Macrocephalites macrocephalus

[Eleganticeras]

Found loose and already broken at Cayton Bay Scarborough.

Matrix of ooliths about 0.4mm.

Grid of 1cm squares 

Referred to plate 33:2 in British Mesozoic Fossils, Natural History museum, British Museum.

Plate Very similar to my find except that the rate of increase in whorl fattening is greater than illustrated.

 

Lateral tubercules correct. However every photo I've seen of M. macrocephalus has no tubercules.

Is it what I've found in the book? The book was published in 1975.

[Ludwigia]

It doesn't look to be a macrocephalus, since the outer whorl width is normally much wider than that in your specimen. It may not even be a Macrocephalites, because of the tubercules and what appears to be a wider umbilicus than would be expected for that genus, but you would have to prepare that out in order to judge better. I'm inclined to think that this may be something like Cadomites. Are you certain that this is of Callovian origin?

[Eleganticeras]

Callovian, no certainty, as the fossil was in a loose fragment. The NatHist guide identifies a M. macrocephalus as from the Cornbrash, Scarborough, but the Cornbrash at Cayton Bay, below Red Cliff, is intensely bioturbated and doesn't have that fine oolitic appearance in the exposures I've looked at. The Cornbrash is lower Callovian.  So I'm not confident about its exact source of my find, but may I add some field details. Above the Cornbrash is a clay then sandstone, the largely unfossiliferous Red Cliff Member of the Callovian Osgodby formation.. There are many fallen blocks from the overlying fine grained oolite sandstone of the upper Red Cliff Member.  Reportedly, this does have fossils and yields occasional Kepplerites... So could my find be that? 

[Ludwigia]

9 hours ago, Eleganticeras said:

this does have fossils and yields occasional Kepplerites

That is another possibility which I had been considering.

[Eleganticeras]

Thanks Ludwigia for you input. I don't have much reference material for mid Jurassic ammonites so your initial M.m. rejection was appreciated.