Phyllocerataceae – the leaf horns – a conservative group with very few (Yorkshire) members

Sutures of Phylloceras (Zetoceras) zetes, upper Pliensbachian, Reutlingen / Germany

Sutures of Phylloceras (Zetoceras) zetes, upper Pliensbachian, Reutlingen / Germany

The Phyllocerataceae are a superfamily of ammonites that is very much like the Lytocerataceae – they’re thought to have been deep water denizens, often only straggeling into Yorkshire from the Tethys  when a passage opened up, they’re quite conservative (there’s not a lot of change and not many species, at least not in Yorkshire), they’re not very common (though probably slightly less rare than Lytoceras) and they’re very beautiful and highly sought after ammonites.

The sculpture of the Phyllocerataceae consists mostly of finer or coarser ribs but the beauty of these ammonites also lies in the sutures they show when preserved as an internal mould :  Complex leaf-like structures of an almost fractal nature, which also have been immortalized in the genus name Phyllo-ceras = Leaf horn, as shown above.

Two families of the Phyllocerataceae are represented in Yorkshire, the Phylloceratidae with the genus Phylloceras in the Toarcian and the Juraphyllitidae with Tragophylloceras in the Pliensbachian and (rare to the extreme) Meneghiniceras in the lower toarcian with the following species :

  • Phylloceras heterophyllum (SOWERBY, 1820)
  • Tragophylloceras numismale (QUENSTEDT, 1845)
  • Tragophyllocas loscombi  (SOWERBY, 1817)
  • Meneghiniceras lariense (MENEGHINI, 1875)
Meneghiniceras has most probably been found only once (see literature section at the bottom) – if you think you have another one, let me know…

The index fossil of the ibex zone, Tragophylloceras ibex, has not been found in Yorkshire, neither have been to my knowledge the species Tragophylloceras undulatum and Tragophylloceras carinatum.

For this post I’ve nevertheless decided (apart from the title picture) to include some reference specimen of T. ibex and a coarsely ribbed T. undulatum from my collection from the french Fresney-le Puceux quarry, which I had the opportunity to visit on a guided excursion more than 30 years ago,  and a beautiful complete finer ribbed specimen of T. undulatum from the Radstock/Somerset area which by wonderful coincidence came up in the eBay shop of Mark Varah while I was writing this post – of course it was a chance  too good to miss…

 

Tragophylloceras numismale (QUENSTEDT, 1845)

Tragophylloceras numismale, 1.6 cm, Robin Hoods Bay

Tragophylloceras numismale, 1.6 cm, Robin Hoods Bay

Tragophylloceras numismale, 12 cm, Robin Hoods Bay

Tragophylloceras numismale, 12 cm, Robin Hoods Bay

Tragophylloceras numismale can sometimes be found in the polymorphus subzone as small pyritized phragmocones, the body chamber usually either not preserved at all or flattened. The small ammonites show characteristic repeating constrictions on the inner mould which do not persist onto larger whorls.

The larger specimen above was a lucky find from a very fresh small cliff fall maybe 2-3 m above the beds where the pyritized specimen occur. It must literally have fallen only hours before I passed the area about 3 hours after high tide as it had not been touched by the sea.

 

Tragophylloceras loscombi (SOWERBY, 1817)

Tragophylloceras loscombi, 3 cm with Androgynoceras maculatum, Robin Hoods Bay

Tragophylloceras loscombi, 3 cm with Androgynoceras maculatum, Robin Hoods Bay

In contrast to similar beds in Dorset, where Tragophylloceras loscombi and Androgynoceras often occur together, the Yorkshire  T. loscombi specimen only rarely accompany Androgynoceras in the Yorkshire maculatum subzone and are generally very hard to find and most of the time relatively small.
It´s range seems to be rather long, from the luridum subzone up to the stokesi subzone. The ammonite exhibits fine ribbing, and only very fine undulations at the venter.

 

Tragophylloceras undulatum (SMITH, 1817)  (coarsely and finely ribbed variants)

Tragophylloceras undulatum, finely ribbed variant, complete shell with mouth border, 5 cm, Radstock / Somerset

Tragophylloceras undulatum, finely ribbed variant, complete shell with mouth border, 5 cm, Radstock / Somerset

Tragophylloceras undulatum, coarsely ribbed variant, 7 cm, Fresney-le-Puceux / France

Tragophylloceras undulatum, coarsely ribbed variant, 7 cm, Fresney-le-Puceux / France

More or less fine ribbing with regular undulations at the venter.

 

Tragophylloceras ibex (QUENSTEDT, 1843)

Tragophylloceras ibex - 6 cm, Fresney-le-Puceux/France

Tragophylloceras ibex – 6 cm, Fresney-le-Puceux/France

Tragophylloceras ibex has the most coarse undulations at the venter.

 

Phylloceras heterophyllum (SOWERBY, 1820)

Phylloceras heterophyllum, 12 cm, Kettleness

Phylloceras heterophyllum, 12 cm, Kettleness

A large 3D preserved Phylloceras is most fossil collector’s dream – it still is for me, the largest Phylloceras I’ve found is about 4″ / 10 cm…

The specimen pictured above has been purchased from Mike Marshall.

Phylloceras is a genus which can get quite large, probably one of the largest genera in the Yorkshire lias, up there together with some of the Schlotheimia and Coroniceras genera from the lower lias.

This flattened specimen pictured below is from the falciferum zone at Ravenscar and is about 80 cm in diameter, it must have been a marvellous sight when alive, leisurely and majestically drifting through the liassic seas…
It also shows the broader waves of seconday ribbing on the body chamber that develops on larger specimen.

Phylloceras heterophyllum, approx. 80 cm, Ravenscar

Phylloceras heterophyllum, approx. 80 cm, Ravenscar

It was left in place as it was too large and possibly too fragile to attempt to split off – but I have no doubt that it will not remain there for long,

as natural erosion will soon take its toll.

AndyS

Literature :

M. K. HOWARTH, D.T. DONOVAN :

Ammonites of the Liassic Family Juraphyllitidae in Britain,
Palaeontology Vol 7, part 2, 1964, pp 286-305, pls 48-49

M.K. HOWARTH:

An Occurrence of the Tethyan Ammonite Meneghiniceras in the
Upper Lias of the Yorkshire Coast
Palaeontology, Vol 19, part 4, 1976, pp 773-777

Both these papers are available online at the Palaeontological Association at http://www.palass.org/beta/publications/palaeontology-backissues/

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3 Comments

  1. David

     /  October 6, 2014

    Hi Andy the Tragophylloceras numismale, Is it from the same bed as the grammoceras ? As I think I have one with a grammoceras on the back of it,keep up with the blog look forward to reading. David

    Reply
    • David,
      Tragophylloceras numismale occurs from the taylori to jamesoni subzones of the lower lias and therefore is about 8 to 9 millions years away from any Grammoceras of the upper lias –
      I guess you have found something different…

      All the best,
      Andy

      Reply
  2. Steve

     /  October 27, 2014

    Andy….Your not wrong there about a big Phylo is everyones dream…. I once spotted a big one fresh out of rusty corner and because it looked crushed in the body chamber and I knew no different I left it…. I told Mike later on the way home and Ive a feeling it became the one with the 30 odd tumbling dacs attached……

    Reply

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