But these comments on homeomorphy (Schloenbachia varians and Forresteria alluaudi) are pertinent
Could do with comment from somebody with local knowledge...
Thank you for you advice.
I have taken another view of the ammonite.It does not have any keels or grooves on the ventrum.
It is from the the upper greensand so the age would be Upper Albian.
On the wikipedia link of Schloenbachia, it seems this ammonite is from Cenomanian in age so I am not sure
whether it also occurs in lower beds.
I have also found a heteromorph ammonite which I think is of Family Anisoceratidae-possibly Idiohamites sp?
from the Upper Albian.
I believe Schloenbachia does extend down to the Albian, though that earlier Wiki link does not mention it; see this one, however - http://en.wikipedia.org/wiki/Albian#Originating_in_Upper_Albian_Strata.
The complete lack of a keel is a good observation, and tends to rule out Schloenbachia.
The other one:
Scaphites always comes to my mind with heteromorphs, but the ribbing is wrong.
Yes - Idiohamites is a distinct possibility. But also Anisoceras, eg. http://www.discussfossils.com/forum/forum_posts.asp?TID=2419&PID=25598 (search that page for 'Anisoceras I found').
Protanisoceras looks similar (http://jsdammonites.fr/488.html (last photo) but I can't suggest it since it does not seem to be recorded from the Albian.
Sorry, I don't have a key for these ammonites.
Still could do with comment from somebody with local knowledge...
Thank you Mike,Polacanthus.
Yes, I was also thinking of the possibility of the 'hoplites' group. Euhoplites sp. usually have a concave venter but some do have flat venters so not totally excludes this.
I am brousing this website(http://www.gaultammonite.co.uk/Pages/Link_Pages/Ammonites_Link.htm) to find
any matches for the ammonite but I cannot seem to find an ammonite that has these simple but strong ribs and
tubercles with a flat venter.
The heteromorph ammonite does resemble Anisoceras with prominent ribs and tubercles and these come from
late Albian as well so it could be possibly Anisoceras sp.
Thanks for your help.
You could also try the Dorset County Museum - http://en.wikipedia.org/wiki/Dorset_County_Museum.
It has plenty of specimens from the Jurassic Coast - http://www.dorsetcountymuseum.org/geology
- If you look at this list of museums in Dorset, you'll see several include geology.
- Lyme Regis Museum gives a contact email which should get you to palaeontologists with local knowledge - http://www.lymeregismuseum.co.uk/research-at-lyme-regis