Cave Diver here who's had a lot of dives in that area of Mexico. There is a site call Chan Hol we dove, it has a human skelton/burial site about a 30 min swim in and numerous fire pits. You can make out black marks on the wall/ceiling and remains of the pit itself. They are all over this one cave, it was very active.

The human skeleton is in what could only be called a burial site, it's very high limestone slab, above what would have been the floor and could have been only been placed there when the water table was much lower. The amount of effort suggests a coordinated effort but it's debatable, not all the skeleton is there.

A team of Mexican scientist radio-carbon dated the sites and the conclusion is 11,000 years ago. The body being an adult female.