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Green River Fm. Insect

Northern Sharks

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On a whim Saturday, I bought this beetle(?) and I'd appreciate it if anyone can provide an ID for it. It's eocene, Green River Fm from Garfield County, Colorado and measures 18mm nose to tail -or whatever the correct name is for equivalent bug parts. Thanks in advance



There's no limit to what you can accomplish when you're supposed to be doing something else

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Pterolophosoma otiliae is lower Miocene and looks similar.


Edited by Batty
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Don't know but that's nice----Tom

Grow Old Kicking And Screaming !!
"Don't Tread On Me"

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Always interested in fossil insects and this is a nice example. I have a hunch there are many more found but not detected because fern and plant collectors aren't looking for them generally, and other collectors are looking for other things. Would like to see more insect fossils on the forum.

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Whoa, nice!

It looks like an F-14 Tomcat.

Context is critical.

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Hi Northern Sharks,

Nice beetle! It is not Pterolophosoma otiliae as I wouldn't place it within the Cerambycidae. I would place this beetle within the family Chrysomelidae, the leaf beetles.

To me it bears a close resemblance to modern frog-legged leaf beetles, family Chrysomelidae, subfamily Sagrinae. No members of this subfamily are found in North America in modern times, however, there are a number of genera found in parts of South America. I'll run your images by a few Coleoptera experts here at Purdue tomorrow and see what they think.

It is the combination of enlarged hind femur, and antennal form that reminds me of this particular subfamily. The size of 18 mm also fits well for these beetles, though some modern species can be much larger. Here is a modern tropical species of Sagrinae for comparison.


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"They ... savoured the strange warm glow of being much more ignorant than ordinary people, who were only ignorant of ordinary things."

-- Terry Pratchett

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Bet it would have "bugged" you if you had passed it up! :P Nice specimen with some great detail!



Geologists on the whole are inconsistent drivers. When a roadcut presents itself, they tend to lurch and weave. To them, the roadcut is a portal, a fragment of a regional story, a proscenium arch that leads their imaginations into the earth and through the surrounding terrain. - John McPhee

If I'm going to drive safely, I can't do geology. - John McPhee

Check out my Blog for more fossils I've found: http://viewsofthemahantango.blogspot.com/

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  • 7 years later...

Dear Northern Sharks,

AgrilusHunter is correct. This looks very much like a species of Sagrinae. Only a few fossil Sagrinae have been described, apparently only from Geiseltal, Eckfelder Maar, and Menat. I am currently describing another sagrine species from Green River (which has a less froggy appearance). I might be interested to look at your specimens in a few years. It might well be a new species. Do you still have it?

Cheers, Frank

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@Northern Sharks



@Frank Krell I've tagged Northern Sharks so that he gets a notification of your reply ;) 

Max Derème


"I feel an echo of the lightning each time I find a fossil. [...] That is why I am a hunter: to feel that bolt of lightning every day."

   - Mary Anning >< Remarkable Creatures, Tracy Chevalier


Instagram: @world_of_fossils

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Dear @Northern Sharks,

thanks, and keep it, please. I cannot promise a timeline, but in a few years I might come back to you when I have time to deal with other fossil sagrines.

Alll the best


(Denver Museum of Nature & Science)

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