Sunday, December 11, 2016

A New Exposed Trackway on the Bright Angel Trail in Grand Canyon

Last month Helen and I got to visit Indian Garden located 4.5 miles down the Bright Angel Trail in Grand Canyon. Down in the Pennsylvanian Supai Formation, about 2.5 miles in, we came across a new exposure of a great reptile trackway. I took a few pictures and share them here.
During the summer monsoon, a number rocks were dislodged from the cliff on the left and rolled down onto the trail. Since then, the trail crew has cleared the rocks from the tread and placed them alongside the trail. This is a place where parallel joints are evident in the sandstone. These joints are parallel to the Bright Angel Fault and slivers of rock are always falling at this location.

Blasting was needed to move the rocks off the trail and it is unknown to me if the new trackway was exposed when the rocks fell off the nearby cliff or from subsequent blasting. What is known is that the trail crew was aware of the trackway and placed this boulder in perfect alignment to admire it.

Being closer to the trackway shows some well preserved claw marks in the individual prints (bottom). This must have been a lumbering type of reptile with each track closely spaced but the individual prints about 3 to 4 inches wide.

More claw marks. Two ichnofauna's are described from the Supai - Limnopus and Batrachichnus. A web search did not specify which these might belong to. Another likely candidate for these is Eryops and fossil skeletons that are Pennsylvanian in age have been found in nearby New Mexico. A description of this animal can be found here.

An example of Eryops reconstructed from fossil bones.

A fossil specimen of Eryops on display at the National Museum (Smithsonian, Washington D.C.)

It is possible that this is a set of two individuals walking one after the other. Most descriptions of reptiles from this time period suggest that the back and front tracks are nearly on top of each other and there are four lines of tracks here.

The block is big enough that it should remain in place for a long time.

Thanks to the Grand Canyon trail crew for making this specimen so readily observable.

3 comments:

Ed said...

Interesting read, a bit concerning that the park's geological resources staff find out about these types of things through social media.

bruce maxwell said...

Turns out that social media "Trumps" the MSM.

vebiltdervan said...

Thanks for the info, Wayne! It'll be impossible to miss seeing it, but can you estimate about where in the Supai this is? And speaking of reptile trackways, do you know if there are any visible in the Coconino along the BA Trail? I know the ones along Hermit Tr, but not any along the BA.