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| Allosaurus fragilis v Carnotaurus sastrei | |
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| Tweet Topic Started: Jun 17 2013, 09:04 PM (12,181 Views) | |
| Taipan | Jun 17 2013, 09:04 PM Post #1 |
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Allosaurus fragilis Allosaurus (play /ˌælɵˈsɔrəs/) is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period (Kimmeridgian to early Tithonian). Allosaurus was a large bipedal predator. Its skull was large and equipped with dozens of large, sharp teeth. It averaged 8.5 meters (28 ft) in length, though fragmentary remains suggest it could have reached over 12 meters (39 ft). Relative to the large and powerful hindlimbs, its three-fingered forelimbs were small, and the body was balanced by a long, heavy tail. As the most abundant large predator in the Morrison Formation, Allosaurus was at the top of the food chain, probably preying on contemporaneous large herbivorous dinosaurs and perhaps even other predators (e.g. Ceratosaurus). Potential prey included ornithopods, stegosaurids, and sauropods. Allosaurus was a typical large theropod, having a massive skull on a short neck, a long tail and reduced forelimbs. Allosaurus fragilis, the best-known species, had an average length of 8.5 meters (28 ft), with the largest definitive Allosaurus specimen (AMNH 680) estimated at 9.7 meters long (32 ft), and an estimated weight of 2.3 metric tons (2.5 short tons). In his 1976 monograph on Allosaurus, James Madsen mentioned a range of bone sizes which he interpreted to show a maximum length of 12 to 13 meters (40 to 43 ft). As with dinosaurs in general, weight estimates are debatable, and since 1980 have ranged between 1500 kilograms (3300 lb), 1000 to 4000 kilograms (2200 to 8800 lb), and 1010 kilograms (2230 lb) for modal adult weight (not maximum). John Foster, a specialist on the Morrison Formation, suggests that 1000 kg (2200 lb) is reasonable for large adults of A. fragilis, but that 700 kg (1500 lb) is a closer estimate for individuals represented by the average-sized thigh bones he has measured. Using the subadult specimen nicknamed "Big Al", researchers using computer modelling arrived at a best estimate of 1,500 kilograms (3,300 lb) for the individual, but by varying parameters they found a range from approximately 1,400 kilograms (3,100 lb) to approximately 2,000 kilograms (4,400 lb). ![]() Carnotaurus sastrei Carnotaurus was a large predatory dinosaur. Only one species, Carnotaurus sastrei has been described so far. Carnotaurus lived in Patagonia, Argentina (La Colonia Formation) during the Campanian or Maastrichtian stage of the Late Cretaceous. Carnotaurus was a large theropod, about 8 metres (26 ft) in length, weighing between 1488 kg and 2626 kg (1.6–2.9 short tons), depending on the method of estimation. The most distinctive features of Carnotaurus are the two thick horns above the eyes, and the extremely reduced forelimbs with four basic digits, though only the middle two of these ended in finger bones, while the fourth was splint-like and may have represented an external 'spur.' The fingers themselves were fused and immobile, and lacked claws. It is also characterized by its unusually long neck (compared to other abelisaurs), and its small head with box-shaped jaws. The eyes of Carnotaurus faced forward, which is unusual in a dinosaur, and may indicate binocular vision and depth perception. There is a rather puzzling contrast between Carnotaurus’ deep, robust-looking skull and its shallow, slender lower jaw. So far no one has worked out what this might imply about its methods of feeding. ____________________________________________________________________
Ceratosaurus is probably too small, so lets try this first. |
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| DarkGricer | Jun 21 2013, 07:52 AM Post #16 |
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Omnivore
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No. The largest confirmed Allosaurus is a bit below 10 meters. Allosaurus' size is often exaggerated. Edited by DarkGricer, Jun 21 2013, 07:52 AM.
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| Ausar | Jun 21 2013, 08:24 AM Post #17 |
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Xi-miqa-can! Xi-miqa-can! Xi-miqa-can!
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I believe he is referring to Epanterias amplexus, which is 12 meters long and thought by some people to be synonymous with Allosaurus. However, this matchup is with the smaller Allosaurus fragilis. Either way, Allosaurus wins. |
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| SpinoInWonderland | Jun 21 2013, 01:20 PM Post #18 |
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The madness has come back...
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Epanterias amplexus is likely synonymous with Allosaurus fragilis. |
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| Spinodontosaurus | Jun 21 2013, 04:33 PM Post #19 |
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Herbivore
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'Most likely'? Its nearly 4 million years younger than Allosaurus fragilis... Unless more evidence is found to the contrary, keeping them seperate is probably the safer option, even aside from Epanterias appearing to be notably larger than even the largest known A. fragilis. |
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| SpinoInWonderland | Jun 21 2013, 04:35 PM Post #20 |
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The madness has come back...
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Well, successful species can last more than 4+ million years. |
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| Spinodontosaurus | Jun 21 2013, 04:43 PM Post #21 |
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Herbivore
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Can. Doesn't mean they always do. A. fragilis already has a span of a few million years, and is a very well-known theropod. Yet, as far as I know, there is nothing to bridge the 3-4 million year gap between the youngest known A. fragilis and the type specimen of Epanterias. |
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| SpinoInWonderland | Jun 21 2013, 04:53 PM Post #22 |
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The madness has come back...
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The Epanterias specimen is not diagnostic. There is virtually no other distinctive factors other than size and temporal location, which can both be simply solved by extending the size and temporal ranges of A. fragilis. Doing so isn't unacceptable, as the fossil record is know for being incomplete. |
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| Jinfengopteryx | Jun 21 2013, 06:41 PM Post #23 |
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Aspiring paleontologist, science enthusiast and armchair speculative fiction/evolution writer
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Not often. Many only survive for 3 million years. P.S. You said synonymous with Allosaurus fragilis. This would mean that you don't even view it as an own species (A. amplexus). Well, such a specimen would for sure be a freak specimen, what shouldn't be taken into account. A 10 m long A. fragillis is already a very large specimen. Edited by Jinfengopteryx, Jun 21 2013, 06:44 PM.
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| theropod | Jun 21 2013, 08:41 PM Post #24 |
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palaeontology, open source and survival enthusiast
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Many animals are known for tremendous variation in size. Take as an example varanus komodoensis. They average mere 23kg, yet there are also many non freaks that exceed 60kg. All in the same species. I think one should just specify which size, because more or less everything gets completely different depending on whether you take average of maximum. At least two other specimens of A fragilis reach or exceed 10m. Yes, those are large and the average is below 9m, but even when including Epanterias the size range is not unnormal or freaky. Size alone is no diagnostic character. You would have to consider differently sized grizzlies, leopards or komodo dragons different species. Temporal range is not either, otherwise how would temporal range of a species ever be extended, if we would consider living later or earlier a dignostic character for separation. Species would not base on traits any more, but on strata, and hence be no actual indicator of what animal you are talking about unless when talking aboout animals fromtn he exact same time. |
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| Jinfengopteryx | Jun 21 2013, 08:53 PM Post #25 |
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Aspiring paleontologist, science enthusiast and armchair speculative fiction/evolution writer
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I know about the komodo dragon example, but you need to keep in mind that reptiles can grow all their lives, but it seems like theropods don't. Birds don't do so and most of the adult Tyrannosaurus specimen had a similar size (a range of 11-12 m). |
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| theropod | Jun 22 2013, 12:02 AM Post #26 |
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palaeontology, open source and survival enthusiast
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Individual variation nevertheless plays a role, otherwise freaks would not be possible either. Yes, apanterias may be close to 70% bigger in volumetric terms than the next largest Allosaurus, however that is not a variation you cannot see even in extant mammals (eg. different populations of grizzly or leopard. You can even find this degree of variations in humans!). It is possibly it simply grew to a larger size some million years later. Size alone is not diagnostic, it is very variable in all animals. Edited by theropod, Jun 22 2013, 12:06 AM.
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| Jinfengopteryx | Jun 22 2013, 12:23 AM Post #27 |
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Aspiring paleontologist, science enthusiast and armchair speculative fiction/evolution writer
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But if the Epanterias specimen is not diagnostic, how can we know that it belongs to Allosaurus fragilis either? Why is it being a subspecies more likely than it being another Allosaurus species or another Genus? |
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| theropod | Jun 22 2013, 12:47 AM Post #28 |
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palaeontology, open source and survival enthusiast
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^The temporal and magnitudinal differences are not diagnostic. whether the fossils themselves are is a different question. In a case of uncertainity, it's a matter of your individual philosophy (lumper/splitter?), but I suggest if there are no differences no new taxon should be erected, just like with Bahariasaurus/"Deltadromeus" and Cristatusaurus/"Suchomimus". Chure didn't consider the fossils undiagnosable, tough Paul apparently did. He found only minor, likely allometric differences that did not justify a new species or genus. |
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| blaze | Jun 22 2013, 02:08 AM Post #29 |
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Carnivore
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The Komodo dragon is a bad example because what constitutes an adult in extant reptiles is different to what people think as an adult in dinosaurs, people think that only dinosaurs that have reached maximum size are adults and then if they find another very large adult it implies variation but that is not the case with dinosaurs, like extant reptiles, dinosaurs reach adulthood while still actively growing, at least sauropods and theropods (I'm not sure about the others) according to recent bone histology studies, reaching adulthood at around 50-60% maximum size in linear dimensions, the adult variation already exists, is just that people are ignoring it, treating UUVP 6000 as if it was the lower bound of adult size when its actually a large specimen. A. fragilis holotype is as undiagnostic as that of Epanterias, if Carcharodontosaurus was known by remains as poor, I'm pretty sure there will be people seriously finding Giganotosaurus, Mapusaurus and Tyrannotitan synonymous with it (Paul has attempted something like this though haha) Epanterias comes from the very top of the Morrison formation, what other giant allosaurus-like theropod lived at the same time? the answer is Saurophaganax. The other very large specimen from the top of the formation that people claim is a large allosaurus, NMMNH P-26083, it wasn't classified beyond Allosauridae and there's studies that found it too big to be just a big and old specimen of Allosaurus fragilis (Rinehart et al. 2002) (based on Cleveland Lloyd spcimens). So I will jump the gun and say that is likely just another specimen of Saurophaganax. In the end I think Saurophanax and Epanterias will be sinked into Allosaurus but as their own species, just like we have Camarasuarus maximus, Apatosaurus ajax and so on. Edited by blaze, Jun 22 2013, 02:12 AM.
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| theropod | Jun 22 2013, 02:14 AM Post #30 |
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palaeontology, open source and survival enthusiast
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^Why does Chure consider Epanterias a synonym of A. fragilis, but not Saurophaganax? And isn't the latter Kimmeridgian in age? I know, I just noticed that in nearly every response to you I'm only asking questions!
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