Since it's both #Crustmas and #FossilFriday, let's talk about the earliest crabs 220-190 million years ago. Unfortunately only 3 fossil species known. Probably their ancestors were not fully crabby, making carcinization more remarkable 🧪 onlinelibrary.wiley.com/doi/abs/10.1... @franzanth.bsky.social - ThreadSky

jopabinia.bsky.social • 82 days ago

Since it's both #Crustmas and #FossilFriday, let's talk about the earliest crabs 220-190 million years ago. Unfortunately only 3 fossil species known. Probably their ancestors were not fully crabby, making carcinization more remarkable 🧪
https://onlinelibrary.wiley.com/doi/abs/10.1002/bies.202100020
@franzanth.bsky.social

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ichnologist.bsky.social•82 days ago

This is very cool! We also start getting crabby trace fossils (burrows & tracks) in coastal-intertidal deposits by the Middle Jurassic, with both types in Portugal. Somewhere I have photos of the tracks in carbonate tidal-flat facies. 🧪🦀 #Crustmas

jopabinia.bsky.social•82 days ago

Hmmm interesting, how sure are you that they are Meiura and not mud shrimp/lobster?

ichnologist.bsky.social•82 days ago

Purported crab trackways show sideways walking, so the tracemakers were at least crab-like. Not as sure are the burrows, but they also resemble geologically younger crab burrows. Detailed discussion of early crabs & their possible trace fossils in this 2016 article:
https://www.lneg.pt/wp-content/uploads/2020/03/04-Long-trackways-of-crabs-b_Layout-1.pdf 🦀

jopabinia.bsky.social•82 days ago

Interesting... @javiluque.bsky.social didn't mention it when we were writing Bioessays, nor did he cite it in his amber crab paper. Either he didn't know (unlikely) or there's something suspicious...

ichnologist.bsky.social•82 days ago

Saw them on a field trip there in 2016 & thought they were convincing as crab-like traces because of leg numbers (4 per set) & lateral-movement patterns. One was 12.3 m long (!), which the authors noted was the longest known fossil invertebrate trackway. Amazing assemblage of other traces, too.

jopabinia.bsky.social•82 days ago

I have zero ability to judge trace fossils tbh. While sideways need not be only a true crab (or only a carcinized shaped one, or all carcinized shaped ones...), I do not think it occurs outside of Meiura.

That we know of...

jopabinia.bsky.social•82 days ago

* 3 species refers to fossils in the STEM group (early cousins, not within the group - like dinosaurs are to birds). We have thousands of fossils that we know are fully within true and false crabs!

altmetric.com•82 days ago

Eosopron is giving me the fear

jopabinia.bsky.social•81 days ago

It's pretty smol, only a couple of cm

altmetric.com•81 days ago

I am back on board with Eoprosopron

jopabinia.bsky.social•81 days ago

At the time @franzanth.bsky.social had the idea to make it scavenging (might have been a guess from a paper) but he wanted to make it grotesque. I think he wasn't sure if Eons would even like it?

But, history was made and crabs remained victorious over verts

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