Mammals rebound

The paper that was posted posits that the carbonate in the concretions came from rotting organic matter in the critters that were buried, not from bones. The bones (or shells, etc.) would be left to fossilize by other means. And though the paper is on marine fossils, I can’t see any necessity for seawater in the process- any water with decent calcium content would work the same.
The concretions in my house’s water heater show that. Edited by Coragyps, : No reason given.

That’s different, and out of my limited expertise. Apparently it was a surprise to the researchers as well. But they did say that it was fossils inside the concretions - I claim ignorance of how calcium phosphate concretions form, unless it’s the apatite of bones dissolving and recrystallizing as the concretion. Weird.