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Earth Science

New Theory Suggests Dinosaurs Were Already Dying When Asteroid Hit (phys.org) 167

Posted by EditorDavid from the lost-worlds dept.
The new "biotic revenge hypothesis" suggests that dinosaurs were killed off by toxic plants. (And an inability to recognize the taste of a toxic plant.) the gmr summarizes a new paper reported at Phys.org: The dinosaur population had been drastically decreasing before the asteroid impact, [and] the appearance of the first flowering plants -- angiosperms -- in the fossil record coincides with the gradual disappearance of the dinosaurs... The scientists concluded that though the asteroid played a role in the extinction of dinosaurs, the "plants had already placed severe strain on the species."
Crocodiles (believed to be descended from dinosaurs) also can't recognize the taste of toxic plants -- the researchers tested 10 different species. And they point out that not only did dinosaurs start to disappear before the asteroid impact -- they continued to "gradually disappear for millions of years afterward."
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New Theory Suggests Dinosaurs Were Already Dying When Asteroid Hit More

New Theory Suggests Dinosaurs Were Already Dying When Asteroid Hit

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  • aren't we?

  • Crocodiles are dinosaurs - since when? (Score:5, Insightful)

    by willy_me ( 212994 ) on Saturday April 07, 2018 @03:54PM (#56398815)

    A quick quote from Wikipedia [wikipedia.org],

    As such, birds were the only dinosaur lineage to survive the Cretaceous–Paleogene extinction event 66 million years ago.

    Crocodiles are not decedents of dinosaurs - they are reptiles. If this paper can not even see this then I can not put much weight into their theory.

    • Even if we gave them the benefit of the doubt and said "yes, gators and crocs and caiman and ... are all modern versions of dinosaurs, the result of evolution"... *why* would an animal that is totally carnivorous be able to identify (in any way...) a plant that will do Nasty Things to it if eaten?

      Now if we stretch the gators and such to include iguanas, and they did a study on them (or any other vegitarian/omnivor reptile or perhaps amphibian type beast) then they may have half a flicker of a half baked ide

      • It won't. But it will simply starve to death when their food source gets removed from the ecosystem. If all the big herbivores die off, then sometime later the carnivores too will have a mass extinction. Or so the idea goes.

      • Re: (Score:2)

        by Xest ( 935314 )

        As a counterpoint to their crocodile argument, turtles which first arose in the Jurassic period, and are largely herbivorous can recognise and deal with toxic plants (and coral and much other poisonous sea life) and are about as closely related to dinos as crocs are.

    • Crocodiles are not decedents of dinosaurs - they are reptiles.

      Eh?

      Dinosaurs are a diverse group of reptiles [wikipedia.org]

      You're right that they're not descendants of dinosaurs, but it's not because dinosaurs aren't reptiles.

      • Re:Crocodiles are dinosaurs - since when? (Score:4, Insightful)

        by AJWM ( 19027 ) on Saturday April 07, 2018 @04:38PM (#56398945) Homepage

        Pro tip: don't believe everything you read in Wikipedia.

        That's a vast oversimplification -- sure, trace a cladogram back far enough and you'll see something called Reptilia as the ancestor of both dinosaurs (and birds) and things ancestral to turtles, snakes and crocodilians. Dinosaurs are as much reptiles as birds are (indeed, birds are considered avian dinosaurs.)

        Trace mammals back far enough and you come to synapsids aka "mammal-like reptiles" -- which aren't reptiles either.

        • Pro tip: don't believe everything you read in Wikipedia.

          Okay, how about "pretty much every dictionary definition of the word 'dinosaur' I could find"? Plus the guy who proposed the name in the first place.

    • New genome research suggests birds and reptiles are descendants of dinosaurs, with crocodilians [arizona.edu] being the reptile most closely related to birds.

      It's certainly plausible the asteroid impact was not the absolute end for many of the dinosaurs, but merely a Toba-event bottleneck they could not outlast.

      • Re:Crocodiles are dinosaurs - since when? (Score:5, Informative)

        by Entrope ( 68843 ) on Saturday April 07, 2018 @04:56PM (#56399029) Homepage

        Crocodiles are not descended from dinosaurs. They are related, as part of a group called archosaurs. Birds and crocodilians are (by the definition of Archosauria) the two surviving groups of archosaurs.

        The reptiles most closely related to birds were the non-avian dinosaurs, but they are all dead. The most recent common ancestor of birds and crocodilians probably lived about 250 million years ago, so they are not that closely related.

    • ... then I can not put much weight into their theory.

      Ahhh, c'mon. The Dinos are all dead, SOMETHING killed them. Asteroids, meteors, tar magnets, poisonous plants, global warming, SOMETHING. It's a heavy subject. So what if they got a few supporting things wrong? It's almost like you doubt their conclusions or something. If it feels right, it IS right -- right?

      After all, everyone knows THIS [google.com] is what actually happened.,

      • The Dinos are all dead

        Umm, no. They're not. There's a nest of avian dinosaurs living in my greenhouse. And my dino-feeder is very popular with the local wood-pecking dinos (Downy, Red-headed, and Red-bellied, at least one pair of each in the back yard)....

    • Re:Crocodiles are dinosaurs - since when? (Score:4, Informative)

      by clovis ( 4684 ) on Saturday April 07, 2018 @05:58PM (#56399255)

      This is once again an example of Slashdot summary disease.
      Summary says: "Crocodiles (believed to be descended from dinosaurs) also can't recognize the taste of toxic plants " etc

      Except that the actual paper does not say that crocodiles descended from dinosaurs. This is what the paper says:

      Since crocodilians are descendent from the same creatures that gave rise to dinosaurs, this creates the opportunity to evaluate the tenability of the proposition that dinosaurs went extinct due to an inherent inability to learn to avoid eating toxic plants

      The funny thing about crocodiles is that they are evolutionarily less like lizards and are evolutionarily the closest living relative to birds and non-avian dinosaurs. Crocodilians evolved in the Triassic as part of the Archosaur group which is crocodiles, non-avian dinosaurs, birds.
      So it's not completely ridiculous to use crocodiles in their experiment.

      • Re: (Score:2)

        by jeremyp ( 130771 )

        So it's not completely ridiculous to use crocodiles in their experiment

        Apart from the fact that crocodiles, being carnivores are likely to avoid toxic plants on the grounds of them being plants.

    • If you bothered to RTFA you would see it says "Crocodilians are descendent from the precursors to...dinosaurs".

  • Can birds taste the toxins? (Score:3)

    by RobinH ( 124750 ) on Saturday April 07, 2018 @03:56PM (#56398823) Homepage
    I wonder if birds can taste the toxins then, since they're descended from dinosaurs and survived, though apparently at their worst they were down to a fairly small population on a remote island somewhere. (Can't remember where I read that...)

    • My thought exactly. Crocodiles are NOT descended from dinosaurs, they pre-date them. Other reptiles had split off from the evolutionary branch that led to dinosaurs a bit sooner, but not dramatically so. Birds are pretty much the only living species that are descended from dinosaurs. (hadn't heard about the bottleneck before, I may have to investigate.)

      Moreover, the last time I checked crocodiles are carnivores, and have been since before the dinosaurs arose - meaning that being able to taste plant toxins

    • I wonder if birds can taste the toxins then, since they're descended from dinosaurs and survived, though apparently at their worst they were down to a fairly small population on a remote island somewhere. (Can't remember where I read that...)

      According to the summary at the link, no:

      Gallup and Frederick examined whether or not birds (considered to be a descendant of dinosaurs) and crocodilians (also considered to be descended from dinosaurs) could develop taste aversions. They found that the birds, rather than forming aversions to taste, developed aversions to the visual features of whatever made them sick. Still, they knew what they shouldn't eat in order to survive.

      • Re: (Score:2)

        by pots ( 5047349 )
        Little side note: this is why hot peppers are hot. Birds can't taste the capsaicin (though maybe "taste" isn't the right word here), so by making their fruits spicy the pepper plants can select which animals spread their seeds. Preferentially choosing birds, because they'll spread the seeds further.

      • Re: (Score:2)

        by RobinH ( 124750 )
        Saying that crocodilians are generally considered descended from dinosaurs doesn't seem to be correct. See here [berkeley.edu] for instance. Crocodilians and dinosaurs are both archosaurs, sharing a common ancestor. Birds are descended from the dinosaurs, likely

  • Dinosaurs are not extinct (Score:1)

    by Anonymous Coward

    Dinosaurs are not extinct. Over the past few decades, research showed that birds are closely related to dinosaurs. They are directly descended from theropods and are now classified as dinosaurs. Scientists now classify birds as feathered dinosaurs and, as a result, that means dinosaurs never went extinct. It's certainly reasonable that the populations of many dinosaurs were already declining prior to the asteroid impact, and it's plausible that toxic plants may have contributed to this. It is somewhat remar

  • "Crocodiles (believed to be descended from dinosaurs) also can't recognize the taste of toxic plants..."

    Are you fucking kidding me!!!???

    They are strict carnivores! Why in hell they would give a damn about a plant, toxic or otherwise!?

    Ooooh! but they tested (so they say) about crocodillian ability to discern toxic food (not only plants)... Crocodillians come from a lineage about 200M year old -they haven't find ANY damn thing that makes them real sick so, why they should bother!?

    Stuff that matter, they say..

  • I'll wait for experimental conformation of this theory's predictions.

  • The article doesn't claim that the decline of dinosaurs is a new theory. The fossil record clearly shows that dinosaurs were already on the decline before and died out well after Chicxulub. The asteroid contributed, but it was only one of several reasons for their extinction.
  • Dinosaurs never went extinct. They survived the asteroid impact. Shows how thriving they were.

    All the birds we see today are the descendants of the dinosaurs.

  • Ammonites? (Score:4, Interesting)

    by AJWM ( 19027 ) on Saturday April 07, 2018 @04:44PM (#56398987) Homepage

    This may (although it doesn't, really) explain the decline of dinosaurs, but it says nothing about why thousands of other species (including all the ammonites) went extinct at the same time.

    And the theory that dinosaurs were already dying off before the K/Pg boundary is hardly new. Part of that is an artifact of how fossils are formed and found. A species could have lasted several million years after its latest-known fossil, it just didn't happen to leave any fossils that have yet been found. (Conversely, the last surviving member of a species could have been fossilized. Unlikely though, except in the case of a mass extinction event.)

    • Guess that is the cue to mention the coelacanth

    • Also, pretty sure that not being able to detect poisonous plants doesn't explain why say, Spinosaurus, would go extinct. After all, they supposedly ate fish, not plants...

      • But when all the other dinosaurs died, what would they eat? Oh, yeah, fish. Never mind.

      • It is also a little strange to posit that plants became very toxic when being slightly toxic in the first place does not at all save you from being eaten by voracious herbivores. I am not dismissing the idea out of hand, but there are significant missing pieces from this tale, like why those plants who invested precious metabolic activity in toxins outcompeted existing ubiquitous plants that did not.

      • Some kind of food chain collapse I would guess. Given how we routinely fail to comprehend modern ecosystems I would honestly be very surprised if we ever figured out such ancient systems with much certainty.

    • This may (although it doesn't, really) explain the decline of dinosaurs, but it says nothing about why thousands of other species (including all the ammonites) went extinct at the same time.

      And the theory that dinosaurs were already dying off before the K/Pg boundary is hardly new. Part of that is an artifact of how fossils are formed and found. A species could have lasted several million years after its latest-known fossil, it just didn't happen to leave any fossils that have yet been found. (Conversely, the last surviving member of a species could have been fossilized. Unlikely though, except in the case of a mass extinction event.)

      I think the summary is a bit of a misdirect, the paper isn't trying to claim that the asteroid didn't wipe out the dinosaurs, nor invent the idea that the dinosaurs were already in trouble. The papers is trying to come up with the reason they were already in trouble, which was the emergence of plant toxicity.

      It seems quite plausible, at least for the larger herbivores, even if they could evolve fast enough to learn to avoid toxic plants they might not have been able to find enough non-toxic food, and when t

  • Cool (Score:5, Funny)

    by fahrbot-bot ( 874524 ) on Saturday April 07, 2018 @04:58PM (#56399033)

    Anyone know if florists will deliver to Congress?

  • Rubbish, I know what happend. (Score:4, Informative)

    by CaptnCrud ( 938493 ) on Saturday April 07, 2018 @05:00PM (#56399043)

    First the Earth cooled. And then the dinosaurs came, but they got too big and fat, so they all died and they turned into oil. And then the Arabs came and they bought Mercedes Benzes. [McCroskey walks off] And Prince Charles started wearing all of Lady Di's clothes. I couldn't believe it- [Jacobs turns and starts to walk away, continuing to speak, trailing off as he gets further from the camera] he took her best summer dress and he put it on and went to town...

  • This is a case where it's difficult to be specific, because the evidence is scant. If you're only getting one good fossil per thousand years, detecting a decline is dubious. But it does seem that some species of dinosaur were already in decline. And others weren't. A few appear to have been flourishing.

    OTOH, accepted theory as of a few years ago is that birds are not descended from dinosaurs, they descend from a line that branched off before the dinosaurs separated from the rest of the reptiles. The or

    • Re: (Score:2)

      by SEE ( 7681 )

      You seem to have run into some confusion.

      It is true that birds are not descended from ornithischian dinosaurs. But birds are descended from dinosaurs. The birds are descendants of the theropods, traditionally classed as one of the major divisions of saurischians.

      (There is a recent suggestion that a reclassification is necessary, that most theropods are actually closer-related to the ornithischians than the rest of the saurischians. But either way, birds are descended from theropod dinosaurs while not bei

      • They might want to rename the divisions too, as birds not being descended from the bird-hipped group looks somewhat silly now.

      • Re: (Score:2)

        by HiThere ( 15173 )

        You sure about that? When I studied it (well, informally) birds were said to have branched off before the dinosaurs were a separate group. Sort of like the Pterosaurs, which also branched off before the dinosaurs had separated.

        OTOH, all these recent fossils with feathers may have caused people to reorganize things.

  • Given that the vast majority of dinosaurs were already extinct by that period, I'd say there's a good chance the effects of that asteroid are somewhat over-stated.

  • This includes 1.5 tonne monstrosities like Yutyrannus Huali, (related to Tyranosaurous Rex) https://news.nationalgeographi... [nationalgeographic.com]

    Discoveries and detailed analysis of recent dinosaur fossils indicate that they were covered with feathers long before flight evolved. And they are now believed to have been warm-blooded. this is confirmed by CT scans of well-preserved fossils (e.g. 600 pound herbivore) showing a 4-chambered heart with *ONE* aorta http://contenidopatrocinado.cn... [cnn.com] This is a physiological sign of a warm blooded animal.

    So dinosaurs had feathers and were warm blooded. Birds have feathers and are warm blooded. Birds are one group of dinosaurs that survived the asteroid. This was probably due to small size and being able to scavenge scarce food right after the impact.

  • Once upon a time, there was all the time in the world.

    The human race rested comfortably for millennia in warm nests of tales that the world had been created especially for us, and later science stepped in to supplant this quaint notion with immeasurable expanses of geologic time in which a rich compost of academic theory might take root and prosper. Everything that had come before us had made way for us, dinosaurs died so that we might live. Children calmed their nightmares with this simple idea after the

  • Dinosaurs were changing with their environments for many millions of years and suddenly they all got poisoned? I don't buy it. I suggest it has more to do with the rise of mammals. Perhaps mammals were destroying their ground-based nests, eating their eggs. It would give impetus to a move into the trees. Those who moved survived to this day as birds. Those who didn't became extinct. Further, notice where many birds go to have land-based nests. These locations are usually far and desolate to protect against

  • Did not know that? Also how do they test to see if the crocs can recognize the taste of toxic flowering plants? Force feed them and see if they spit them out?

    Just a weird thing to read ...

  • Crocodilians are descendent from the
    precursors to, not only dinosaurs, but pterosaurs as well.
    Based on this connection, Gallup and Suarez (1987)
    examined crocodilians for their capacity, or lack thereof,
    to form learned taste aversions. Since crocodilians are
    descendent from the same creatures that gave rise to
    dinosaurs, this creates the opportunity to evaluate the
    tenability of the proposition that dinosaurs went extinct
    due to an inherent inability to learn to avoid eating toxic
    plants.

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