Anadara diluvii ?? - Styrian Basin of Austria - Miocene, Badenium (ca. 15 Ma)

[FranzBernhard]

Hello,

 

and another bivalve from the Miocene Styrian basin of Austria. It has some resemblance with Anadara diluvii, but I am not totally sure. It is associated with a brackisch fauna (Crassostrea gryphoides, Pirenella picta, Terebralia bidentata).

 

For comparison a typical Anadara diluvii from the same area, but another locality, is also attached (size 2 cm). This type is also abundant at other localities in the area (typically with marine fauna).

 

All suggestions and comments are greatly appreciated!
Franz Bernhar

[tmaier]

I'm not familiar with your formation, but the two shells you show above seem to be different species.

The feature of the beads on the radial ribs is very different between the two. Also the annualar growth rings on the top specimen are very prominent on the top specimen, but totally absent on the bottom one. That seems very significant.

Also, for classification of a specimen it is best to expose as much diagnostic features as possible, and the hinge area is obscured in the lower specimen. The hinge geometry is often a very good marker, so you might want to expose that for analysis.

A species often has regional variations in it's morphology, but I think the differences here are too great, but that is just my guess.

Also, the top specimen has question marks after the species declaration, and that usually indicates an uncertainty as to the classification. Is that your unknown, or is the specimen at the bottom the unknown? You need some images of a known specimen to base the comparison off of.

It can be very difficult to differentiate species until you become familar with the distinctive features that define that species. Having a bunch of them in your hands really makes it easy, because when you line them up in front of you, the differences will jump right out. Looking at them one at a time often makes the differences become invisible. That brings up the funny story of the "discovery" of the bonobo chimp. The bonobo is a rare species and they were sometimes captured in with the troglodytes species. Nobody really noticed the difference for a long time, but when you line all the chimps up and compare them side-by-side, the differences become obvious and easy to spot. So they discovered a new species that they had already been collecting for many years! These subtle but definitive differences that are the marks of a species can be difficult to see without side-by-side comparison, and in-hand is the best way to learn the difference.

Anyway... I think these images above are different species.

[FranzBernhard]

Hello,

 

thank you very much for your helpfull response and comment!

 

The top specimens are the unknown. I have serval specimens of the lower one from different localities in the same formation, some completely free of matrix. They are generally identified as Anadara diluvii. The hinge area of these is similar to the top specimen with lots of tiny teeth, but I haven´t checked if they are really totally the same, just look very similar.

 

The bonobo story is a good one! Thats the same situation here: I you have the top specimens on their own, they might go for Anadara diluvii. But they stand out in comparision to the real Anadara diluvii from the other localities in the same formation. So my question.

 

These annular growh rings - could the depend on the habit? Maybe characteristic for tidal or brackisch environment?

 

Again, thank you very much for your help and opinion!

Franz Bernhard

 

 

 

 

 

 

 

[tmaier]

The smoothness of the beads and the sharpness of the annular growth rings can be related to the habitat. A clam that dies and gets kicked around in the sand by the tide can have smoothed ribs and ornamentation. The harsh annular growth rings can be caused by radical changes in the growth environment.

Also, there is individual variation of a population, and regional variation (within the same species... a regional variety).

So for some species there can be a lot of leeway in appearance. For other species there seems to be very little variations, and the shells all look like stamped out copies of each other, over wide geographical regions and periods of time. The person who defines the species has to take those things in to account as much as possible before defining the new species. Sometimes all the details are not known until later (like with the bonobo chimp).

So even though some species have wide variablity, I'm still suspicious that the two shown here are pushing it a bit too much. Do you know if there are any more Ark shells to be considered as possibilities for this area you are hunting in?

[FranzBernhard]

Yes, the old literature mentions:

Arca/Anadara barbata (medium abundant)

Arca/Anadara turoniensis/turonica (abundance unknown), but abundant (according to literature) at the nearby (10 km) famous Weitendorf locality in the same formation.

Arca/Anadara clathrata (rare)

But most abundant (according to the old literature) seems to be Arca diluvii (= Anadara diluvii).

 

Interestingly, the suspiceous species occurs (with one execption, see attached image, and at this locality the A. diluvii occurs also), in only one locality (Fuggaberg), but is quite abundant there. And there are other localities with brackisch fauna (Crassostrea gryphoides, Pirenella picta) nearby, which contain the usual A. diluvii.

 

Ok, googling for the above mentiioned species makes me unsure, if all my supposed A. diluvii  are really A. diluvii...

 

Thanks a lot!
Franz Bernhard

 

 

 

 

 

[FranzBernhard]

Here is the direct comparision of A. turonica (2, top) with A. diluvii (3, lower, and 4) from the Atlas of Hoernes (1870).

Confusing, isn´t it?

Franz Bernhard

[abyssunder]

I agree with the above statements, and I'm sure you are more documented than me.
In my opinion the specimens in question  belongs to genus Anadara, but I'm not sure about the species. The mentioned (in different documents) species present in the Lower-Middle Miocene of Austria are : Anadara fichteli (Deshayes), A. fichteli grandis (Shaffer), A. moltensis elongata (Shaffer), A. diluvii (Lamarck), A. turonica (Dujardin) and others not specified, under the generic Anadara sp.. For an accurate determination it is necessary a sample of more specimens from the same location, individuals extracted carefully from sediments (if possible) or found free of matrix; samples which could be considered as reference (picures of them, preferably from museum collections, or individual collections accepted by museums) for comparative reasons (as tmaier said previously); descriptions of them made by considerable scientists in the domain familiar with the studied area.

For example:
" Anadara diluvii (LAMARCK, 1805) (Pl. 2, Fig. 3)
2001 Anadara diluvii (LAMARCK, 1805) - HARZHAUSER & MANDIC, p. 721, pl. 3, figs. 8-10.
M a t e r i a l : Mühlbach (Mü1) – one badly abraded, fragmented right valve of a young individual; its inferred shell height is of about 5 mm.
Shell is centrally convex, with a broadly inflated, dorsally incurved, opistogyrate umbo. It has 29 ribs, each marked only by radial ridge pair that remained after exterior surface
abrasion.
The earliest certain record of Anadara (A.) diluvii is from the Late Oligocene of the Central Paratethys (BALDI 1973). This (semi)infaunal, byssate species is still present in the Mediterranean on sandy and muddy bottoms from 5 to 500 m depth (MILISIC 1991, POPPE & GOTO 1993). " - Molluscs from the Badenian (Middle Miocene) of the
Gaindorf Formation (Alpine Molasse Basin, NE Austria) – Taxonomy, Paleoecology and Biostratigraphy - Oleg MANDIC & Mathias HARZHAUSER, 2003.

 

Also your specimens could be not recorded previously in the absence of the studied area, or is not considered as extinct species.

If I had to choose between A. diluvii and A. turonica, I'll choose the latter.

 

[FranzBernhard]

Thank you very much for your comments, abyssunder!

 

The main problem seems to be that there is NO modern revision (modern? There is no revision!) of the molluscs of the Western Styrian basin ("Florianer Schichten"). More then 300 gastropod and bivalve species have been described from that area (early to middle Badenian, marine to brackish) from 1856 to 1901.

 

Interestingly, the most abundant species groups seem to be especially problematic:

Turritella partschi / badensis

Cerithium florianum / pictum

Terebralia bidentata / lignitarum (seems to be one species)

Anadara group as discussed above.

Acanthocardia turonica / clavata

In some works they are mentioned as synonyms of each other, in others not, but how to choose as an amateur?

 

I think I have to stick to the genus with the mentioning of possible species. What do you think about that kind of presentation?

 

Thanks a lot again!
Franz Bernhard

[tmaier]

As confusing as it all seems, if you had a bunch of these shells poured on to a table, you could easily sort them into piles according to species. The differences are obvious when it is side-by-side with the other shells. Looking at photos and drawing can be frustrating.

Some genus are called "prolific speciators" because the branch out into so many species like this. The Conus and Turritella and Anadara are like that. What may seem like an individual variation can easily be a whole new species.

[abyssunder]

That is fair enough.
How many ribs are visible on the shells in question ?
Also, could you take a closer view with a scale of one of the best preserved shells putting it in the same position as the following Anadara turonica is ?

 

 

Pictures from

http://www.lithotheque.ac-aix-marseille.fr/webphp/Miocene/photo_fossile.php?id=24
http://www.lithotheque.ac-aix-marseille.fr/webphp/Miocene/photo_fossile.php?id=25

[doushantuo]

Don't know of you have this one already:

lhttps://ia601509.us.archive.org/27/items/abhandlungenderk00kkge_2/abhandlungenderk00kkge_2.pdf

Not sure if Bivalvia Neogenica (Piller,ed.,2001(fossilium catalogus Austriae))covers the Florianer Schichten,but it seems a save bet

[FranzBernhard]

Thank you for all your comments and suggestions!

Abyssunder, I will take these photograph, but it will take some time.

Doushantou, thanks for the reference. I don´t have it. This formation is a little bit older then the "Florianer Schichten",but only about 3-5 Ma, so I will have a look at it!

I never had a look in the "fossilium catalogus Austriae". I don´t even know if it is just a "book of pictures with names" or a real revision work (I think the former).

Thanks to all!
Franz Bernhard

 

PS: Pictures fresh from today´s field trip: A newly discovered, natural, unexploited, fantastic outcrop in a small, steep creek (as usual for the area) of the "Florianer Schichten" with lots of fossils.

[abyssunder]

That could be an excellent fossil hunting site ! As always, when I find such places, first I take a deep breath, than a cigar. Thanks for sharing.

[FranzBernhard]

My steps are:

- taking a deep breath

- taking photographs of well exposed fossil

- Leaving the outcrop as it is and going away.

Its much to nice to dig in. I know of several more of such nice outcrops in this area that I leave alone, especially that in the steep creeks.

But there are also outcrops that deserve digging:

Those under fallen trees  ("Wurzeltelleraufschlüsse"), but also not so well exposed sites like that in Fuggaberg. After each dig, they become better and better...

http://franzbernhard.jimdo.com/app/download/6404119964/Fossilfundstellen_Internet_Fuggaberg_3.pdf?t=1476682149

Happy hunting!

Franz Bernhard

[FranzBernhard]

I managed to take photographs of two Anadara. These are they only ones which have the inside exposed. A. turonica or A. diluvii??

Unfortunatelly, I haven´t catched the area on the photograph. It is horizontally stripped. According to Hoernes (1870), this is an important characteristic of A. turonica. But his pictures are not toally clear.

Franz Bernhard

[abyssunder]

Thank you, Franz, for the excellent pictures you provided.
As I posted previously citing from MANDIC &  HARZHAUSER, 2003 - in the underlined part of the description - A diluvii has 29 ribs.
Here is another description in Simon Schneider • Oleg Mandic. Middle Ottnangian (late Burdigalian) mollusks from the Rott Valley (SE Germany): the ultimate marine fauna of the Western Paratethys. Pala¨ontol Z (2014) 88:375–403  https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=31&ved=0ahUKEwjfrrzwvOLPAhUwSJoKHXYxDas4HhAWCBswAA&url=https%3A%2F%2Fwww.researchgate.net%2Ffile.PostFileLoader.html%3Fid%3D5683726a64e9b202408b4568%26assetKey%3DAS%3A312239368671234%401451455074633&usg=AFQjCNFtAqBzI4O30ieFvQzA9QvcDDgbrw&bvm=bv.135974163,d.bGs&cad=rja

 

" Anadara diluvii Brocchi, 1814 (Fig. 6A, B)—This species is common in the Miocene and Pliocene of Europe and is also among the most abundant species of the Rott Valley fauna, where it occurs with relatively elongate and slender shells, and was thus confused with Anadara turonica (Dujardin), a contemporaneous eastern Atlantic species, by Traub (Traub in Neumaier and Wieseneder 1939; Traub in Zo¨belein 1940) (Table 2). The latter species is distinguished from A. diluvii by its more numerous ribs (usually >30 in A. turonica and ca. 26–28 in A. diluvii) and a more transversal shape, including a relatively straight ventral margin (Cossmann and Peyrot 1913; Dollfus and Dautzenberg 1913; personal observation). "

 

 

Your specimens (as far as I could see) have more than 30 ribs. In conclusion they could't be Anadara diluvii.

Hope this helps.

[FranzBernhard]

Yes, thank you very much, this helps a lot!

So the outline of the shell isn´t really a disdinguisching feature!

Rip countig is quite easy and I have done it on all specimens where it is possilble. These are the results:

Locality                       Nr        Rips     Species

Oisnitz-SE-1                --         31-33   A. turonica (see photo above)

Wetzelsdorfberg-5        2676    31        A. turonica (see photo above)

Wetzelsdorfberg-5        2698    32        A. turonica

Bramberg-1                 2663    31        A. turonica

Koglberg-2                  2684    28        A. diluvii

Oisnitz-SE-1                2572    28-29   A. diluvii

Höllerkogel-10             2708    29        A. diluvii

And finaly Fuggaberg, the specimens from the first photo of my post:

Fuggaberg (three specimens)   30-33    A. turonica

And a very small (13 mm), quite elongated one, also from Fuggaberg: 28-29: A. diluvii (see photo)

From the outline, one would think the small one is A. turonica and the large ones are A. diluvii...

Conclusion: There are both speciec present, even at the same locality.

Thanks a lot again

Franz Bernhard