Why are marine animals (such as later ichthyosaurs, whales, and manatees) born tail-first? That way their airways aren't exposed to seawater until they're all the way out and able to swim to the surface for their first breaths.

Aaw, dead babies. :-(

@2 Underwater landslide on a massive scale. Or pyroclastic flow into the sea would have instantly boiled them.

@2: Pope Peabrain has the right idea. We've seen similar fossils in the Gobi Desert of dinosaurs atop their nests, suggesting some sort of brooding behavior. The line of thought there is that a dune collapsed and buried them.