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Thread: Another important intermediate species found in whale evolution found

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    Another important intermediate species found in whale evolution found

    Another important intermediate species found in whale evolution found

    Source: https://phys.org/news/2019-12-newly-fossil-whale-intermediate-stage.html



    Newly described fossil whale represents intermediate stage between foot-powered and tail-powered swimming

    A newly described fossil whale represents a new species and an important step in the evolution of whale locomotion, according to a University of Michigan paleontologist and his colleagues.


    The fossilized remains of Aegicetus gehennae were recovered in the Egyptian desert in 2007 and were dated to around 35 million years ago. The creature appears to have been well-adapted for swimming through undulation of the mid-body and tail, somewhat as crocodiles swim today, according to U-M's Philip Gingerich.

    The discovery is detailed in a paper scheduled for publication Dec. 11 in the journal PLOS ONE.

    The fossil record of whale evolution tracks the transition from land-dwelling ancestors to ocean-dwelling cetaceans. Protocetids are a group of early, semi-aquatic whales known from the middle of the Eocene, a geological epoch that began 56 million years ago and ended 33.9 million years ago. Protocetid remains have been found in Africa, Asia and the Americas.

    While modern whales are fully aquatic and use their tails to propel themselves through the water, most protocetids are thought to have been semi-aquatic and swam mainly with their limbs.

    In their PLOS ONE paper, Gingerich and his colleagues describe a new genus and species, Aegicetus gehennae, the first late-Eocene protocetid. Its body shape is similar to that of other ancient whales of its time, such as the famous Basilosaurus.

    The researchers suggest that an undulatory swimming style might represent a transitional stage between the foot-powered swimming of early whales and the tail-powered swimming of modern whales.

    "Early protocetid whales living 47 to 41 million years ago were foot-powered swimmers. Later, starting about 37 million years ago, whales became tail-powered swimmers," said Gingerich, a professor emeritus in the U-M Department of Earth and Environmental Sciences and curator emeritus at the U-M Museum of Paleontology.

    "This newly discovered fossil whale, Aegicetus, was intermediate in time and form and was transitional functionally in having the larger and more powerful vertebral column of a tail-powered swimmer," said Gingerich, who is also a professor emeritus of ecology and evolutionary biology and of anthropology.

    The fossilized bones were discovered in the Wadi Al Hitan World Heritage Site in the Western Desert of Egypt. Aegicetus is the youngest-known protocetid and is known from one exceptionally complete skeleton—roughly two-thirds of the individual's bones were recovered—and a partial second specimen, making it among the best-preserved ancient whales.

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    Glendower: I can call spirits from the vasty deep.
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    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

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    Frank

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    From the original publication:

    Source: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0225391#sec001



    Aegicetus gehennae, a new late Eocene protocetid (Cetacea, Archaeoceti) from Wadi Al Hitan, Egypt, and the transition to tail-powered swimming in whales

    Abstract
    Aegicetus gehennae is a new African protocetid whale based on a partial skull with much of an associated postcranial skeleton. The type specimen, Egyptian Geological Museum, Cairo [CGM] 60584, was found near the base of the early-Priabonian-age (earliest late Eocene) Gehannam Formation of the Wadi Al Hitan World Heritage Site in Egypt. The cranium is distinctive in having ventrally-deflected exoccipitals. The vertebral column is complete from cervical C1 through caudal Ca9, with a vertebral formula of 7:15:4:4:9+, representing, respectively, the number of cervical, thoracic, lumbar, sacral, and caudal vertebrae. CGM 60584 has two more rib-bearing thoracic vertebrae than other known protocetids, and two fewer lumbars. Sacral centra are unfused, and there is no defined auricular surface on the ilium. Thus there was no weight-bearing sacroiliac joint. The sternum is distinctive in being exceptionally broad and flat. The body weight of CGM 60584, a putative male, is estimated to have been about 890 kg in life. Long bones of the fore and hind limbs are shorter than expected for a protocetid of this size. Bones of the manus are similar in length and more robust compared to those of the pes. A log vertebral length profile for CGM 60584 parallels that of middle Eocene Maiacetus inuus through the anterior and middle thorax, but more posterior vertebrae are proportionally longer. Vertebral elongation, loss of a sacroiliac articulation, and hind limb reduction indicate that Aegicetus gehennae was more fully aquatic and less specialized as a foot-powered swimmer than earlier protocetids. It is doubtful that A. gehennae had a tail fluke, and the caudal flattening known for basilosaurids is shorter relative to vertebral column length than flattening associated with a fluke in any modern whale. Late protocetids and basilosaurids had relatively long skeletons, longer than those known earlier and later, and the middle-to-late Eocene transition from foot-powered to tail-powered swimming seemingly involved some form of mid-body-and-tail undulation.

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    The article is well illustrated with maps, figures and pictures.
    Glendower: I can call spirits from the vasty deep.
    Hotspur: Why, so can I, or so can any man;
    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

    go with the flow the river knows . . .

    Frank

    I do not know, therefore everything is in pencil.

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