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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."

11 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.

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

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

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

      How is the different than anything else in evolutionary theory. No actual observational science, a couple of fossils here and there, no soft tissue to examine. Then bang, an possible/probable ancestral relationship is declared by somebody -- often discarded later due to other discoveries. It is what it is and will always be unless you manage to make a time machine.

    3. 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.

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    4. Re:More Info Please... by Anonymous Coward · · Score: 2, Insightful

      How does the phrase "..., a new study suggests." qualify as an assertion of fact?

    5. 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.

    6. 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.

    7. Re:More Info Please... by Anonymous Coward · · Score: 2, Insightful

      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.

      That's actually false. The Flying Spaghetti Monster and Catholic Christian religions both have equally good or better explanations, that amount to "God plays little tricks on ya, for yer own damn good!". If you posit that an omnipotent deity exists, then nothing else is really provable scientifically, unless said deity is both benevolent and willing to let you have your own interactions with reality. The reason that evolution is our best theory is that we can observe its operation in nature, and know for a fact that it has occurred and is still occurring, not because it's the only logically self-consistent explanation of reality. Therefore it is not necessary to invoke faith-based explanations for phenomena that are adequately explained by evolution, and if an omnipotent benevolent force exists it will have no problem with such behavior on our part; it's only with the omnipotent force is malevolent, or if the benevolent force is not omnipotent, that we have to worry about science/faith interactions at all.

      People try to substitute science for religion, and they betray both in the process. A good religion is 100% compatible with science, and vice versa, and frankly it's not clear that everyone even needs religion - people closer to the autism end of the spectrum may not need it at all. So don't substitute "faith in science" for "faith in Baaphomet" or whatever your parents' fetish was; science enshrines skepticism and has no place for unconditional unproven belief (aka "faith") , not even when you are talking about the scientific method itself. If you can't live with conditional belief at all levels, get yourself a nice religion that does not harm others or offend your aethetic and/or moral sensibilities and reap the health and social benefits it can give you. If you can question the very basis of science itself, though, maybe you don't need religion, and you'll certainly be a better scientist for it.

  2. uh..."revealed"? by Theolojin · · Score: 1, Insightful

    "The hypothetical creature, not found in the fossil record but inferred from it..." I know this is /., but c'mon.

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    1. 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.

  3. 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.

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