Ovaticeras or End of the line

Section of septarian nodule with Dacytlioceras sp (fron) and Ovaticeras ovatum (back)

Section of septarian nodule with Dactylioceras sp (front) and Ovaticeras ovatum (back)

If you read the title of this blog and start to worry that I might stop working on the book and on the blog – well, don’t. This is just referring to the subject of this post, the ammonite genus Ovaticeras…
The title specimen by the way (you might have guessed by the quality of the prepwork) is a specimen purchased from Mike Marshall. Maximum size of the Ovaticeras on this piece is 8 cm.

Ovaticeras is a somewhat rarer ammonite which seems to be very restricted, both in terms of local distribution (it’s apparently only really documented from Britain, with its main occurrence in Yorkshire) and in terms of its relative short-livedness (it has only been found in the approx. 35 cm of the so called ovatum bed at the top of the falciferum subzone of the lower toarcian (of course named after the species O. ovatum) and shortly below it. It is thought to have descended from Harpocas falciferum (HOWARTH 1992) and apparently left no descendants itself – end of the line.
I have found Ovaticeras ovatum at Saltwick Bay, at Hawsker and at Ravenscar, but you should be able to find it everywhere on the Yorkshire coast,
where there’s an outcrop of the aforementioned bed.
View of Ovaticeras keel and typical oval whorl section

View of Ovaticeras keel and typical oval whorl section

The oval whorl shape of Ovaticeras is quite characteristic, as are the sloping umbilical walls without an edge,
which differentiates it from large Eleganticeras body chambers.
Comparison of umbilical edges of Eleganticeras (top) and Ovaticeras (bottom), both approx. 12 cm

Comparison of umbilical edges of Eleganticeras (top) and Ovaticeras (bottom), both approx. 12 cm

Adult specimen have  a bit of a “hood” at the end of the body chamber, where the keel slightly overarches the whorl.
The ribs are those of a typical Harpoceratid, of weak falcoid form, receding to mere sinuous growth stripes on adult specimens’ body chambers.
It does have a simple keel with smooth areas to the side of it that also grows weaker on large body chambers.
Large 17 cm Ovaticeras ovatum

Large 17 cm Ovaticeras ovatum

This large, 17 cm, complete specimen was found on Oct 7, 1991 at Saltwick Bay in a large nodule with a strong pyrite crust and was
extracted from the nodule using hammer and small chisels alone (on the kitchen table of our holiday flat, if you need to know…)
It is not my prettiest specimen, but my largest and the first of the species I’ve found.
Suture of Ovaticeras

Suture of Ovaticeras

This partial specimen shows the nice characteristical sutures of Ovaticeras.
Must be getting close to Christmas, I see Christmas trees everywhere…
AndyS
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1 Comment

  1. s tymon

     /  December 29, 2012

    thank you once again Andy Brilliant read!

    shaun

    Reply

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