Ancient sea cows played a vital role in maintaining healthy ecosystems more than 20 million years ago, a fossil site in Qatar has revealed.
Their modern descendants, the dugong, continue to shape the sea floor as they graze on seagrass.
Researchers say that studying the Gulf's “bone bed” can provide important insights into the health of the marine ecosystem, which is increasingly under pressure from climate change and pollution.
In a paper published in the journal PeerJ, researchers at the Smithsonian’s National Museum of Natural History worked with Qatar Museums to name a new species of sea cow that was a miniature version of the dugong. Salwasiren qatarensis, named after the nearby Bay of Salwa, was the size of a panda – about eight times smaller than a dugong.
“We discovered a distant relative of dugongs in rocks less than 10 miles [16km] away from a bay with seagrass meadows that make up their prime habitat today,” said Nicholas Pyenson, curator of fossil marine mammals at the National Museum of Natural History, who helped lead the new study. “This part of the world has been prime sea cow habitat for the past 21 million years – it’s just that the sea cow role has been occupied by different species over time.”
Dugongs inhabit coastal waters from western Africa through the Indo-Pacific and into northern Australia. The Arabian Gulf is home to the largest individual herd in the world.
By grazing on seagrass, they create feeding trails that release buried nutrients into the surrounding water for other aquatic animals and plants to use.
Dugongs have a burly build and a downturned snout lined with sensitive bristles. They resemble manatees, except that they have fluked tails like a dolphin. Despite the similarity, dugongs are more closely related to elephants than dolphins, whales or porpoises.
The fossils revealed that ancient dugong relatives have grazed on aquatic vegetation around the world for about 50 million years.
However, in the Gulf, the seagrass meadows they rely on are threatened by rising temperatures and salinity levels, while they can also be accidentally caught by local fishermen.
Ferhan Sakal, an archaeologist who is the head of excavation and site management at Qatar Museums, said key insights into the fate of dugongs and seagrasses in the Gulf are preserved in the region’s rocks.
“If we can learn from past records how the seagrass communities survived climate stress or other major disturbances like sea-level changes and salinity shifts, we might set goals for a better future of the Arabian Gulf,” he said.
The fossils, formed from the sturdier bones of ancient herbivores, offer researchers insights into past marine ecosystems, with Al Maszhabiya in south-western Qatar one of the best preserved sites. The Gulf was a particular hotspot for biodiversity at the time.
The bone bed was initially discovered when geologists conducted mining and petroleum surveys in the 1970s and noted abundant “reptile” bones scattered across the desert. In the early 2000s, palaeontologists returned to the area and realised that the fossils were not from ancient reptiles but sea cows.
“The area was called ‘dugong cemetery’ among the members of our authority,” Mr Sakal said. “But at the time, we had no idea just how rich and vast the bone bed actually was.”
Based on the surrounding rocks, the team dated the bone bed to about 21 million years ago, uncovering fossils that revealed that the area was once a shallow marine environment also inhabited by sharks, barracuda-like fish, prehistoric dolphins and sea turtles.
The team identified more than 170 locations containing sea cow fossils throughout the Al Maszhabiya site, enough to rival well-known marine mammal deposits such as Cerro Ballena in Chile’s Atacama Desert, where an ancient graveyard of stranded whales was discovered.
The fossilised bones at Al Maszhabiya resembled the skeletons of living dugongs, although they still possessed hind limb bones, which modern dugongs and manatees have lost through evolution. The prehistoric sea cows also had a straighter snout and smaller tusks than their living relatives.
“The density of the Al Maszhabiya bone bed gives us a big clue that Salwasiren played the role of a seagrass ecosystem engineer the way that dugongs do today,” Mr Pyenson said. “There’s been a full replacement of the evolutionary actors but not their ecological roles.”
Mr Sakal and his colleagues are planning to nominate the area for protection as a Unesco World Heritage site.
“The most important part of our collaboration is ensuring that we provide the best possible protection and management for these sites, so we can preserve them for future generations,” he said.
