Frechiella or A nautilus with an ammonite suture…

Frechiella subcarinata (YOUNG & BIRD, 1822), 8.5 cm diameter, Port Mulgrave, with a Dactylioceras fragment and a belemnite phragmocone in the aperture

Frechiella subcarinata (YOUNG & BIRD, 1822), 8.5 cm diameter, Port Mulgrave, with a Dactylioceras fragment and a belemnite phragmocone in the aperture

Frechiella is one of the rarest Yorkshire lias ammonites and in some respects also one of the oddest.

It comes from a so-called “aberrant” line of ammonites, previously thought to come from one subfamily Bouleiceratinae of the family Hildoceratidae,
but nowadays after some more analysis (Rouleau et al 2003) is being split up into the 3 subfamilies Bouleiceratinae (lower Toarcian),
Leukadiellinae (middle Toarcian) and Paroniceratinae (upper Toarcian, including Frechiella) but all still under Hildoceratidae.
All are much more common in the tethyan realm, and are rare “strays” into the north-west european faunal province.
All members show a characteristically reduced, sometimes “ceratitic” suture (named after the triassic ammonite genus Ceratites, which showed a similar suture).
Oxyparoniceras telemachi (RENZ), 2 cm This is a member of the same subfamily, but not found in Britain, but somewhat further south from Barjac in the south of France (and purchased by me).

Oxyparoniceras telemachi (RENZ), 2 cm
This is a member of the same subfamily, but not found in Britain, but somewhat further south from Barjac in the south of France (and purchased by me).

This is also the main diagnostic feature, otherwise one could easily confuse these very involute ammonites with a nautilus , especially when they are wave-rolled –
In fact, Frechiella subcarinata was originally called Nautilus subcarinatus YOUNG & BIRD, 1822 –
you can just believe that, if it weren’t for the very characteristic suture, and I guess some of you might now go checking the nautilus in their collections …
(and of course : Frechiella is an ammonite, not a nautilus !)
Well preserved specimen show a faint keel on a rounded, sometimes slightly rectangular venter, faint radial ribs, sometimes flat waves can be seen close to the umbilicus.
With almost all specimen I’ve seen (and that’s not many…) the body chamber is more or less crushed or imploded.
Frechiella subcarinata (YOUNG & BIRD, 1822), 10 cm, Hawsker Bottoms

Frechiella subcarinata (YOUNG & BIRD, 1822), 10 cm, Hawsker Bottoms

Frechiella subcarinata (YOUNG & BIRD, 1822) , the only Yorkshire species in the genus Frechiella found so far,
occurs only in the main alum shales, commune subzone, bed 54 (HOWARTH 1992).
It is one of the rarest Yorkshire coast lias ammonites, and many regard it as the “holy grail” of upper lias ammonites.
I had for a time almost given up on trying to find one myself, and bought an unprepared specimen, found at Port Mulgrave (the one pictured below the title),
from Mike Marshall in September 2003.
But as it happened – and doesn´t it always happen like this ?!  – a year later in September 2004 one twinkled up at me from the cliff debris on one of my favourite
spots around Hawsker Bottoms – this is the one pictured above – I have not found one since, not even a fragment.
AndyS
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1 Comment

  1. s tymon

     /  January 6, 2013

    BRILLIANT ONCE AGAIN! would love to find a Frechiella…stunning ammonites you have pictured there Andy!

    regards
    shaun

    Reply

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