Ice Age Salamanders in the Dry West
The scientists of the Mammoth Site include a wide breadth of researchers – some with positions at the institution in Hot Springs, South Dakota, and others elsewhere such as with the members of our Science Associates. Over the next number of months, you will see in our blog post that there is a tremendous amount of research being conducted by Mammoth Site researchers and their affiliate colleagues. I will be sure to get our researchers to let you know about all the various projects. I think you will be interested and impressed.
I have one project that has been keeping me busy for a while – the Pleistocene (Ice Age) salamanders of arid Arizona and New Mexico. One does not typically think of salamanders living in this desert region! Today only the terrestrial barred tiger salamander (Ambystoma mavortium) lives in the region – always not all that far from some sort of free water so it can breed and grow from their larval stage.
Interestingly, there are isolated populations of two plethodontid salamanders, which are actually lungless, that live in the wetter habitats high up in the Sacramento and Jemez mountains of central New Mexico: Aneides hardii and Plethodon neomexicana. Today related plethodontids occur either in wet regions of coastal California to Washington or in the Appalachian Mountains region of eastern USA.
When did these salamanders disperse through what we now see as our Arid Southwest – and – what habitats must have been in that region to permit them to move through and then become isolated in the high, montane islands that we call mountains. The fossil evidence still only is recording a pretty nice record of the barred tiger salamander. The fossils sometime show a morphologic character to their vertebrae that indicates these salamanders were neotonic. This means that they were sexually mature adults but living still within their larval body in water (they had gills to breathe). Facultative neotony happens in these salamanders when the environment and climate outside of the pond/lake/stream habitat is detrimental – that is, they would perish. So the history of Ambystoma is beginning to be understood for this dry land; its fossil record is beginning to help us understand the Ice Age environments and climate. BUT, we still do not know actually when those little plethdontid salamanders dispersed into the region and became isolated. I feel it was most likely in the Eocene or Oligocene – maybe 33 to 23 million years ago. We have yet to recover their history in the desert Southwest.
In the same way, the Black Hills here at the Mammoth Site are also a ‘montane island’ mass. We are just beginning to recover what secrets its caves are archiving for us to better understand.
Jim I. Mead