Birds, the only group of dinosaurs still alive today, evolved to settle just about everywhere, from digging burrows underground to soaring over the oceans for thousands of miles without stop. And then there are the penguins, who dive a quarter of a mile deep in the icy waters in search of food.
It now appears that modern birds aren’t the only group of dinosaurs to adopt the dive-and-prey lifestyle. A team of researchers claim to have found the first example of an extinct dinosaur with a streamlined body for diving. They described the dinosaur discovery in the journal Communications Biology on Thursday.
The new duck-sized dinosaur was initially overlooked. In 2008, Robin Sissons, then a master’s student at the University of Alberta, was digging in the Gobi Desert in Mongolia when she noticed a “chain of white chunks sticking out of the rock.” After sharing a photo of what she saw with her colleagues over lunch, they drove to the location and eventually transported the fossil to South Korea for further study. (The fossil has since been returned to the Mongolian Academy of Sciences.)
“After the preparation in Korea, an entire skeleton was discovered,” said Yuong-Nam Lee of Seoul National University, who led the expedition and is one of the authors of the new study. “The specimen was so delicate yet beautifully preserved. Instantly we realized it was something important.
Researchers found the fossil had a mouth full of over 100 tiny, sharp teeth and a long, thin neck. These features indicated a dinosaur that spent time at the water’s edge, Dr Lee said, with teeth, packed into the front of the snout, capable of latching onto slippery, restless fish.
Similar fossils have also been found in Mongolia, including one called Halszkaraptor escuilliei, and scientists have wondered if it was semi-aquatic. But the new dinosaur before Dr. Lee was better preserved than Halszkaraptor, particularly in one key area: its ribs, which were slightly flattened and pointed toward the animal’s tail.
“Although the rib cage was not completely preserved, the orientation and shape of the ribs clearly indicate that this animal had a streamlined body, as penguins do,” Dr Lee said. That made the ribcage irrefutable proof that not only did this dinosaur eat fish, the researchers said, but it had an elegant body that was perfect for diving. The name they chose for it reflects this statement: Natovenator polydontus, “many-toothed swimmer”.
If the researchers are correct, Natovenator is among the first dinosaurs (besides birds) to dive for its dinner. But some other paleontologists are skeptical.
“I’m always on the lookout for largely aquatic dinosaurs, because I’m the type that says, ‘I think there’s more out there,'” said Nizar Ibrahim, a paleontologist at the University of Portsmouth in England, who argued that the giant predator Spinosaurus hunted underwater. But when it comes to adding Natovenator to the ranks of swimming dinosaurs, Dr. Ibrahim said, “I’m not entirely sold yet.”
Dr Ibrahim said he might be attracted to “stronger evidence”, such as further study of Natovenator’s biomechanical abilities and more comparisons with other aquatic animals, including characteristics such as bone density. Dr. Ibrahim helped show that it correlates with an animal’s ability to submerge itself.
Lindsay Zanno, a paleontologist at the North Carolina Museum of Natural Sciences, said she also wanted to see other studies. “The time has come, now that we have several animals that we think are semi-aquatic, to take a broader look at the anatomical correlations with this way of life in living and extinct taxa,” she said.
Dr. Zanno noted that a potentially diving dino helps flesh out scientists’ understanding of how theropod dinosaurs, from Natovenator to T. rex to the pigeon outside your window, became so incredibly diverse, which is “The Million Dollar Question”. Answering this may involve reversing paleontology’s tendency to assume that dinosaurs were earthlings.
“Finding semi-aquatic dinosaurs means that ecological diversity was very high among dinosaurs, and it could change our assumptions about how dinosaurs lived,” Dr Lee said. “More than 30 different lineages of tetrapods have independently invaded aquatic ecosystems. Why not for dinosaurs?
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