Who Hunted the Sauropods?

A reader asks an excellent question: if T. Rex was in fact a scavenger rather than a hunter, then what predators could possibly have brought down fully grown sauropods like Brachiosaurus or Apatosaurus?

The answer can be inferred from a modern-day giant, the elephant. No lion pack in its right mind would attempt to hunt down and kill a full-grown elephant; if they were really hungry, they might focus on a juvenile, though this has its own hazards, as you can imagine. The fact is, fully grown elephants (and whales, and hippopotamuses) are virtually immune to predation, as were adult Brachiosauruses and Apatosauruses.

So what did kill these house-sized herbivores? The usual suspects: disease, old age, and the occasional wrong turn into a tar pit or raging sandstorm.