New Jersey Cretaceous bone (Plesiosaur?)

[Guns]

1 hour ago, frankh8147 said:

Mosasaur collection

Wow . very very nice collection !

[pachy-pleuro-whatnot-odon]

9 hours ago, RuMert said:

This could be a primitive plesiosaur (if any). What is the provenance?

 

9 hours ago, Paleoworld-101 said:

It is from Lyme Regis which is why i wondered how much the paddle morphology can be generalised, elasmosaurids and polycotylids vs. more basal Jurassic forms etc

 

4 hours ago, Paleoworld-101 said:

You were generalising when you said "plesiosaur digits are more robust and not so flattened". I agree this one is more likely mosasaurian but it is good to clarify why. "Cretaceous plesiosaurs" is also a very broad category, with surely a considerable range of morphological variation. More specifically what formation is this from and what taxa are reported from it? 

 

3 hours ago, RuMert said:

I was obviously referring to this specific case, which relates to late Cretaceous. Plesiosaur digits are more robust and not so flattened? Yes they are. You don't think so? We'll be happy to get acquainted with your own position and proof.

 

Just to chip in on the discussion on the dorsoventral compression of plesiosaur versus mosasaur phalangi: you'll find both. Some plesiosaur paddle digits may be just as compressed as those of mosasaurs, whereas certain mosasaur phalangi may be just as robust as those of plesiosaurs. In fact, I have a pliosaur and mosasaur phalanx here that, when put next to each other, are almost indistinguishable: both are almost equally long and equally robust. The pliosaur derives from the Oxford Clay of England, while the mosasaur is from Azrú in Morocco.

As I hadn't heard that plesiosaur phalangi are more robust in more derived species before, I can't comment on that. However, I do have a partial plesiosaur (supposed pliosaur) paddle from the Oxford Clay of England here with extremely compressed paddle bones. Assuming this is not an artefact of plastic compression, this would mean that "flat-boned" plesiosaurs were around at least through the Kimmeridgian Jurassic, and probably until the Cretaceous. Unfortunately, I haven't seen too many Cretaceous specimens to remark upon the degree of compression in species from this era. However, from what I've seen from Goulmima, the plesiosaurs there indeed had less dorsoventrally compressed phalangi. That being said, the paddle digits of the Manemergus anguirostris specimen I photographed at Sainte Marie-aux-Mines last year (figured below) appear rather dorsoventrally compressed, albeit not to the extent as either the specimen I have over here or the early Jurassic species found at Lyme Regis and Holzmaden.

 

 

In fact, I'd be very interested in your source of information, @RuMert, just to read up on this curious morphological trend a bit more. I suspect that plastic deformation also plays its role in this, as it can't entirely be a coincidence that early specimens found in shale like that of Lyme Regis and Holzmaden, which are known to significantly compress fossils, would also be the exact same species that have the most compressed phalangi, whereas specimens derived from sediments that better preserve the shape of the bone would also show more rounded phalangi - whether it concern species either earlier or later in time.

 

Whatever the case, it is generally true that the degree of dorsoventral compression is a good indication of whether a phalanx is of plesiosaurid or of mosasauroid origin. However, seeing as the possible variability described above, I'd say it's not entirely conclusive. I therefore frequently also look at the degree of flaring shown by the epiphyses. Plesiosaurs have more equal flaring at both ends of the bone, while the paddle digits of mosasaurs have a tendency to flare out more on one end of the phalanx than on the other.

 

As the bone in question here is both dorsoventrally compressed and flares out more on the one end than on the other, I'd say this is indeed a clear case for mosasaur.

[hokietech96]

On 9/7/2020 at 8:35 AM, frankh8147 said:

 

Thank you! It's something I haven't found before and looks great in my Mosasaur collection! I'm betting this just popped out of the cliffs because it's tough to imagine it surviving the streams for long

Amazing display!

[RuMert]

58 minutes ago, pachy-pleuro-whatnot-odon said:

to read up on this curious morphological trend

I'm not sure where I read this, but I've never had a reason to doubt. I'm even surprised not everybody sees the difference. Some digits in some species can be similar in both creatures, but overall the difference is IMHO clear. In fact, if you just google "mosasaur paddle" and "plesiosaur paddle" you'll see that mosasaur digits are nearly always more slender, elongated, hourglass-shaped and overall look of paddles are more hand-like compared to later plesiosaurs. It's probably due to the fact mosasaurs had less time to evolve and completely convert paws to paddles (they also used tail while plesiosaurs relied on paddles only). Plesiosaurs were moving to cylinder-like digits, more adapted to the forceful paddle movements they used. Robustness is visible in your pics though not that expressed

[pachy-pleuro-whatnot-odon]

3 minutes ago, RuMert said:

I'm not sure where I read this, but I've never had a reason to doubt. I'm even surprised not everybody sees the difference. Some digits in some species can be similar in both animals, but overall the difference is IMHO clear. In fact, if you just google "mosasaur paddle" and "plesiosaur paddle" you'll see that mosasaur digits are more slender and elongated, and overall look of paddles are more hand-like compared to plesiosaur. It's probably due to the fact mosasaurs had less time to evolve and completely convert paws to paddles. Plesiosaurs were moving to cylinder-like digits, more adapted to the forceful paddle movements they used.

Well, if you're comparing entire paddles, I doubt many people would find it difficult to spot the difference. As you said, the one looks distinctly like a hand, whereas the other looks distinctly like an actual solid rowing paddle. When it comes to individual bones, however, I think the picture becomes more nuanced and therefore more complicated for the less initiated people. I mean: yes, you do have the clearly distinct prototypes of a plesiosaur versus mosasaur paddle digit. But I find there can be some overlap. Plesiosaur phalangi can be slender as well, and might sometimes appear to have unevenly flaring epiphyses. I have a plesiosaur digit in my collection that in most aspects looks just as compressed, slender and with uneven flaring edges as the specimen in this post. Would I confuse it for a mosasaur? Certainly not, as it derives from the Lower Jurassic of England, meaning 1) mosasaurs hadn't evolved yet and 2) British mosasaur material is generally rather scarce. In addition, my specimen has another condition often seen in plesiosaur phalangi, which is that the epiphyseal flare on one end of the bone is more prominent towards the left while the flare is more prominent on the right on the other end of the bone (i.e. the flare might be equal in size, but not in direction/twist) - another one of these characteristics that differentiate plesiosaur digits but are not always present in more derived specimens.

 

Also, with time, I think people who work with a certain kind of material get a feel for that type of material - a knack if you will. It makes it hard to define to others what exactly it is that makes you sure of your conclusions, but also makes it difficult to see that your conclusion might not be as obvious for others. It's a condition know as connoisseurship, and some interesting works have been written about the uses and misuses of claims of being a connoisseur (although those I'm familiar with pertain to archaeology, I think similar arguments can just as easily be upheld for palaeontology). The thing is, if you know plesiosaur and mosasaur paddle digits well enough, you won't be scoring them for presence or absence of any of the mentioned traits: may be just one will be enough to have the bone scream out at you that it's one or the other. But if you're not too familiar with the material yet, you'll resort to scoring traits - which might, I think, in certain cases, even lead you to wrong conclusions, simply because you're not familiar enough with the material and will make mistakes while scoring.

[RuMert]

Exactly: they do overlap and the final verdict depends mostly on the provenance (site, period) and various conditions. You can even take a plesiosaur bone for a hadrosaur or a sauropod vert for a pliosaur one (real story). Let alone even prominent paleontologists often have conflicting views and fantastic mistakes (elasmosaur head on the tail, lizard instead of a dino in burmite, ammonite section described as a skull etc)

[pachy-pleuro-whatnot-odon]

15 minutes ago, RuMert said:

Exactly: they do overlap and the final verdict depends mostly on the provenance (site, period) and various conditions. You can even take a plesiosaur bone for a hadrosaur or a sauropod vert for a pliosaur one (real story). Let alone even prominent paleontologists often have conflicting views and fantastic mistakes (elasmosaur head on the tail, lizard instead of a dino in burmite, ammonite described is a reptile skull etc)

Not familiar with the last case in your examples, but definitely true - though I doubt anybody would stick an elasmosaur head on its tail these days any more (then again, I did come across a case where the feather duster supplied with a Native American headdress to keep it clean had been placed inside the headdress as part of the display in a museum in London) But, yes, you're right... In fact, I have some pliosaur digits in my collection that I had a hard time considering marine reptile for their morphology, when I first saw them (i.e. those close to the carpals and tarsals)

P.S.: Another case in point are the frequent misidentifications of dinosaur material amongst the otherwise marine Oxford Clay material.

[jonnyquest]

Nice, look like all personal finds.  Good hunting.

[frankh8147]

Thank you again everyone!! @jonnyquest yes, these were found by me and are all from New Jersey.

[Paleoworld-101]

17 hours ago, RuMert said:

I was obviously referring to this specific case, which relates to late Cretaceous. Plesiosaur digits are more robust and not so flattened? Yes they are. You don't think so? We'll be happy to get acquainted with your own position and arguments.

It was not obvious. These things should be clarified rather than assumed everyone will know what you mean. 

[hemipristis]

19 hours ago, pachy-pleuro-whatnot-odon said:

What he said! That's one impressive collection and an awesome find. I'm jealous!

Ditto!  The number of hours I have spent screening stream gravels in central NJ, and nada.  LOL

[frankh8147]

7 hours ago, hemipristis said:

Ditto!  The number of hours I have spent screening stream gravels in central NJ, and nada.  LOL

Thank you! The New Jersey Cretaceous stream definitely take some patience!

[RuMert]

18 hours ago, Paleoworld-101 said:

These things should be clarified

You should be sharing your thoughts and arguments on the subject instead of teaching me anything. 

[FossilDAWG]

Gentlemen, let's continue to keep this civil.

 

Don

[Petalodus12]

Is there a comprehensive listing of the marine reptiles that can be found in the formation that crops out at big brook? I’m aware that the record is rather fragmentary so forgive my ignorance if there isn’t one. This might be help to narrow down the options. Whatever it is, it’s a wonderful find and a great example of convergent evolution considering how hard it is to tell what it comes from

[Paleoworld-101]

3 hours ago, RuMert said:

You should be sharing your thoughts and arguments on the subject instead of teaching me anything. 

Which is exactly what i did, i argued your generalisation didn't hold up for all plesiosaurs and wanted to know if it was indeed reasonable to automatically exclude Late Cretaceous gracile plesiosaur phalanx morphologies. 

3 hours ago, FossilDAWG said:

Gentlemen, let's continue to keep this civil.

 

Don

Everything on my end has been. 

[fifbrindacier]

Nice Frank, congratulqtions, lucky fossil hunter. 

[Carl]

Sorry for the late response. My gut also says mosasaur but I don't claim to know plesiosaur and mosasaur phalanges all that well.