Every fossil horseshoe crab

[Halichoeres]

Horseshoe crabs don't fossilize as well as decapods (true crabs, shrimp, etc.) because their cuticle isn't mineralized. But there's still a pretty good record of them from the right deposits. Last year, Russell Bicknell and Stephen Pates published a complete guide to all the horseshoe crabs living and extinct, with photos of each. It's a really incredible resource!

Open access in Frontiers in Earth Science: https://www.frontiersin.org/articles/10.3389/feart.2020.00098/full

[Faelrin]

Nice to see a compendium of fossil horseshoe crabs. Incredible something like this was made and freely shared.

It makes me wonder if there is something like that out there for trilobites, and other invertebrates (such as crinoids, cephalopods, etc)?

[Halichoeres]

That would be really difficult, because we have much more extensive records of all of those things. Horseshoe crabs fossilize rarely enough that it's possible to put something like this together, but for animals with mineralized skeletons, you're talking about hundreds or thousands of genera. However, Jack Sepkoski posthumously published a compendium of marine genera. Not pictorial, but still an unparalleled resource. Shanan Peters at the University of Wisconsin hosts an online version: http://strata.geology.wisc.edu/jack/

[Faelrin]

Very excellent point. Just skimming through the lists on wikipedia (say for trilobites at least) shows how daunting a task that would be, especially if it were one person only (or maybe even a team still), especially for something with images.

However I do appreciate you sending that resource. Looks like there's a lot of digging in there I need to do. I like how everything is sorted along with the option to select Cambrian or Paleozoic only faunas, etc.