The ancestors of modern whales made their transition from land to sea about 53 million years ago. Now, a new study from San Diego State University has found that, at one point during the middle of this transition, whales had mouths full of teeth as well as baleen. I know both . Let us remember that blue, humpback and gray whales are born without teeth because they have what we know as a beard, a series of plates composed of hair-like structures that grow from the roof of the mouth and that serve as a sieve to filter their food. But they have teeth in the womb.
We now know that this was not always the case, that embryonic teeth are evidence of a time when ancient whales did possess teeth and consumed larger prey.
Evolution
For this study, the researchers used the high-resolution computed tomography (CT) technique to scan a 25-million-year-old fossilized whale skull that belonged to Aetiocetus weltoni, an evolutionary “cousin” of modern whales now extinct and whose fossils they were found north of the Pacific, in Orégón (USA). The analysis revealed that he had teeth and beards at the same time in adulthood.
This transitional fossil was therefore discovered along the Oregon coast by graduate students of the Museum of Paleontology at the University of California, Berkeley, and loaned to the biologist and lead author of the study, Eric Ekdale, of the State University of San Diego, and paleontologist Thomas Deméré of the San Diego Museum of Natural History. Since barbs decompose and are rarely preserved intact in fossils, the scientists had to base their experiments on digital reconstructions with CT images to look for evidence of barbs in Aetiocetus, whose skull had about forty-four teeth (molars with crowns, curved canines and incisors). The study revealed grooves and holes in the roof of the mouth that connect internally with a vascular canal in a manner consistent with the pattern of blood vessels leading to whiskers in modern specimens.
The study also revealed separate connections that would have brought blood to the upper teeth, which is consistent with the pattern of blood supply to the teeth of tooth-bearing whales such as sperm whales and killer whales, porpoises or even dolphins.
From carnivores to filter feeding
“We have found evidence to support a concurrency of teeth and beards, indicating that the transition from tooth to beard occurred in a staggered fashion from just teeth, to teeth and beards, to just beards,” Ekdale clarifies. “Our study provides tangible fossil evidence of a major change in feeding behavior from a carnivorous raptorial mode of feeding to a bulk filter feeding mode for food, among the largest animals ever to live in the oceans of the United States. Land”.
The ancestors of whales evolved over many tens of millions of years, first on land as land mammals and then in the aquatic environment. It is this transition and subsequent diversification of absolutely aquatic whales that fascinates scientists, and discoveries similar to theirs point to how interesting it is to discover the historical past of life on our planet.
Referencia: Eric G Ekdale, Thomas A Deméré. Neurovascular evidence for a co-occurrence of teeth and baleen in an Oligocene mysticete and the transition to filter-feeding in baleen whales. Zoological Journal of the Linnean Society, 2021; DOI: 10.1093/zoolinnean/zlab017
