Humerus or femur seareptile

[sjaak]

Hello everyone. I am sorting out some old finds in this lockdown period. 

This one was found in the Boulonnais area, North of France. Upper Jurassic, mainly marine sediments.

I have always assumed this is a humerus or femur of a sea reptile with missing joints. Plio- or plesiosaurus.

There is a big muscle attachment.

Can anyone confirm or  not?

 

Regards,

 

 

Niels

[jpc]

I think you might be right but it can be difficult to tell the difference between a humerus and femur from plesiosaurs, esp an incomplete one.  Nice find, though.

[pachy-pleuro-whatnot-odon]

I find this bit of a tricky one. It certainly looks like a marine reptile podial, and when laid out flat on the table there seems little doubt that this is a plesiosaurian one at that. But when seen from the lateral view, the bone looks somewhat thicker than you would expect for a bone this size - especially down towards the distal end. This kind of thickness, to me, would suggest ichthyosaurian, rather. Notwithstanding, an ichthyosaurian podial would not be so evenly dorsoventrally flat. So, back to plesiosaur it is. The proximal end of the bone, including the articulation, is missing, but the distal end seems mostly complete (judging from bone texture).

 

Hard to say whether it's a humerus or femur, though, as I've found that for plesiosaurian plesiosaurs identification depends either on the overall shape of the complete bone or just its distal end, while in pliosaurian plesiosaurs it's rather the size that's telling. The bone most likely belongs to a plesiosaurian plesiosaur, though, as certain cryptoclidid species, in fact, have rather thick distal ends (a morphotype that I'd still very much like to add to my collection). See the below example of Muraenosaurus leedsi in the Palaeontological Collections of the MUT Tübingen (longer paddle on the left):

 

 

The distal is rounded, which normally implicates pliosaur. However, as the morphology of the podial as a whole appears rather short and stout, I doubt the specimen is pliosaurian. Rather, I'm thinking juvenile cryptoclidid, possibly something along the lines of the Colymbosaurus trochantericus illustrated below (the distal end of your specimen seems to flare out somewhat, as in Colymbosaurus, and the latter species matches your find in time; source: Wikipedia):

 

 

I'm proposing juvenile due to the size, the porous and roughened condition of the distal articulation - which suggests incomplete epiphyseal fusion - and the fact that the distal articulation of juvenile plesiosaurian plesiosaurs looks a lot more like the distal ends of pliosaurian podials - that is, more rounded and without their species trademark shape.

 

Hope this helps!

 

Anyway, an awesome find, and very good quality for the location!

[sjaak]

Thanks for your replies, Jpc and Pachy.

It is indeed difficult to distinguish between femur and humerus. 

So it seems we agree about sauropterygian.

I was wondering if the big muscle attachment could provide any clues. See the attached picture.

I don't see this here: http://fossilesboulonnais.free.fr/os/humerus/humerus.html

[pachy-pleuro-whatnot-odon]

55 minutes ago, sjaak said:

Thanks for your replies, Jpc and Pachy.

It is indeed difficult to distinguish between femur and humerus. 

So it seems we agree about sauropterygian.

I was wondering if the big muscle attachment could provide any clues. See the attached picture.

I don't see this here: http://fossilesboulonnais.free.fr/os/humerus/humerus.html

 

Hi Niels,

 

I hadn't paid particular attention to that muscle attachment site before, but it's indeed of notable size - especially for a juvenile. Based on that, I'd say we're definitely dealing with a femur here, then. It would've been the attachment site for the caudofemoralis-muscle that is present in nearly all tetrapods possessing a tail. I don't think it will be of much help in identifying the animal this bone came from, however, as both plesiosauromorph and pliosauromorph plesiosaurs have then, irrespective of chronological placement. They are not often preserved, though, as the heads of podials are frequently damaged during fossilisation - as one will quickly find from a perusal of museum specimens. Just one note, though: I would label this as "Plesiosauria indet." rather then "Sauropterygia indet.", as the former is a monophyletic grouping and the latter is polyphyletic and, therefore, less precise.

[sjaak]

thanks again!

 

[sjaak]

I now have reason to believe its part of an ilium.

[pachy-pleuro-whatnot-odon]

Mind sharing this reason with us?

Would you humer-us? 

 

Also, just to be clear, we're still talking plesiosaurian, right? At least, that's what I would imagine judging from both the shape and outcome of our previous discussion.

Edited April 13, 2021 by pachy-pleuro-whatnot-odon

[pachy-pleuro-whatnot-odon]

Hi Niels,

 

I hadn't considered that! Indeed, if I look at the shaft of your specimen, it looks somewhat angular, and certainly not as round as the typical propodial. Similarly, the articulation surfuce on the left in your last photograph - the supposed propodial's head, if you will - also looks less rounded than I would expect from a propodial. The problem with determining whether this is a plesiosaur ilium or not, however, is that I find images of plesiosaur ilia rather scarce in literature: there's simply very little to compare against. Below are the only three images from publicly accessible scientific articles figuring plesiosaur (sensu lato) ilia I could find, for example (rhomaleosaurid specimens from figures 2 and 3 from Benson, Zverkov and Arkhangelsky [2015] respectively, the Leurospondylus-specimen from Barnum Brown [1913], sourced from Wikipedia):

 

 

Rhomaleosaurid ilium (left image) and ischium with attached ilium (left hand side, right image)

 

 

 

 

 

 

 

 

 

Leurospondylus ultimus pelvic girdle; ilia right top and bottom

 

 

 

 

 

 

 

 

 

 

This being the case, I had a look through my own reference photographs and came up with the following:

 

Peloneustes philarchus at the Naturmuseum Senckenberg in Frankfurt; ilia (left and right) circled in red

 

 

 

 

 

 

 

 

 

 

Peloneustes philarchus at the Paläontologische Sammlung MUT Tübingen; ilium circled in red

 

 

 

 

 

 

 

 

 

 

Liopleurodon ferox at the Paläontologische Sammlung MUT Tübingen; ilium circled in red

 

 

 

 

 

 

 

 

 

Cast of Rhomaleosaurus victor at the Zoological and Palaeontological Collections of the University of Zürich; ilium circled in red

 

 

 

 

 

 

 

 

Plesiosaurus dolichodeirus at the Naturalis Biodiversity Center in Leiden; ilium circled in red

 

 

 

 

 

 

 

 

 

 

 

Cryptoclidus sp. at the Naturkundemuseum Stuttgart

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As can be seen in the above images, there's quite some morphological intergeneric (if not interspecific) variation in plesiosaur ilia. However, the general structure seems to be a shaft with a slightly widening and thickened proximal end, where the ilium articulates with the pubis and ischium, and a dorsoventrally compressed distal end that flares out to the sides. The shaft seems narrower than tall - that is, it is thicker in the plane perpendicular to the to the direction of compression on the distal end - and may exhibit a slight twist. The degree by with the proximal head extends beyond the shaft varies, likely per genus if not species.

 

 

Quote

 

Now back to your specimen: though it has some strange bony outgrowths, it does indeed appear more like an ilium than a femur. As already remarked upon, the shaft is not as rounded as a propodial's and appears to be flat-backed with the opposite side being pronounced. That is, the height of the shaft is greater than the width, which matches expectations for an ilium. Similarly, the articulation surface on the left in your latest picture also looks more like the flat surface seen on an ilium than a femural head (especially compare my photograph of Plesiosaurus dolichodeirus). So, I agree this is probably not a plesiosaur femur then.

 

I still maintain this is not an ichthyosaurian bone. And while sauropod remains are found with certain frequency in the region, I'd say the bone is both too small and shows too notable a disparity with sauropod phalangi (see images below) to make this a reasonable candidate. Thus, putting dinosaurian material aside, your find must therefore belong to either plesiosaur (sensu lato) or marine crocodile - which remains, as I understand, are quite commonly found in the area you found the bone. Yet, while the triangular, flat-backed shape of your fossil's supposed diaphysis would seem a good candidate for crocodile long bone (this shape is, in fact, relatively common in all types of long bones of distinct animal genera), from the only references images I have teleosaurid long bones seem to be more rounded (again, see images below)...

 

The right hind foot of Rhoetosaurus brownei in dorsal view (source)

 

 

 

 

 

 

 

 

 

 

 

 

 

Haplocanthasaurus sp. (source)

 

 

 

 

 

 

 

 

 

 

 

 

Camarasaurus sp. left front foot in dorsal view (source)

 

 

 

 

 

 

 

 

 

 

 

 

Mekosuchine crocodile humeri from the Australian Eocene. Figure 1 from Stein et al., 2020. Quantitatively assessing mekosuchine crocodile locomotion by geometric morphometric and finite element analysis of the forelimb

 

 

 

 

 

 

 

 

 

 

 

 

Machimosaurus sp. pectoral girdle at Paléospace l'Odyssée in Villers-sur-Mer

 

 

 

 

 

 

 

 

 

 

 

 

Femura of A. Steneosaurus edwardsi and B. 'Steneosaurus' obtusidens. Figure 3 from Johnson, Young, Steel and Lepage, 2015. Steneosaurus edwardsi (Thalattosuchia: Teleosauridae), the largest known crocodylomorph of the Middle Jurassic

 

 

 

 

 

 

 

 

 

 

 

This leaves plesiosaur as the most likely candidate, and when considering plesiosaurian bones - and then, having disregarded the extremities, especially the girdles - the ilium as the most likely option. So, I think you're indeed right. However, may be @paulgdls or @DE&i can way in with their experience on plesiosaurs. In any case, a find that keeps intriguing.

[paulgdls]

Yes, it looks like a plesiosaur ilium. Could well be Colymbosaurus from the Kimmeridge Clay. As @pachy-pleuro-whatnot-odon (what a great summary from you above full of useful information, thanks) says there is a shortage of images and drawings. The pliosaur ilia tend to be more crushed than those from plesiosaurs I've found since the bone structure is spongier.

 

Plesiosaur rear girdle from the Etches collection:

 

 

Proximal (?) end of plesiosaur ilium from the de la Salle collection (Kimmeridge Clay of Westbury):

 

 

 

Distal end (?) of Cryptoclidus (?) ilium from the Lower Oxford Clay of Gloucestershire, de la Salle collection:

 

 

 

Ilia of Simolestes (top) and Peloneustes (bottom), de la Salle collection:

 

 

 

 

 

 

[pachy-pleuro-whatnot-odon]

Beautiful specimens, Paul! And very informative to see some plesiosaurian ilia "loose" like that. Thanks!

[sjaak]

Wow, thank you all very much with all the great and detailled information !! I will keep this as a reference!
The reason I thought this is a plesio ilium was rather simple: I saw another find from the same site that looked like my fossil, especially the morphology and the muscular attachment.