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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."

27 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 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.

    4. 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.

    5. 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.
    6. Re:More Info Please... by Anonymous Coward · · Score: 2, Insightful

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

    7. 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?

    8. Re:More Info Please... by dudpixel · · Score: 2

      Correct - but I was talking about the Joe Sixpack definition, which as you pointed out, equals 'proof'.

      Thanks for the correction :-)

      --
      This seemed like a reasonable sig at the time.
    9. 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.

    10. 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.

    11. Re:More Info Please... by kwyjibo87 · · Score: 2

      Observation -> Hypothesis -> Theory--> Test---> Scientific fact.

      I'd only add:

      Observation -> Hypothesis -> Theory -> Predictions -> Test -> Scientific fact.

    12. 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
    13. Re:More Info Please... by rainmouse · · Score: 2

      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.

      An enormous catalogue of fossil history, geo distribution of species also provides massive evidence especially in recently observable separators such as archipelagos, the bounty genetic evidence, the ability to recreate observable evolution in our timescale on the bacterial level and our ability to force changes through selective breeding all combine to provide an irrefutable level of evidence. Each of these fields could also be used to disprove evolution if not for the fact that no reliable evidence contradictory to the theory has ever been produced. Anyone who can objectively examine even a portion of the evidence (there's so much it would take a lifetime to look at it all) and continue to refute the theory almost certainly has another agenda, either religious or political.

    14. Re:More Info Please... by dunkelfalke · · Score: 2

      No it doesn't. You think you are actually able to reason with creationists but this is not the case. Creationist operate on the belief level, outside of reason, thus it does not matter how good the scientific facts are. Write creationists off and go on with your life.

      --
      "It's such a fine line between stupid and clever" -- David St. Hubbins, Spinal Tap
    15. 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.

    16. Re:More Info Please... by cusco · · Score: 2

      Case in point: I can give 100 people the same 1 frame from the same movie that none of them (or I) have seen before and ask them to tell me the plot and I'll get 100 different answers

      Then you're doing it wrong. Give them each a different frame from a different point in the movie, and then let them get together to put them in a hopefully coherent whole. A few frames will be out of order, or perhaps reversed or upside down, but you'll end up with a pretty good approximation of the plot. We don't have just one eohippus fossil, nor do scientists work in a vacuum.

      how do you measure your measuring stick

      You compare it against every other item of known length that you have. That means that radioactive decay gets compared to stratigraphy which gets compared to geology which gets compared to known rates of deposition which gets compared to known erosion patterns etc, etc. all the way out to astrophysical measurements. To just about everyone's surprise they correlate very well. Again, scientists don't work in a vacuum, data and research cross disciplines all the time, and it's no longer unusual to have an experimental physicist working with a geologist or a archeologist.

      I'm not as smart as they are

      Apparently not, if you're willing to expound at such length about something that you so grossly misunderstand.

      --
      "Think about how stupid the average person is. Now, realise that half of them are dumber than that." - George Carlin
  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. Typical Redneck Response by tdp252 · · Score: 2, Funny

    Damn them whacky scientists. Me and my girl didn't come out some squirrel's butthole !

  4. 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.
  5. video from discovery here by miknix · · Score: 2

    There is this video from discovery channel which shows the hypothetical furry creature as one of evolutionary steps to mankind, I personally find it interesting:

    http://www.youtube.com/watch?v=HwxCnV2PL2k

  6. 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.

  7. Re:What about ornithorhynchus? by manu0601 · · Score: 2

    If it lays eggs then it's not a placental mammal (is that right? I think that's right).

    It is difficult to be sure about anything for this odd creature. It has venom (for males only), electric field sensitivity, 5 pair of sexual chromosomes... If nature proceeds from an intelligent design, then the creating intelligence was probably intoxicated the day it created ornithorhynchus

  8. 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
  9. Re:Pics or it didn't happen by ByOhTek · · Score: 2

    I have mod points, and wanted to use them... but there is no "+1 Horrible".

    --
    Self proclaimed typo king, and inventor of the bear destroying coffee table (patent not pending).
  10. Re:What about ornithorhynchus? by OakDragon · · Score: 2

    It is difficult to be sure about anything for this odd creature. It has venom (for males only)...

    Of course it has venom, it's from Australia.

    Am I right, people!?

    --
    Dark Reflection
  11. Re:What about ornithorhynchus? by manu0601 · · Score: 2

    I was not sure about the common name. In my native language, which happens to be french, the common name is Ornithorynque. Now you can troll french speakers for being natively pretentious :-)