• Various articles

    From DD'eDeN aka note/nickname/alas_my_l@21:1/5 to All on Wed Nov 3 22:18:46 2021
    https://www-sciencealert-com.cdn.ampproject.org/v/s/www.sciencealert.com/useless-specks-of-dust-turn-out-to-be-ancient-building-blocks-of-all-vertebrate-genomes/amp?amp_gsa=1&amp_js_v=a6&usqp=mq331AQIKAGwASCAAgM%3D#amp_tf=From%20%251%24s&aoh=
    16360006435992&csi=0&referrer=https%3A%2F%2Fwww.google.com&ampshare=https%3A%2F%2Fwww.sciencealert.com%2Fuseless-specks-of-dust-turn-out-to-be-ancient-building-blocks-of-all-vertebrate-genomes
    Mammals vs non-mammal vertebrates:
    Microchromosomes

    https://phys-org.cdn.ampproject.org/v/s/phys.org/news/2021-11-mammals-noses-reptiles-jaws-evolutionary.amp?amp_gsa=1&amp_js_v=a6&usqp=mq331AQIKAGwASCAAgM%3D#amp_tf=From%20%251%24s&aoh=16360006435992&csi=0&referrer=https%3A%2F%2Fwww.google.com&ampshare=
    https%3A%2F%2Fphys.org%2Fnews%2F2021-11-mammals-noses-reptiles-jaws-evolutionary.html
    Mammal protruding nose (and chin) vs non-mammal vertebrates jaw

    A group of cells called the frontonasal prominence forms the jaw tip in reptiles, but becomes the protruding nose in mammals. Mammals' jaw tips form instead from a separate group of cells called the maxillary prominence.

    This separation of the nose and jaw gives mammals their unique ability to "sniff," using muscles to flare the nostrils and deeply inhale odors from the environment.

    "This finding is a key innovation in the evolution of our and other mammals' motile nose, which contributes to mammals' highly sensitive sense of smell," said Higashiyama.

    Distinguishing and recognizing so many odors may have also helped mammals develop larger, more complex brains than earlier ancestor species


    66ma primates became non-arboreal?

    https://phys.org/news/2021-10-primates-ancestors-left-trees-survive.html

    The study, "Ecological Selectivity and the Evolution of Mammalian Substrate Preference Across the K-Pg Boundary," published October 11 in the journal Ecology and Evolution.

    The earliest mammals appeared roughly 300 million years ago and may have diversified in tandem with an expansion of flowering plants about 20 million years prior to the K-Pg event. When the asteroid struck, many of these mammal lineages died off, Hughes
    said.

    "At the same time, the mammals that did survive diversified into all the new ecological niches that opened up when dinosaurs and other species became extinct," Hughes said.

    In the study, the researchers used published phylogenies (branching, tree-like diagrams that show evolutionary relatedness among groups of organisms) for mammals. They then classified each living mammal on those phylogenies into three categories –
    arboreal, semi-arboreal and non-arboreal – based on their preferred habitats. They also designed computer models that reconstructed the evolutionary history of mammals.

    Mammal fossils from around the K-Pg are very rare and are difficult to use to interpret an animal's habitat preference. The researchers compared information known from living mammals against available fossils to help provide additional context for their
    results.

    Generally, the models showed that surviving species were predominantly non-arboreal through the K-Pg event, with two possible exceptions: ancestors of primates and marsupials. Primate ancestors and their closest relatives were found to be arboreal
    right before the K-Pg event in every model. Marsupial ancestors were found to be arboreal in half of the model reconstructions.

    The researchers also examined how mammals as a group may have been changing over time.

    "We were able to see that leading up to the K-Pg event, around that time frame, there was a big spike in transitions from arboreal and semi-arboreal to non-arboreal, so it's not just that we are seeing mostly non-arboreal [species], but things were
    rapidly transitioning away from arboreality," Hughes said.

    https://phys-org.cdn.ampproject.org/v/s/phys.org/news/2021-11-pinniped-craniofacial-musculature-insight-role.amp?amp_gsa=1&amp_js_v=a6&usqp=mq331AQIKAGwASCAAgM%3D#amp_tf=From%20%251%24s&aoh=16360025823643&csi=0&referrer=https%3A%2F%2Fwww.google.com&
    ampshare=https%3A%2F%2Fphys.org%2Fnews%2F2021-11-pinniped-craniofacial-musculature-insight-role.html

    Pinnipeds—a group including seals, sea lions and walruses—are relatively recently derived marine mammals that evolved from terrestrial carnivorans and reentered the marine environment. Their recent adaptations to an amphibious lifestyle make their
    evolutionary anatomy of particular interest to Baylor University researcher Sarah Kienle, Ph.D., assistant professor of biology.

    "I'm fascinated by how animals feed underwater," Kienle said. "Mammals that have reinvaded the marine environment—whales, dolphins, pinnipeds, sea otters and polar bears—are all carnivores that have converged on the same feeding strategies when
    entering the water environment. You're also getting the repeated evolution of suction feeding and filter feeding. It's pretty amazing to see these independent lineages all converging on similar feeding strategies—suction feeding, biting and filter
    feeding."

    Kienle recently led a study, published in the Journal of Anatomy, comparing pinniped craniofacial musculature and its potential role in aquatic feeding.

    "I was interested in looking at how these different facial muscles potentially play a role in different aquatic feeding strategies. I was looking at the skull morphology to see if there were morphological specializations for feeding and that
    automatically led to the question of what do the muscles look like?" Kienle said.

    Data on the pinniped craniofacial musculoskeletal system and its function in aquatic feeding are rare. In fact, Kienle's research provides foundational data for further studies on pinnipeds and the evolution of their functional morphology.

    "The first part of the study was surprising because there was no reference material for doing these dissections. There aren't detailed drawings of what the muscles should look like," Kienle said. "I knew, roughly, they should have a masseter (a facial
    muscle that plays a role in opening and closing the jaw for chewing), but what it specifically looked like in pinnipeds wasn't clear. The first few dissections, I didn't know what muscles to expect besides a few general ones. For a while, we would write
    out a little tag that read 'mystery muscle' with a question mark until we figured out what it was."

    The researchers performed anatomic dissections of 35 specimens across six pinniped species—bearded seals, California sea lions, harbor seals, northern elephant seals, ringed seals and Weddell seals. Through the dissections, 32 pinniped craniofacial
    muscles were described, including facial expression, mastication, tongue, hyoid and soft palate muscles.

    "It was interesting seeing what was present and absent in different species. I came into this study thinking that it would be pretty continuous among pinnipeds—that the species would have the same muscles present. That was not always the case," Kienle
    said.

    While pinnipeds broadly conform to mammalian patterns of craniofacial musculature, they also exhibit unique musculoskeletal morphologies. Differences can be seen in muscle position, attachments and size and likely represent adaptions for different
    aquatic feeding strategies.

    Bearded and northern elephant seals are suction feeding specialists and have a significantly larger masseter muscle than biters. Additionally, northern elephant seals have large and unique tongue and hyoid muscle morphologies compared with other
    pinniped species. Comparatively, biting species, like California sea lions, harbor, ringed and Weddell seals, don't show consistent craniofacial musculoskeletal adaptations that differentiate them from suction feeders.

    "Pinnipeds are generalists as a whole and really opportunistic, which is great for them in terms of adapting to a changing environment, which they've done in the past and are doing now," Kienle said. "From an evolutionary perspective, you expect closely
    related species to be more similar than distantly related species. Maybe there are ecological pressures that are driving the muscular anatomy more so than evolutionary history."

    The researchers note that the robust facial morphology of pinnipeds allows them to switch feeding strategies depending on the environmental context. This skill would be critical to survival in varied and rapidly changing underwater habitats.

    The researchers used studies of various other mammals to assist in distinguishing craniofacial muscles and their use. Existing data on mammalian craniofacial musculature, beyond humans, was also difficult to find, said Kienle.

    "I find it so fascinating how little we know about the internal anatomy of these huge marine carnivores. That's the thing that surprises me the most

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