Fish? From An Ancient Seabed Near Canberra Australia

[Sarn]

Hi all,

I know very little about fossils but recently went with my family to the site of an ancient seabed near Wee Jasper NSW Australia. Information of the general area can be found here: http://www.heritageaustralia.com.au/pdfs/%20Heritage%200610_Burrinjuck.pdf

Please note that the exact location we went to is open to the public for fossiking and you are allowed to take specimens.

Anyway I found what I believe to be two interesting fossils. One looks to me to be a fish, but its interesting in that the specimen is composed entirely of crystal like structures. Black crystals forming the body and red crystals the head like shape. There also appears to be a fin composed of white crystals. The head looks to have an eye socket outlined in white crystals and the body has a line of white crystals that look like it might be a spine. The length is approx. 6cm (can take another photo with measurement if required)

This specimen was entirely encased in rock which I believe to be limestone (the entire area is covered in limestone). My husband noticed a dark discoloration on the surface of the rock and cracked it open revealing the fish shaped object. I have shown pictures of the specimen to someone who visits the area frequently and he mentioned that it is a specimen he has not seen before and may potentially be rare to the region (although he does himself admit that he is not a fossil expert

The second specimen looks like it might be a coral? We found it as is just lying on the surface. The length is approx. 10cm

Any help identifying these would be greatly appreciated

Edited October 22, 2013 by Sarn

[Auspex]

It's very hard for me to interpret these well from photographs (not the fault of the photos, they're very good), but even with my native skepticism, I have to say that you may be onto it with the first specimen. Someone else here may have experience with this type of material, and I encourage them to please chime in; I am very interested!

[Wrangellian]

I can't say for sure what that first thing is but it doesn't scream 'fish' to me... I do see a brachiopod right next to the big crescent-shaped thing (on the freshly spit side).

I see similar things to both your specimens here in my local Cretaceous shale (in concretions) but I have never known what to make of them except that they generally don't have a regular pattern that I would recognize as fossil. Maybe more septarian-related.

[Sarn]

Ok, so they may not be fossils at all?

Thanks for the info

[Wrangellian]

Might not. The brachiopod certainly is though.

[Rodney]

Could your first picture be some type of sea ray, for some reason I noticed that?

I`m no expert either.

Rodney

[Sarn]

Is the Branchiopod the bit that I thought may have been a fin? That part too is full of crystals

[Sarn]

Could your first picture be some type of sea ray, for some reason I noticed that?

I`m no expert either.

Rodney

The first picture is the rock that I split to reveal the fish shaped thing. I place the two pieces back together to show where the rock was split. the other pictures are the inside of that same rock.

[Rodney]

OK.

Rodney

[Sarn]

It does have a very stingray shape, or jellyfish - if it were a jellyfish would that explain the crystallization?

[Auspex]

The crystals are a geologic artifact, do not be distracted by them.

From what I've read, the site is Devonian, and is famous for its 3-D preservation of armored fish. I think there is good likelihood that this is what you have with the first specimen. The second, I am on the fence about whether it is geologic or biologic.

[Sarn]

Thanks Auspex.

So from what you have posted the crystals are irrelevant? Sorry but I know nothing about fossils.

It sounds like you think I have an armored fish, do you mind my asking why you think that? - would love to learn, to me it looks like a fairly modern type of fish, but I have literally zero knowledge in this stuff. Do you mind explaining to me (in laymens terms lol)? I am keen and interested to learn.

[Fossildude19]

The time period involved here (Devonian - Age of Fish) indicates that most fish fossils from that era would probably be a Placoderm, which were the most numerous types of fish during this time period.

Ray finned fish and lobe finned fishes were just starting to emerge at this time. Armored fish, due to their structure (hard, bone-like plates), would be more apt to fossilize, especially since they were the more predominant types of fish around then.

The shape of the item in your first pic vaguely resembles a head or body plate of a placoderm, maybe something similar to Cephalaspis.

I use the word vaguely, as I am not entirely convinced this is a fish fossil. It could very well be a fortuitously shaped geolgic structure.

The crystals may just be an artifact of the diagenesis of the rock/fossil as it formed. So they are less relevant.

Hope that helps.

Regards,

EDIT: for link added.

Edited October 22, 2013 by Fossildude19

[Sarn]

Wow, thank you. Even if my fossil turns out to be geologic structure at least learnt a lot, all this info is much appreciated.

[Plax]

second object looks like the impression of a glass sponge. First one looks like a cross section through a deep dish bivalve or brach. just guesses of course!

[izak_]

No, the first fossils are probably Gastropoda or nautiloids, and the second one is probably just weathering. However I have found placoderms there before, good luck!