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DrScottHartman — Tylosaurus pembinensis
#evolution #lizard #mesozoic #science #skeletal
Published: 2015-06-30 18:47:48 +0000 UTC; Views: 20942; Favourites: 336; Downloads: 0
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Description
The giant Cretaceous marine lizard Tylosaurus. And yes, they're really just lizards, not some exotic extinct group like plesiosaurs or ichthyosaurs. The most recent studies place mosasaurs near snakes (which are also lizards, so please stop saying "lizards and snakes"), although previous studies have placed them closer to monitor lizards.Anyhow, I couldn't decide between the closed mouth pose, which I find more aesthetically attractive and would have been a more common life view, and the mouth-agape-feeding-and-looking-badass version that better shows off the teeth. So I did both. For those of you who haven't kept up with recent revelations with mosasaur soft-tissue, it turns out that they had tail flukes and stiffer bodies than previously thought, swimming more like a shark than a giant sea snake as has been depicted in the past.
Edit: Updated the sternal elements, made some changes to the articular angle of the chevrons at the tail bend, and also updated the tail fluke to a slightly more contemporary interpretation.
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Comments: 125
That was such a monster to see hanging up in Carnegie
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Something that intrigues me is how whale like some lizards became, when i first saw this skeletal, the first thing that came to My mind was a whale, and i wasn’t wrong, i re-watched both skeletons side to side, it seems like the Convergent evolution is strong in these ones!
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Dear Friend, Scott
Thank you for answer to my questions!
You are a great friend!
The tail shape is correct in this illustration?
Just compare Tylosaurus and Mosasaurus anatomy with each other?
A) Why fingers in Mosasaurus is close each other but have distance in Tylosaurus?
What is its role in their life this difference?
B) Why thumb bone of hands and legs of Mosasaurus is smaller than thumb bone of hands and legs in Tylosaurus?
C) the skull ratio to total body length of Mosasaurus was the smaller skull ratio to total body length of Tylosaurus ?
D) why bones bellow the end of the tail is longer in Mosasaurus in compare of Tylosaurus?
1) which one have the more the ribs?
2) which one have the more teeth?
3) which one have the more vertebrae in neck, back and tail?
Professor Mike Everhart told me some of opinions exist about pelvic in Mosasaurs is separate of backbone. therefore, legs are useless. Do you hear this theory? Is this theory correct or out of date now? Do you think pelvic attach to vertebra or separate in mosasaurs? Please explain your reasons.
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I think I can cover most of these:
I based the tail fluke shape off the restoration provided by Lindgren et al. 2011, though with a more sharply angled fluke. We have no data for Mosasaurus's soft tissues as far as I'm aware. It's about as correct as anyone else's really.
A+B) Mosasaurines and Tylosaurines seem to have inhabited different habitats, and may have even evolved their flippers independently from each other, resulting in flippers with different shapes for different hydrodynamic uses. Seems to vary between genera anyway - Prognathodon had more triangular flippers than Mosasaurus, despite being a close relative. For what it's worth, the "thumbs" are actually the pinkie fingers and toes. The true thumbs are actually the leading edges of the flippers.
C) Not really. They're the same tbh. Mosa has a longer body and shorter tail which may give the illusion of a proportionally smaller skull, while Tylosaurus has a longer, more slender snout which adds to total length. Platecarpus and Plotosaurus have proportionally smaller skulls still by some margin.
D) Mosasaurines seem to have had more developed flukes than russellosaurines across the board. That being said, Mosasaurus is about 10 million years younger than Tylosaurus, so that's about 10 million years worth of fluke development in the genus. I think Prognathodon migt be more on par with Tylosaurus's fluke, but I'll have to give that a proper look another time.
1) Mosasaurus.
2) Haven't counted, but I think TYLOSAURUS had more teeth. Mosasaurus had a shorter snout, and HUGE teeth.
3) Both had 7 in the neck. Mosasaurus had 32 to 38 dorsals (18 of which had long ribs), which is WAY more than Tylosaurus. Tylosaurus had a longer tail base with more vertebrae than Mosasaurus, but I've not counted how many verts are in Tylosaurus's fluke yet.
I have no opinion on Everhart's hypothesis. I've never heard it before, and I'm neither qualified enough, or in any position to actually test it.
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Thank you for your nice answers!
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He mention you in his page now. Please see it now
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Dear Scott
What is your opinion about this Mosasaurus skeleton?
orig04.deviantart.net/d0e7/f/2…
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I haven't looked at M. hoffmanni in detail, so I don't really have a detailed opinion to share. The overall interpretation looks reasonable enough to me, and the style and pose seem to have been heavily influenced by my Tylosaurus, which is OK but it'd be nice for it to be mentioned in his post.
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Damn, I knew I forgot to reference something! I'll go update that description.
For what it's worth, the pose is somewhere in between your Tylosaurus and the Platecarpus skeletal from Lindgren et al. 2010.
I should probably mention that too...
Sorry!
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Thanks - I certainly wasn't going to ask for a takedown or anything, but I do appreciate the reference. Assuming the proportions are right (not throwing shade, I've simply not looked at Mosasaurus at all), it's great, as we need more mosasaur skeletals that aren't awful.
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I can definitely see why good quality mosasaur skeletals are so rare. At least for Mosasaurus anyway. It barely has anything substantial pictured that's available online, despite having so much written about a lot of very specific details from supposedly fairly complete specimens.
That and I found the vertebrae are such a grind to draw.
If you ever do end up looking into Mosasaurus, I really hope it goes a lot more smoothly for you than it did for me, lol.
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Soooo many vertebrae. Not as annoying to illustrate as ray-finned fish, but still pretty bad.
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Thanks anyway, I asked because I was wondering if Bruce is the same specimen that is said to actually have an extra 26 vertebrae from another mosasaur atributed to it, I'm not sure but it might be it or at least the mounted skeleton could be influenced by it, because it has 48 precaudals (including pygals), which is excessive for Tylosaurus.
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That sounds like a reasonable speculation - it's certainly high for Tylosaurus.
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BTW, how many caudals (excluding pygals) does your skeletal has? I could count up to 80 but due to the resolution I'm not sure if it reaches 90.
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Hey Scott, this is great truly amazing. But wondering if you agree with my theory hypothesis...do you think that some of the later developed Mosasaurs did lack the tail fluke; do you think they're could've been two types of Mosasaurs swimmers or no?
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I suspect all derived mosasaurs had some form of tail fluke (they all have tails that kink down to support them), but there was probably a range of how well developed it was in different clades.
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I guess so, but then how would you explain the early Mosasaur, Dallasaurus and Cretaceous relatives Mosasaurus and Tylosaurus with at least one imprint or two from what I found lacking a fluke?
It will be hard to find the image, but I can try to find it again.
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Dallasaurus is waaaay primitive - it's like one or two steps past marine iguanas in terms of aquatic adaptations, and isn't a good model for the more derived forms. Most importantly, it doesn't have the kink down in the tail that the derived forms do.
There is no imprint of Tylosaurus or Mosasaurus lacking a fluke, and frankly it would be pretty shocking if they didn't.
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Yes I know, but I wouldn't include Dallasaurus if it wasn't a good reason. And actually from the images I found there are...I took the time to look at imprints of several Mosasaur skeletons in museums or so and three of them lacked any form of a tail fluke. Further information that I found is that when the fossils are usually are encased around glass or are one the ground those are the real ones. This is how I know these ones are real enough to support some evidence.
Here are the pictures I've come to inspect with a couple of new ones, with some of the contours at least there seems to be no sign of a fluke and the fossils are practically 100% genuine. I would even more good evidence, but I can't find the picture I saw before so I'm sorry for that, but this is all I can provide. So take a look a tell what you think about it...
2.bp.blogspot.com/_ZHv_I4h7INY…
2.bp.blogspot.com/-VaNr0UxjGJ8…
www.hgms.org/client_youth/Pale…
2.bp.blogspot.com/-ekdoa6V0jGw…
www.kansastravel.org/11naturer…
oceansofkansas.com/Lindgren/s-…
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Those images don't have tail skin impressions at all! You can't look at a fossil that doesn't have the right skin impressions and then say "see, no fluke!". The only advanced mosasaurs with skin impressions on the tail show a fluke, and in every single other group of marine reptiles, including metriorhynchid crocodiles, when there is a king in the tail like in advanved mosasaurs AND there are skin impressions they always, always have a tail fluke. So it's a fallacy called "special pleading" to try and say there wasn't a fluke in a mosasaur with the same tail anatomy without very clear evidence.
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Well I say this because I examined them; and it's not some cheap play calling to be even bias about. Plus have seen any other Mosasaur skin impressions other than in Prognathodon and Platecarpus (which I may add aren't even classified in the same families as Mosasaurus and Tylosaurus)?
The problem with Science and paleontology today is still the same thing went on since those crybabies Edward Drinker Cope and Othneil Marsh were still on with the Bone Wars; that being accusation, we all still go through this one swirl of acceptance that when one thing is changed and seen how it is everything must follow the same trend and personally I don't believe that. It's like with all the theropods (namely Coelurosaurs) we found only ten or six that have feathers and now we label all of them to have them, but in the case that the super predator ones didn't have any like T-rex; yes maybe the medium sized ones like Yutyrannus and Nanuqsaurus had down and fur, but it was only for warmth for the climates they lived under; Tyrannosaurus on the other hand at least as an adult may of never had feathers or Utahraptor and Gallimimus look like plump turkeys on Thanksgiving (though I still show respect for the conception; thank you, Dr. Grant). I know skin imprints from Mosasaurs are a rare thing, but from all the Mosasaurus and Tylosaurus fossils that have been found for centuries; have Paleontologists at least found one piece of evidence showing Mosasaurians and Tylosaurians to have a tail fluke (at least other than Plotosaurus of course)?
All going to show if they didn't have no then they'd still be good swimmers and be able to progress and the most ferocious sea creatures of their oceans up to date. The Plesiosaurs are the best example of evolution divergence among their species, some of them had really long-necks, some had short-necks and the others (the Pliosaurs) had fitted they're lives to eating other meats and have bigger heads and bodies than their cervically elongated cousins and even the Ichthyosaurs have some divergences in their families as well, with some having dorsal fins while others didn't and most eating fish while others went for other creatures like Cymbospondylus. If they lack bilobed tail; these Mosasaur familes could've used a similar method of swimming like crocodilians do; I mean prefeerentially Mosasaurs had their tails down like a crocodilians so in other cases they could've used that method of swimming like they're cousins today use. Yes you may note indeed that Metriorhynchids did have kinks in their tails to help them swim more efficiently within open-ocean currents, but then the crocodilian, Teleosaurus was an open-sea predator as well and it really didn't need a fluke or kink bend to support itself within the waters; this also going for modern crocodilians like the Salt-water Crocodile that usually swims long distances in the water, even the Mosasaurs' living relative the Komodo Dragon swims across long distances to get to other islands on the shores of Komodo and they use their powerful tails to swim across and rarely use their own limbs.
I don't mean tamper with you're further analysis on the assessments given, but you also have to prepare for the impact if somebody like were to come along with their idea, I mean it's like not like I'm wrong and neither are you, but there is the thought that maybe Mosasaurs came into two separate groups when it came to swimming methods; I mean what as the suggested the estimated number of dinosaur species is over 1000 and yet we still discovery new ones every year and what Mosasaurs made up at least 60% that roamed the earth and yet there are still new species discovered and that one could've had a flukeless and still be fully developed like the Cretaceous mosasaurs. So just like the other sea creatures Mosasaurs had different types ...like ones with kneeled scales!? www.wired.com/wp-content/uploa…
In other words it's best to take other speculations as well get and increase you're no how; this way to further analyze the situation; other wise it make you unaware of what to expect in the least.
oceansofkansas.com/Mosasaurs/v…
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OK, first of all, you asked for my take so I gave it to you. You can believe they flew and had neon feathers if you want, I was just trying to share with you the state of science. Second, what do you mean by "you examined them"? Have you seen them in person? Have you published your data? Science isn't about who has ideas or who has ego, it's about what the data shows, and just hopping on the internet and making statements doesn't make it data. If you have photos or some other data that isn't published that you'd like to share that's great, otherwise what am I supposed to comment on?
Third, and this is really pretty cut and dried, but Prognathodon is in the Mosasaurinae with Mosasaurus, and Platecarpus is in the Russellosaurina with Tylosaurus, so both are found in subfamilies with known fluke impressions. There's only two accepted mosasaur families, and both are represented. Getting basic facts like this wrong doesn't lend much credence to claiming that others are biased against you.
Fourth, this is nothing like the Bone Wars. Cope and Marsh hated each other and would sometimes take a stance simply to disagree with the other. I don't even work on squamates,and I certainly don't care which side is right, but the actual, published scientific literature is clear: mosasaurs from both families have been found with tail fluke soft-tissue evidence, and outside of Dallasaurus (which is really primitive) all known mosasaurs share the characteristic downturn in the tail that is associated with tail flukes in every other known marine vertebrate that has them. This isn't accusation, it's just the data. Now is it possible that there is some explanation for the downturn AND the preserved tail flukes in both the Mosasaurinae and the Russellosaurina? Sure, but without any shred of evidence to explain why that's just special pleading. "Special pleading" isn't an accusation either, it's just the term for when someone is trying to invoke a non-parsimonious explanation without offering substantiating evidence.
Fifth, and speaking of special pleading - Until we find a single coelurosaur without some sort of fuzz or feathers, then it's special pleading to try and claim that any lacked them. Of course it's possible that say T. rex lacked them (and my presentation at SVP might have even hinted at why), but without evidence saying "they might have" is special pleading, period. Also, why Utahraptor and Gallimimus? Neither is anywhere near big enough to qualify for wanting to lose insulation for thermophysiological reasons, so it would seem like the only reason to bring them up is simple emotional attachment (who cares if it looks silly - it either was or wasn't, how it would look to us isn't a form of evidence).
You do bring up some interesting analogies with other marine reptiles. You are 100% right that plesiosaurs are a great example of a huge amount of phenotypic divergence, but remember that plesiosaurs had almost 140 million years to evolve those divurgent forms, while mosasaurs only had 26 million years. None of them could be that crazy different from one another, because there wasn't enough time for it to evolve. You are also right that ichthyosaurs show a divergence of taxa with very weak tail flukes to those with tuna-like heterocercal tail flukes. But the primitive forms are all very early on in the Triassic or earliest Jurassic, and soon they were all replaced by advanced forms with well-developed tail flukes. This is more or less what we see with mosasaurs, where the primitive Dallasaurus doesn't have a tail fluke (or a downturn in the tail) and more advanced forms have the downturn (like advanced ichthyosaurs) and almost certainly had tail flukes. You are also right that mosasaurs _could_ have been like Teleosaurus, or extant salt water crocs, or like komodo dragons. But we know for a fact that they _weren't_ like those animals, because their vertebral anatomy (not to mention their limb anatomy!) is completely different. Maybe we will find more mosasaurs that won't have this anatomy - it would seem like we should eventually find primitive forms close to Dallasaurus that either lack tail flukes or have weakly formed ones. But Mosasaurus and Tylosaurus are not those animals - we have their tails, and they clearly have tail-fluke morphology in them.
I don't quite understand your last couple of links. We expect mosasaurs to have lizard-like scales, after all, they are lizards! So why would a keeled scale be surprising? Also, why did you link to that mount at Oceans of Kansas? That image doesn't show anything that would help you. In fact you can clearly see in it both the kink in the tail where it is broken to try and straighten it out, as well as the displaced chevrons where the curve should occur. Here, I'll point it out: drive.google.com/file/d/0Bxtac…
That specimen without a doubt has a downturn in the tail, it's just mounted completely wrong, and it's so obvious that you can see it in a low resolution image on the internet without even having to go there in person, though of course seeing it in person and writing it up for submission would be necessary before it became scientific data.
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I was wondering, is there any evidence for the presence of this downcurve in mosasaurs like Pannoniasaurus or Tethysaurus?
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I haven't examined either in person, but the fossil of Tethysaurus is preserved in articulation with a downcurve in the tail in the same place so I'd presume so. I can't find any photos of the posterior vertebral column for Pannoniasaurus, and the paper shows some gaps in the vertebral series, so it may not be something we can be sure about either way without additional remains.
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Interesting...flukes must have started to appear rather early on then.
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That's what it seems like. Which undercuts the argument that tail flukes were rare, or not found in all derived mosasaurs. This probably isn't surprising - most clades of secondarily aquatic tetrapods are to be quick to develop some sort of fluke to improve swimming.
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Indeed, it is quite of surprising that no one had guessed at that before, seeing as they were already known from ichthyosaurs and metriorhynchids...
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It felt like a "well, duh" moment to me as well, but there are still quite a few people that are attached to the older view.
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Thank you Scott, I find your reconstructions to be most helpful. I commend you for your time spent on these, and dearly hope you continue. (So long as you enjoy it.)
Also, about time we had a tylosaurus reconstruction, I believe yours is the only one I've seen.
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I thought so too, but I discovered last week that Greg Paul did several mosasaurs, including Tylosaurus, for a display at the Perot Museum of Nature and Science in Dallas. Not sure if they've been published anywhere else.
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Dear Scott
you have a Model of Tylosaurus that have a Tail shape according opinion of Mike Everhart.....I love it...is it possible for you that you change S-shape vertebrates of its back too (for make a snake form of Tylosaurus according opinion of Mike).....for me having a complete imagination of Tylosaurus model of Mike is very important but I do not haqve such skill and knowledge for make his model.....I always wqant to see his Tylosaurus model...It si possible for you make a Tylosaurus version with Mike opinion (back vertebrates without S-shape)?
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Hi Amin. Sorry, but it's not possible. First off, I strongly suspect Mike is wrong about the back. Second, the tail change (which is also wrong - the evidence overwhelmingly supports flukes) was something I could do in like 25 minutes - change the entire vertebral column like what you are suggesting would take me several hours, and that's just time I don't have.
If evidence gets published that supports Mike's interpretation then I would change it, but right now the evidence is not on his side. There are simply zero mosasaurs that preserve the type of tail he wants. Worse, there are zero other aquatic animal groups with a sharp downturn in the tail that don't have flukes - even groups with much smaller curves in their tail (like Geosaurus) have been preserved with a fluke.
As for the back, the same degree of curvature I illustrated has been found in several articulated mosasaur specimens. I admit that the exact degree of curvature isn't known as well as I would like, but there's no positive evidence to support a flat, snake-like vertebral column either.
I know you are a big fan of Mike's view on mosasaurs, and he certainly has made many valuable contributions to the field over the years. But at this point the majority of published data doesn't support his view of very snake-like mosasaurs, and unless such evidence ever materializes I can't take that much time away from another skeletal reconstruction, or research, or grading papers, etc.
Sorry!
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I still don't see why it would need a tail fluke.
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It's not a question of "need", it's a question of "did". The only mosasaurs with tail skin impressions have them, and all derived mosasaurs (including Tylosaurus) have the downturn in the tail that is associated with tail flukes. So it would seem the only real question is how large and what shape it was in the ones that don't have skin impressions preserved.
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So is it because the angle that the tail points downwards that causes the assumption that they did have a tail fluke?
Sorry, it may seem like a stupid question, but I'm just trying to get a grasp of how you paleontologists know it had a tail fluke. >-<
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There's two parts to that answer. First, yes, all aquatic animals with a sharp down curve in their tail that have been found with skin impressions have bilobed tail flukes. This even includes groups with much more modest down curves, like metriorhynchid crocodiles. Second, we actually have impressions of a fluke in other mosasaurs, just not (yet) for Tylosaurus.
Some (like Mike Everhart) have tried to say that since we only have a couple of species that preserve the tail fluke than perhaps we shouldn't assume they all do, but the problem is that 1) Absolutely zero mosasaurs are preserved with the sort of tail soft-tissue that Mike wants, and 2) Tylosaurus has the same degree of tail flexure as the ones preserved with a tail fluke (and more of one than metriorhynchids, some basal ichthyosaurs, etc.).
So IMO the only interpretation supported by data at this point is a fluke - other interpretations at this point are relying on special pleading.
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Does Bruce have a lower jaw ~1.85m long? that's how long it'll be based on your skeletal and the Guinness records measurement of 13m, that'll make it the largest known mosasaur by a good margin, as far as I know the largest Mosasaurus hoffmanni and Hainosaurus bernardi specimens have lower jaws of ~1.7m (Grigoriev 2014, Lindgren 2005).
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while we compare this Tylosaurus with Platecarpus(2010), we can see differences. in your art, in neck exist less muscles. even whales have the more muscles in this place. the skull is very lower than column...why? Mike told me the back of Tylosaurus is flat without any bump...... but your Tylosaurus have a pump in back....S shape of column is very severe in your Tylosaurus and skull is very lower than column that make a bump in back. even the platecarpus(2010) do not have such severe bump.....rib cage in your art is very deep and none-bone part of it is different of all of previous illustrations.....Tylosaurus live in surface and do not need to such deep rib cage. Mike believed Tylosaurus was different of sperm whales and live in surface......documents exist about pressure ill of Tylosaurus but the ill may occure for other reason.....yet, I think the more flesh shoud exist under tail ...prbably thay have a wide tail column instead of shark tail....the column vertebrates were flexible in Mosasaurs, different of Ichthyosaurs and Elasmosaurs....for a wave move, a wide column tail is good and a shark tail is useless....with a shark tail a Mosasaur with flexible vertebrates can perform nothing. Do an Elsamosaurus can use its paddles if it have a flexible vertebrates column like Mosasaurs? No. similar issue exist for Tylosaurus.....Ichthyosaurus and the great White shake have a solid structure that lonely way for swimming is their fish tail. but a Tylosaurus had a different vertebra structure that give it a flexible movement and wave movement. therefore, they use of all of their column for swimming!
Lindgren J, Caldwell MW, Konishi T, Chiappe LM (2010) Convergent Evolution in Aquatic Tetrapods: Insights from an Exceptional Fossil Mosasaur. PLoS ONE 5(8): e11998.
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Many thanks for drawing of Tylosaurus skeleton! Now, we have a good illustration about this animal!
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Do you think Mosasaurs may have had labial scales that surround the edges of their mouths, covering their teeth? Extant snakes today have those, and lizards in general don't have teeth showing.
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I think that is the most reasonable assumption, given the lack of direct evidence.
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The spacing of the phalanges is curious. The last digit is spaced very far from the others. I usually see the phalanges in other species spread evenly to form the flipper. The way the last digit is spaced makes it look like a thumb (which wouldn't make sense, since reptile never had thumbs), and gives the impression that the flippers are "palms up". Is that digit analogous to the thumb, or is it actually the pinky?
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It's the pinky, and it seems to rotate relative to the other digits. This isn't unprecedented, as some ornithischian dinosaurs do it as well. Also, while it may seem counterintuitive to us primates, evolving a divergent fifth digit isn't really any stranger than doing so with the first digit.
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