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Thanks to the submersible Fendouzhe, researchers explored the seafloor at depths between 13,800 and 23,000 feet (4,200 and 7,000 meters). In 32 dives, they spotted 476 fossils and five recent carcasses, known as "whale falls." Up to 2,840 organisms per square meter were counted around the carcasses.
a - Partially destroyed skull and articulated mandible of a baleen whale.
b - Articulated lumbar and caudal vertebrae of a beaked whale.
c - Disarticulated skeleton of an undetermined cetacean.
d - Fragmentary vertebrae of an undetermined cetacean.
e - Fragmentary skull bones of a baleen whale.
The exterior of these skeletons is mainly occupied by the common megafauna of hard substrates, such as the stalked sea anemone Galatheanthemum profundale (yellow arrows) and the starfish Freyastera sp. (orange arrows).
Scale: 8 in (20 cm).
The largest carcass measures 16 feet (5 m) long and belongs to an Antarctic minke whale. However, most remains come from beaked whales, cetaceans still poorly studied because they live offshore and dive very deeply. The oldest fossils date back about 5.3 million years.
Bacteria that develop on the carcasses without light or oxygen produce hydrogen sulfide. This energy source attracts a varied fauna: jellyfish, brittle stars, bone-eating worms, and bivalve mollusks. Most of these species are probably new to science, as only a few could be identified with certainty.
This exceptional site shows how beaked whales have evolved over geological time scales, with extinct species coexisting with species still alive today.
Several explanations have been proposed to understand such an accumulation of carcasses. The area could be an ideal hunting ground for beaked whales, rich in fish and squid. The V-shaped topography of the canyon could also concentrate sinking carcasses. Finally, extremely slow sedimentation allows bones to remain exposed for hundreds of thousands, even millions, of years.
Distribution of fossils and carcasses in the Diamantina zone. Orange dots indicate observed sites. Credit: Wiley, under CC BY 4.0 license
Similar "necropolises" could exist off the coast of South Africa, the Iberian Peninsula, and the Crozet and Kerguelen Islands. Fossils have already been discovered there by chance during trawling.
Whale falls
When a whale dies and sinks to the ocean floor, its body becomes a temporary ecosystem. This phenomenon, called a "whale fall," unfolds in several stages.
First, scavengers like sharks and fish consume the soft tissues. Then, specialized bacteria decompose the fats and bones, producing hydrogen sulfide. This chemical compound serves as an energy source for unique communities of invertebrates, such as vestimentiferan worms or mussels.
A single carcass can feed hundreds of species for decades, making whale falls oases of life in the deep sea.
A 5-meter (16 ft) whale on the seafloor, hosting 26 species of invertebrates.
Credit: Global TREnD, IDSSE
Beaked whales
Beaked whales form a family of enigmatic cetaceans. Their elongated snout gives them their name. They live in open oceans and dive to dizzying depths to hunt squid and fish. Their dive duration can exceed one hour.
Very elusive, they are rarely observed at the surface, making their study difficult. The fossils discovered in the Diamantina zone show that current and extinct species coexisted in this region. Their rostrums, extremely dense, are better preserved than the rest of the skeleton, allowing paleontologists to trace their evolution over several million years.