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Without teeth, a 33-million-year-old whale could become an evolutionary "missing link"

A closer look at the fossils discovered more than four decades ago led to the identification of a new type of whale – a 33 millionth cetacean, with no teeth or baleen. His discovery may solve a long-standing mystery about the origin of whales that feed on filtration, but some scientists say that the new analysis is not completely convincing.

Entering Maiabalaena nesbittae, a completely new genus and species of ancient whale. Approximately the size of a modern white whale, this 4.57 mm cetacean did not have teeth or baleen (rows of hairy plates that whales use to filter tiny prey from water), relying instead on suction.

As such Maiabalaena nesbittae, which means "mother whale", is an intermediate stage between the ancient toothed whales and modern filter feeders, according to a new study published today in Current Biology.

Today, whales can be combined into two main groups: jagged whales, such as orcs and dolphins, and whales that feed on filtration (or mysticals), such as humpback whales, finles, blue whales, and small whales. Baleen is a remarkable evolutionary invention that makes it possible to feed filters, allowing large sea whales to consume several tons of food every day, without having to grind or chew.

Whales are the first and only mammals that develop slaughter, but the origin of this feeding strategy is not entirely clear. Whales are descended from land mammals that have retained their teeth after adapting the aquatic lifestyle.

With their sharp, sharp teeth, the ancient whales continued to chew their food. But the environment has changed, as well as their prey, so these whales had to adopt new feeding strategies. Ultimately, this led to the appearance of whales feeding on filters.

As for how the whales went from teeth to drying out – a substance made from keratin, which is what hair and nails are made of, is the subject of much controversy.

Some scientists have suggested that ancient whales used their teeth to sift water, and this feeding strategy led directly to grazing. This theory received a direct hit last year by paleontologists at Monash University, who showed that the sharp teeth used by ancient whales could not be used as filters, with the result that ancient whales never went through the teeth-based filtration phase and something it seems there should be an intermediate, not yet found.

Part of the problem is that keratin does not preserve well in the fossil record. For paleontologists who study ancient whales, this mystery is akin to studying flight to ancient animals and seemingly endless search to find the “missing link” between sliding birds and those who are able to control their own flight.

In the case of whales, paleontologists looked for an intermediate whale species, located between the notched whales and the whales feeding on the filters. The discovery of the toothless, lifeless Maiabalaena nesbittae may well be this missing link.

Partial skeleton Maiabalaena nesbittae, which includes an almost complete skull, was discovered in Oregon as early as the 1970s, and since then it has languished in the national collection of the Smithsonian people. At this point, a detailed analysis of the fossil was not possible because it was flooded with stones and other materials.

The lead author of the new study, Carlos Mauricio Peredo, from George Mason University and the National Museum of Natural History, looked at this old fossil with new eyes using modern CT scan technology. Peering into the rock, the researchers were able to identify the telltale signs of a toothless and lifeless whale, including a thin and narrow upper jaw, which did not have a proper surface from which to stop the slaughter.

“The live mustache has a large, wide roof in its mouth and is also thickened to create places for attachment to the estate,” said Peredo in a statement. "Maiabalaena not. We can quite convincingly tell you that these fossil species do not have teeth, and it is more likely that it did not have catches. ”

Other evidence points to this animal as a filter feeder. Muscle attachments on the bones of his throat imply the presence of strong cheeks and a retractable tongue – characteristics that would allow this whale to suck water into its mouth, tearing off fish and small squids in the process.

These whales, equipped with this ability, no longer needed their chompers, so their teeth gradually disappeared. The possible loss of teeth and the origin of baleen, the researchers argue, where, therefore, separate evolutionary events.

As for why the whales refused to bite and chew in favor of sucking, the researchers say that this was a transition imposed on them by changing the environment. Maiabalaena lived in the transition period, which divided the Eocene from the Oligocene, which occurred about 33 million years ago. This was a critical time for the whales, as the continents shifted and separated, and ocean currents from the Antarctic cooled the oceans.

As the geology of the planet changed, the oceanic setting was also her animals. Researchers suggest that the extraction of toothed whales has changed or disappeared, forcing them to find new prey, which has led to a transition from the dentate to the suction. Eventually, about 5–7 million years later, about 26–28 million years ago, toothless whales began to sprout baleen, facilitating another transition, this time from suction to filtration.

“In general, I think this is a good study, and I agree with its general conclusions,” said Gizmodo Felix G. Marks, a paleontologist at Monash University, who is not associated with this new study. "However, Maiabalaena it seems to be right in the middle of this transition, without teeth and, possibly, without a whisker. "

Probably not a mustache.

Here is the key phrase. As already noted, the mustache, which is made of soft tissue, does not harden very well. Scientists can usually detect the presence of a manor in a fossil by looking at the traces of the corresponding blood vessels on their bones. And in fact, traces of blood vessels were found in Maiabalaena fossil. The question, however, is that these blood vessels always correlate with slaughter.

"The new study says no, and claims that similar structures existed among ancient gear whales, which clearly did not filter the feed," said Marx. “I agree, but this is still an interpretation, and I suspect that not everyone will buy it. Fortunately, there is one more thing that we can do to resolve this issue, for example, by studying how the female actually develops in the womb. "

A paleontologist at Monash University, Alistair Evans, co-author of the aforementioned 2017 study, agrees with Marx’s assessment, stating that the absence of teeth in this species is rather obvious, but the absence of baleen is not so much.

“Because the manor is so rarely petrified that its presence is rarely seen directly,” said Evans Gizmodo. "As suggested earlier – and [as this new paper] gives more evidence – there are no silver bullets in the bones that could tell us exactly that the bastard was present. So, unfortunately, there is no convincing evidence of the absence of the estate, but we also will never find such evidence. ”

Evans says that the findings of the new study are “reasonable enough,” but he would like to see other specimens of this species and kindred, which are better preserved in the region where they exist if they existed.

“I was happy that they found a fossil that we predicted would happen, but the evidence is not a slam shut, that it really did fit into this slot,” added Evans.

So that Maiabalaena nesbittae the missing link we were looking for? It is possible, yes, but we will not know for sure until more minerals are restored.

[Current Biology]

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