Jump to content

Unknown Oyster, Madagascar


Spoons

Recommended Posts

Hey everyone!

 

I recently acquired this oyster from Tulear province, Madagascar. The seller has listed it as Rastellum carinatum, but doing any research online, I’ve only found other sellers selling similar fossils. 
 

I did come across a Wikipedia article for Agerostrea sp. It appears to be the same shell, and it lists it as occurring in rocks that are Maastrichtian age from Madagascar. 
 

Are these the same species just under different names or are they separate? If so, what genus does my specimen belong too?

 

Any response would be greatly appreciated from you guys, we’ll see how challenging this might be to figure out. 
 

Thanks again

-Nick

28216B87-6D75-4EB2-B7A0-2D7E721CF8ED.jpeg

1C2921F8-A679-462C-89FC-A9F6A0BF0EBD.jpeg

FE0F9F49-D5E4-46CA-B330-6D73F326C3AC.jpeg

E8697E21-783A-48A0-8316-C28A3BA40B70.jpeg

530F13DD-22F0-4E33-A2C7-DC3E3F38C6FD.jpeg

Link to post
Share on other sites

Photo from Wikipedia on Agerostrea. This specimen apparently comes from Madagascar and is labeled Agerostrea ungulata.

6C6A85E9-24EB-410C-8882-1CFB9D98633D.jpeg

Link to post
Share on other sites

Is it possible that Rattleum represents a genus known from the Jurassic and that Agerostrea is a genus from the Cretaceous? Both genre are reported to occur in Madagascar.

 

Is it possible that both genre just happen to look practically identical, just being separated by millions of years?

  

  • I found this Informative 1
Link to post
Share on other sites
Tidgy's Dad

As I understand it, Agerostrea is a Late Cretaceous (and possibly Pliocene) genus while Rastellum ranges from the Callovian (end of the Middle Jurassic) to the end of the Creatceous, so they overlap. 

Although they are both in the true oyster family Ostreidae, they belong to different subfamilies, so I guess they have different internal morphology. 

I haven't got far with my own researches yet, as i have the same problem as you.

Zigzag.thumb.jpg.ddc653a66e8e4dea590abb5b0875217b.jpg

 

  • I found this Informative 2
Link to post
Share on other sites

 

17 minutes ago, Tidgy's Dad said:

I haven't got far with my own researches yet, as i have the same problem as you.

Seems we have our work cut out for us

  • I found this Informative 1
Link to post
Share on other sites
Tidgy's Dad
1 hour ago, Spoons said:

 

Seems we have our work cut out for us

Indeed, but as I'm still sorting out my Upper Ordovician and will be working through the following periods in order, i think I'll be dealing with my Cretaceous stuff in about 2050. :D

Link to post
Share on other sites

No clue on the ID, but that's an amazing-looking shell. Such wild shapes for an oyster.

Link to post
Share on other sites
fifbrindacier

I think you're right with your identification of Agerostrea, the specimen you showed looks like yours very much.

I think the Rastellum "teeth" are larger.

Here is a valve of Rastellum carinatum i found in the Cretaceous of Touraine :

PA050047.JPG.35d83a5eedbbf22b4b1ed716d17959cc.thumb.jpg.f5dc83dac1b4889223604aadb9b660af.jpg

  • I found this Informative 2
Link to post
Share on other sites

Well, here in the Pyrenees (Upper Campanian), they overlap.

 

The clue I use is: Agerostrea has shorter ribs, and even smooth surfaces (externally and internally). Rastellum have long ribs, forming a sort of spike.

 

As example, those are the biggest pieces I have (never found a complete specimen). Agerostrea in the left side.DSC_0576.JPG.75c060d7948aef0632770cc724181857.JPGDSC_0577.JPG.154ecd983275d2ec0c935d76d752a305.JPG

 

My guess for your specimen is Agerostrea ungulata

 

 

 

 

  • I found this Informative 2
Link to post
Share on other sites

@FishkeeperThank you! It thought so too, and it was a bit of an impulse buy for me for sure.

9 minutes ago, fifbrindacier said:

I think you're right with your identification of Agerostrea, the specimen you showed looks like yours very much.

I think the Rastellum "teeth" are larger.

Here is a valve of Rastellum carinatum i found in the Cretaceous of Touraine :

PA050047.JPG.35d83a5eedbbf22b4b1ed716d17959cc.thumb.jpg.f5dc83dac1b4889223604aadb9b660af.jpg

I still really can’t tell the difference. Can you provide a scale so I can see how much larger the teeth are on your specimen than mine?


Thank you all for the input I really appreciate it.

-Nick

 

Link to post
Share on other sites

@Quer & @fifbrindacier say Agerostrea ungulata. 
 

I’m inclined to agree. Is drew what you both mean by larger “teeth” now.

 

@Tidgy's Dad I think we may have found the wander to our question, and a lot sooner that 2050!

 

As I said before, I really appreciate everyone’s input. I’m really honored to be a part of such a wonderful community. I look forward to drawing upon your resources again. 
-Nick

  • I found this Informative 2
Link to post
Share on other sites
Tidgy's Dad

Thanks everyone. 

Very useful input. 

I'll scribble a note on my sleeve for use in 2050. :)

Link to post
Share on other sites

As this is a recurrent ID issue, I think that this paper could be useful to know.

 

From page 12:

"The species (Agerostrea ungulata) is distinguished from falcate congeners and species of Rastellum (Faujas-Saint-Fond, 1799) by its smooth central field in both valves and general absence of shell chambers (with respect to Rastellum). (...)

Agerostrea ungulata is well known from the upper Campanian? and lower Maastrichtian of Madagascar (...) It es extremely abundant at localities exposing lower Maastrichtian rocks on the east coast (...)

Agerostrea ungulata typically occurs in marly limestones and chalk of Campanian to Maastrichtian age in western Europe, northern Africa, Pakistan (Baluchistan), India and Madagascar."

 

  • I found this Informative 2
Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...