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Sea cows—including manatees and dugongs—are the only marine mammals that aren’t carnivores. In contrast to seals and whales, sea cows munch exclusively on aquatic plants. Knowing that their closest relatives are elephants puts the vegetarian diet of sea cows in context. Their prodigious appetites for sea grasses render both manatees and dugongs influential in engineering their ecosystems.
Research findings reported in a new study published in Peer J show how, even 21 million years ago, sea cows were shaping seafloors. Paleontologists from the Smithsonian Institution and Qatar Museums explored a fossil bed in Qatar—Al Maszhabiya—that was locally known as a “dugong cemetery.” In surveying the bed, they found that it was once a marine habitat with sharks, prehistoric dolphins, sea turtles, and a new species of sea cow. The bonebed yielded the richest assemblage of sea cow fossils known, with more than 170 distinct locations.
While the fossils looked like the bones of modern dugongs, some differences marked them as a new species to science, which the researchers dubbed Salwasiren qatarensis. The Late Miocene dugongs had hind limbs, which are absent in today’s sea cows, as well as a straighter snout and smaller tusks than their living relatives. But, according to the study authors, they played an equivalent ecological role.
Read more: “The Hidden Fruits of the Deep”
“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,” said Smithsonian paleontologist and study author Nick Pyenson in a statement.
Sea grasses rarely fossilize, but the body morphology of the ancient dugongs revealed their ecosystem engineering potential. At an estimated 250 pounds, they were small for sea cows. Still, considering that sea cows must consume at least 10 percent of their body weight per day, just one S. qatarensis would have eaten 25 pounds of aquatic vegetation daily. Furthermore, their abundance would have magnified the impact.
“The density of the Al Maszhabiya bonebed gives us a big clue that Salwasiren played the role of a seagrass ecosystem engineer in the Early Miocene the way that dugongs do today,” added Pyenson. “There’s been a full replacement of the evolutionary actors but not their ecological roles.”
Today, as dugongs in the Arabian Gulf munch on seagrasses, they leave nutrient-rich trails on the seafloor that other animals can use. But, with decreasing populations threatened by hunting, incidental capture in fishing gear, boat strikes, and declines in seagrasses, dugongs face an uncertain future.
“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,” said Qatar Museum archaeologist and study co-author Ferhan Sakal. 
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Lead image: BlaCkBlitZ / Shutterstock
