When a whale dies out in the open ocean, its body slowly drifts to the seafloor, where it breathes life into a temporary ecosystem. But whales weren't the first ones to live on after death; Jurassic giants did too.
When a whale's lifeless body finally rests on the ocean's floor, tiny deep sea creatures turn the whale's carcass into both food and shelter, and eventually the community disappears as quickly as it appeared. But the seas were teeming with life well before the first whales evolved, and there's no reason to believe that Ichthyosaurs - large dinosaur-era marine reptiles - didn't serve a similar role in ocean ecosystems.
This week in Nature Communications, researchers Silvia Danise, Richard J. Twitchett, and Katie Matts reveal evidence that Ichthyosaurs did, indeed, create "falls."
Ichthyosaurs, they write, "were a diverse, cosmopolitan group of Mesozoic marine reptiles that ranged from the late Early Triassic to the Late Cretaceous" periods. Some species reached lengths of a whopping 21 meters - almost as long as today's blue whales. "Like many cetaceans, they were active predators fully adapted to aquatic life, capable of rapid sustained swimming, and able to dive to depths of 500m or more," they add. The researchers' assessment of the fossil remains of an Ichthyosaur called Ophthalmosaurus (see photo above) showed that when it died and fell to the bottom of the ancient sea, it "supported a very similar community succession to that of modern and fossil shallow-water whale falls."
Rib showing sharp, narrow grooves (white arrows) probably left by the scavenging action of small fishes.
There's one big difference between modern whale falls and ancient Ichthyosaur falls, though. After most of a whale's carcass is consumed, the worm Osedax makes quick work of the bones, destroying the skeleton in just a few years. But Ichthyosaur bones, according to Danise, Titchett, and Matts, weren't consumed so quickly. (Osedax's ancestors didn't actually evolve until the Late Cretaceous.) Instead, Ichthyosaur skeletons created longer-lasting artificial reefs, "with prolonged exposure and colonization of the bones prior to final burial."
The details may differ, but it seems as if the bottom of the ocean hosted temporary communities assembled around the lifeless corpses of dead giants, long before the first whale paddled into the waves.
Read the whole paper at Nature Communications.
Header image: Reconstruction of Ophthalmosaurus icenius, Middle Jurassic, via Captmondo/Wikimedia Commons.