Did you miss me ?

Long time, no blog post. Did you miss me ?

I´m currently working very hard. Sadly, not on the book, not on the blog, but in my bread-winning job, which is making me work a lot of hours these days,
on a very tight timeline, which has nothing to do with fossils. So I´m not really having much spare time at the moment, and if I do I need it to recover, reload my batteries so to speak. That´s also why I had to skip our traditional spring time holiday on the Yorkshire coast, which is quite annoying, but unavoidable.
So no fresh fossils at the moment…

But there is light at the end of the tunnel (or is it the oncoming train ?), and I´m slowly beginning to reclaim some of the things I love doing outside of my daily job.

This is probably the first fossil I laid hands on to do a little bit of prep work in 3-4 months, and I still have a pile of stuff to do from last year´s summer holiday…

Cleviceras exaratum, 6 cm

Cleviceras exaratum, 6 cm

It is a 6 cm Cleviceras exaratum, found at Hawsker almost exactly 5 years ago to the date. It was already mostly prepped before, but I decided to do some finishing by grinding the aperture to prepare it for the next “real” blog post which will start to cover some of the Harpoceratinae, i.e. Tiltoniceras, Eleganticeras, Cleviceras.

More soon…

AndyS

 

Gleviceras – a small Riparioceras in a big cloak

 

Gleviceras at Robin Hoods Bay is very rare – at least for me – to the point that I do not have much more than a small bit of a whorl, found at the time of the rebuilding of the sewage pipe (link) on May 1, 1996, a small bit of Gleviceras subguibalianum, from the upper Sinemurian, aplanatum subzone, Robin Hoods Bay  which is not really representable, and as usual, if you have a better one from the area, let me know !

 

The following is a Radstock/ Somerset specimen to show you what a whole Gleviceras looks like :

 
Gleviceras sp. from Radstock / Somerset, 17 cm, inner whorl not preserved

Gleviceras sp. from Radstock / Somerset, 17 cm, inner whorl not preserved

 

So did you wonder what I meant with the title of this post ?

 

Well, the astounding thing about Gleviceras is, and allthough I´ve had some discussion about it with a regular reader of this blog (that´s you Joe !) in 2012,
I’ve only relatively recently become really aware of this through Mike Howarth’s Treatise #57 volume, even as it looks very much like a member of the
Oxynoticeratidae family that it is from the outside, it starts as a tiny “Riparioceras” on the inside.

 
A 3.5 cm Gleviceras sp. from Gloucestershire shows where the journey is going...

A 3.5 cm Gleviceras sp. from Gloucestershire shows where the journey is going…

 

If you had found a pyrite “Riparioceras” at the usual size of e.g. max. 1-2 cm you’d be well excused to think that this could never,
ever develop into a Gleviceras like shown from Radstock above, and I would certainly have thought the same.

 

That is, before I saw final living (actually quite long dead) proof in this Dorset specimen on eBay below :

 
 

It is not the finest preservation that can be found, but it is just eroded enough around the umbilicus to reveal its “Riparioceras” state beginning,
something you would not see in the un-eroded state – I just had to get it, see it with my own eyes and show you…

 

Gleviceras BUCKMAN 1918 has precedence over Riparioceras SCHINDEWOLF 1962, so that “degrades” Riparioceras to a synonym for Gleviceras.

 

Just shows again, a species should never be erected on the basis of non-adult specimen only…

 

AndyS

A new Amaltheus species for the collection

Amaltheus gloriosus HYATT, 38 mm diameter

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.

Back at home I prepped the little ammonite, put a label of “Amaltheus subnodosus” on it and forgot all about it.

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)

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

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

Rib density matches well with what HOWARTH documented for another Hawsker specimen, as does the given description and a figure mentioned from QUENSTEDT´s
“Der Jura” (table 20, fig. 9-12). A very good match was also found in A.E. Richter´s Book “Südfrankreich und seine Fossilien”, page 69 fig 49.

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

F.A. QUENSTEDT 1858, Der Jura, Reprint Goldschneck Verlag 1987
A.E. RICHTER, Südfrankreich und seine Fossilien, Kosmos Frankh 1979

The lost Porpoceras…

The lost Porpoceras...

The lost Porpoceras…

I bought the ammonite in the picture above on eBay UK in the middle of December 2013 and had it sent to a friend in the Whitby area to save postage – and I did not want it to get lost in the Christmas post rush on the way to Germany.

The courier’s tracking log shows delivery on December 19, shortly before 6 pm – but our friend was not in at the time, no package was in the post box and no note to say where it was delivered instead. All searches around the house and inquiries at the neighbours brought up no result, the courier insists it was delivered – in effect it seems the ammonite is lost.

I was really looking forward to this ammonite – it looks like it could have been the center piece for the next post – Should it turn up anywhere, just let me know.

AndyS

Looped ribs and spiny tubercles – Peronoceras

The result of my between-the-years prep project : A complete Peronoceras turriculatum, 9cm, and Peronoceras subarmatum, 6.5 cm from an Alum Shale nodule, Hawsker Bottoms

The result of my between-the-years prep project :
A complete Peronoceras turriculatum, 9cm, and Peronoceras subarmatum, 6.5 cm from an Alum Shale nodule, Hawsker Bottoms

At the top of the commune subzone, the spiny members of the Dactylioceratidae family developed, probably from an intermediate form between Peronoceras turriculatum and Dactylioceras athleticum. Over the years there have been some differences of opinion under which genus (Peronoceras, Porpoceras, Catacoeloceras) the different species have to be placed,
I’m here following HOWARTH’s 1978 classification which he has re-iterated in the 2013 Treatise of Invertebrate Palaeontlogy #57, Part L, Revised, Volume 3B, Chapter 4:”Psiloceratoidea, Eodoceratoidea, Hildoceratoidea” and will describe the following species under the genus Peronoceras in this post :

Peronoceras fibulatum (SOWERBY, 1823)
Peronoceras turriculatum (SIMPSON, 1855)
Peronoceras subarmatum (YOUNG & BIRD, 1822)
Peronoceras perarmatum (YOUNG & BIRD, 1822)

So if you see the same species name under another genus, e.g. Catacoeloceras perarmatum – it’s the same ammonite. I have only added synonyms to the species below if the synonym has a different species name.

What unites these species is their stratigraphical range (lower part of fibulatum subzone, Whitby beds 60-63 of the lower toarcian)), and their principal style of ribbing (fibulation – ribs pairwise looped together, forming a tubercle at the end, see graphic below), so HOWARTH placed them into one genus instead of dividing them into different genera.

Fibulation ribbing pattern

Fibulation ribbing pattern

Genera outside this stratigraphical range (Porpoceras – upper part of the fibulatium subzone, part of bed 72) and genera without or only very occasional fibulation (Catacoeloceras, Nodicoeloceras) will be described in later posts…

Peronoceras turriculatum (SIMPSON,1855)

 
Peronoceras turriculatum, 7 cm, with constriction at mouth border

Peronoceras turriculatum, 7 cm, with constriction at mouth border

P. turriculatum has very fine ribbing until approx. 3-4 cm. Ribs are sometimes looped together, but tubercles are very small or occur only occasionally.
On the outer whorl, nearly every primary rib carries a stong tubercle. The ribs cross the venter bending foward towards the aperture, almost at an angle.

Comparison of the venter of Peronoceras turriculatum (top) and Dactylioceras cf. praepositum (bottom)

Comparison of the venter of Peronoceras turriculatum (top) and Dactylioceras cf. praepositum (bottom)

When I compared one of the ammonites from the previous post about Dactylioceras (link) - I had then called it D. cf. athleticum – with the P. turriculatum in the first picture at the top of this post, it occurred to me that there is just a small step, the addition of fibulation, to go from this ammonite to a P. turriculatum.

HOWARTH frequently names Dactylioceras praepositum (BUCKMAN) as a possible ancestor to P. turriculatum, unfortunately the figure of the holotype in BUCKMAN´s Yorkshire Type Ammonites 6, table DCCI, is somewhat blurry and I have found no other good figure in any other publication – but I think this is it – I´ll have to change the name of this one to Dactylioceras cf. praepositum (BUCKMAN).

Peronoceras fibulatum (SOWERBY, 1823)

 
Peronoceras fibulatum, 6 cm

Peronoceras fibulatum, 6 cm

 

P. fibulatum has stronger ribbing on inner whorls and fibulation is rather the rule than the exception. Ribs are crossing the venter bending forwards, but in a less angled, more convex way than P. turriculatum.

Peronoceras subarmatum (YOUNG & BIRD, 1822)

(Syn. Peronoceras semiarmatum)
Peronoceras subarmatum, 6.5 cm

Peronoceras subarmatum, 6.5 cm

P. subarmatum is a more depressed (thicker) ammonite, with strong tubercles and fibulation also on the inner whorls.

Spines of Peronoceras subarmatum

Spines of Peronoceras subarmatum

Most of the time it is difficult to preserve the full beauty of the tubercles above the internal mould, but when possible like in this specimen,
where the nodule surrounding the fossil was sufficiently weathered (I found it at Bay Ness, probably from glacial drift) to soften the otherwise hard matrix, it shows what a spiny ammonite this really was when alive…

Peronoceras perarmatum (YOUNG & BIRD, 1822)

(Syn. Peronoceras andraei)
Peronoceras perarmatum, 8 cm, slight pathology on the body chamber

Peronoceras perarmatum, 8 cm, slight pathology on the body chamber

P. perarmatum differs from P. subarmatum in having mostly wider spaced, single ribs on the inner whorls. It tends to have even thicker whorls and very strong tubercles.

The direct comparison in detail pictures shows the diagnostic differences in the pair  of compressed forms (P. turriculatum and P. fibulatum)
and the in the pair of more depressed forms (P. subarmatum and P. perarmatum) :

 

Comparison of the inner whorls between Peronoceras turriculatum (left) and Peronoceras fibulatum (right), width of view both about 5 cm.

Comparison of the inner whorls between Peronoceras turriculatum (left) and Peronoceras fibulatum (right), width of view both about 5 cm.

 

Comparison of the inner whorls between Peronoceras perarmatum (left) and Peronoceras subarmatum (right), width of view both about 5 cm.

Comparison of the inner whorls between Peronoceras perarmatum (left) and Peronoceras subarmatum (right), width of view both about 5 cm.

P. fibulatum and P. turriculatum can often be found complete, with a strong constriction on the internal mould at the mouth border  - I have not seen this on P. subarmatum or P. perarmatum (and it does not show on that one complete specimen shown above – but this one has shell on the outer whorl and is also slightly pathological, so might not be representative) but this may just be a case of not having really found a fully complete, adult specimen without shell on the last whorl – if you have one with a constriction, I´d love to see it …

Looking through the lens to photograph these specimen has also (again) all too clearly shown me the limitations in my prepwork, the better specimen (especially on the inner whorls) are the results of lucky, clean splits. One of my New Year resolutions : Don’t hurry so much, take more time to do things (fossil prep work and removing dust from specimen before photographing them – amongst other things) properly…

Have a great 2014…

AndyS

Literature :
M.K. HOWARTH : Treatise of Invertebrate Palaeontlogy #57, Part L, Revised, Volume 3B, Chapter 4:”Psiloceratoidea, Eodoceratoidea, Hildoceratoidea”, 2013
M.K. HOWARTH : “The Stratigraphy and Ammonite Fauna of the Upper Lias of Northamptonshire”, 1978

 

Merry and Happy and A prep project for the days inbetween…

Merry and Happy !

Merry and Happy !

I wish you a Merry Christmas and a Happy New Year…

For the days inbetween, I´ve picked myself a prep project that is also leading to the topic of my next post,
it is an Alums Shale nodule with a large 9 cm Peronoceras turriculatum and another smaller Peronoceras, possibly P. subarmatum.

Alum shale nodule with 2 Peronoceras, found summer 2013

Alum shale nodule with 2 Peronoceras, found summer 2013

Unsharp picture (just teasing !) of a 9 cm Peronoceras, half prepped (I just could not wait...)

Unsharp picture (just teasing !) of a 9 cm Peronoceras, half prepped (I just could not wait…)

Looking through my collection, I´ve also found some more Peronoceras specimen that need a re-prep to make them presentable,
so you´ll see the next post some time shortly before or after the new year…

Until then, have a great time and be safe.

AndyS

The Whitby Ammonite or a Whole lot of variation…

2 large D. commune adult specimen - both 10 cm - as large as they come !

2 large D. commune adult specimen – both 10 cm – as large as they come !

If there is one ammonite genus that is typical for the Yorkshire coast, more specifically for the coast around Whitby,
it has to be Dactylioceras. Do a search on UK ebay for “Whitby ammonite” and what you get is at least 50 % Dactylioceras, in natural form or sliced and polished…

The Whitby Town coat of arms (fuimus et sumus – we have been and we are – quite fitting)  bears 3 Ammonites, most likely Dactylioceras, with snake heads attached to commemorate the legend of abbess Hilda (see also link).

This all of course is due to its abundance on this stretch of coast, when walking on a beach where the cliff exposes the upper toarcian beds of the lias,
there is almost no way you cannot find a Dactylioceras (fragment), if you keep your eyes open…

A very worn pebble with a Dactylioceras sp. on Robin Hoods Bay beach

A very worn pebble with a Dactylioceras sp. on Robin Hoods Bay beach

In this blog post I´d like to introduce you to the 2 most common species of Dactylioceras : Dactylioceras commune (SOWERBY, 1815) and Dactylioceras athleticum (SIMPSON, 1855).

For the main comparison I´ve chosen two similarily sized, mid size ammonites (each about 7 cm) :

Direct comparison between D. athleticum (left) and D. commune (right), both about 7 cm.

Direct comparison between D. athleticum (left) and D. commune (right), both about 7 cm.

So what differences are there ?

Whorl section : First of all, D.commune has a whorl section that`s as round as a circle, while D. athleticum´s is more oval. I’ve re-prepped these two specimen especially to show this characteristic.

Ribbing : With D. commune the ribs run straight or just slightly convex across the venter, while with D. athleticum the ribs cross in a much more convex way, sometimes almost angled. With D. athleticum, ribbing is much finer on the inner whorls, and the rate of ribs/whorl does not change much on the outer whorls. D. commune has more coarse ribbing on the outer whorls, and finer ribbing on the inner whorls.

Both D. commune and D. athleticum occur in the commune subzone of the upper toarcian, in the Main Alum shale beds, D. commune in the lower part of the subzone (commune biohorizon) down into the Hard Shales (beds 49-54, approx. 15.9 m),  D. athleticum in the upper part (athleticum biohorizon), beds 55-59, approx. 2.8 m.(at Whitby according to K.N.Page in “British Lower Jurassic Stratigraphy”).

The maximum size for these 2 species seems to be around the 9-11 cm mark, with D. athleticum usually a bit smaller, but finding one of this size is quite rare these days. Adult specimen develop a constriction at the mouth border, which is mostly invisible on the surface of the shell, only showing clearly on the internal mold when the shell is removed. As seen on the D. athleticum above, there are some very fine ribs that mark the very end of the adult shell, when preserved.

So far, so good…

Now consider these ammonites :

More ribs, less ribs, round whorl section, oval whorl section, they all do look different from the two above ammonites that I’ve shown you as characteristical for the species, but are they different species or is it just whole lot of variation ?

These were not taken from in-situ off well-defined beds, but collected from the more or less wave rolled cliff debris on the beach, as most of us collectors do, as most of previous centuries’ collectors have done.

The answer probably is : Most of it is just natural variation within a species, with some you can take established species as a reference point and call them e.g. Dactylioceras cf. athleticum (cf : latin confer, compare to) . With some of them, if you don´t really know which bed they come from, it´s sometimes best to just call them Dactylioceras sp. – until you find another one in a defined bed.
Too little work has been done to really identify bed-by-bed variation of the Dactylioceras genus – imagine what could have been done in this regard when the big Yorkshire coast alum quarries were dug in the 18th and 19th century…

Saltwick Bay at low tide - Black Nab at the water line, the disused Alum works in the left background

Saltwick Bay at low tide – Black Nab at the water line, the disused Alum works in the left background

We’ll continue looking at the Dactylioceratidae on the next posts…

AndyS

The colours of the rainbow or Right time, right place…

Peronoceras sp., close-up of iridecent shell remnants

Peronoceras sp., close-up of iridecent shell remnants

In some rare occasions, a little bit of the original shell of an ammonite is preserved and shows all the colors of the rainbow due to an effect called iridescence, thin film interference on the fine layers of shell material.

On the Yorkshire Coast, this is very rare and mostly seen only on Dactylioceratidae, probably due to certain environmental conditions (e.g. shell structure, lack of oxygen, composition of sediment,…) during the time of fossilization in the upper toarcian that were not prevalent to that extent during any other timeframe.

Dacytlioceras commune, 7 cm, with iridescent shell remnants

Dacytlioceras commune, 7 cm, with iridescent shell remnants

Of course, you have to lucky enough to find the ammonite, before the sea catches it – rolling around in the waves very quickly destroys the fine shell layers.

The sensitive patches on this Dactylioceras commune that I found freshly fallen into a dry heap of cliff debris at Hawsker at low tide some years back would have been destroyed quickly if the  tide had reached it 4 hours later – right time, right place – that mix of luck, experience, right choice of place and more luck that can make a collecting day successful.

Happy hunting,

AndyS

Transitions or A late “straight-fingered” survivor on an upper toarcian bed of belemnites ?

Dactylioceras (Orthodactylites) cf. semiannulatum, as found

Dactylioceras (Orthodactylites) cf. semiannulatum, as found

This 7 cm ammonite sits above (or below ? – I have found no indication like e.g. a fossilized level that would allow this decision) a bed of belemnites and was found
at Hawsker March 13, 2008. The matrix around the ammonite was full of brownish-black glistening fragments of what I assume are belemnite hooks.
I seem to remember that the ammonite was not visible initially, and that I split the rock to make it smaller for the sole purpose of grinding and polishing the beautiful other side of the rock displaying the belemnite sections – the entry in my little red book seems to corroborate that – I found very little else on that day and must have been desperate ;-)
It shows again you sometimes need to look in unusual places to find something special…

Block with belemnites from other side

Block with belemnites from other side

 

This matrix almost shouts “falcifer” zone, more specifically this could be from a belemnite accumulation usually associated with the ovatum band of the upper falciferum subzone, although this is only an educated guess, since the matrix block was found ex situ and could also come from a slightly lower bed. It´s composition and appearance, however, matches very well with one given in the paper : DOYLE, MACDONALD, 1993: Belemnite battlefields.

Dactylioceras (Orthodactylites) cf. semiannulatum on belemnite block

Dactylioceras (Orthodactylites) cf. semiannulatum on belemnite block

 

What makes this ammonite interesting is that it has some of the characteristics of the Orthodactylites (literally translated from the latin as “straight-fingered”) subgenus of Dactylioceras that I described from the lower toarcian in an earlier post (link) which predominantly have straight, single, usually non-bifurcating ribs, including the classical preservation with “capped” ribs that have a kind of predetermined breaking point, as the outer shell stayed in the negative and took the top of the ribs with it.

 

Howarth described a similar type of ammonite as Dactylioceras (Orthodactylites) semiannulatum in his 1978 paper “The stratigraphy and ammonite fauna of the Upper lias of Northamptonshire”.   It is a late survivor of the Orthodactylites subgenus, in later beds replaced by ammonites with mostly bifurcating ribs of the Dactylioceras genus. I´m hesitant to attribute this specimen to this species, however, since the measurements – apart from the whorl width, which is much smaller – would rather point to Nodicoeloceras. Howarth´s D. semiannulatum specimen were also a bit smaller, though.

There is one other option, which is Dactylioceras consimile (BUCKMAN), of which I´ve got conflicting descriptions/pictures – I need to take a look at one of these in a museum.

 

The conundrum presenting itself of course is a pattern that applies to most of the Dactylioceratidae, especially the lesser known species :

  • You can’t always rely on morphology alone, you need to know the bed from which the ammonite originates to verify the species
    and this can be surprisingly difficult when you mostly collect from the cliff debris, i.e. ex situ
  • There are transitions between the different species, as this probably is. And mutations, pathologies…
  • There is always variation within a species that can not be fully recognized when you look at a small number of specimen.
  • Early descriptions  (BUCKMAN, WRIGHT, SIMPSON…) often relied on single specimen – see above.

 

No clear solution this time, then – I will however label this one, to point out my conviction that this ammonite is closer to D. semiannulatum than to Nodicoeloceras :

Dactylioceras (Orthodactylites) cf. semiannulatum HOWARTH.

 

As promised earlier, the next couple of posts (too much for just one !) will predominantly deal with the upper toarcian Dactylioceratidae – hopefully with less undefined identifications like this one – sorry you had to wait until after the 50th post (which is this one, hurrah !)  - thanks for bearing with me for so long !

 

AndyS

Yorkshire (and adjacent areas) Asteroceratinae in all shapes & forms

Asteroceras obtusum, 9 cm, Charmouth / Dorset

Asteroceras obtusum, 9 cm, Charmouth / Dorset

(Starting this post with a Dorset Asteroceras – bit cheeky, I know, but it´s going to be the only Dorset specimen in this post, I promise !)

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.

The green shelled Asteroceratinae from the old, long closed Conersby quarry in Scunthorpe, Lincolnshire are of course a visual highlight; when the shell is removed, predominantly white chambers fillings with additional greens/yellows/pinks & browns and dark chamber walls produce a striking contrast, that is highly sought after (and paid for) these days…
From what I´ve seen, theses so called “Scunnies” belong to species that are basically the same as on the Yorkshire coast.

 Opportunities to find Asteroceratinae ammonites in Robin Hoods Bay have become relatively rare;  more often than not, the beds containing these ammonites are covered by sand or rocks in Robin Hoods Bay.  Larger specimen are particularly rare, but they are there – the picture below was shot on day in March 2012 where a window down to the beds below a boulder field had opened – I was counting 6 large Asteroceras in an area of about 20 x 20 m – all of them were eroded like the one pictured. Two days later, that window had closed. Also remember – this is an SSSI exposure, please collect responsibly !

Asteroceras sp. in situ, approx. 20 cm

Asteroceras sp. in situ, approx. 20 cm

HOWARTH lists the following species of the Asteroceratinae subfamily in the Bairstow collection from Robin Hoods Bay:

Asteroceras obtusum         23 ribs / whorl

Asteroceras confusum       30-34 ribs / whorl
Asteroceras stellare          32-40 ribs / whorl
Asteroceras blakei            26-28 ribs / whorl
Aegastoceras crassum        22-26 ribs / whorl
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 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

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 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

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 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

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

Caenisites brooki, 10 cm, Scunthorpe

Caenisites brooki, 10 cm, Scunthorpe

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

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

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)
Asteroceras confusum SPATH, 1925
Asteroceras stellare (SOWERBY, 1815)

AndyS

Literature :

S. GUÉRIN-FRANIATTE : Ammonites du Lias Inférieur de France, Centre National de la Recherche Scientifique, Paris 1966
R. SCHLEGELMILCH : Die Ammoniten des süddeutschen Lias, Gustav Fischer Verlag, 2. Edition 1992
M.K. HOWARTH : The Lower Lias of Robin Hood´s Bay, Yorkshire, and the work of Leslie Bairstow, Bulletin of The Natural History Museum Geology Series Vol. 58/2, London 2002
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