daysofbreeze t1_itoyb4u wrote on October 25, 2022 at 6:33 AM

They are significantly harder than in modern arthropods. This is due to the fact that the exoskeletons of ancient arthropods were typically made of chitin, a long-chain molecule made of sugar and protein. (found in the cell walls of fungi and the exoskeletons of insects, crustaceans, and other arthropods). Chitin is a natural polymer a much harder material than the exoskeletons of modern arthropods, which are typically made of chitin and protein.

One of the largest ancient arthropod exoskeletons found to date are those of the millipede-like creature Pulmonoscorpius kirktonensis, which could reach up to 2.5 meters (8.2 ft) in length. But Some of the largest known arthropods could have had exoskeletons quite larger.

Chitin is a tough, insoluble material and therefore difficult to break. The average force required to break chitin is reported to be around 4,000 newtons. which would be enough to snap a human spine in half.

StupidPencil t1_itpbsxb wrote on October 25, 2022 at 9:46 AM

I thought chitin is more on the soft side and mixing it with other appropriate proteins makes it stronger.

https://en.m.wikipedia.org/wiki/Sclerotin

GeriatricZergling t1_itvj3kx wrote on October 26, 2022 at 4:49 PM

This is correct. Plus, it's possible to mineralize exoskeletons as well. Crustaceans do this for most larger species, but some insects can as well.

PlaidBastard t1_itqf0vm wrote on October 25, 2022 at 3:28 PM

How is that chitin resisting the 4000 Newtons, in terms of the orientation of the forces being exerted on the material? Tensile strength? Compressive? Resistance to buckling? Stiffness?

I sincerely doubt that value is a fair or meaningful comparison to a human spine any more than, for example, me letting everyone know that chicken eggs have an ultimate strength of 14,000 Newtons if you apply the load properly.

I'm perfectly willing to believe that the rest of what you say is true, but that specific bit really stuck out and cast doubt on all what you said, for me. A solid block of calcium carbonate would be impossible to crush with your hands, but, well, eggs are like eggs are, because of how thin that incredibly hard shell is.

If those paleoarthropods had thicker exoskeletons relative to their other proportions, or if we had some numbers backing up that chitin with less protein in its matrix has a higher tensile/compressive strength, I think maybe some of these 2.5m creatures could resist a guy with reasonably good boots on, but I don't think you've shown any of that to be true yet.