Mystery bone from the Boulonnais

[pachy-pleuro-whatnot-odon]

Hi all,

Back once more with a find from the Boulonnais. This time found between Boulogne-sur-Mer and Wimereux. The geology there is Kimmeridgian marine deposit, and the fossil presented here derives from a block of yellow sandstone with marine inclusions. It was embedded in an enclosure of soft, porous sand, which I hadn't quite expected and is the reason it's currently in the state it is in. I managed to find a rock with a pycnodont fish tooth and some similarly coloured (i.e. white) bone fragments in the area, in comparable yet harder sandstone.

 

So my first impression was some kind of fish bone. However, I'm having a hard time figuring out what kind of fish bone, seeing as my piece is flat on one side and appears to have a bit of a twist (or may be a depression where another bone would have gone) on another.

 

As such, the flat side made me think of a jaw bone, of a marine reptile in particular. Yet, the bone seems to extend away from it's flat side, which wouldn't quite fit what one would expect of a jaw bone.

 

My third guess, based on the slight depression on one side of the bone and the rounded end at one of the short sides (which kind of reminds me of the epiphysis of a long bone), was some kind of long bone - lower arm or lower leg, where you'll typically find two bones lying closely together - but I'm not sure of this either. Moreover, this would be the feature of a terrestrial animal, not a marine one - with the exception of crocodiles (which lower extremity bones, however, are not closely spaced together, so wouldn't match my hypothesis).

 

I realise the bone is fragmentary and not even in the best of states. But I hope enough has been preserved to determine something of it's origin, if even just in terms of marine vs. terrestrial, reptile vs. fish or mammal, etc.

 

Dimensions: 86.5mm/3.40" long, 42.6mm/1.67" wide, and 23.5mm/0.92" tall

 

Thanks in advance for your help! Don't hesitate to ask for additional details.

 

 

 

[pachy-pleuro-whatnot-odon]

And some additional images showing the bone's texture...

[val horn]

wow.    I can not help with id at all    the cavity opening on one end does suggest jaw to me as in a large neurovascular bundle as for the inferior alveolar nerve but i would not want to try to really defend that concept.

[pachy-pleuro-whatnot-odon]

Thanks for weighing in anyway, @10313horn! At this point any suggestion or opinion is more than I had before, so is very welcome Let's see what others make of it...

[LabRatKing]

Inn not seeing claw here. Lots of spongiform vascularization that indicates bone farther up the limbs. The fracture faces tell me there was more to this structure. It’s right up there with this fragment in my book:

(it’s bone, it’s Eocene, but beyond that is just a find)

[sjaak]

Difficult to say with such a fragment.  I have a bone from the same site and sandy sediments, with the same fossilation which turned out to be part of a croc skull. Maybe you can look into that direction. 
 

As the bones from the Boulonnais are often fragments, I thought about the possibility to ID on bone structure or density, to distinguish between marine and terrestrial animals, but this seems to be difficult or impossible.

[pachy-pleuro-whatnot-odon]

@LabRatKing, the passing idea I had of jaw was mostly based on my thoughts about where you'd find flat bones straight like that in a marine reptile or fish. The only place I could come up with was jaw. But the rest of the bone indeed doesn't seem to match. Unfortunately, the area where I found this is known for it's fragmentary and oft hard to identify bone, most of it embedded in giant boulders (see images below).

 

 

The only other bone I found at that location that was in a somewhat portable boulder (but I still left behind judging it too heavy to carry back for such a weathered and unidentifiable piece - my best estimate being skull-fragment) is the one below:

 

 

 

When I found the bone I started the thread about, it was already cut in half, with the other part of the boulder nowhere to be seen. However, since it had nice vascularization I decided on an attempt to extract it from the rock (it seemed rather accessible). Of course, I hadn't counted on the shock-waves of the hammer-blow on the hard stone matrix ripping through the much finer sandstone and bone, so mostly ended up with dust. But that's a different matter (and a learning experience)...

 

 

Anyway, the first question I'm hoping to answer is whether it's possible to tell (e.g. from the degree of vascularization) whether this might be fish or reptile - and, in case of the latter, whether marine or terrestrial...

[caterpillar]

It could be a croc bone but difficult to say with just pictures.

Try to find it in this doc

https://www.researchgate.net/publication/285838769_Catalogue_descriptif_anatomique_geologique_et_historique_des_fossiles_presentes_a_lexposition_les_Crocodiliens_fossiles_de_Normandie

[pachy-pleuro-whatnot-odon]

14 minutes ago, sjaak said:

Difficult to say with such a fragment.  I have a bone from the same site and sandy sediments, with the same fossilation which turned out to be part of a croc skull. Maybe you can look into that direction. 
 

As the bones from the Boulonnais are often fragments, I thought about the possibility to ID on bone structure or density, to distinguish between marine and terrestrial animals, but this seems to be difficult or impossible.

Thanks, @sjaak! I had wanted to ping you in on this, but I'm glad to see the thread has found its way to you already

 

Yeah, I realise that it's hard with these kinds of fragments. But seeing as I think one would be able to tell ichthyosaur bone apart due to it's great density, and know that most marine animals are pachyostic due to their need to achieve neutral buoyancy, I was hoping there'd be some way to make at least this distinction based on the visible bone structure. Without narrowing it down to at least this level, it would be near impossible to define a starting point to even begin searching for the clade of animals this bone came from. But may be crocodile skull is a good place to start. I might have a look into that! Thanks for the tip!

[pachy-pleuro-whatnot-odon]

4 minutes ago, caterpillar said:

It could be a croc bone but difficult to say with just pictures.

Try to find it in this doc

https://www.researchgate.net/publication/285838769_Catalogue_descriptif_anatomique_geologique_et_historique_des_fossiles_presentes_a_lexposition_les_Crocodiliens_fossiles_de_Normandie

Cool! Looks like an excellent document with a lot of useful reference images! Will have a look through there and report back on what I find. Thanks!

[sjaak]

1 hour ago, pachy-pleuro-whatnot-odon said:

Thanks, @sjaak! I had wanted to ping you in on this, but I'm glad to see the thread has found its way to you already

 

Yeah, I realise that it's hard with these kinds of fragments. But seeing as I think one would be able to tell ichthyosaur bone apart due to it's great density, and know that most marine animals are pachyostic due to their need to achieve neutral buoyancy, I was hoping there'd be some way to make at least this distinction based on the visible bone structure. Without narrowing it down to at least this level, it would be near impossible to define a starting point to even begin searching for the clade of animals this bone came from. But may be crocodile skull is a good place to start. I might have a look into that! Thanks for the tip!

I will send you a PM later.

[LabRatKing]

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

@LabRatKing, the passing idea I had of jaw was mostly based on my thoughts about where you'd find flat bones straight like that in a marine reptile or fish. The only place I could come up with was jaw. But the rest of the bone indeed doesn't seem to match. Unfortunately, the area where I found this is known for it's fragmentary and oft hard to identify bone, most of it embedded in giant boulders (see images below).

 

 

The only other bone I found at that location that was in a somewhat portable boulder (but I still left behind judging it too heavy to carry back for such a weathered and unidentifiable piece - my best estimate being skull-fragment) is the one below:

 

 

 

When I found the bone I started the thread about, it was already cut in half, with the other part of the boulder nowhere to be seen. However, since it had nice vascularization I decided on an attempt to extract it from the rock (it seemed rather accessible). Of course, I hadn't counted on the shock-waves of the hammer-blow on the hard stone matrix ripping through the much finer sandstone and bone, so mostly ended up with dust. But that's a different matter (and a learning experience)...

 

 

Anyway, the first question I'm hoping to answer is whether it's possible to tell (e.g. from the degree of vascularization) whether this might be fish or reptile - and, in case of the latter, whether marine or terrestrial...

Either way, this looks like a really interesting site. I'm a bit jealous! Don't feel bad, I inadvertently damaged a few in my time too. I have a few spots geotagged to hopefully go back with better tools for some. Sadly, I can't be much help on IDing these...I may have been a bit in my cups last night....LOL

[pachy-pleuro-whatnot-odon]

So, from communication with both @sjaak and a friend of mine, it seems likely that the bone would be crocodilian in origin - with these kinds of remains being commonly found along the Bolounnais coast from Cap Gris Nez all the way down to Boulogne-sur-Mer, apparently. If I compare my bone with Niels', it's obvious that it derives from the same type of matrix and has the same type of bone structure (vascularisation). Now, all of this is, of course, circumstantial evidence, but enough to warrant careful analysis of @caterpillar's document. This, however, is where things get complicated, as finding a matching piece of skull bone turns out to be extremely tricky...

 

After having rejected the proximal part of the dentary (on the mandible, closest to the coronoid) as being too rounded for my piece of bone, the only remaining option, in my opinion, would be a part of the cranium that forms the border of a hole in the skull, such as either the post-orbital or orbit itself. That is, a skull-part that shows a clear edge between two planes, one or which is curved and the other of which forms a raised edge. Such a morphology can be seen in the postorbital bone of Metriorhynchus cf. hastifer in the dorsal view of the cranium below (marked "por"), for example:

Fig. 2, p. 87, from: Lepage, Buffetaut, Hua, Martin and Tabouelle, 2008. Catalogue descriptif, anatomique, géologique et historique des fossiles présentés à l'exposition « Les Crocodiliens fossiles de Normandie » (6 novembre - 14 décembre 2008)

 

 

 

 

 

 

 

 

 

 

 

 

 

Similarly, in the images below (fig. 1, p. 114 & fig. 4, p. 115, ibid.) from the skull of Metriorhynchus moreli:

 

 

 

The same part can be seen in below images of the back part and paraoccipital-quadrate (?) of the cranium of a Metriorhynchus sp. (figs. 1-2, p. 47, ibid.). Observe how the vascularisation of the bone in the second image is very similar to the darker coloured rounded end in the part that appears split in my bone:

 

por = postorbital; boc = basioccipital; co = occipital condyle; prp = paraoccipital process

 

 

 

 

 

 

 

 

 

 

 

 

Although all these examples pertain to the postorbital region of the skull, I think the orbital margin itself may also be a good candidate. For instance, compare with the sharp corner in the top-left quadrant of the orbit of the Pelagosaurus typus cranium figured below (fig. 5, p. 151, ibid.):

 

 

All in all, then, I feel that my specimen derives from the periorbital region of a crocodilian skull, in particular from one of the marine genera, such as Metriorhynchus or Steneosaurus. However, since both of these derive from different families, the closest grouping I think I'll be able to get to is Thalattosuchia, which conveniently also encompasses both Dakosaurus and Pelagosaurus (although the former would already have been included by Metriorhynchidae, and the latter - depending on which phylogeny you follow - would've been part of Teleosauridae). As such, the most likely identification of the piece of bone in question would, I think, be "Thalattosuchia indet. periorbital fragment".

 

Thanks all for helping me along my quest to identify this otherwise rather untelling piece of bone! Obviously, my identification is not set in stone, so please let me know if I've overlooked something.