Washed-Up Dead Coral, Or Fossil Coral?

[Naturalist Jim]

The Caribbean beach here in southern Quintana Roo, Yucatan Peninsula, Mexico, is strewen with tons of coral fragments. Is there a neat way of figuring out whether these pieces of coral were recently broken off the reef just offshore, or whether they might be fossils millions of years old? Certainly there is an abundance of fossils in the limestone bedrock, and many of them are in the process of being eroded from the rock. I read that our rocky points are probably Miocene-Pliocene in age -- 1.8 to 23 million years old.

Of course if what's found is a little different from today's species, that's a vote for "fossil." The same if the specimen is highly eroded.

The attached pictures, I assume, show a typical Brain Coral, Diploria strigosa, which is very common just offshore. The close-up shows a highly eroded surface, however. Seeing such erosion, would one guess that it's a million-year-old fossil, or something swept ashore fairly recently by a hurricane, or is it simply impossible to tell without lab work?

Thanks for any thoughts on the matter.

Jim

[Kosmoceras]

Looks recent to me, but I am not an expert with coral, so I would not be sure.