The Whales Lost Their Teeth Before They Exhibited Beards

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Rivalizing with the evolution of feathers in dinosaurs , one of the most extraordinary transformations in the history of life was the evolution of beards in whales.

These are rows of flexible hair-shaped plates used by blue whales, humpback whales and other marine mammals to filter relatively small prey from seawater. This unusual structure allows the world’s largest creatures to consume several tons of food each day, never chewing or biting.

Now, scientists from the Smithsonian Institute in Washington, United States, have discovered an important intermediate link in the evolution of this innovative feeding strategy: an ancient whale that had neither teeth nor beards. In this Thursday’s issue of Current Biology , scientists from the Smithsonian’s National Museum of Natural History and their colleagues describe for the first time ‘Maiabalaena nesbittae’, a whale that lived approximately 33 million years ago.

Using new methods to analyze fossils discovered long ago located in the Smithsonian’s national collection, the team, which includes scientists from George Mason University, Texas A & M University and the Burke Museum of Natural History and Culture of Seattle, all in United, it has determined that this 15 foot (4.57 meter) toothless whale probably did not have a beard, showing a surprising intermediate step between the baleen whales that live today and their jagged ancestors.

“When we talk about the evolution of whales, textbooks tend to focus on the initial stages, when the whales left the land to the sea,” says the marine mammal curator at the National Museum of Natural History. “Maiabalaena” shows that the second phase of whale evolution is very important for large-scale evolution.For the first time, we can now specify the origin of filtration feeding, which is one of the main innovations in the history of the whales, “he adds.

When the whales evolved for the first time, they used their teeth to chew their food, just like their terrestrial ancestors. With the passage of time, many descendants of these first whales continued to chew their food, inheriting this trait from their predecessors. But as the oceans around them changed and the animals evolved, completely new feeding strategies emerged, including filter feeding thanks to the beards , says the National Museum of Natural History’s pre-doctoral researcher Carlos Mauricio Peredo, lead author of the study that analyzed the fossils of ‘Maiabalaena’.

Whales were the first mammals to evolve, and no other mammal uses an even remotely similar anatomical structure to consume its prey. But frustratingly, beards, whose chemical composition is more like that of hair or nails than bone, do not keep well. They are rarely found in the fossil record, leaving paleontologists without direct evidence of their past or origins. Instead, scientists have had to rely on fossil inferences and studies on the fetal development of the whale in the womb to gather clues about how beards evolved.

As a result, it is not clear if, as they evolved, the first whales kept their ancestors’ teeth until a filtration feeding system was established. One of the first initial hypotheses, according to Peredo, was that the mammals that inhabit the ocean must have needed teeth or barbs to eat, but several living whales contradict that idea. Sperm whales have teeth in their lower jaw, but none in the upper part, so they can not bite or chew. The only teeth of the narwhals are their long fangs, which they do not use to feed themselves. And some species of beaked whales, despite being classified as toothed whales, do not have any teeth.

The Whales Lost Their Teeth Before They Exhibited Beards

ADAPTABILITY OF WHALES

Due to their age, Peredo explains, paleontologists suspected that ‘Maiabalaena’ could have important clues about the evolution of beards. The fossil comes from a period of massive geological changes during the second main phase of the evolution of the whale, around the time when the Eocene epoch was in transition towards the Oligocene.

With the continents changing and separating, ocean currents swirled around Antarctica for the first time, significantly cooling the waters.

The fossil record indicates that the feeding styles of the whales diverged rapidly during this period of time, with one group leading to whales that feed by filtration today and the other that leads to whale echolocation.

As a result, ‘Maiabalaena’ had been subject to much scrutiny since its discovery in Oregon in the 1970s, but the rock matrix and the material in which the fossil was collected still hid many of its characteristics. It was not until Peredo finally cleaned the fossil and examined it with the most modern computerized tomography (CT) scanning technology that its most notable characteristics became evident. The lack of ‘Maiabalaena’ teeth was evident from the preserved bone, but the CT scans which revealed the internal anatomy of the fossil, indicated to the scientists something new: the upper jaw of ‘Maiabalaena’ was thin and narrow, so which is an inadequate surface from which to suspend the beard.

“A live bearded whale has a large, wide roof in its mouth, and it is also thickened to create places to hold the beard,” says Peredo. “‘Maiabalaena’ did not have it so we can tell you conclusively that this fossil species he had no teeth, and it is more likely that he did not have beards either. ”

Although ‘Maiabalaena’ could not chew or filter the food, the muscle joints in the bones of her throat indicate that she probably had strong cheeks and a retractable tongue. These features would have allowed him to suck water with his mouth, catching fish and small squid in the process. The ability to suck food would have made the teeth, whose development requires a lot of energy to grow, unnecessary. The loss of teeth, then, seems to have established the evolutionary state of the beard, which scientists estimate to have arisen approximately 5-7 million years later.

Peredo and Pyenson consider that studying the evolution of whales is key to understanding their survival in the oceans that are changing rapidly today. Like the appearance of beards, the loss of teeth in whales is a test of adaptability, suggesting that whales could adapt to the challenges posed in the ocean today. Even so, warns Peredo, evolutionary change can be slow for larger whales, which have a long lifespan and take a long time to reproduce.

“Given the scale and rate of changes in the ocean today, we do not know exactly what will that mean for all the different species of whales that feed by filtering he points out. We know that in the past have changed. It ‘s just a question of whether they can keep up with whatever the oceans are doing, and now we are changing the oceans pretty quickly. ”

 

 

Source: Europa Press