New species of Pliosaurus

[DinoToyForum]

Three new species to be exact, but the focus is on Pliosaurus kevani - The Weymouth Bay Pliosaur. I'm a coathor on this one, so here's the open access paper http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0065989 , and I've also just bogged about it if you want an easy-to-digest summary: http://www.plesiosauria.com/news/index.php/pliosaurus-kevani-the-weymouth-bay-pliosaur/

Now you know why I was painting a Pliosaurus head in my artwork thread - that's P. kevani.

[Blade-of-the-Moon]

That skull looks fantastic..it's great the fellow collected it all, shame he didn't mention it when he started finding it though.  Is there a current excavation at the site to try and find anymore ?

[wings]

Three new species to be exact, but the focus is on Pliosaurus kevani - The Weymouth Bay Pliosaur. I'm a coathor on this one, so here's the open access paper http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0065989 , and I've also just bogged about it if you want an easy-to-digest summary: http://www.plesiosauria.com/news/index.php/pliosaurus-kevani-the-weymouth-bay-pliosaur/

Now you know why I was painting a Pliosaurus head in my artwork thread - that's P. kevani.

Just curious to know; is there any reasons to why the back part of the head compressed more than any other areas of the skull? If you compare the actual specimen against the reconstruction then you'll see that the "parietal crest" (parcr) or "parietal" (par) is quite low on the specimen but it was quite high on the reconstruction. I do understand that the "crest" border isn't complete but from what is there it doesn't look like it would have raise to that height. The arc of the "suspensorium" (fig. 9) doesn't look like the element is really that deformed. Would it be possible that the animal has a skull profile similar to the illustration (fig. 8.7) in Everhart's book ("Oceans of Kansas") where the back of the head is fairly low? Or perhaps there is an unpublished more 3 dimensional skull that indicates otherwise? This is not to say whether the reconstruction is right or wrong but I just would like to know what is the thinking behind it since you are one of the authors.

[DinoToyForum]

Thanks for the comments. The rear of the skull is more prone to deformation because it consists of relatively thin sheets of bone and lots of empty space (for the temporal musculature). In fact, the only uncompressed part of the cranium in P. kevani is the anterior-most part of the snout. We haven't increased the size of the parietal crest in the reconstruction, we've just raised the entire element relative to the rest of the skull. Other pliosaurid specimens, such as the Peloneustes skull pictured below, show that the suspensorium was tall in life. The same was true in polycotylids, so the head in figure 8.7 in OOK is too compressed. Check out the polycotylid skulls figured elsewhere in that chapter and you'll see this is the case (although lateral compression can accentuate the height of the suspensorium somewhat too).

[wings]

Ah, I see. Thanks for the quick reply :-)

In OOK, I thought that EverHart would have said something to the illustrator if the Polycotylus/Dolichorhynchops skull is too compressed. That"s the only reason why I thought it was actually possible. I suppose the "high crest" on the Peloneustes can't be created by lateral compression right (If I'm applying the same logic (lateral rather than dorsal/ventral compression) then the orbital and postorbital elements are pressed to more of a profile and the skull would appear to be deeper...I wonder)... Just a silly idea.

[DinoToyForum]

The Peloneustes skull is minimally compressed - almost natural -  although you are right that lateral compression would potentially increase the apparent height of the temporal region.

[DinoToyForum]

To help illustrate the degree to which pliosaur skull cans (and usually do) become compressed, here's a figure from Ketchum & Benson (2011) showing the uncushed skull of peloneustes (A-D, the one I showed above) alongside a typical crushed skull of the same taxon (E-F). Big difference!



you'll notice that E looks rather like the compressed skull of Pliosaurus kevani.

[wings]

Is there a dorsal view for NHMUK R3318 (is there one provided by the paper)? I would imagine that the posterior region of the skull would be much much wider than NHMUK R4058; and how does it compare with P. kevani? Since the dorsal view of NHMUK R4058 (fig. c and d, almost natural) looks very similar to the dorsal view of DORCM G.13,675 (fig. 2 ; especially the condition of the temporal region on the right side). Not that I'm questioning about whether the back of the skull is compressed but I'm just not sure to what degree.

[DinoToyForum]

Sorry, no dorsal view of 3318. The elements don't tend to spread out when crushed dorsoventrally though, they just get compressed/crushed, so the general shape of the skull in dorsal view isn't distorted by the process much.

[wings]

Sorry, no dorsal view of 3318. The elements don't tend to spread out when crushed dorsoventrally though, they just get compressed/crushed, so the general shape of the skull in dorsal view isn't distorted by the process much.

Thanks, in that case I'll just have to take your word for it. Because the reasoning doesn't really make sense to me; If the "crest" element is crushed and broken then sure the skull shape of the temporal region doesn't change much however, if the "crest" is not broken but rather just bent/distorted then I would imagine the element would in turn pushes the squamosals (sq) and widen the skull (as the volume of these skeletal elements doesn't change). That's very much what I have problem with the reasoning, where is the missing volume of these elements?

[DinoToyForum]

Thanks, in that case I'll just have to take your word for it. Because the reasoning doesn't really make sense to me; If the "crest" element is crushed and broken then sure the skull shape of the temporal region doesn't change much however, if the "crest" is not broken but rather just bent/distorted then I would imagine the element would in turn pushes the squamosals (sq) and widen the skull (as the volume of these skeletal elements doesn't change). That's very much what I have problem with the reasoning, where is the missing volume of these elements?

The temporal region is mostly empty space so its not like squishing a lump of solid clay. The whole posterior part of the cranium is crushed, broken, bent, and distorted, to various degrees.

[Jetoar]

Awesome skull of this pliosaur. I am happy that the plaeontologist find new species  .

[ZoPteryx]

Very cool specimen and great restoration too!   I find it interesting that amongst pliosaurs, it seems that only Liopleurodon lacked that sloping forehead with its more or less rectangular skull.  A sign that Lio took larger prey than its relatives perhaps? Please correct me if I'm wrong, perhaps I'm just overly influenced by WWD.

[DinoToyForum]

Very cool specimen and great restoration too!   I find it interesting that amongst pliosaurs, it seems that only Liopleurodon lacked that sloping forehead with its more or less rectangular skull.  A sign that Lio took larger prey than its relatives perhaps? Please correct me if I'm wrong, perhaps I'm just overly influenced by WWD.

No, Liopleurodon looks pretty similar:

[FUTABA]

Just got to commend everyone who worked on the descriptions and publications of the new species. The introduction of these as well as the newly proposed Thalassophonean group has really shaken things up a bit, for me at least. Seems I need to do some more homework and get with the times a bit! 

By the way, is the Weymouth Bay Pliosaur skull still at the Dorchester County Museum? And if so, will it remain there indefinitely? I'm going to Weymouth in the summer and really want to see the skull. Been waiting ages for the opportunity. 

[wings]

...The temporal region is mostly empty space so its not like squishing a lump of solid clay. The whole posterior part of the cranium is crushed, broken, bent, and distorted, to various degrees.

I'm referring to the skeletal struts which is solid (like the parietal and squamosal). Unless the "contacts" between these struts are broken; I honestly can't see how the mass/volume of these "struts" would just disappear if the element is not broken but just being distorted. Even though that you are saying the back of the skull is crushed, broken, bent, and distorted; when view from the back (posterior view, fig.9), you've still managed to piece together the "top border" of the squamosals. It doesn't look like the top has been missing that much. So I'm not sure how much could you stretch the element (squamosal)?



As you can see that the front borders (red dotted lines on the middle and bottom line drawings) are rather complete (maybe deformed by not broken) and we know roughly the thickness of the process from the squamosal to the jugal so an estimate of the height of the back border of the skull (red line on the top image) should be possibly be approximated.

[DinoToyForum]

Just got to commend everyone who worked on the descriptions and publications of the new species. The introduction of these as well as the newly proposed Thalassophonean group has really shaken things up a bit, for me at least. Seems I need to do some more homework and get with the times a bit! 

By the way, is the Weymouth Bay Pliosaur skull still at the Dorchester County Museum? And if so, will it remain there indefinitely? I'm going to Weymouth in the summer and really want to see the skull. Been waiting ages for the opportunity. 

Yes, on permanent display in Dorchester, check it out!

[DinoToyForum]

@wings. There are several factors at play. 1. The squamosals are dorsoventrally crushed, especially on the midline, so they have become distorted into a sort of "M"-shape in posterior view, instead of being arched. They have cracked and broken under these stresses - see the cracks on the posterior surface of the skull. 2. The ventral parts of the squamosals, and the quadrates, are missing in the fossil, but restored in the illustration, and these also add dorsoventral height to the rear of the skull 3. A small amount of "splaying" has occurred (as I say, there isn't much, but there is some), so the rear of the skull in the reconstruction is narrower in dorsal/ventral view than the fossil. Add these together and you end up with a rather tall suspensorium. 

[wings]

@wings. The squamosals are dorsoventrally crushed, especially on the midline, so they have become distorted into a sort of "M"-shape in posterior view, instead of being arched. Also, the ventral parts of the squamosals, and the quadrates, are missing in the fossil, but restored in the illustration. These also add dorsoventral height to the rear of the skull

I don't deny the fact that the elements (squamosals) have been distorted. I completely agreeing with you on that. It's just I don't see I have enough materials to prop the crest up to as much as what is on your reconstruction. As for the quadrate; I suppose you are referring to the little cap (dotted line at the tip of the squamosals which articulate with the lower jaw. That is why I didn't included the quadrate height in the previous diagram since it was missing), yes it does add a bit to the height but not that much 



Also, if I have the front border (see diagram below, dotted arrows) regardless how much I have added to the back border; somehow the length can't be too different to the front...

@wings. There are several factors at play. 1. The squamosals are dorsoventrally crushed, especially on the midline, so they have become distorted into a sort of "M"-shape in posterior view, instead of being arched. They have cracked and broken under these stresses - see the cracks on the posterior surface of the skull. 2. The ventral parts of the squamosals, and the quadrates, are missing in the fossil, but restored in the illustration, and these also add dorsoventral height to the rear of the skull 3. A small amount of "splaying" has occurred (as I say, there isn't much, but there is some), so the rear of the skull in the reconstruction is narrower in dorsal/ventral view than the fossil. Add these together and you end up with a rather tall suspensorium. 

Now that you are saying there is "splaying" and the skull shape is actually narrower to compensate for the missing "volume"; then it would make more sense in your reasoning.

[DinoToyForum]

OK