An ancient Leviathan named for King Tut, but Moby-Dinky sized

by MMC
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In 1842, a large, almost intact skeleton was discovered on a plantation in Alabama; it was quickly identified as a member of Basilosaurus, a recently named genus of prehistoric sea serpent. But when some of its enormous bones were shipped to England, Richard Owen, an anatomist, noticed that its molars had two roots, not one, a dental morphology unknown in any reptile. He determined that the fossil was actually a marine mammal: a primitive whale. Herman Melville names the giant – Mr. Owen called it Zeuglodon – in chapter 104 of “Moby-Dick,” and Mr. Owen, in a paper he read at the London Geological Society, declared it “ one of the most extraordinary.” creatures that the mutations of the globe have erased from existence.

In August, a team of paleontologists announced the discovery of another extraordinary creature that went extinct. Eleven years ago, while working in the Fayoum Depression in Egypt’s Western Desert, the team unearthed the fossil of what they initially thought was a small amphibian. But closer inspection revealed that the bones belonged to a previously unknown species of miniature whale that existed in the late Middle Eocene, in a period called the Bartonian Age, which lasted from about 48 to 38 million years old. The species, described in an article in the journal Communications Biologyinhabited the Tethys Sea, the tropical precursor to the Mediterranean, which covered about a third of what is now North Africa.

Ishmael, the protagonist of “Moby-Dick”, somewhat disingenuously claims that a whale is a “spouting fish with a horizontal tail.” The newly documented specimen looked less like a fish and more like a bottlenose dolphin, with a less bulbous forehead and a more elongated body and tail. Based on fragments of skull, jaw, teeth and vertebrae embedded in compacted limestone, the researchers deduced that the small whale, which dates back about 41 million years, was about eight feet long and weighed approximately 400 pounds, making it the smallest known member of the species. basilosaurid family.

All whales are descended from land animals that ventured into the sea. Some of the earliest whales evolved into forms that ventured onto land; Basilosaurids are believed to be the first widespread group to have stuck to marine life. They were also the last to have hind limbs still recognizable as legs, which probably served less for locomotion than as breeding guides to help orient the whales during sex.

Melville dismissed the taxonomy of whales as “mere sounds, full of Leviathanism, but signifying nothing.” He probably would have had no use for Tutcetus rayanensis, the official name of the ancestor of small whales. Tutcetus combines Tut – reminiscent of the pharaoh Tutankhamun – and cetus, Greek for whale. This designation also follows the centenary of the discovery of King Tutankhamun’s tomb and coincides with the imminent opening of the Grand Egyptian Museum in Giza, Egypt. The “rayan” part of the name derives from the protected area of ​​Wadi El-Rayan, located about 40 km northeast of a site so rich in whale fossils that it has been called Wadi Al-Hitan, or Whale Valley.

Like Tut, who died in the Valley of the Kings at the age of 18, the whale is believed to have been a juvenile approaching adulthood. The research team used CT scanning to analyze Tutcetus’ teeth and bones, reconstructing its growth patterns. The bones of the skull had fused, as had parts of the first vertebrae, and although some teeth had erupted, others were still in transition. The rapid dental development and small size of Tutcetus’ bones suggest a short, fast life compared to larger, later basilosaurids, said Hesham Sallam, a paleontologist at the American University in Cairo and leader of the project.

According to the researchers, the whale could have fed and moved independently almost from birth. The soft enamel and configuration of its teeth suggest that it was a carnivore, feeding on aquatic animals.

The discovery challenges some conventional assumptions about the life history of primitive whales. “The geologic age of Tutcetus is somewhat older than that of other closely related fossil whales, suggesting that some evolutionary changes in whale anatomy occurred somewhat earlier than previously thought,” Nicholas said Pyenson, curator of fossil marine mammals at the Smithsonian National Museum of Science. Natural History, which did not participate in the work. “The fossil pushes back the time when the first whales transitioned from leg-powered to tail-powered movement in the water.”

Whales have an unexpected past. Genetically, they are closely related to hoofed mammals, called ungulates, and within this group they most closely resemble artiodactyls, such as camels, pigs, giraffes, and hippos, all of which have an even number of toes . One of the best-known ancestors of whales was a 50-million-year-old quadruped called Pakicetus that waded the estuaries of South Asia, ate meat and, by some accounts, may have resembled a large domestic cat with hoof-shaped hooves. claws.

Scientists were able to link Pakicetus to the evolutionary lineage of whales because it possessed an ear bone with a feature unique to these modern deep-sea giants. “Importantly, its ankle bones resemble those of artiodactyls and helped support the connection between whales and artiodactyls that had previously been suggested by DNA,” said Erik Seiffert, an anatomist at the University of Southern California who collaborated on the article.

Artiodactyls gave rise to the semi-aquatic Ambulocetus, a so-called walking whale that looked like a crocodile, swam like an otter, and waddled on land like a sea lion. “In fact, Ambulocetus still had fairly well-developed hind limbs, so it would not have had any difficulty moving on land,” Dr. Seiffert said. Ambulocetus, in turn, spawned the Protocetid, a midstream more streamlined creature that fed in the sea, but may have returned to land to rest. As it evolved, its hind limbs became smaller and it maneuvered entirely with its tail.

Eventually, these proto-cetaceans gave rise to the archaeocete, a fully aquatic basilosaurid. Aided by their fins and paddle-shaped tails, basilosaurids spread across oceans around the world. The one that appeared on this Alabama plantation in 1842 may even have crossed the Atlantic.

Mohammed Antar, a paleontologist at Mansoura University who unearthed the Tutcetus fossil and was first author of the new paper, said the climate and location may have made the Fayoum Depression inviting to basilosaurids. “Modern whales are migrating to warmer, shallower waters to mate and reproduce, mirroring the conditions found in Egypt 41 million years ago,” he said.

The setting appears to have provided a relatively safe haven for female whales to give birth in the shallow waters. “Based on the abundant fossils of arboreal primates found there, the area bordering the northern edge of what is now the Sahara was actually a tropical forest during the middle Eocene,” said Dr. Seiffert . North Africa’s protected coasts, he added, “could have allowed calves time to mature and reach a level of navigational and feeding proficiency before heading into the waters.” free, then very deep waters.

In August, shortly before the diminutive Tutcetus was unveiled in Egypt, paleontologists working in Peru reported the discovery of an extinct whale that may have been the heaviest animal ever seen. Perucetus colossus swam in the oceans 38 million years ago and is estimated to have weighed up to 200 tonnes, a figure comparable to that of the blue whale, the current record holder.

Perucetus and Tutcetus existed only a few million years before primitive whales began their evolutionary division into two suborders of today’s cetaceans: the toothed whales, dolphins, and porpoises known as odontocetes , and baleen whales, including blue whales and humpback whales.

“Mysticetes tend to be much larger than odontocetes,” said Jonathan Geisler, an anatomist at the New York Institute of Technology. “And this difference is linked to their different feeding strategies.” Toothed whales hunt individual prey such as fish and squid, while baleen whales filter feed to collect krill, copepods and tiny schools of fish.

“Understanding the size of the ancestor of all modern whales helps us understand how these feeding behaviors and distinct differences in body size evolved,” Dr Geisler said. “Tutcetus is a given in this effort, but it supports the hypothesis that the common ancestor of all living cetaceans was quite small.”

Dr Sallam said that in the same way that Melville, reflecting on the Basilosaurus skeleton discovered in 1842, imagines a time when “the whole world belonged to the whale”, the discovery highlights the ephemeral nature of existence and provides a tangible link to a prehistoric past. . “The significance of this discovery, like the fossils depicted in Moby Dick, extends beyond the field of paleontology,” he said. “This highlights the enduring fascination with Earth’s ancient history.”

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