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Whale-free whale, of 33 million years of age, could be an evolutionary "lost link"


A more detailed exam of a fossil found more than four decades ago has led to the identification of a new species of whale: a 33-million-year-old whale with no teeth or whales. His discovery could solve a long-standing mystery about the origin of whales filtering on food, but some scientists say the new analysis is not entirely convincing.

Presenting Maiabalaena nesbittae, a totally new genus and a kind of ancient whale. Approximately the size of a modern Belarusian beluga whale, this 4.57-m tall hepatic cetacean had no teeth or bullet (rows of hair-like dishes that use whales to filter small water dams ), leaning on, instead of feeding on suction.

As such, Maiabalaena nesbittae, which means "sea whale", represents an intermediate stage between old toothed whales and modern filter-feeders, according to a new research published today in Current Biology.

Nowadays, whales can be grouped into two main groups: toothed whales, such as orchids and dolphins, and filtering whales (or mysticeti), such as cradles, whales, blue whales and minke whales. Baleen is the remarkable evolutionary invention that makes possible the feeding of the filter, allowing big sea whales to consume several tons of food every day without having to chew or chew.

Whales are the first and only mammals to evolve, but the source of this feeding strategy is not entirely clear. Whales are descended from terrestrial mammals, which kept their teeth after adapting to a water life style.

With their sharp teeth, ancient whales kept chewing their food. But the environment changed, just like its prey, so that these whales had to adopt new feeding strategies. Finally, this resulted in the appearance of whales feeding the filter.

Regarding how whales went from having teeth to having whales, a keratin substance, which is what hair and nails and made of, is subject to much controversy.

Some scientists have speculated that the ancient whales used their teeth to slim water and that this diet strategy directly led to the whales. This theory was a direct success last year by the paleontologists of the Monash University who demonstrated that the sharp teeth used by ancient whales could not have been used as filters and concluded that the ancient whales never go going through a phase of leak-based filtration, of intermediate species, still existing, must have existed.

Part of the problem is that keratin is not well preserved in the fossil record. For paleontologists studying ancient whales, this mystery is similar to the flight study in ancient animals and the apparently endless search to discover the "lost link" between sliding birds and those capable of self-propelling the flight .

In the case of whales, paleontologists have been looking for an intermediate whale species located between toothed whales and whales that leak feed. The discovery of the toothless ones, without whales Maiabalaena nesbittae It could well be this lost link.

The partial skeleton of Maiabalaena nesbittae, which includes an almost complete skull, was discovered in Oregon in the seventies, and has suffered in the Smithsonian national collection since then. At this point, a detailed analysis of the fossil can not be done because it is flooded with rock and other materials.

The leading author of the new study, Carlos Mauricio Peredo, George Mason University and the National Natural History Museum, looked at this old fossil with new eyes using the technique of scanning CT. Looking at the rock, the researchers were able to identify the revealing signs of a whale without teeth and no whales, including a thin, narrow jaw that did not have an adequate surface to suspend whales.

"A live whale whale has a broad and wide roof in your mouth, and it's also thickened to create binding sites for whales," said Peredo in a statement. "Maiabalaena he does not. We can say quite enough to conclude that this fossil species had no teeth, and it is more likely that it did not have tampons either. "

Other evidence points to this animal as a filter feeder. Muscle joints in the throat bones involve the presence of strong cheeks and a retractile tongue, characteristics that have allowed this whale to suck water in the mouth, cutting off fish and squid in the process.

Equipped with this ability, these whales no longer needed their buyers, so their teeth gradually faded away. The possible loss of teeth and the baleen origin, the researchers, argue, where, therefore, separate evolutionary events.

As to why abandoned toothed whales bite and chew in favor of suction, researchers say it was a forced transition through a changing environment. Maiabalaena He lived during the transitional period that divided the Eocene from the Oligocene, which he spent about 33 million years ago. This was a critical moment for whales, as the continents moved and separated, and when the ocean currents of the Antarctic cooled the oceans.

As the geology of the planet changed, so did the marine environment and its animals. Toma whales changed or disappeared, forcing them to find new dams, which led to the transition from the toothed feeding to the aspiration, the researchers speculate. Finally, about 5-7 million years later, around 26-28 million years ago, whales suddenly began to flutter, facilitating a new transition, this time from suction to feed on filter

"Overall, I think it's a good study, and I am in agreement with its general conclusions," Gizmodo Felix G. Marx, a paleontologist at the Monash University, was not afraid of. This new investigation. "Crucially, however, Maiabalaena It seems to be right in the middle of this transition, without teeth, and possibly there is no bullet. "

Possibly there is no bullet.

This is the key phrase, here. As noted, the whale, which is made of soft tissue, does not fossilize very well. In general, scientists can detect the presence of whales in a fossil seeking traces of blood vessels corresponding to their bones. And, in fact, traces of blood vessels were detected at Maiabalaena fossil The question, however, is whether these blood vessels always correlate with whales.

"The new study says no, and argues that there were similar structures in the old toothed whales that clearly did not filter feed," said Marx. "I agree, but this is still an interpretation, and I suspect that not everyone bought it. Fortunately, there are more things we can do to address this issue, for example, by examining how it develops in the uterus ".

The paleontologist of the Monash University, Alistair Evans, co-author of the 2017 study, is in agreement with Marx's evaluation, stating that the absence of teeth in this species is quite Evident, but the absence of whales, not so much.

"Because they are whitewashed are so rarely fossilized, their presence can rarely be seen directly," Evans told Gizmodo. "As previously suggested – i [as this new paper] It gives more evidence: there are no silver bullets in the bones that can ensure that whales were present. Therefore, unfortunately, there is no solid evidence of the absence of whales, but we can not find such evidence either. "

Evans says the conclusions of the new study are "quite reasonable," but I would like to see other specimens of this species and those related better that are kept in the region where the whale would be present.

"I liked finding a fossil that we predicted would occur, but the evidence is not an outbreak that really fit into this space," added Evans.

That's right Maiabalaena nesbittae Lost link we've been looking for? Very possibly yes, but we will not know for sure until more fossils are recovered.

[Current Biology]
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