Slashdot Mirror

← Back to Stories (view on slashdot.org)

Ancestor of All Placental Mammals Revealed

Posted by samzenpus on from the back-in-the-day dept.

sciencehabit writes "The ancestor of all placental mammals—the diverse lineage that includes almost all species of mammals living today, including humans—was a tiny, furry-tailed creature that evolved shortly after the dinosaurs disappeared, a new study suggests. The hypothetical creature, not found in the fossil record but inferred from it, probably was a tree-climbing, insect-eating mammal that weighed between 6 and 245 grams—somewhere between a small shrew and a mid-sized rat. It was furry, had a long tail, gave birth to a single young, and had a complex brain with a large lobe for interpreting smells and a corpus callosum, the bundle of nerve fibers that connects the left and right hemispheres of the brain. The period following the dinosaur die-offs could be considered a 'big bang' of mammalian diversification, with species representing as many as 10 major groups of placentals appearing within a 200,000-year interval."

13 of 123 comments (clear)

  1. More Info Please... by Frosty+Piss · · Score: 5, Insightful

    A *POSSIBLE* ancestor that a study suggests *MIGHT* be what they thing. Maybe. Possibly.

    In other words, the headline is, as usual, misleading.

    --
    If you want news from today, you have to come back tomorrow.
    1. Re:More Info Please... by Anonymous Coward · · Score: 5, Funny

      Here's what may have happened to the little guy...

    2. Re:More Info Please... by Theovon · · Score: 3, Insightful

      I guess you might say they interpolated what a likely ancestor was probably like.

    3. Re:More Info Please... by Anonymous Coward · · Score: 3, Informative

      We're starting to sequence the genomes and map species after species at an accelerating rate. Within the century we'll have a gene-by-gene map of the ancestry of most of the biosphere.

    4. Re:More Info Please... by dudpixel · · Score: 3, Insightful

      The genome project offers a fair bit more credibility than this, and it's more than "a couple" of fossils here and there.

      No one's saying it is all indisputable fact (science doesn't deal with facts) but to date no other theory has been put forward that can offer a better explanation of all the known data.

      That's how science works...so until a more plausible theory shows up, evolution is where we are at.

      As for this study, yeah there's a bit too much uncertainty for it to be much more than an opinion piece.

      --
      This seemed like a reasonable sig at the time.
    5. Re:More Info Please... by dbug78 · · Score: 5, Informative

      science doesn't deal with facts

      Uh, what? Facts are the foundation of science. If science has any issue with facts it's that Joe Sixpack thinks the hierarchy is...

      Hypothesis -> Theory -> Facts

      In actuality, it's...

      Facts -> Hypothesis -> Theory

      Hypotheses and theories are built on facts. Maybe you meant science doesn't deal with proof?

    6. Re:More Info Please... by ichthyoboy · · Score: 4, Insightful

      Technically what we'll have is a good snapshot of current genomic diversity, from which we can infer the ancestry of that snapshot. We have some pretty good inferential methods, but each and every phylogeny that you see is simply a hypothesis of evolutionary relationships.

    7. Re:More Info Please... by kwyjibo87 · · Score: 5, Insightful

      Well, yes, the headline is misleading, but it's also a bit more than a "possible" ancestor.

      The researchers in the study wanted to create a better phylogenetic reconstruction of the evolution of mammals than had been previously accomplished, to resolve whether divergence of placental mammals from non-plancental mammals (egg-laying / marsupials) occurred before or after the extinction of the Dinosaurs (the K-T boundary), and also to make predictions of the biology of that last common ancestor. Previous phylogenetic reconstructions had been done with molecular data (DNA or protein sequences), but molecular data is limited to extant species and makes a lot of assumptions about the rates of changes in DNA that get more unreliable the further back in time you go. This study combined molecular data with character traits they call 'phenomic' characters - from the paper: "4541 phenomic characters de novo for 86 fossil and living species." The resulting matrix of traits, both molecular and character, was used to generate a tree based on maximum parsimony - a method which minimizes the number of trait changes over time when building a tree. This resulted in a single, highest scoring tree predicting the evolution of these species and the changes in their traits over time. The resulting tree is then "clocked" (called 'time-calibration in the paper) to known rates of evolution for the molecular data (good for recent divergence of species) and by fossil data to give time ranges for the deeper sections of the tree. This last part is key, as you cannot get molecular data from fossils, and fossils allow you to map the existence of certain traits within a group to a certain point in the history of these organisms.

      The result is a time-range in which the last common ancestor between placental and NON-placental mammals must have lived, given the data provided and the parsimony criterion. As the tree makes claims about when the phenomic characters evolved or were lost, it also predicts which phenomic characters the last common ancestor had.

    8. Re:More Info Please... by Vreejack · · Score: 3, Informative

      The characteristics of the first placental are not really controversial. The real news here is that a lot of the work on placentals and eutherians is wrong and must be re-evaluated. Granted, a lot of the placental work was already merely tentative. Molecular phylogenetics estimates had placentals appearing about 105 Mya, This new work ignores the molecular results and comes up with a later date. From what I can see, dating of the relevant available fossils is equivocal.

      Also curious is that according to this interpretation, the ancestral afrotherian (elephants, aardvarks, manatees, etc.) originated in South America and somehow migrated across the then 1000-mile ocean to Africa. Prepare for further revision.

      --
      "Will future ages believe that such stupid bigotry ever existed!" -- Ivanhoe
  2. i feel a disney movie by decora · · Score: 5, Funny

    The rough group of placentals from the wrong side of the tracks has a young placental who falls in love with a nice placental from the meadow.. but their parents disapprove...

  3. Re:No intermediate steps to prove! by Aardpig · · Score: 5, Informative

    Within the past 200,000 years of human history, we're aware that Homo Sapiens Sapiens existed alongside other members of the Homo genus, including Homo Neanderthalis and Homo Floresiensis.

    --
    Tubal-Cain smokes the white owl.
  4. Re:uh..."revealed"? by Myopic · · Score: 5, Insightful

    This is what we mean when we say that science makes predictions. Remember tiktaalik? Based on the rest of the fossil record and based on geology, scientists predicted that a certain fossil of a certain creature would be found in a certain kind of rock at a certain depth. It took them several years of digging but they found that fossil at that depth in that rock. Science made a specific prediction and it came true.

    Likewise, based on the rest of the fossil record we believe this creature must have existed. We might be able to predict where we would find fossils for it.

  5. Re:What about ornithorhynchus? by ichthus · · Score: 5, Insightful

    You know, you could have just said "platypus." You didn't have to get all pretentious and shit.

    --
    sig: sauer