammoths of Channel Islands National Park
You may remember our adorably undersized island elephant friends from last year. One of the things I mentioned was that a tusk had been recently found (October 2013) on Santa Rosa Island from a mammoth that lived around 80,000 years ago. This tusk is an important part of a new publication (Muhs et al. 2015).
One of the questions about the pygmy mammoths is when their forebears got out to the islands and started downsizing. As I wrote in the previous post, people once thought the mammoths hiked out there, but this idea has been laid to rest in favor of swimming mammoths. If you're familiar with the Pleistocene, you probably know that it wasn't all ice, all the time, everywhere; instead, ice sheets would advance and retreat, and they never got as far south as California. However, the expansion and retreat of ice causes sea level to fall and rise. Therefore, there were multiple times when the northern Channel Islands made a large landmass, and multiple times when they were separated like today. One of the interesting points of the October 2013 tusk and other recent finds is that they can be tied to an episode of relatively high sea level before the most recent glacial period, meaning mammoths either first got there when the sea level was comparable to the present and the islands had similar shorelines to the present, or during an earlier glacial period and an earlier super-island. Another interesting implication is that the mammoths could live on the northern Channel Islands without there having to be a larger landmass. This means that climate change and loss of habitat are not necessarily sufficient to have done them in during the most recent post-glacial period (the one in which we're living), if these factors couldn't do them in during this older warm period. The door remains open for human agency, and as was mentioned in the previous post, Santa Rosa Island also has about the most ancient human remains in the Western Hemisphere, at about 13,000 years old.
|This series of photos of the tusk as it was found comes from the Channel Islands NP Facebook page.|
From a place that has mammoths to a place named Mammoth...
If you think of a cave, what's one of the first kind of animals you put in that cave? Bats, right? And what do bats put in caves? (Don't think too hard here. It's not like they can carry anything all that big.) Well, bat guano, of course. Mammoth Cave National Park is no stranger to bats and their very special sedimentary layers. (Incidentally, bat leavings are not the only form of excrement that can make thick deposits. In the drier West, caves have been found with layers of sloth or mammoth dung, and packrat middens count for a certain value of excrement.) The guano at Mammoth Cave was even mined at one point to produce saltpeter. Nowadays, we can mine guano for information on past local environments, as described in Widga and Colburn (2015).
The guano deposits at Mammoth Cave range in age from the recent past to an undetermined time in the late Pleistocene, exceeding the limits of radiocarbon dating (about 54,000 years at this time) at the oldest. Several areas were selected for the current study, including points in the Historic Section, Historic Lantern Tour, Gothic Avenue, Cleveland Avenue, Frozen Niagara, and Great Onyx Cave. The guano produced a variety of bones as well as bat hair and abundant fragments of insects, and archeological material in the upper bat-strata; the hair and insect bits were used for chemical analysis. Not surprisingly, the bones were mostly from expired bats. Although the paleontologists did not find any extinct species, the most abundant identifiable bat in the oldest layers was Tadarida brasiliensis, the Mexican free-tailed bat, which has pulled up stakes since the late Pleistocene and moved south to about the southern Tennessee state line. Evidently, T. brasiliensis was using the cave as a maternity roost, probably during a warm period between glaciations. Several other insectivorous bats of a variety of sizes and flight capabilities also occupied the cave during this time, with a variety of habitat preferences, suggesting both open grasslands and more closed forests in the vicinity. A limited fauna of reptiles, birds, and non-bat mammals has been found in the youngest, culturally associated layers (about 5,500 years ago to the present), but the only other identifiable vertebrate remains in the old layers are a handful of weasel, deer mouse, and packrat bones.
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.
Widga, C., and M. Colburn. 2015. Paleontology and paleoecology of guano deposits in Mammoth Cave, Kentucky, USA. Quaternary Research 83:427–436.