At this time sea levels were high, and so most of the fossils come from marine rocks. (sciencedaily.com)
The primary difference is that most marine rocks come from calcium and / or magnesium deposits, which means they will slowly release these compounds into the water. (petbusiness.com)
«We discovered this new fossil in marine rocks, and many of the features of its skull and jaws point to it having been a marine inhabitant, like modern oceanic dolphins,» said the study's lead author Nicholas D. Pyenson, curator of fossil marine mammals at the Smithsonian's National Museum of Natural History. (sciencedaily.com)