Beetle, orthop or something else?

I had such helpful participation with my first fossil ID request that I thought I would go to the well again. This one is not so enigmatic as the first—it is clearly an insect, but it’s the only insect fossil among the batch that I haven’t settled on at least an order-level identification. Again, this is one of a set of 20 fossils loaned to me by a local collector for photographs and possible identifications, all coming from the Green River Formation in Colorado and dating back to the early to mid-Eocene (45–50 mya).

USA: Colorado, Rio Blanco Co., Parachute Creek Member. Body length = 11.05 mm.

USA: Colorado, Rio Blanco Co., Parachute Creek Member. Body length = 11.05 mm.

The label for this fossil indicates “Planthopper; Homoptera; Fulgoridae”; however, the short, robust legs and overall gestalt do not look right for either a planthopper or really any of the other hemipteran groups. What I see is an indistinct (mandibulate?) head, a distinct and well-developed pronotum, mes0- and metathoracic segments that are not nearly as heavily sclerotized as the pronotum but also lacking any sign of wings, a distinctly segmented abdomen with 9 or 10 segments, and short robust legs. I’m thinking an apterous/brachypterous coleopteran (Staphylinidae?) or a wingless member of one of the orthopteroid orders (although size alone excludes many of the latter—at more than 11 mm in length it is too large for something like Zoraptera). At first I thought the extension near the apex of the abdomen was a cercus, but I now think this is part of the piece of debris over the abdomen as there is no evidence of a cercus on the left side—another knock against something orthopteroid. Still, the lack of any trace of elytra—however shortened—keeps me from fully endorsing Coleoptera. Okay, so what do you guys think?

Copyright © Ted C. MacRae 2012

22 thoughts on “Beetle, orthop or something else?

  1. It looks to me like an Isopteran, with the head indistinct or missing. The relatively short legs would seem to rule out Orthoptera.

  2. I like Charley’s suggestion. It looks like there might even be a trace of the left cercus. On the other hand, the head seems rather too small.

      • Hi Ted – Looks like this post crept under my radar! I too would like to see a shot of this taken under ethanol (70-80%) as it will enhance the contrast and help make lightly mineralized structures more visible. The specimen is rather poorly preserved and the legs are clearly incomplete. Nevertheless, it does look orthopteran to me with the morphology of the pronotum consistent with an as yet undescribed gryllid that is fairly common in the Green River Fm (we eagerly await Gorochov’s monograph on the fauna!).

  3. In general, 11 mm is too small for several of the suggestions and too big for the other. It looks most to me like a wingless Dermapteran (earwig) but with the abdominal apex damaged. Or it could just be a Rorschach splotch. 😉

  4. Ignoring the apparent pronotum, rest of fossil looks a lot like an dragonfly nymph. Not saying its the case here, but one needs to be aware of possibility of parts from two creatures being compressed together when considering ID options.

  5. The “cerci” appears to me to be a horseshoe shaped reminant of something else, and not necessarily a part of the insect. My first impression (assuming that the specimen is intact) was Coleoptera: Staphylinidae. It would be interesting to see the opposing piece of rock and what is attached to it.


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