Gemmellaroceras rutilans (SIMPSON, 1843), diameter 40 mm

 

In May this year, Byron messaged me a picture of an ammonite which had been found
by Ricky at Ravenscar (presumably the side towards Robin Hoods Bay, i.e. Wine Haven),
asking me for an identification.

The small ammonite has a diameter of exactly 40 mm and is preserved as a somewhat
pyritic internal mould on a small block of shelly matrix.

Significantly, this matrix also contains pieces of Pinna bivalves which is usually indicative
of the jamesoni zone, taylori subzone, of the lower lias – so no guessing necessary for
identifying the stratigraphy, which can be a big bonus when identifying ex-situ ammonites
from the Yorkshire coast.

At that point I was prepping another small specimen from this zone with an Apoderoceras
so I figured it had to be the same thing and identified it as such…

A few days later Byron put this ammonite up for sale and (you know me) I could not resist….
The ammonite was picked up from Byron´s shop in Whitby this summer and went home
with me. Usually, ready-for-drawer ammonites like this one queue up on my desk for final
identification and a label.

A few months later, until this weekend in fact, it was still sitting on my desk for
identification…It had turned out that identification was not as easy as I had hoped,
it was not an Apoderoceras, no nodes on the thin ribs, and from the small remaining
bits of shell it looks like the ribs would barely be visible under the shell…

The ammonite at 40 mm diameter is a mostly complete adult, as the crowding of the sutures
suggests, and has about half a whorl of body chamber preserved.

Trifid lateral lobe of the suture (marked L) and crowding of sutures towards the aperature, indicating an adult specimen

I had identified a possible match with Epideroceras sociale, especially with the style of
ribbing on the inner whorls, but since Epideroceras is getting much larger and develops
much thicker whorls when adult, this match fell through…

Having about half an hour to kill before lunch would be ready this Sunday,  I was
browsing Howarth´s 1962 “The Yorkshire Type Ammonites and Nautiloids of YOUNG
and BIRD, PHILLIPS, and Martin SIMPSON”, looking for something entirely different
and stumbled across the pictures of Polymorphites rutilans (SIMPSON, 1843)
(now Gemmellaroceras rutilans) on table 15 – a perfect match with the crenelated keel
of my ammonite.

The ribs crossing the venter created a crenelated venter

I had not had Gemmellaroceras on my list assuming they would only be much smaller
(like Gemmellaroceras tubellum), but reading HOWARTH´s
“The Lower Lias of Robin Hood´s Bay, Yorkshire, and the work of Leslie Bairstow” again,
found that this is indeed the larger species and can be found,
(how blind can one sometimes be…)  explicitly mentioned, in Bairstow bed 530,
associated with Pinna folium…

There is another subgenus which is apparently similar, just stratigraphically slightly
older – Leptonotoceras – in which the lateral lobe of the suture is only split twice
(bifid) instead of three times (trifid) as in Gemmellaroceras – the lateral lobe is trifid
in this ammonite so we´re also clear about this.

So that´s about enough to round up this identification, and it´s also a species that can be
scratched off my “Wanted” list – done !

Scratched off the “Wanted…” list !

Now let´s see if I have the smaller species of this genus, G. tubellum, hiding in my collection
somewhere…

AndyS

* Gaetano Giorgio Gemmellaro (1832-1904) was an italian paleaontologist and geologist,
founder of the Palermo Geological museum and researcher, among many other topics,
on sicilian pygme elephants. Alpheus Hyatt named the genus after him in 1900, presumably
to reciprocate for an honour which  Gemmellaro had bestowed upon him in 1887 by naming
a permian ammonite genus (Hyattoceras) after him…

Amaltheus gloriosus HYATT, 38 mm diameter

I found a species new to my collection today – in the drawer !
After almost 25 years collecting on the Yorkshire coast, finding a species that I do not have yet in my collection does not happen very often.
I was labeling some finds that I had prepped recently and was sorting them into the appropriate drawer, when I looked again at an ammonite that
I had found at Hawsker in the summer last year. I remember the circumstances of that find very well, there was a piece of dark shale that had fallen from somewhere higher in the cliff, and the piece looked like it came from the upper lias. There was a small greyish nodule embedded in that piece of shale and something that looked like a separate, non-nodularized whorl of a flat ammonite beside it. The nodule looked like it was rebedded, it had what looks like cracks on the outside that had been filled again with shale material. I got curious and split the nodule – and was surpized to find a small Amaltheus inside. The separate piece of ammonite whorl looked very worn and I could not really identify what it was.

So when I saw it again this morning, I took it out of the drawer and decided to take a second look…it looked different.
Counting the ribs I found it had 12 ribs at around 20 mm, and 17 ribs at around 35 mm, compared to an A. subnodosus with 16 ribs at 20 mm and 21 ribs at 34 mm.

On the inner whorls the tubercles are very strong and almost elongated, the tubercles almost are the ribs, on an A. subnodosus they are a lot less strong.

Direct comparison between Amaltheus gloriosus (left) and similarliy sized Amaltheus subnodosus (right)

My conclusion is that this ammonite is an Amaltheus gloriosus HYATT, 1867.

And that´s one more ammonite off the “wants list”- the Yorkshire coast never ceases to surprise me !

AndyS

Literature

M.K. HOWARTH 1957, The Ammonites of the Family Amaltheidae in Britain, Palaeontographical Society

Asteroceras obtusum, 9 cm, Charmouth / Dorset

Asteroceratinae is a subfamily of ammonites more usually associated with the Dorset coast, the beautiful, sometimes large, ammonites in all shades of calcite from deep brown to light yellow come to mind. In Yorkshire species like Asteroceras or Eparietites  are less common in such nice a preservation, and I have not seen the beautiful brown & honey colors –  greys & blacks are more prevailing in Yorkshire coast specimen;  body chambers without inner whorls can be seen quite often on the scars, complete specimen can usually only be found in concretions, which are usually soft enough to prep the ammonites completely with shell – carefully done, it reveals shell details that you rarely see from anywhere else.

Asteroceras sp. in situ, approx. 20 cm

Aegasteroceras sagittarium  22-26 ribs / whorl

Caenisites turneri             42 ribs / whorl

Caenisites brooki              40 ribs / whorl

Eparietites impedens        shallow ribs, keel very prominent, no real keel furrows

Eparietites bairstowi         large specimen with almost no ribbing

Epophioceras landrioti      almost like an Echioceras

As a rule of thumb, the genera can be distinguished in the following manner :Asteroceras – more or less thick whorls with keel
Aegasteroceras – more or less thick whorls without keel
Caenisites – thinner whorls with keel, fine deep ribbing, deep keel furrows, more evolute than Eparietites, umbilical width between 40 and 50 %
Eparietites – thinner whorls with very prominent keel, fine shallow ribbing, more involute than Caenisites, umbilical width between 22 and 35 %
Epophioceras – looks more like a Gagaticeras or an Echioceras, only in this subfamily due to similar suture.

(Numbers  given for ribs/whorl and umbilical width are from SCHLEGELMILCH and GUÉRIN-FRANIATTE, for references see below)

Of course, some of these species can also be found on the Cleveland coast and in the glacial drift at the Holderness coast.

Asteroceras obtusum (SOWERBY, 1817)

Asteroceras obtusum seems to be relatively rare, I have only a few specimen in my collection. It´s whorls are thicker than the ones

from A. blakei and it has the least ribs/whorl of the species.

Asteroceras obtusum, 5.5 cm, Robin Hoods Bay

Asteroceras obtusum, 5.5 cm, Robin Hoods Bay, keel view

Asteroceras blakei SPATH, 1925

Asteroceras blakei seems to be the most common species at Robin Hoods Bay, at least in my collection…

I´ve shown you Keeley & Adrian specimen of this species before (link), here is another one :

Asteroceras blakei, 6.5 cm, Robin Hoods Bay

Aegasteroceras cf. crassum SPATH, 1925

This is a thicker species of Aegasteroceras which has even less of a keel compared to Aegastoceras saggittarium.

Keel shot here only, the specimen needs a bit of re-prep. It was on my “wants list” before, I “found” it in my drawers while

working on this post…

Aegasteroceras cf. crassum, 7.5 cm, keel view

Aegasteroceras sagittarium (BLAKE, 1876)

I have many Aegasteroceras saggittarium in my collection, but none of the are very well preserved.

Here is a keel shot only to show the almost non-existent keel. There are some more that need re-prepping…

Aegasteroceras sagittarium, 5.5 cm, Robin Hoods Bay, keel view

Caenisites tuneri (SOWERBY, 1824)

Caenisites turneri seems to be very rare from Robin Hoods Bay, this is the only specimen I have found so far, and it is badly crushed in the inner whorls.

Caenisites turneri, 5 cm, mostly crushed, Robin Hoods Bay

Caenisites brooki (SOWERBY, 1818)

Caenisites brooki is also quite rare and sits in the middle between Eparietites impedens and Caenisites turneri : It´s middle keel rises above the

side keels and it has deeper ribbing than Eparietites. It has deep keel furrows, it´s umbilical width is somewhat variable, I guess there are many intermediates
between the genera.

Direkt comparison between Eparietites impedens (left) and Caenisites brooki (right), both 3.5 cm, Robin Hoods Bay

Caenisites brooki, 10 cm, Scunthorpe

Caenisites cf. brooki, 3 specimen 4-5 cm, Robin Hoods Bay, purchased from B. Blessed

The 3 ammonites in this specimen seem to be intermediates beween C. brooki and C. turneri –

thicker whorls than C. brooki, a bit more evolute, but the keel rises above the side keels.

Eparietites impedens (YOUNG & BIRD, 1828)

The Eparietites shown here is a find from July 2013. It is a beautiful specimen, that is comprised of most of the shelled inner whorls of a larger specimen

shown in the previous post – sadly the outer whorl was mostly eroded. It´s most diagnostic feature is the strong keel that has no real side furrows.
I´m particularly fond of this specimen since it has most of it´s shell preserved, and it has such a nice fine structure…

Eparietites impedens, 8 cm, Robin Hoods Bay

Species I think I do not currently have in my collection from Yorkshire include :

Eparietites bairstowi HOWARTH 2002 (some doubtful large specimen, mud filled chambers with no inner whorls)

Epophioceras landriotti (D´ORBIGNY, 1849)