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Home / Science / Whales lost their teeth before evolving hair-like baleen in their mouths

Whales lost their teeth before evolving hair-like baleen in their mouths



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IMAGE: This is an artistic reconstruction of a mother and a calf of Maiabalaena nesbittae who breastfeeds off Oregon during Oligocene, about 33 millions of years ago. While Maiabalaena would not have had …
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Credit: Alex Boersma

Revisiting the evolution of feathers in dinosaurs, one of the most extraordinary transformations in the history of life has been the evolution of baleen ̵

1; rows of similar flexible plates to hair that blue whales, humps and other marine mammals use to filter relatively small prey from sips of ocean water. The unusual structure allows the biggest 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 ancient whale that had neither teeth nor baleen.

In the November 29 issue of the journal Current Biology scientists of the National Museum of Natural History Smithsonian and colleagues describe for the first time Maiabalaena nesbittae a whale who lived about 33 millions of years ago. Using new methods to analyze long-established fossils hosted in the Smithsonian National Collection, the team, which includes scientists from George Mason University, Texas A & M University and the Burke Museum of Natural History and Culture in Seattle, determined that this without teeth, 15 the whale with feet probably did not have a baleen, showing a surprising intermediate step between the fanatics living today and their ancestors.

"When we talk about the evolution of whales, textbooks tend to focus on the early stages, when the whales moved from one land to another," said the marine mammalian fossil National Museum of Natural History. " Maiabalaena shows that the second phase of the evolution of whales is just as important for the evolution of large scales. For the first time, we can now identify the origin of the filter, which is one of the main innovations in the history of whales. "

When the whales evolved for the first time, they used their teeth to chew their food, just like their earth ancestors. Over time, many descendants of these early whales continued to chew their food, inheriting this feature from their predecessors. But as the oceans around them change and the animals evolve, new feeding strategies are born, including the baleen feeding filter, says the predecessor partner of the National Museum of Natural History, Carlos Mauricio Peredo, the lead author of the study that analyzed Maiabalaena fossils.

The whales were the first mammals to evolve the fanatics and no other mammal used any anatomical structure even remotely similar to that to consume the prey. But frustratedly, the baleen, whose chemical composition is more similar to that of hair or bone nails, does not preserve well. It is rarely found in the fossil record, leaving paleontologists without direct evidence of its past or origins. Instead, scientists had to rely on inferences from fossils and studies on the development of the fetal whale in the womb to put together clues about how the baleen evolved.

As a result, it has not yet been clarified whether, as they evolved, the first whale fanons retained the teeth of their ancestors until a filter feed system was established. A first initial assumption, said Peredo, was that the mammals living in the ocean had to need teeth or baleen to eat – but many living whales contradict this idea. The sperm whales have teeth in the lower jaw, but none in the upper part, so they can not bite or chew. The only teeth of Narwhal are their long fangs, which they do not use for feeding. And some species of beaked whales, despite being classified as toothed whales, have no teeth at all.

Because of his age, said Peredo, the palaeontologists suspected Maiabalaena could contain important clues about the evolution of the fans. The fossil comes from a period of massive geological changes during the second major phase of the evolution of whales, in the period when the eocene era was moving towards Oligocene. With the continents moving and separating, the ocean currents turned for the first time around Antarctica, significantly cooling the waters. The fossil record indicates that whale feeding styles quickly diverged during this period of time, with a group that led to today's artificially fed whales and the other that led to echolocation.

Consequently, Maiabalaena had received many scrutiny since its discovery in Oregon in the 1970s, but the rock matrix and the material that the fossil had been harvested still obscured many of its characteristics . It was only after Peredo cleaned the fossil and then examined it with a CT scan technology at the vanguard that its most striking features became clear. Maiabalaena's toothlessness was evident from the preserved bone, but CT scans, which revealed the internal anatomy of the fossil, told scientists something new: The upper jaw of Maiabalaena was thin and narrow, which makes it an inadequate surface from which to suspend the baleen.

"A living baleen whale has a large, wide roof in its mouth, and is also thickened to create sites of attack for fanatics," said Peredo. " Maiabalaena No. We can say conclusively that this fossil species had no teeth, and it's more likely that it did not even have fans."

While Maiabalaena would not be able to chew or filter the feed, the muscular attachments on the bones of her throat indicate that she probably had strong cheeks and a retractable tongue. These traits would have allowed sucking water into his mouth, taking small fish and squid in the process. The suction feeding capacity would have made the teeth, the development of which requires a lot of energy to grow, useless. The loss of the teeth, therefore, seems to have set the evolutionary stage for the fanatics, which scientists estimate have risen about 5-7 million years later.

Peredo and Pyenson see the study of the evolution of whales as key to understanding their survival in rapidly changing oceans. As the emergence of baleen, the loss of teeth in whales is proof of adaptability, suggesting that whales may be able to adapt to the challenges posed today in the ocean. However, Peredo cautions, the evolutionary change can be slow for larger whales, which have a long life and take a long time to reproduce.

"Given the scale and rate of changes in the ocean today, we do not know exactly what it will mean for all the different species of whales that feed on filters," he said. "We know they've changed in the past, it's just a matter of being able to keep up with whatever the oceans are doing and we're changing the oceans pretty quickly right now."

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