We found this fossil a couple of months ago, near Watchet in Somerset. It's about 3.5 inches long, and was found in some shale from the lower lias.
It's a very unusual fossil. It has a large 3D structure in the centre and good detail, but I've been unable to positively identify it. I've enclosed some macro photos in case these are helpful. It has a very small juvenile ammonite on one half of the plate, which I believe is almost certainly psiloceras planorbis, which dates it to around 200m years ago.
I took it to my local museum and they couldn't identify it, and told me to ask here and let them know! I would be very grateful for any ideas.
Thanks for your time,
They are excellent photos.
...Which gives me less excuse for being perplexed!
My thoughts, for what they're worth:
1. I note there is significant faulting in the area, and my immediate reaction on seeing your photos was 'slickensides'. In this case, it would actually be slickenfibres because the striated appearance is manifested in vein mineral (the pale orange mineral more than the white mineral). But I am sure that is a false impression; various factors are wrong. So, having considered it, I now discount it.
2. It looks plant-related, but I haven't found much about fossil plants from Watchet (reptiles and ammonites, etc.:yes).
Update: some plants from around that time, irrespective of location - Fig.141 in http://ageofdinosaurs.com/books/ancient_earth_alleyne_nicholson_ch15.htm (I can't give a link to the figure, but it features Voltzia heterophylla, Pterophyllum jaegeri, Podozamites lanceolatus)
I note, however, that your specimen is not carbonaceous (many plant fossils would be carbonaceous).
3. ...and fish
BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY),
GEOLOGY, VOL. IV, 1959-1961
"REVISION OF ACTINOPTERYGIAN AND COELACANTH FISHES 243
The earliest descriptions go back to Egerton (1852) and were revised by Woodward
at the end of the last century in the British Museum Catalogue of Fossil Fishes.
More recently Rayner (1941, 1948) has redescribed several of the more important
Holosteans and attempted a classification of the group.
England has produced the majority of the known fishes from the Lower Lias,
Lyme Regis being by far the richest locality. Other localities include Watchett
and Street, in Somerset; Stratford-on-Avon, Warwickshire ; Barrow-on-Soar,
Leicestershire ; Bushley, Gloucestershire. Abroad, specimens come from Alsace-
Lorraine, Wiirtemburg and a few other German localities. The main collection is in
the British Museum (Natural History).
The fauna is large and well preserved. It includes Elasmobranchs, Chimaeroids,
Sturgeons, Coelacanths, Palaeoniscoids, Subholosteans, and many Holosteans,
which last form the bulk of the collections. The limy matrix in which the specimens
are preserved makes possible the application of the modern technique of acid prepara-
tion (Toombs 1948 ; Rixon 1949).
The fauna is important as it throws light both on the origin of the Holostei and
on the evolution, from the Holostei, of the present day Teleosts."
But the laths in your specimen do not have the texture of coelacanth skin
4. In photo 'positive.jpg': In the elongate hump in the middle of the area of interest, I note a sinuous dark line, which may be significant (ditto the elongate hump a a whole, suggestive of a log perhaps).
Give it a day or two in case somebody manages an ID,
otherwise, I suggest you bring or send it to the NHM for a closer look.
Thanks very much for the suggestions, guys, you've put forward some interesting ideas! I'd love to be able to confirm one of them!
Here's another picture, this one doesn't show the 3D structures so well, but it does show more of the surrounding rock.
The extra photo doesn't tell me anything more (but thanks).
So I suggest you bring or send it to the NHM for a closer look.
One of the things the folks at the NHM would be looking for would be cell structure, and microstructure at real edges (as opposed to damaged edges). You might be able to see some of that yourself if you had a good hand lens (at least x10) or binocular microscope.