The Geology P.A.G.E.: Neoichnology - Beetle Traces in the Sand

Wednesday, March 24, 2021

Neoichnology - Beetle Traces in the Sand

Ichnology is the scientific study of traces and traces of animals, specifically these tracks and traces are typically preserved in the geological rock record. I go into depth on what exactly is a Trace Fossil in a previous post.

Neoichnology is the scientific study of tracks and traces in modern sediments, made by currently extant (living) organisms. Scientists, specifically ichnologists, biologists, geologists, and paleontologists, will look at modern traces in order to better understand fossil traces.

As someone who is an ichnologist by training, I am fascinated by the traces left behind by both modern and ancient organisms and I will frequently find myself taking pictures of tracks and traces left behind in various substrates. While on vacation in central Utah, at Yuba State Park, I came across one such series of interesting traces within the sand dunes of the park.

Trace fossils, like regular fossils, are also named based on their morphology. That means different traces will get an ichnospecies and an ichnogenus (just like an animal is identified by its genus and species). Modern day traces, although not technically trace fossils, can often be tied back to traces in the rock record. So, for these tracks we can identify an ichnogenus and an ichnospecies for them just as if they were trace fossils. For the trace above it would most likely be identified as Lithographus (as the ichnogenus). [Thanks to Simon Braddy and Patrick R Getty on the Ichnology Facebook group for help with the diagnosis.] Taxonomic classification of trace fossils (inchnotaxonomy) has a defined set of characteristics known as a diagnosis for each particular ichnogenus and ichnospecies. The classification diagnosis for the ichnogenus Lithographus is as such (according to the emended diagnosis of Minter and Braddy, 2009) :

Trackways consisting of staggered to alternating series of up to three tracks, at least one of which is linear to curvilinear, whilst they may also be ovoid or crook shaped. The tracks in a series have different orientations. The longest track is parallel to slightly oblique to the mid-line of the trackway and is either the middle or the inner track. The shortest track is orientated antero-laterally, or parallel, to the mid-line and is either the inner or the middle track. The middle-sized track is generally orientated perpendicularly to the mid-line but can also be orientated postero-laterally or antero-laterally. Straight or sinusoidal single or paired medial impressions may also be present.

Trace fossils in the rock record are also nearly impossible to definitively attribute to a specific animal, unless that animal was physically located in connection to the trace. Often times the maker of a trace fossil can be fairly accurately assumed based on the morphology of the trace and the morphology of animals living at the time and in the same region as the trace fossil. Dinosaur footprints often fall into this category, where specific footprint morphologies can often be tied back to a potential maker. Other times it is completely unknown who made a trace fossil. In modern day traces, it is often much easier to accurately identify the trace maker, since we can often find them making the trace, or at least nearby. As in this case, upon closer inspection, we can actually see the trace maker making the traces. It turns out that these traces were left behind by the beetle seen in the photo, the Ten-lined June Beetle (Polyphylla decemlineata).

The Ten-lined June Beetle (Polyphylla decemlineata). Image courtesy of Bug Guide.

The Ten-lined June Beetle is a fairly common beetle found across western North America with verified occurrences from Nebraska west to the Pacific Ocean, and California north into Canada.

Verified Ten-lined June Beetle occurrences according to Bug Guide.

And of course, as any good scientist would do, I wouldn't want a picture of a trace without a scale bar. And since I didn't have a scale bar with me at the time, my flipflop stood in for reference.