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The toothless, 33 million-year-old whale could be an evolutionary "missing link"



A closer look at the fossil found more than four decades ago led to the identification of a new species of whale, a 33 million-year-old cetacean who had neither teeth nor a bale. His discoveries could solve the long-standing mystery about the whale origin that feeds on the filter, but some scientists say the new analysis is not entirely convincing.

Introducing Maiabalaena nesbittae, a completely new genus and species of ancient whale. Roughly the size of the modern beluga whale, this 4.57m long cetaceans had no teeth or bale (a series of hair-like plates that whales use to filter the small prey of water), relying instead on sucking feed.

Such, Maiabalaena nesbittae, which means "the mother of a whale," represents an intermediate stage between old toothed whales and modern filter feeders, according to a new research published today in Current Biology.

Today, whales can be divided into two main groups: toothed whales such as the orc and dolphins, and whales that feed on the filter, such as whales, whales, blue whales, and mink whales. Baleen is a remarkable evolutionary invention that makes filtering possible, allowing large sea whales to consume several tons of food each day without having to chew or chew.

Whales are the first and only mammals to develop packages, but the origin of this feed strategy is not entirely clear. The whales come from terrestrial mammals that retained their teeth after adjusting the aquatic lifestyle.

With their sharp teeth, the old whales continued to chew their food. But the environment has changed, just as their prey, so these whales have had to adopt new feeding strategies. This eventually resulted in the formation of filter feeds.

Regarding how the whales came from having teeth to have a baleen – a keratin fabric, which is what hair and nails are made of – is the subject of many disputes.

Some scientists speculated that ancient whales used their teeth to sift water, and that this feed strategy led directly to the balens. This theory was taken in the past year by the direct intervention of Monash University paleontologists who showed that the sharp teeth used by ancient whales could not be used as filters, and concluded that ancient whales had never passed a tooth-based filtration phase and that some kind of intermediary species still to be found.

Part of the problem lies in the fact that keratin does not last well in the fossil record. For paleontologists studying ancient whales, this mystery is similar to flight studies in old animals and a seemingly endless search for revealing the "missing link" between gliding birds and those able to fly spontaneously.

In the case of whales, paleontologists have been searching for the middle class of whales, which is located between toothed whales and whale-feeding filters. Discover toothless, lethargic Maiabalaena nesbittae this missing link could be very good.

Partial skeleton Maiabalaena nesbittae, which includes almost a full skull, was uncovered in Oregon in the 1970s and has since collapsed in the Smithsonian National Collection. There was no detailed analysis of fossils on this point because it is flooded with rock and other materials.

The lead author of a new study, Carlos Mauricio Peredo of George Mason University and the National Museum of Natural Sciences, looked at the old fossil with new eyes using state-of-the-art CT scanning technology. Looking at the rock, scientists were able to identify signs of toothless and invertebrate whales – including thin and narrow upper jaws that had no suitable surface from which they could suspend the baleen.

"The live packed whale has a large, wide roof in the mouth and it is also strengthened to create bottleneck attachments," Peredo said in a statement. "Maiabalaena is not. We can quite convincingly say that this fossil species has no teeth and is unlikely that it has not even been packed. "

Other evidence points to this animal as a filter. Muscle supplements on the bones of the throat indicate the presence of strong cheeks and tongue – characteristics that would allow the whale to suck in the water, to repair fish and small squids in the process.

Equipped with this ability, these whales no longer needed their chomps, so their teeth gradually disappeared. For the possible loss of teeth and the origin of baleens, researchers say, where evolutionary events separate.

As for why tooth whales abandoned biting and chewing in favor of sucking, scientists say that it was the transition forced into them in a changing environment. Maiabalaena lived during the transition period that divided Eocene from the oligocene, which happened 33 million years ago. It was a critical time for whales, as the continents shifted and separated, and ocean currents from Antarctica cooled the oceans.

How the planet's geology changed, as well as the ocean environment – and its animals. The loot of jagged whales has changed or disappeared and forced them to find new prey, which has led to a shift from tooth feeding to sucking, researchers speculate. Finally, about 5-7 million years later, about 26-28 million years ago, toothless whales began germinating the bales, facilitating another transition, this time from feeding sucking to filter feeding.

"Generally, I think this is a good study and I agree with her general conclusions," said Gizmodo Felix G. Marx, a Monash University paleontologist not associated with this new research. "Definitely, Maiabalaena it seems to be right in the middle of this transition, without teeth and possibly without packs. "

Maybe no packs.

That's a key phrase, here. As noted, a bale that is made of soft tissue is not fossilized very well. Most scientists can detect the presence of baleen in fossil glasses by looking for traces of matching blood vessels on their bones. And in fact, traces of blood vessels were found in the hair Maiabalaena fossil. The question, however, is whether these blood vessels always correlate with the baleen.

"A new study says no, and claims that a similar structure existed also in old toothed whales that apparently did not filter the feed," Marx said. "I agree, but it's still an interpretation, and I suspect that not everyone will buy it. Fortunately, there are many possibilities to address this issue, for example, by exploring how the baleen is actually developing in the uterus."

The University Paleontologist Monash Alistair Evans, co-author of the above-mentioned study in 2017, agrees with Marx's assessment when he says that the absence of teeth in this species is quite obvious, but the absence of baleen, not so much.

"Because the bale is so seldom petrified, its presence can rarely be seen directly," Evans told Gizmod. "As has been suggested earlier – a [as this new paper] gives more evidence – there are no silver balls in the bones that could surely tell us that the bale was present. So, unfortunately, there is no strong evidence that there is no bale, but we will never find such evidence. "

Evans says the conclusions made in the new study are "quite reasonable," but he would like to see other specimens of this species and related species that are better preserved in the area where they would be packed if present.

"I was happy to find the fossil that we had supposed to appear on, but the evidence does not mean that it would fit into this slot," Evans added.

So it is Maiabalaena nesbittae Missing link we searched for? Maybe yes – but we certainly will not know until further fossils are restored.

[Current Biology]

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