Ichthyosaur paddle Lias Epsilon Altdorf, ID?

[Mahnmut]

Ahoi,

I got myself some ichthysaur paddle bones.

They are from the Lias Epsilon of Altdorf, Germany.

Can someone tell me a species? @pachy-pleuro-whatnot-odon perhaps?

Stenopterygius?

I plan to try and shape a paddle from clay with imprints to hold the fossils loosely in place.

That will be for the paleo-recreation section then, but first I have to know what shape of paddle to make.

Best Regards,

J

[pachy-pleuro-whatnot-odon]

Hi Jan,

 

That's a spectacular paddle!  I don't think I've seen that many paddles so beautifully released from matrix in private collections, so this definitely ranks among the top for me!

How sure are you that this material is associated - that is, comes from one paddle? I'm asking as the only other paddles like this I've seen outside of museum were either composited or heavily reconstructed.

One issue with paddles like this, of course, is that it's hard to be sure about the exact anatomical position in the paddle that specific phalanxes would have taken, making it hard to determine how complete the paddle is. And it's exactly these aspects - length and number of digits - that, in addition to the shape of individual phalanxes, are diagnostic as to genus and/or species. However, I'm not very versed in this topic (owing to the pertinent publications being pay-walled). You'll probably want to read Lomax and Massare (2017) on this topic, though. At least it's a forefin, so determination should be possible. Please note, though, that it looks like preservational conditions may cause individual phalanxes in ichthyosaur paddles to become rounded, complicating identification of their owner.

 

All the same, based on what I've seen, I'd say this paddle doesn't belong to either of the genera Ichthyosaurus or Temnodontosaurus, the first have much smaller, wider, rounder and many more phalanxes, whereas those of the latter are also much more rounded, with those of the first digit being angular in a much more symmetrical way. See below specimens for comparison:

 

Ichtyosaurus sp. paddle from Lyme Regis at the Teyler's Museum in Haarlem

 

Temnodontosaurus sp. front-paddle from Lyme Regis at the Teyler's Museum in Haarlem

 

Temnodontosaurus sp. front-paddle from Baden-Württemberg at the Paläontologische Sammlung at the MUT Tübingen

 

Temnodontosaurus sp. forefin from Lyme Regis

 

This, I believe, leaves Stenopterygius and Eurhinosaurus as the only two other realistic options. Of these, I believe Stenopterygius to be the most likely candidate, since it's phalanxes appear to be slightly more angular than those of Eurhinosaurus (in addition, Eurhinosaurus seems to be somewhat less common as a genus than Stenopterygius). Both genera, however, have four digits, short subequally symmetrical phalanxes on the first digit, and widened phalanxes on the second and third digits. The paddle of Eurhinosaurus is significantly longer than those of other contemporaneous ichthyosaurs, though, but this cannot be measured either from size or using an incomplete paddle. Here are some further photographs for comparison:

 

Eurhinosaurus longirostris front paddles from Baden-Württemberg at the Naturmuseum Senckenberg in Frankfurt

 

Eurhinosaurus longirostris front paddle from the Posidonia Shale at the Paläontologische Sammlung at MUT Tübingen

 

Front paddle of Stenopterygius quadriscissus from Holzmaden at the Paläontologische Sammlung at MUT Tübingen

 

Hope this helps...

Edited December 21, 2021 by pachy-pleuro-whatnot-odon

[Mahnmut]

Thanks for your answer!

The seller states that the bones have been found close together but not associated in a construction sites debris, there are some more little pieces, the pic only shows what the seller began to reassemble, so I am looking forward to a nice puzzle.

 

[pachy-pleuro-whatnot-odon]

Yeah, I know what you mean... I once got offered an "entire" (plenty of pieces missing, but you get the drift) ichthyosaur like that. I passed on it, as there were certainly nice bits present, but having to buy everything else too, just for those, would've been too expensive. Interestingly, this was one of the few specimens I ever saw with matrix-free paddle bones semi-articulated

[Mahnmut]

Oh, puzzles are fine for me, its definitely more fun than buying one bone and putting it on the shelf.

I think this one is less complete than the arrangement in the pic wants to make believe, and I begin to wonder if it is rather a longitudinal half (as in 2.5 fingers) than a complete proximal half. The small rounded parts to the left do not look as if they belong there.

Anyway, reassembling this will be fun.

Best Regards,

J

[pachy-pleuro-whatnot-odon]

8 hours ago, Mahnmut said:

Oh, puzzles are fine for me, its definitely more fun than buying one bone and putting it on the shelf.

 

While I agree on the puzzle-part of what you're saying, I prefer not to overly invest in many small partials, but would rather go for one more complete specimen

 

8 hours ago, Mahnmut said:

I think this one is less complete than the arrangement in the pic wants to make believe, and I begin to wonder if it is rather a longitudinal half (as in 2.5 fingers) than a complete proximal half. The small rounded parts to the left do not look as if they belong there.

Anyway, reassembling this will be fun.

 

Again, I agree. And that's what makes identifying specimens like these so tricky, as you first need to obtain a reasonable impression of how all the parts fit together before you can decide what kind of paddle that results in. But, in order to get to that stage, you'll first already need to decide what kind of paddle you're dealing with, so that you've got a model to base yourself off of. In this case, I think the most reasonable assumption is for the paddle to be Stenopterygius, which would indeed mean that, even with the flipper containing three digits, the paddle would be incomplete. However, I also agree with your observation that the paddle-bones of the left-most digit probably belong somewhere more distally down the hand, possibly on the second digit from right...

[Mahnmut]

Ok, now I do have them here.

it seems to be the bigger half of one paddle, maybe with some bones from another one added.

The big ones (Radius, Ulna, Intermedium and Radiale according to this graphic https://wessexcoastgeology.soton.ac.uk/jpg/3OS-Ichthyosaur-paddle-Lydekker.jpg quoted here

http://www.thefossilforum.com/index.php?/topic/84488-small-ichthyosaurus-paddle-bone/) do seem to fit well together, the rest is guesswork.

At the bottom of the photograph I think there is a Vertebra to the left, then a part that looks like a stilted stalked bulb and a saddle-like shape (croissant in the picture), no idea what these may be.

Can anyone tell me what function of the notches in the anterior row of bones was?

Thanks and regards,

J

 

 

 

Edited January 1, 2022 by Mahnmut
vocabulary

[pachy-pleuro-whatnot-odon]

Once again, that's a really nice paddle, and looks much more natural the way you've pieced it together there! Well done! The top left hourglass-shaped bit of bone does indeed appear to be a vertebra, as does the piece on the lower right. The saddle-like shaped bones (I believe I again see two) look like coracoids to me, much like the one in the photograph below:

 

 

As to your question about the notches: I'm not sure whether an explanation for that exists, although I must say I haven't read up too much on ichthyosaur paddle anatomy. To me, however, these are vestigial traits, from when these bones would've been proper long-bones, which have just been highly proximodistally compressed. The same type of changes, but expressed differently, can be seen in mosasaur paddles where you can often also still recognize the shape of the corresponding bone in terrestrial animals. Another argument for this interpretation would be the evolution of the paddle itself, illustrated by the below figure 4 from Motani (2005).