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Ekrixinatosaurus novasi v Tarbosaurus bataar
Topic Started: Oct 20 2013, 07:20 PM (5,881 Views)
Taipan
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Ekrixinatosaurus novasi
Ekrixinatosaurus (Explosion-Born Reptile) is a genus of dinosaur which lived during the Late Cretaceous. It was a theropod believed to be one of the abelisaurs. Its fossils have been found in Argentina. The type species, Ekrixinatosaurus novasi, was first described in 2004 by Argentinian paleontologist Jorge Calvo, and Chilean paleontologists David Rubilar-Rogers and Karen Moreno. Ekrixinatosaurus is perhaps the largest abelisaurid known to date, estimated as 10 to 11 metres (33 to 36 ft) long. It was also particularly robust and had a relatively large head, suggesting that it was a powerful predator or scavenger, able to scare other predators away from their kills.

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Tarbosaurus bataar
Tarbosaurus belongs in the subfamily Tyrannosaurinae within the family Tyrannosauridae, along with the earlier Daspletosaurus, the more recent Tyrannosaurus and possibly Alioramus. Animals in this subfamily are more closely related to Tyrannosaurus than to Albertosaurus and are known for their robust build with proportionally larger skulls and longer femurs than in the other subfamily, the Albertosaurinae. Although many specimens of this genus have been found, little definite data was confirmed on the dinosaur as of 1986, though it was presumed to share many characteristics with other tyrannosaurids. The close similarities have prompted some scientists to suggest a possible link between the North American and Eurasian continents at that time, perhaps in the form of a land bridge. As with most dinosaurs, Tarbosaurus size estimates have varied through recent years. It could have been 10 meters long, with a weight of 4 to 5 - 7 tons.

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Daspletosaurus
Oct 20 2013, 08:55 AM
Tarbosaurus vs. Ekrixinatosaurus
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Vobby
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I don't really know about the different size estimates, but I feel like Ekrixinatosaurus could win if the weight was similar. It was build like a tank, not only for abelisaurids standards.
Quoting from Juarez 2011 (thanks for posting Spino)

a. The combination of characters in Ekrixinatosaurus, including a (1) large,
transversely-expanded skull, (2) prominent supraorbital ridge above the dorsal aspect of the orbit,
(3) anteroposteriorly compressed cervical vertebrae, (4) robust and proportionally short hindlimbs with a tibia shorter than femur, indicates that this form represents a massive animal with an
enhanced capacity to sustain injuries incurred via intra- or interspecific combat


This guy is one hell of a good fighter if you ask me.
Edited by Vobby, Oct 21 2013, 11:50 PM.
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Ausar
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Didn't Verdugo post evidence that abelisaurids didn't have particularly strong bites for theropods?
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Vobby
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I actually don't know. I'm sure that tyrannosaurids were generally the strongest biters, but there is a lot of diversity within clades, so it's probably not a good idea to associate the bite of this abelisaurid with, say, that of Carnotaurus. It is worth noting that Tarbosaurus skull is much more elongated than Ekrixinatosaurus one, so I guess the latter could be at least more suited to resist damage, which is quite important in a face-biting match.

Edit: I know that Verdugo follows Andrea Cau blog, and he wrote a post about the different kind of bites amongst theropods. Abelisaurids are described as very fast, but relatively weak biters, with very flexible (snake like) jaws. Cau suggested that abelisaurids were suited to hunt preys which could have been killed trough violent shaking, supported by strong neck muscles, and swallowed whole. But, this post is from 2009, 2 years before Juarez's article, which describes a fairly massive and robust Ekrixinatosaurus. The article says nothing about bite force, but describes a quite robust skull. Cau also wrote a post about Ekrixinatosaurus, but didn't investigated much is paleoecology.
The two posts:

http://translate.google.com/translate?u=http%3A//theropoda.blogspot.it/2009/04/ad-ognuno-il-suo-morso-i-giunti.html&hl=en&langpair=it|en&tbb=1&ie=UTF-8

http://translate.google.com/translate?u=http%3A//theropoda.blogspot.it/2011/01/un-abelisauro-gigante-che-se-ne-frega.html%23more&hl=en&langpair=it|en&tbb=1&ie=UTF-8
Edited by Vobby, Oct 22 2013, 09:23 AM.
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Daspletosaurus
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Jinfengopteryx
Oct 21 2013, 10:40 PM
Daspletosaurus
Oct 21 2013, 06:48 AM
Well I still support the 10 m to 11 m estimate for Ekrixinatosaurus, and if it is smaller then there was no point in requesting this match-up.
You support it on what basis?
You could bring both at 9 m, then it would as fair as putting both at 10-11 m.
Your right, your logic is unassailable :) ; and as for supporting the lengths, my support is bases off the latest paper on Ekrixinatosaurus, to my knowledge it is the most up to date info.
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Jinfengopteryx
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Blaze has pointed out that this paper used incorrect proportions for Skorpiovenator (6 m is more likely than 7 m+). As it was used for scaling, Ekrixinatosaurus would be smaller as well.
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theropod
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As far as I know snake-like kinetic jaws allowing swallowing of large prey are currently not accepted for any theropod. At the same time, a shaking-bite does not fit this hypothesis in the slightest, since...
A: a shaking motion would be very inefficient if the skull yield considerably
B: shaking motions require relatively strong bite forces (compare: tyrannosaurines which are poresumed to have employed shaking) for the mandible to resist resulting lateral, dorsal and torsional loads which are similar to holding onto a struggling prey item with the jaws.

This wouldn't make sense at all for a weak biter with a kinetic skull, on the other hand it does make sense for a strong biter with mostly akinetic skull.
Abelisaurids having at least moderately strong bite forces is everything but unrealistic, and I haven't seen any concrete data against this.
They have short, laterally expanded, thick-boned skulls, features they share with tyrannosaurines. They also have high mechanical advantage in their jaws (Sakamoto, 2010). Like tyrannosaurines, Carnotaurus has laterally pointing paroccipital processes, an adaption for lateroflexion (ie. shaking, contra Bakker, 1998 who proposed an allosaurid-like downward stroke).
As a notable difference, it has relatively short teeth, more like Allosaurus, but that's the only major thing setting them apart.

Abelisaurs as sort of a dinosaurian bulldog make sense.

Tarbosaurus has one of the narrowest skulls among tyrannosaurs (see Hurum & Sabath, 2003) and it is unlikely it relied on massive crushing power.

BTW that Tyrannosaurs in general were particularly strong biters may be nothing more than a myth. Gorgosaurus and even Daspletosaurus' teeth have similar yielding strenghts to those of similar-sized Allosaurus (Snively et al., 2006). They probably employed much greater adductor-forces than Allosaurids, but they are hardly special in this regard.
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Ausar
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So it could apply to just Tyrannosaurus then. I still believe they had some of the strongest dinosaur bites, though probably not as great as before (except probably T.rex).
Edited by Ausar, Oct 23 2013, 06:52 AM.
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Daspletosaurus
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Jinfengopteryx
Oct 23 2013, 02:09 AM
Blaze has pointed out that this paper used incorrect proportions for Skorpiovenator (6 m is more likely than 7 m+). As it was used for scaling, Ekrixinatosaurus would be smaller as well.
I'd do have to admit that if they are scaling from Skorpiovenator then 9 meters is a little more possible then 11meters.
But also I see skorpiovenator as being max 7 meters so 10 meters for ekrixinatosaurus would not be out of the realm of
Possibility.
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Vobby
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theropod
Oct 23 2013, 03:59 AM
As far as I know snake-like kinetic jaws allowing swallowing of large prey are currently not accepted for any theropod. At the same time, a shaking-bite does not fit this hypothesis in the slightest, since...
A: a shaking motion would be very inefficient if the skull yield considerably
B: shaking motions require relatively strong bite forces (compare: tyrannosaurines which are poresumed to have employed shaking) for the mandible to resist resulting lateral, dorsal and torsional loads which are similar to holding onto a struggling prey item with the jaws.

"Snake-like jaws" was an exaggeration of mine, sorry. It's just a matter of jaw flexibility, it's clear they couldn't enlarge their mouth.
About shaking, there are varanids, like the perentie if I remember correctly, which kill smaller prey trough violent shaking, and they are not the strongest biters amongst reptiles. I used to associate crushing bites with bite and shaking motion, but for now I'm not sure if it is always correct. BTW, Cau explained to me that he didn't meant to say that abelisaurids had weak bites in absolute terms, only that they are relatively weak in the continuum which have Tyrannosaurids on top.

Short skull and jaws can be adaptations for fast biting against smaller prey, I guess, not only for strong bites, but again, also the association of ALL abelisaurids with weak bites doesn't convince me now.
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Carcharadon
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Did i also forget to mention that abelisaurids also had rather small skulls for their size? A similar sized tyrannosaurid or carnosaur would have a bigger skull and sharper dentition.
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Daspletosaurus
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theropod
Oct 23 2013, 03:59 AM
As far as I know snake-like kinetic jaws allowing swallowing of large prey are currently not accepted for any theropod. At the same time, a shaking-bite does not fit this hypothesis in the slightest, since...
A: a shaking motion would be very inefficient if the skull yield considerably
B: shaking motions require relatively strong bite forces (compare: tyrannosaurines which are poresumed to have employed shaking) for the mandible to resist resulting lateral, dorsal and torsional loads which are similar to holding onto a struggling prey item with the jaws.

This wouldn't make sense at all for a weak biter with a kinetic skull, on the other hand it does make sense for a strong biter with mostly akinetic skull.
Abelisaurids having at least moderately strong bite forces is everything but unrealistic, and I haven't seen any concrete data against this.
They have short, laterally expanded, thick-boned skulls, features they share with tyrannosaurines. They also have high mechanical advantage in their jaws (Sakamoto, 2010). Like tyrannosaurines, Carnotaurus has laterally pointing paroccipital processes, an adaption for lateroflexion (ie. shaking, contra Bakker, 1998 who proposed an allosaurid-like downward stroke).
As a notable difference, it has relatively short teeth, more like Allosaurus, but that's the only major thing setting them apart.

Abelisaurs as sort of a dinosaurian bulldog make sense.

Tarbosaurus has one of the narrowest skulls among tyrannosaurs (see Hurum & Sabath, 2003) and it is unlikely it relied on massive crushing power.

BTW that Tyrannosaurs in general were particularly strong biters may be nothing more than a myth. Gorgosaurus and even Daspletosaurus' teeth have similar yielding strenghts to those of similar-sized Allosaurus (Snively et al., 2006). They probably employed much greater adductor-forces than Allosaurids, but they are hardly special in this regard.
I like your analogy of Abelisaurs as sort of a dinosaurian bulldog.

Now I'm not familiar with Adductor Forces can you explain this, I've tried looking it up but cant make heads or tails of the info that comes up.
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Jinfengopteryx
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Adductor forces seem to be the bite force values we usually read for carnivores (although they are not exactly the forces the prey animal will experience, because many predators will also shake or use other techniques for increasing the lethality of their bites).
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Teratophoneus
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Tarbosaurus win. Even assuming that Ekrixinatosaurus was 11 m, it would be more or less equal in lenght with Tarbosaurus (the largest know Tarbosaurus was about to 10,7 m or so), but tarbosaurus would have a proportionally larger skull=a very strong bite, and it was bulkier.
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Vobby
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How do you know Tarbosaurus was bulkier? Its skull is quite narrow compared to that of its bigger relative, but also if compared to Ekrixinatosaurus. About overall body robustness, the last description of Ekrixinatosaurus specifically address it as a quite robust animal.
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theropod
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Adductor musculature is the musculature that adducts (= ~it rises or pulls it towards the upper jaw) the lower jaw, ie. adductor force is the force excerted by a simple static bite were the mandible is pulled upwards, with nothing else applied. This is the kind of force usually given in bite force figures. There is a notable difference between this and the force actually excerted on the victim in total, because many predators enhance the power of their bites significantly by cervical or other postcranial motions of pulling, shaking, striking/stabbing etc. (take for example sharks or varanids).
I found the term "adductor force" quite suitable and precise because it makes clear what exactly is being referred to.

It's true some monitor lizards with rather kinetic jaws (as far as I know at least) shake their prey (stuff like rats and such) to kill it. However this only seems to work well on comparatively small prey, not on large prey like what some dog breeds do or Tyrannosaurines may have done. By comparison, for an animal with such traits to attack large prey a pulling bite, like in oras, is a much better attack style.

It's possible Abelisaurs mostly (that is, more than other theropods) fed on small animals, but it doesn't convince me. The skulls seem very resistant and rather akinetic, they don't have the traits of kinetic jaws such as a light, fenestrate built with many gaps, open spaces, thin bones and loose connections. Quite the contrary, the bones are thick and compact, with small fenestrae-not a structure that seems to be built to yield under stress.

Of course this is just an observation based on the primary sources, not the specimens themselves which I of course haven't examined. But in the absence of much conrete data on that, I don't think Abelisaurs in general were small-prey specialists (not saying some of them couldn't have been tough).

Their jaw structure can be explained as that of a specialised macropredator.
Robust, resistant skulls and short teeth to hold onto prey and rip off meat, likely in combination with inertial feeding (perhaps even somewhat crocodile-like?) and maybe gregarious behaviour. As a positive side effect, the relatively small skull may have allowed very quick strikes, which is not just advantageous against small game.

There is not necessarily a perfect extant analogy for every extinct predator and its ecology, its often a jigsaw of various traits. Abelisaurids have a very interesting combination of features (and are obviously difficult to interpret, even just explain).
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