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Comparing the evolution of feathers in dinosaurs, one of the most extraordinary transformations in the history of life has been the evolution of baleen – rows of soft plates resembling hairs Blue whales, humpback whales and other marine mammals use to filter relatively tiny prey from seawater gulps. The unusual structure allows the largest creatures in the world to consume several tons of food every day, without ever chewing or biting. Now, Smithsonian scientists have discovered an important intermediate link in the evolution of this innovative feeding strategy: an old whale that had no teeth or whalebone.
In the November 29 issue of the journal Current biologyScientists from the Smithsonian National Museum of Natural History and their colleagues describe for the first time Maiabalaena nesbittae, a whale that lived about 33 million years ago. Using new methods to analyze the fossils discovered long ago, preserved in the Smithsonian's national collection, the team, which includes scientists from George Mason University, A & M University of Texas and the Burke Museum of Natural History and Culture of Seattle, determined that this The foot whale probably had no baleen, which shows an astonishing intermediate step between the baleen whales that live today and their toothed ancestors.
"When we talk about the evolution of whales, textbooks tend to focus on the early stages, when whales have moved from land to sea," said the National Marine Museum's Fossil Marine Mammal Curator of Natural History. "Maiabalaena shows that the second phase of whale evolution is equally important for large-scale evolution. For the first time, we can now determine the origin of filter feeding, which is one of the major innovations in the history of whales. "
At the beginning of their evolution, whales used teeth to chew their food, as did their ancestors who inhabited the land. Over time, many descendants of these early whales continued to chew their food, inheriting this trait from their predecessors. But as the oceans around them have changed and animals have evolved, new feeding strategies have emerged, including bale-filter feeding, says the National Museum of Natural History's Undergraduate Scholar. the main author of the study, who analyzed the Maiabalaena fossils.
Whales were the first mammals to produce baleen, and no other mammal uses an anatomical structure, even very similar to it, to devour prey. But, frustrating, the baleen, whose chemical composition is more like that of the hair or nails than the bone, do not keep well. It is rarely found in the fossil record, leaving palaeontologists without direct evidence of its past or origins. Instead, scientists had to rely on fossil findings and studies on fetal development in the womb to reconstruct clues as to how the baleen were evolving.
As a result, it has not been clearly established whether, as they evolved, the first whalebone whales retained the teeth of their ancestors until a filter feeding system was put in place. square. According to Peredo, one of the first initial assumptions was that mammals living in the ocean would need teeth or baleen for feeding – but many live whales contradict this idea. Sperm whales have teeth in the lower jaw, but not at the top, so they can not bite or chew. The only teeth of narwhals are their long tusks, which they do not use to feed themselves. And some species of beaked whales, although classified as toothed whales, have no teeth at all.
Due to his age, paleontologists suspected of being suspected Maiabalaena could contain important clues about the evolution of the baleen. The fossil comes from a period of massive geological changes during the second major phase of whale evolution, roughly at the time of the transition from Eocene to london. 39; Oligocène. As continents moved and separated, ocean currents swirled around Antarctica for the first time, cooling the waters considerably. The fossil record indicates that whale feeding styles have diverged rapidly over this period, a group that has led to filtering whales from today and the other to the present day. echo.
Therefore, Maiabalaena had been the subject of many examinations since its discovery in Oregon in the 1970s, but the matrix and rock material in which the fossil was collected still hid many of its features. It was only when Peredo finally cleaned the fossil and then examined it with advanced tomodensitometry technology that its most striking features became clear. MaiabalaenaThe lack of bone teeth was evident in the preserved bone, but the CT scan, which revealed the fossil's internal anatomy, indicated something new to scientists: MaiabalaenaThe upper jaw was thin and narrow, making it an inadequate surface for hanging baleen.
"A living baleen whale has a wide, broad roof in its mouth, and it's also thickened to create attachment points for baleen," Peredo said. "Maiabalaena does not. We can tell you quite conclusively that this fossil species has no teeth, and it is more likely that it does not have any baleen either. "
While Maiabalaena would not have been able to chew or filter food, muscle attachments to throat bones indicate strong cheeks and retractable tongue. These traits would have allowed him to suck water into his mouth, thus taking fish and small squids. The suction capacity of the food would have made unnecessary the teeth whose development requires a lot of energy. The loss of teeth thus seems to have laid the foundation for the evolution of baleen, estimated by scientists about 5 to 7 million years later.
Peredo and Pyenson consider the study of whale evolution as an essential means to understand their survival in rapidly changing oceans. Along with the emergence of baleen whales, tooth loss in whales is evidence of adaptability, suggesting that whales might be able to adapt to the challenges posed by the ocean today. Still, warns Peredo, evolutionary change can be slow for larger whales, which have a long life and take a long time to reproduce.
"Given the magnitude and pace of change in the ocean today, we do not know exactly what this will mean for all the different species of filtering whales," he said. declared. "We know that they have changed in the past.The question is whether they can keep up with the pace of the oceans – and we're changing them pretty quickly right now."
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