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Post by Infinity Blade on Apr 12, 2018 22:21:59 GMT 5
That's an interesting idea and one I've been wondering about for some time now. That is, could ichthyosaurs ram? Some (if not most?) seem to have elongated mandibles that look ill suited for taking the high amounts of stress from ramming them into another animal, but then again dolphins have gracile jaws too and ram with them (and marlins and swordfish with their bills too). Ferrón describes sikanniensis as a slow moving giant. So I have my doubts about that. These giants are reptilian giant beaked whales which are not exactly warriors or big game killers. There are other ichthyosaurs with such a potential. I was referring to ichthyosaurs in general, not merely the shastasaurids among them. I agree they would probably have difficulty picking up the momentum for a ram in the first place. I think the later(?) and more active, thunniform ichthyosaurs are better candidates for ramming. |
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Post by coherentsheaf on Apr 12, 2018 23:50:50 GMT 5
Regarding ramming: Very large ichthyosaurs would likely not been able to do this. Giat Physeterids need considerably adaptations for it, I think it is very unlikely that the rather gracile looking skulls would withstand the stress.
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Post by Grey on Jun 9, 2018 3:09:35 GMT 5
Dean Lomax who described the new gigantic shastasaurids claim that possibly they could have been macropredators, if based on S. popularis.
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Post by Grey on Sept 2, 2018 20:10:28 GMT 5
Could these gigantic shastasaurids ichthyosaurs have been raptorial top macropredators ?
Here are some comments from Dean Lomax on FB :
"...Several of the very larger shastasaurids have actually been found with teeth and stomach contents, including various squid and other vertebrates. Seems the toothlessness 'may' in part be due to a preservation bias."
"Yes, that abstract (about Shonisaurus popularis being macropredaceous) is most recent but it goes back to the early discoveries and studies, including by Camp, 1980 and Motani's paper in the Ancient Marine Reptiles book/volume. I'm not suggesting anything on the basis of isolated jaws, but considering that S. sikanniensis is closely related with S. popularis it's not impossible. It's not impossible considering megalodon as an example. Obviously, very different animal but it's plausible that Shonisaurus was a top predator. As ever, we need more specimens."
"I think there is a possibility that this could be the case. Sure, these were clearly giant animals, but from their teeth and stomach contents it clearly shows they were feeding on varied prey. Of course, again, this is mostly based around S. popularis, which is 15 m, though. Thanks for the link. No, we can't really say too much based on the surangular, this is all inferred from S. sikanniensis which has an incomplete skull that has data inferred from S. popularis... So you see the issues haha."
Comments from paleosir on deviant :
"Probably not as placid as whales, at all.
Stomach contents from the Xiaowa formation show that Shastasaurus-like ichthyosaurs usually gulped down large quantities of cephalopods (quite a bit larger than krill), sometimes placodonts, and one even swallowed an ichthyosaur 1/8 it´s own mass."
"Applying the same logic to this animal, it would be able to swallow great white sharks whole, even using the lowest estimates."
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Post by theropod on Sept 2, 2018 20:59:56 GMT 5
I don’t think anybody is comparing Shonisaurus to baleen whales (except in size), but rather to sperm whales. Sperm whales are technically macrophagous, and some of their prey is large in absolute terms too (colossal squid, megamouth sharks…), but not really in the same league as raptorial predators like orcas, pliosaurs, stem-physeteroids or sharks. And a maximum prey size 1/8th that of the predator isn’t really in that league either, although we can hardly claim to be able to ascertain the maximum prey size based on fossil stomach contents.
But the paper on Shonisaurus ecology is certainly going to be very interesting. Do you happen to know anything what’s planned in that regard?
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Post by prehistorican on Apr 12, 2019 6:13:15 GMT 5
Considering the bite force of Temnodontosaurus of 3 tonnes at around 10 tonnes body mass, it makes you wonder if Aust Cliff's bite force could have had much more bite force. It seems that people in online circles (including paleosir) think it wa quite a large animal fin-blue whale tier in length maybe even mass. Shonisaurus seems to be the most representative of giant ichthyosaurs. The "type" body.   I wonder about the size estimates of Aust Cliff up to 33.8m as the upper but what about lower? And the weight estimates for giant ichthyosaurs seem heavier than I've seen posted on the forum. |
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Post by theropod on Apr 13, 2019 0:02:45 GMT 5
Considering the bite force of Temnodontosaurus of 3 tonnes at around 10 tonnes body mass, it makes you wonder if Aust Cliff's bite force could have had much more bite force. It seems that people in online circles (including paleosir) think it wa quite a large animal fin-blue whale tier in length maybe even mass. Shonisaurus seems to be the most representative of giant ichthyosaurs. The "type" body. I wonder about the size estimates of Aust Cliff up to 33.8m as the upper but what about lower? And the weight estimates for giant ichthyosaurs seem heavier than I've seen posted on the forum. Where did you get that bite force estimate from? |
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Post by prehistorican on Apr 13, 2019 2:24:52 GMT 5
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Post by theropod on Apr 13, 2019 2:54:14 GMT 5
Quite the contrary, that is very interesting, I just wasn't aware of it, that's all. 3t for small-toothed, relatively slender-snouted T. platyodon is actually pretty impressive. |
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Post by Grey on Apr 13, 2019 19:04:26 GMT 5
That is very interesting.
Now, it is doubtful the gigantic ichthyosaurs from Aust or Lilstock were as raptorial as Temnodontosaurus, even if the thought of it is intriguing.
Knowing the largest relative ichthyosaur known by a good skeleton was quite slender shaped, I doubt it is more reasonable to make these giants blue whale-like in body shape even if reaching 100 tonnes for them is not implausible.
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Post by theropod on Apr 13, 2019 20:30:33 GMT 5
This estimate itself seems to be based on T. platyodon, which is not commonly regarded as very macropredaceous here. Isolated teeth from the lower jurassic reach almost three times the length of the largest known T. platyodon. This makes it highly unlikely that these were proportioned the same as T. platyodon (otherwise we could have a 25m Ichthyosaur with a 5m skull and a 23t bite force on our hands…), it is far more probable that there was a large, highly raptorial ichthyosaur, which then wouldn’t be that huge, but presumably have a much more robust jaw morphology, similar to T. eurycephalus.
We have already discussed the other material possibly pertaining to such a taxon, but what’s new is that even T. platyodon would have had quite a hefty bite force according to this research (granted, that is a large skull, but it’s still quite slender). This is interesting for several reasons.
Firstly, no animal would need such a powerful bite for just feeding on small fish and squid, so this confirms that the well-known, Temnodontosaurus species were at least somewhat generalist feeders broadly overlapping with modern macroraptorial sharks or cetaceans, despite their rather small teeth and long skulls not looking very "impressive" to the casual observer (not compared to the likes of a pliosaur, at any rate).
Secondly an even larger, more specialised macropredator (say, around 14-16m, as implied by the largest skeletal material from the Lower Jurassic) with the more massive skull implied by its teeth would presumably have bitten a lot harder than that.
That’s not considering fragmentary, more distantly related Triassic taxa that may have grown much bigger, but were probably small-prey specialists more comparable to a sperm whale. This also makes one really wonder how hard Thalattoarchon or Himalayasaurus could bite.
It is a shame this research doesn’t seem to have been published, macroraptorial ichthyosaur feeding apparata are chronically understudied.
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Post by Grey on Apr 13, 2019 20:52:41 GMT 5
I m certainly opened to the idea that raptorial ichthyosaurs would have outclassed even the mightiest later pliosaurs.
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Post by theropod on Apr 13, 2019 21:09:08 GMT 5
prehistorican: The reported diameter for the fragmentary proposed surangular from Aust Cliff is 30-50% bigger than in the Lilstock specimen, which in turn is 26% bigger than S. sikanniensis, also based on diameter (but at a different position in the bone). I don’t think we can talk of a lower estimate here though (certainly not a lower bound estimate), there are too many variables involved. A reasonable lower bound for something that fragmentary may be more like "no size estimate at all", because the bone might not even be what it was identified at, or might be too variable to produce any useful predictions. But then again, there are plenty of estimates based on similarly scrappy material floating around, so…
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Post by prehistorican on Apr 13, 2019 21:32:28 GMT 5
I understand these are very fragmentary remains and there isn't much to go about. If we had a lot more similar fossils we could probably establish a pattern but it seems giant ichthyosaurs vary noticeably in jaw shape, body shape, etc. Also theropod I have never seen the 50% larger than Lilistock estimate, is there any calculations to support that, is it a guesstimate, etc?
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Post by theropod on Apr 14, 2019 2:14:03 GMT 5
I understand these are very fragmentary remains and there isn't much to go about. If we had a lot more similar fossils we could probably establish a pattern but it seems giant ichthyosaurs vary noticeably in jaw shape, body shape, etc. Also theropod I have never seen the 50% larger than Lilistock estimate, is there any calculations to support that, is it a guesstimate, etc? No, I don’t guess about things like this, unless I specifically say that I am guessing. This comes straight from the paper: The same method has its limitations, but a comparison can be made to the Aust specimen (BRSMG Cb3869) that might be a portion of surangular. The maximum cross-sectional dimension of the Aust fragment is 13.8 cm ([15]; DRL, PDLS pers. obs.), which is similar in cross-sectional shape to a portion of the Lilstock surangular anterior to the coronoid, where the bone is roughly cylindrical. That region of the Lilstock specimen has a dorsoventral height of 10.6–9.2 cm, suggesting that the Aust ichthyosaur was a much larger animal, perhaps more than 30% larger. they compared it to a region of the surangular in the Lilstock specimen with a range of diameters. Those diameters directly translate to a range of size ratios: 13.8/10.6=1.3 13.8/9.2=1.5 I think it’s obvious why the lower end of this range was the one specifically listed. This is a published technical paper, and should uphold certain standards of caution. Certain less cautious works in the past notwithstanding, it is usually good practice to not put too much emphasis on the upper estimate for an animal whose lower estimate would already imply an unprecedented size, in this case the size of a large blue whale (at least in length), especially in the scientific literature, especially if it is an estimate based on a fragment whose identity isn’t even readily identifiable. The Aust Cliff bone is appropriately described as "perhaps more than 30% larger", and that’s about as far as I’d go in a scientific paper, at least when not specifically testing size estimates, which might justify giving several figures (but should also provide a conclusion that is conservative with respect to the hypothesis being tested, not necessarily, but usually, working in favour of the lower size estimates). Experience has shown that "science"-journalists are usually both unqualified to accurately describe the contents of a scientific paper to the public (that can be a challenge even for scientists not familiar with at least closely related fields), and that it will probably end up being the highest possible number that they report, ignoring all the rest. To avoid that hyperbole, a good trick is to have all the raw data there, so people knowing what exactly to calculate can make up their own minds, but only spelling out lower figure. Lomax et al. is actually an excellent example of this. They start out with the Lilstock specimen, for which they estimate actual overall size figures, one larger, the second somewhat lower. With the Aust Cliff’s "lower" size figure, they already only give a percentage, and the upper figure they only provide in the form of the comparative measurements, which conveniently makes sure someone who even gets to that upper figure understands what it means. Of course there are also scientific works that don’t do such a good job at that, and that usually ends up with the media subsequently spitting out lots of hyperbole by citing the highest figure they can find, and ignoring all the rest. That does not mean it’s impossible these were blue-whale sized ichthyosaurs, but had they written that in the paper, a day afterwards the newspapers would have read "ancient aquatic dinosaur was larger than a blue whale" or similar hogwash. There is no particular reason to say it wasn’t as much larger as implied by the comparative diameters provided (which I hope we do) we trust Lomax et al to get the identification and the measurements right, but that of course does not make this factual or a true "lower bound" estimate on account of how fragmentary the material is. It is of course also plausible that this bone did not come from an ichthyosaur that large, but simply one with a proportionately thicker surangular, and/or that the bone wasn’t identified correctly to begin with. Those possibilities are not directly indicated, therefore cannot be factored into a calculation like that, are of course implied, but likely wouldn’t be understood by a journalist reading the thing. That’s why giving a lower-bound estimate is difficult. Maybe the Aust ichthyosaur was not bigger at all, and just had a thicker jaw. That just isn’t directly indicated by anything and hence wouldn’t generally be considered an estimate in the strict sense, but it’s certainly possible. |
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