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Dinosaurlike creature spread in Triassic times


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triassic early dinosaur relative asilsaurusIt looked like a dinosaur, walked like a dinosaur, and ate like, well, some dinosaurs, but a newly discovered species of archosaur, which lived 240 million years ago, was not a dinosaur.

It was an ancient silesaur, which emerged 10 million years before true dinos did. And its unearthing in Tanzania—the first early dinosaur-like animal to be found in Africa—adds new detail to the sketchy understanding of the primitive Ornithodira lineage that would eventually produce T. rex and turkeys alike.

Described in the March 4 edition of Nature from the fossils of 14 individuals, the new species, Asilisaurus kongwe, was uncovered among fossils of ancient crocodiles, a group from which it had likely split recently (Scientific American is part of Nature Publishing Group). It lived some 10 million years before the first dinosaurs emerged and was likely an omnivore—revealing that plant-eating evolved not once, but at least three times in the Triassic: in Asilisaurus and two early dinosaur lineages.

The four-legged Asilisaurus would have measured one to three meters long and weighed in at about 10 to 30 kilograms. Despite its superficial similarities to the Dinosauria taxon, the researchers conclude in their paper that "all silesaurids lack classical dinosaurian character states." 

"This goes to show that there are whole groups of animals out there that we’ve never even found evidence of that were very abundant during the Triassic," Sterling Nesbitt, a postdoctoral researcher at the Jackson School of Geosciences at the University of Texas at Austin and lead study author, said in a prepared statement. It also helps to put dinosaurs in context, he noted. "They were really only one of several large and distinct groups of animals that exploded in diversity in the Triassic, including silesaurs, pterosaurs, and several groups of crocodilian relatives."

Image of Asilisaurus kongwe courtesy of Marlene Hill Donnelly/FIeld Museum

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  1. 1. jtdwyer 11:07 am 03/4/2010

    Since fossilization occurs only in specific conditions present only in special circumstances, the fossil record is not a statistically representative sampling of populations.

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  2. 2. Tucker M 2:52 pm 03/4/2010

    jtdwyer,

    Goodness, what certainty! I take it you did a count of fossil specimens discovered from this period, assessed the degree to which the "special circumstances" you mention might bias the range of specimens captured, and calculated a standard deviation to determine whether or not the discoveries to date have statistical relevance…? Must have been quite some calculation, you should share that with everyone. Otherwise, you know, people might suspect you were mouthing off without really knowing what you were talking about.

    You wouldn’t want that.

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  3. 3. candide 3:33 pm 03/4/2010

    So, if it "was not a dinosaur" – how did it differ from dinosaurs? There is an amazing lack of pertinent details in this article.

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  4. 4. jtdwyer 3:47 pm 03/4/2010

    Tucker M – I don’t want or need anything – I’m just trying to help. I was very blunt – I’m so sorry if I’ve offended anyone else.

    I was responding to the statement in the article: "This goes to show that there are whole groups of animals out there that we’ve never even found evidence of that were very abundant during the Triassic," Sterling Nesbitt, a postdoctoral researcher at the Jackson School of Geosciences at the University of Texas at Austin and lead study author, said…"

    I was merely attempting to explain how this could happen. My point is that it is not particularly useful to count the number of fossils ‘captured’, as you put it, and calculate anything, since the preserved population does not provide a representative sample of the living population.

    Paleontologists studying, for example, dozens of duck-bill dinosaurs fossils all found together sometimes conclude that hadrosaurs were very common at that time. However, since they likely likely fed on fish, they may have lived in an area near water, which may have increased the probability of their demise in an area favorable to their being buried in sediment, resulting in their fossilization. These kinds of presumptions are only human nature.

    My personal favorite specific example of this is the famous paleontologist who recently asked the pointed question: "If the dinosaurs were all suddenly killed by a giant asteroid, where are all the fossils?" Apparently he did not realize that their incineration would not favor their preservation.

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  5. 5. jtdwyer 4:05 pm 03/4/2010

    candide – That is the most critical issue with this article. I even tried following all the links and reading the Nature abstract, but I couldn’t find a clear explanation. Perhaps the author had the same problem…

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  6. 6. Tucker M 4:32 pm 03/4/2010

    jtdwyer – That’s a much more interesting post, thank you! Thanks for the clarification, and sorry to be so snippy earlier.

    And to be clear, I was just trying to make the reverse point. That is, just because fossilization happens only under rare conditions, that doesn’t necessarily mean that the "capture" is NOT representative; it may still be. It’s just that you have a particular snapshot taken at a particular geological place and time, with all the limitations such a snapshot implies. Whether or not the sample is representative has more to do with the randomness of the sampling method (as your hadrosaur example illustrates) than the (admittedly limited) sample size. Not sure we’re actually disagreeing.

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  7. 7. thurtado 5:03 pm 03/4/2010

    Addressing some of the comments here…

    Hadrosaurs were herbivores – do no fish diet.

    Death by asteroid was unlikely to produce incineration in all but the closest locations (I dunno… a few hundred miles radius?). It was the temporary "nuclear winter" and associated temporary "climate change" that probably did the most damage to life of that era.

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  8. 8. jtdwyer 5:04 pm 03/4/2010

    Tucker M – Thanks. You’re right, of course: not all such inferences are invalid.

    I did fail to mention the title "Dinosaurlike creature spread in Triassic times" of a report of 14 fossils found in Tanzania.

    Back to the dinosaurs’ demise, scientists often interchange the phrases ’75% of all life’ and ’75% of all species’, which, of course are quite different ‘animals’. I’m also unsure whether either considers the insect species… Oh, well.

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  9. 9. jtdwyer 5:16 pm 03/4/2010

    thurtado – Thanks – you’re correct: the specific example contrived to illustrate my point is invalid. I’m neither a paleontologist nor a scholar.

    My current understanding is that the material excavated by the proposed meteorite was sent into space and rained down on the entire planet, heating the atmosphere to incinerate all surface material. I could be wrong, of course: feel free to research this for yourself.

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  10. 10. calvin 5:37 pm 03/4/2010

    From the Nature article: "All silesaurids lack classical dinosaurian character states such as a laterally open acetabulum, an elongate deltopectoral crest of the humerus, and an extension of the supratemporal fossa onto the posterodorsal surface of the frontal."

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  11. 11. jtdwyer 5:39 pm 03/4/2010

    Also, the global incineration hypothesis accounts for the global carbonaceous composition of the thin K-T boundary containing the telling iridium.

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  12. 12. jtdwyer 5:45 pm 03/4/2010

    calvin – Thanks – now its clear! (lol)

    Link to this
  13. 13. jtdwyer 6:14 pm 03/4/2010

    Just one more thing on the dinos’ extinction, referring to the timely article "A Theory Set in Stone: An Asteroid Killed the Dinosaurs, After All", that article did not mention global incineration, but did remind me of the global acid rain, which would also mitigate against fossilization. I still think the incineration hypothesis is quite likely, though.

    Whatever the actual event scenario was, this new panel apparently did not consider the referenced paleontologist’s disease hypothesis, in which he failed to account for the missing fossils.

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  14. 14. jtdwyer 8:41 pm 03/4/2010

    OK, I now see where the extinction article did state: "The impact spewed rock so high, some of it likely was shot into orbit, whereas other pieces entered the upper atmosphere, reheating as they fell back to the ground", but did not mention global incineration.

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  15. 15. way2ec 3:54 am 03/5/2010

    Geez, it can get more than just a bit "snippy" in these "discussions". Is it a bird?, Is it a plane? No it’s Superman. And then the author is supposed to define what all three are? Isn’t "species of archosaur", "ancient silesaur" (my spellchecker just went bonkers), and "Ornithodira lineage" (OK dear spellchecker… trust the author, OK?) sufficient? Jtdwyer follows up on the author’s reference to hey, wow, if this is a new one, how many other new ones are out there, and won’t it be cool as more of the blanks are filled in… and comes back apologizing for not being a paleontologist nor a scholar… Like since when does inference not qualify as a tool of science? Let alone good old fashioned speculation! Our friend calvin comes to our rescue with laterally open acetabulum, elongate deltopectoral crest and supratemporal fossa onto the posterodorsal surface and now I have four more spell checker notices. And I know I have commented more than once about dear Candide’s inability to sort of "go with the flow"… lack of pertinent details??? in FIVE short paragraphs???, which brings us back to archosaurs, silesaurs, and to the relationship between T.rex and TURKEYS! Details anyone? One thing is for sure, I LOVE to mouth off about stuff that I may or may not know much about, always thought it was called a discussion and a wonderful way to learn about new stuff… so to end on a positive note and a detail not yet "dissected"… cool Image of Asilisaurus kongwe courtesy of Marlene Hill Donnelly… cool color combinations, especially the eyes, but hey, now we are talking the intersection of science, art, and some imagination.

    Link to this
  16. 16. way2ec 3:57 am 03/5/2010

    Geez, it can get more than just a bit "snippy" in these "discussions". Is it a bird?, Is it a plane? No it’s Superman. And then the author is supposed to define what all three are? Isn’t "species of archosaur", "ancient silesaur" (my spellchecker just went bonkers), and "Ornithodira lineage" (OK dear spellchecker… trust the author, OK?) sufficient? Jtdwyer follows up on the author’s reference to hey, wow, if this is a new one, how many other new ones are out there, and won’t it be cool as more of the blanks are filled in… and comes back apologizing for not being a paleontologist nor a scholar… Like since when does inference not qualify as a tool of science? Let alone good old fashioned speculation! Our friend calvin comes to our rescue with laterally open acetabulum, elongate deltopectoral crest and supratemporal fossa onto the posterodorsal surface and now I have four more spell checker notices. And I know I have commented more than once about dear Candide’s inability to sort of "go with the flow"… lack of pertinent details??? in FIVE short paragraphs???, which brings us back to archosaurs, silesaurs, and to the relationship between T.rex and TURKEYS! Details anyone? One thing is for sure, I LOVE to mouth off about stuff that I may or may not know much about, always thought it was called a discussion and a wonderful way to learn about new stuff… so to end on a positive note and a detail not yet "dissected"… cool Image of Asilisaurus kongwe courtesy of Marlene Hill Donnelly… cool color combinations, especially the eyes, but hey, now we are talking the intersection of science, art, and some imagination.

    Link to this
  17. 17. jtdwyer 1:45 pm 03/5/2010

    way2ec – Great comment, generally. Yes, I’m serious!

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  18. 18. evision 7:39 am 03/11/2010

    http://www.samgambayard-c-m.com

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  19. 19. zaidabdussamad 12:08 am 03/20/2010

    in all my years i have never heard anything like this i did do research and it does make sense this dinosaur not really being a dinosaur and i want to congragulate the writter of this article as they had really done their homework

    Link to this
  20. 20. zaidabdussamad 12:09 am 03/20/2010

    in all my years i have never heard anything like this i did do research and it does make sense this dinosaur not really being a dinosaur and i want to congragulate the writter of this article as they had really done their homework

    Link to this

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