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kgjにより編集済み: 4/13/2013 8:12:34 PM

DoP 3: Who Needs Arms to Swim?

[url=]Article[/url] [quote]Researchers have found new evidence that dinosaurs were excellent swimmers, according to a study published in Monday’s edition of Chinese Science Bulletin, an academic journal co-sponsored by the Chinese Academy of Sciences and the National Natural Science Foundation of China. In fact, an international team of experts, which included University of Alberta graduate student Scott Persons, located what is being called “strongest evidence ever found that dinosaurs could paddle long distances.” They examined a series of unusual claw marks that were left on the bottom of a Chinese river that is known to have been commonly used by traveling dinosaurs. In addition to easily identified footprints of several Cretaceous era animals, including giant long-neck dinosaurs, Persons and his colleagues discovered claw marks that they claim clearly indicates a coordinated left-right, left-right progression. “What we have are scratches left by the tips of a two-legged dinosaur’s feet,” Persons said in a statement. “The dinosaur’s claw marks show it was swimming along in this river and just its tippy toes were touching bottom.” The claw marks covered a distance of 15 meters (nearly 50 feet), which the authors cite as evidence that dinosaurs had the ability to swim using coordinated leg movements. These particular tracks were made by a carnivorous theropod dinosaur which is believed to have stood an estimated one meter at the hip. Based on fossilized rippling and the evidence of mud cracks, the researchers report that the river – which is located in what is now the Szechuan Province – went through both wet and dry cycles more than 100 million years ago. Persons describes the river bed as a “dinosaur super-highway,” adding that it has provided he and his colleagues with several other full dinosaur footprints, including those of other theropods and gigantic four-legged sauropods. Unfortunately, since the researchers only have the river-bottom claw marks to work with, Persons said that they are unable to identify exactly which dinosaur was responsible for paddling across the body of water. However, he believes it could have been either an early tyrannosaur or a Sinocalliopteryx – two species of predators which were known to have lived in that area of the Asian country. [/quote] Well, this is the first cold hard evidence that's been found for it, but it's long been theorized that theropods would use a paddling method to swim. What's intriguing is the species, and its age- 100 million years ago, from a Tyrannosaurid or Compsognathid (Sinocalliopteryx) dinosaur. The doubt in identity comes from the common ancestor of both families. Both Tyrannosaurids and Compsognathids belong to the Ceolurosauria family. I haven't read the actual paper yet but I'm willing to bet the way they distinguished it is by looking at the print and seeing if it was indicative of locked metatarsals- a hallmark of Ceolurosauria. The 100 million year old age leads to a multitude of candidates for the species' identity. If the species is determined to be a Compsognathid then I believe that Sinocallipoteryx would be the best (or only, due to size) guess. If the species is determined to be a Tyrannosaurid, things get a little more interesting. Sorry to crush dreams or anything, but it's impossible for this to be a Tyrannosaurus (or Albertosaurus/Daspletosaurus/any other famous Tyrannosaurid)- they didn't evolve for a while after. Since the print comes from China, in the Early Cretaceous Period, these are the possible (known) candidates: Xionnguanlong Yutyrannus Dilong Personally I believe the best candidate to be Dilong. Not only was it found in the correct time period, but it fits the size description as well. Since one of the guesses for the animal is Sinocallipoteryx (which is around 5 or 6 feet long... I think), an animal of comparable size is a good guess. Dilong is pretty much the same size (5 feet-ish... again if I remember correctly). No way in hell it's Yutyrannus, that thing is near-T. Rex size, 36+ feet, and if I remember correctly Xionnguanlong is a bit too big (9-ish feet?) as well. So what does it all mean? Well, if the candidate is a Compsognathid, we figure out that Compys could swim by paddling. But if the candidate is a Tyrannosaurid, we figure out that Tyrannosaurids actually did swim- [I]without[/I] their arms. What's interesting though, is that comparatively, Dilong's arms were quite big. Now it's no Therizinosaurus, but the proportions are decently large enough to allow for dextrous manipulation. But if Dilong [I]could[/I] use its arms, why didn't it? It follows with the observed fact of how Tyrannosaurids' arms grew smaller and smaller in time. Now, the argument could be made that this specimen may simply have been a rare occurrence, but the point still stands- if the environment for this specimen was such that it would require some form of aquatic movement, why didn't it develop anything for it? Why did Tyrannosaurids evolve towards ditching their arms? Yet another mystery in the giant puzzle that is them. For now though, we can at least conclude one thing- Dinosaurs could swim, and they didn't need arms to do it. Look out, Jaws.



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