Grouping behavior in a Triassic marine apex predator.

Marine tetrapods occupy important roles in modern marine ecosystems and often gather in large aggregations driven by patchy prey distribution, social or reproductive behaviors, or oceanographic factors. Here, we show that similar grouping behaviors evolved in an early marine tetrapod lineage, documented by dozens of specimens of the giant ichthyosaur Shonisaurus in the Luning Formation in West Union Canyon, Nevada, USA. A concentration of at least seven skeletons closely preserved on a single bedding plane received the bulk of previous attention.