Evolution and Development 9:278-289. She started by studying the skull of Basilosaurus, a serpent-like, predatory whale that lived 37 million years ago, using a three-dimensional digital model generated from CT scans of the fossil that were acquired at the U-M Medical School Department of Radiology. Asymmetry was reduced in baleen whales. Palaios 24:290-302. ANN ARBOR—Skewed skulls may have helped early whales discriminate the direction of sounds in water and are not solely, as previously thought, a later adaptation related to echolocation. It has an unusual bone structure around the animal’s ear. Frustrated, she stared at a cast of the actual skull, puzzling over the problem. But when Fahlke began working with the “corrected” model, the jaws just didn’t fit together right. To study the asymmetry in a more rigorous way, Fahlke and colleagues selected six well-preserved skulls that showed no signs of artificial deformation and measured those skulls’ deviation from a straight line drawn from snout to back of skull. Lion Teeth Roar Fear. This, in concert with the inferred small flukes in Basilosaurus,indicates that nearly the entire body of Basilosaurus undulated up and down during swimming, unlike modern cetaceans, which primarily use the ‘tail’ region during swimming. Sequence stratigraphic control on preservation of late Eocene whales and other vertebrates at Wadi Al-Hitan, Egypt. This is used for long range communication between the elephants. Basilosaurus is a prehistoric whale which lived approximately 40 million to 34 million years ago during the Late Eocene Period. The skulls of archaeocetes and toothed whales are asymmetrical, but the skulls of artiodactyls and baleen whales are symmetrical. The tympanic bulla, a bone which forms the floor of the middle ear cavity, was less connected to the rest of the skull as compared to more primitive whales. Quick view Compare Add to Cart. Journal of Vertebrate Paleontology 10:455-466. The whole skull is affected by a torsion that is clockwise when viewed from the head forward (symbolized by the swirl). Unlike most of the modern species of cetaceans, interaction between members of the same kind were often hostile and lethal. 2009. Credit: Julia M. Fahlke These observations led scientists to believe that archaeocetes?the extinct, ancient whales that gave rise to all modern whales?had symmetrical skulls, and that asymmetry later developed in toothed whales in concert with echolocation. However, it also seems possible that the hindlimbs had no clear function. This is the oldest whale genus with evidence for flukes, although flukes may have occurred in early whales for which the tail is unknown. About Michigan News, Office of the Vice President for Communications Credit: Julia M. Fahlke, Proceedings of the National Academy of Sciences, Office of the Vice President for Communications. Credit: Julia M. Fahlke “Taken together, the six skulls deviate significantly from symmetry,” Fahlke said. Its overall body shape is so unlike those of other whales that it was initially thought to be a marine reptile; hence the name Basilosaurus, which means “king lizard.” The teeth towards the back of the mouth have multiple large serration-like cusps. 2007. Three species of Basilosaurus are known, and specimens have been discovered in fossil sites in the southeastern United States (Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, and Tennessee), England, Egypt, Jordan, and Pakistan, indicating that Basilosaurus inhabited the Northern Atlantic Ocean, Tethys Sea, and the Paratethys Sea (the precursor to the Mediterranean Sea). Asymmetry evolved in archaeocetes and was later exaggerated in toothed whales. Although not positioned at the tip of the snout like more primitive whales (e.g. 2006. “Taken individually, four of them deviate significantly.” The other two appear asymmetrical, but their measurements fall within the range of the symmetrical comparative sample. Reichenbach (1847) erected Basilosaurus kochii for the posterior skull fragment MB Ma.43248, found in the Late Eocene (middle-late Priabonian) Ocala Limestone of Clarksville, Louisiana. The deer has several stomach chambers that allow it to chew, swallow, regurgitate and then re-chew the cud of its food. She didn’t have to go far to explore that idea; the U-M Museum of Paleontology houses one of the world’s largest and most complete archaeocete fossil collections. They had a head more like a land animal with a rostral structure (nose) in relative proportion to the rest of the skull, unlike modern whales that have elongated jaws, called a telescoping skull. “This shows that asymmetry existed much earlier than previously thought?before the baleen whales and toothed whales split,” Fahlke said. Cast of the skull of Basilosaurus isis, seen from the top, showing the deviation of the midline of the skull (red) from a straight line (black) connecting the tip of the snout with the back of the skull. “Under pressure from sediments, fossils oftentimes deform.” To correct for the deformation, coauthor Aaron Wood, a former U-M postdoctoral researcher who is now at the University of Florida, straightened out the skull in the digital model.

basilosaurus skull teeth ear structure

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