The whales lost their teeth before their hair developed in the mouth


PICTURE: It is an artistic reconstruction of the mother and the calf Maiabalaena nesbittae nursing offshore Oregon during the oligocene, about 33 million years ago. While Maiabalaena he should not …
View more

Credit: Alex Boersma

Related to the evolution of dinosaur feathers, one of the most striking changes in the history of life was the development of packages – a series of elastic hair plates that use blue whales, flocks and other marine mammals to filter relatively small prey from ocean water gulps. The unusual structure allows the world's largest creators to consume several tons of food a day without chewing or chewing. Now Smithsonian scientists have discovered an important intermediate link in the development of this innovative feed strategy: an ancient whale that has neither teeth nor wrapped.

In the November 29 issue of the magazine Contemporary biology, for the first time, scientists from the Smithsonian National Museum of Natural History and colleagues Maiabalaena nesbittae, a whale that lived 33 million years ago. Using new methods to analyze long-found fossils located in the Smithsonian National Collection, a team of scientists at George Mason University, Texas A & M University and Burke Museum of Natural History and Culture in Seattle, decided that this toothless whale whale probably it was not packed, which shows a surprising mediating step between the whale whales that live today and their cognizant ancestors.

"When we talk about the development of whales, textbooks usually focus on the initial phase when whales went from land to sea," said the fossil marine mammal curator of the National Museum of Natural Sciences. "Maiabalaena shows that the second phase of whale development is equally important for large-scale development. For the first time, we can deduce the origin of filtering, which is one of the main innovations in the history of whales. "

When the whales first developed, they used their teeth to eat, just like their ancestors. Over time, many offspring of these first whales have always chewed their food, inheriting this feature from their predecessors. But as the oceans around them and animals have evolved, new feeding strategies have emerged, including feeding to the Philippine filter, says the lead physician of the National Museum of Natural Sciences Carlos Mauricio Peredo, the lead author of the study that he analyzed Maiabalaena fossil.

Whales were the first mammals to develop a bale, and no other mammal uses any anatomical structure or remotely similar to consume its prey. But frustrating is that a bale whose chemical composition is more like hair or nails than bones is not saved well. It is rarely found in the fossil record, leaving paleontologists without direct evidence of their past or background. Instead, scientists had to rely on the findings of fossil forms and studies of the evolution of the uterus in the uterus to jointly demonstrate how the parrot developed.

As a result, it was unclear whether the whale whistle had been prevented by their ancestors at the time they evolved until the filter feeding system had been introduced. The premise assumption, Peredo said, was that mammals living in the oceans needed to eat teeth or food packages – but several of these live whales are inconsistent with this idea. Sperm whales have teeth in the lower jaw, but none at the top so they can not bite or chew. Narwhal's only teeth are their long tusks, which they do not use for feeding. And some beak whales, although classified as toothed whales, have no teeth at all.

Because of his age, Peredo said, the paleontologists suspected Maiabalaena could have important traces of the development of the baleens. Fossil comes from a period of massive geological change during the second major phase of whale development, around Eocene's transition to Oligocene. With continents moving and separating, ocean currents flowed around Antarctica for the first time, which greatly cooled the water. The fossil record suggests that whaling feeding styles quickly diverged within this timeframe, with one group leading to today's feed filters, and the other led to the fact that,

Therefore, Maiabalaena has received much attention since its discovery in Oregon in the 1970s, but the rock matrix and material from which the fossil was collected still concealed many of its features. Only after Peredo finally cleared the fossil, and then examined it with the latest CT scanning technology, its clear features appeared. Maiabalaenalack of teeth was readily apparent from protected bone tissue, but the CT examination, which revealed the internal anatomy of the fossil, told scientists something new: Maiabalaenathe upper jaw was thin and narrow, making it an inadequate surface from which packages could be hung.

"A live packaged whale has a large, wide roof in the mouth and it is also strengthened to create binding points for the baleen," Peredo said. "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. "

While Maiabalaena would not be able to chew or filter the feed, the muscles on the bones of the throat suggest that it has probably strong faces and a tongue. These features would allow him to take water into his mouth, and fish and small squids are involved in this process. The ability of intake feed would cause teeth, whose development requires high energy to grow, unnecessary. The loss of teeth then appears to have determined the evolutionary phase for the baleen, which scientists estimate about 5 to 7 million years later.

Peredo and Pyenson see studying whale development as a key to understanding their survival in today's rapidly changing oceans. As well as the occurrence of baleen, the loss of teeth in whales is a proof of adaptability, suggesting that whales could adapt to the challenges that the ocean represents today. However, warns Peredo, an evolutionary change may be slow for the largest whales, which have a long life and last a long time to reproduce.

"Given the magnitude and speed of changes in the oceans, we do not know exactly what this will mean for all sorts of strains fed by the filter," he said. "We know it has changed in the past, it's just a question of whether they can keep up with what the oceans are doing – and we're just changing the oceans right now."


Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of the news posted on EurekAlert! contributing institutions or for the use of any information through the EurekAlert system.

Source link