Ocean trenches, reaching depths of nearly 11,000 metres, are among the least explored and most enigmatic environments on Earth. A study published in Nature reports the results of a series of dives carried out by the Chinese submersible Fendouzhe on the floor of the Diamantina Trench in the southeastern Indian Ocean, at depths ranging from 4,600 to 7,000 metres. The expeditions revealed an unexpectedly high abundance and diversity of both fossil and modern cetacean skeletons scattered across more than 1,200 kilometres of seafloor. Many of the whale carcasses are still decomposing and support unique biological communities, many of whose species remain unknown to science. These specialised organisms are capable of exploiting virtually all the organic matter delivered to the deep seafloor by a sinking whale carcass, including nutrients retained within the bones.
The study of the skeletal remains was carried out by palaeontologists Giovanni Bianucci and Alberto Collareta of the Department of Earth Sciences at the University of Pisa.
“Most of the skeletal remains,” explains Bianucci, “belong to beaked whales, deep-diving cetaceans that forage at great depths. The remains are represented mainly by rostra—the elongated anterior portion of the skull—which are particularly resistant to degradation over time. Many specimens are also covered by thick ferromanganese crusts that have enhanced their preservation. Numerous rostra belong to two living species, Andrews’s beaked whale (Mesoplodon bowdoini) and the strap-toothed whale (Mesoplodon layardii), but fossil species are also present, including Pterocetus diamantinae, a newly described species named after the trench itself.”
“Strontium-isotope dating,” adds Collareta, “indicates that the remains of extant species are the youngest, ranging from 1.2 million years ago to the present, whereas the fossil species date from between 2.4 and 5.3 million years ago. These results not only support our taxonomic identifications but also demonstrate that we are dealing with an extraordinary fossil accumulation that has been forming for more than five million years and continues to grow through the ongoing deposition of whale carcasses on the deep seafloor.”
“These findings,” Bianucci concludes, “fundamentally reshape our understanding of deep-sea ecosystems associated with whale falls and highlight the enormous potential of ocean trenches as fossil archives for reconstructing the evolutionary history of cetaceans through geological time.”
The research was carried out within the framework of the Global Deep-Sea Trench Exploration Program (GHEP), an international initiative aimed at advancing knowledge of the geology, biology and environmental conditions of the world’s deepest oceans (6,000–11,000 metres). The programme combines interdisciplinary expeditions with cutting-edge technologies, including crewed submersibles and autonomous underwater vehicles (AUVs). It is led by the Institute of Deep-Sea Science and Engineering of the Chinese Academy of Sciences. The GHEP steering committee includes 11 researchers from 11 countries, among them Giovanni Bianucci of the University of Pisa, who represents Italy.
