Placoderm ?? Near derby WA Australia

[G Mac]

Hi.  Stopped for road break and saw this in the May river flat not far from derby. Has a definite fin structure.  Keen to find an expert and have it assessed properly. Wondering if it is a pectoral fin and plate from an armoured fish g Mac 

 

 

 

[FossilDAWG]

It's hard to be absolutely certain from a photo of course, but this does not look like a fossil to me.  Rather, it looks like a geological feature, either ripple marks or differential weathering of cross-bedded sandstone. The way the ridges divide and insert between one another is not typical of fin rays, which bifurcate in one direction only, from the fin base out to the margin.  Also there is no indication of actual bone, though that could be true if the specimen was an impression rather than the actual bone.

 

Don

[doushantuo]

Superficial similarity to the ornament on the anterior ventrolateral plate of Hyrcanaspis(which is known from Billiluna).

Dunno if the sculpture would be that pronounced,though

[Fossildude19]

I am in the geologic camp on this, but you should really e-mail John A. Long

He should be able to tell you whether or not it is fish. 

[doushantuo]

Or Gavin Young,but don't take my word for it

The dermal skeleton of placoderms has tripartite layering,BTW(vide Orvig,more recently Dupret(on Romundina),or the miscellaneous

writings of Giles/with or without Donoghue ),e.g. :Journ.Morphol.,2013)

Histological section would provide a definite answer,but it looks geological.

 

[izak_]

I agree that it is geological, not a fossil. 

But Dr. Gavin Young would be a good person to ask anyway...

[Miocene_Mason]

Looks like slickenslides or glaciers scratches to me. You may think that Australia was never glaciated, but you have to remember continental drift, I've heard of glacial scars in Africa. Cross bedding is also a possible culprit.

[G Mac]

thank you so much for your comments. I have emailed prof John.  While it is sandstone not bone. And the fin rays do not radiate and hence may be scratches there are some of the features on the sides that make me think it is fish not geological. will keep you posted as to the verdict. regards g Mac .

[G Mac]

John Long replies to the effect that prob not a fossil.  Thanks everyone.  

[PyritizeMe]

To me it looks to have layers on the side possibility indicating sedimentary rocks , the weathering on the outside is also indicate of river washed , the ornamentation is Interesting but most likely geological, can't be certain unless you clean it well and look closely with a scope to determine its structure .