Mazon ID Assistance - No.5 egg case?

[Jones1rocks]

I have a Palaeoxyris that is significantly larger than this specimen.  Is this a Palaeoxyris, and why would there be such a discrepancy in size between specimens?

[Tidgy's Dad]

Palaeoxyris is the generic name for egg cases of hybodont sharks. 

So the two specimens could be from two entirely different species of differing sizes. 

[Fossildude19]

Yup. Definitely an egg case.

[Jones1rocks]

Thanks guys!

[fossilized6s]

I agree with egg case.

[Archie]

A gorgeous one too!

[oilshale]

Seems to be Palaeoxyris helicteroides Morris in Prestwich, 1840

Chondrichthyan egg capsule card.pdf

[Jones1rocks]

1 hour ago, oilshale said:

Seems to be Palaeoxyris helicteroides Morris in Prestwich, 1840

Chondrichthyan egg capsule card.pdf

 

 

 

Very informative!

[fiddlehead]

The shark egg capsules seen here are called Palaeoxyris prendeli 1870. Lesquereux. They are by far the most prevalent Middle Pennsylvanian egg cases found in North American. But they are unknown in Europe. More on this latter. Egg capsules are identified by band count and suture patterns. E.g., P. helicteroides has a simple and very consistent pattern of large band/small band/large band. P. prendelli has a weak (often missing), complicated and highly variable pattern roughly going small/medium-broad/broad/broad/small. One thing to keep in mind is size of the egg case does not matter in identification. Larger sharks of a species lay larger eggs than younger and smaller sharks do. This character is seen today in modern egg laying sharks.    Though it has not been published yet, there is an privately owned example of P. prendelli with a shark partially emerged which is surrounded by a stain that can be interpreted as embryonic fluid. Based on its features like a long and narrow snout, the shark is easily referable to a Bandringa rayi. It should be noted that B. rayi is unknown in Europe as should be expected since as mentioned earlier, P. prendelli is not found there. 

 

Hope this helps,

Jack