“Seventy million years ago, they all came to drink in the rapidly drying river: long-necked sauropods, fierce theropods, crocodiles, lizards, and raven-sized birds. They never left. The giant and the tiny were entombed together in the riverbed, forming what is now a spectacular series of mass graves in northwestern Madagascar. Last week, researchers proposed a culprit behind this ancient mystery: harmful algal blooms (HABs), in the very water that had lured the animals.”
The buried creatures display the classical dead dino pose, with the neck and head bent back, which suggests suffocation.
The Science article prefers to see algae as the cause thought there is no direct evidence of it.