New finds and acquisitions, June 2013

As you might have gathered, I´ve been collecting on the Yorkshire coast again at the end of March, and there are a few finds worth mentioning, that I have prepared now.

Also there are a few new acquisitions, either through generous gifts / trades from friends or purchases from fossil shops or eBay.
Furthermore, I´ve had the chance to photograph a few more ammonites from friend´s collections (you won’t see those now, though, they’re for the book)
But first things first –

New finds

Aegoceras (Beaniceras) luridum (SIMPSON, 1855)

In a recent blog post (link) I was moaning about not having found a Beaniceras yet – I had been intensely “bed walking” the relevant beds in summer last year and had only found a flattened specimen as proof that I was on the right bed and had almost given up hope to ever find one
– but when I picked up this inner whorl of a Lytoceras  this March on the beach and turned the rock around I knew I finally found one !
This small 1 cm beauty is a Beaniceras luridum, the index fossil of the luridum subzone, that got preserved in the same nodule as the Lytoceras. It is not exactly a large example, but better than nothing…

Pleuroceras anaptychus

This one looked up from a puddle at Shaun and I while we were collecting around Hawsker.
I had shown an aptychus (lower jaw) of a Peronoceras before (link), this now is an anaptychus (upper jaw) of a Pleuroceras. They’re exceedingly rare – first one I’ve found. As it happens, there has just been an article in the May issue of the german “Fossilien” magazine by Prof. Keupp describing an even more complete upper and lower jaw set of a Pleuroceras – apparently, judging from the form of the jaws, Pleuroceras was more of a krill (i.e. tiny shrimp) muncher, it did not have much of a bite…

Gifts/trades

Coroniceras deffneri (OPPEL, 1862)

I had found small (1-3 cm) specimen of this ammonite in the glacial drift at Robin Hoods Bay before, but the problem with identifying such small
Coroniceras ammonites is that usually only very large specimen are pictured in literature and inner whorls are rarely pictured / preserved – so I had not had a lot of confidence in my identification.
As part of a trade, Shaun Tymon gave me this larger (6.5 cm) specimen off the Holderness coast, which can now be confidently identified as Coroniceras deffneri – and it makes the list of specimen for the book one entry longer, since it had not originally been on there ! Thanks again, Shaun !

New purchases

Uptonia lata (QUENSTEDT, 1845)

Uptonia lata, 9 cm, Saltburn

Uptonia lata, 9 cm, Saltburn

This Uptonia lata came from Byron Blessed’s shop and had apparently been part of a larger Saltburn collection, that seems to have been sold to a couple of different dealers as lots – I think I have several different items from this collection, all have come with a characteristic small neat typewritten label.
Well preserved Ammonites from these beds are notoriously difficult to come by – you usually only find well weathered fragments…
With this one, the lower lias “wants” list is now one entry shorter and has been updated accordingly.

Harpoceras soloniacense (LISSAJOUS, 1906)

Harpoceras cf. soloniacense, 6.5 cm, Port Mulgrave

Harpoceras cf. soloniacense, 6.5 cm, Port Mulgrave

I regularly check eBay for interesting finds and this one caught my eye since it was labeled as a species that I had not come across from the Yorkshire coast : Harpoceras soloniacense.
Now misidentifications are not uncommon on eBay, but I took the chance…
Howarth’s Harpoceratidae monograph does not list it as occurring on the Yorkshire coast, but there is really no reason why it should not occur in Yorkshire – Zugodactylites braunianus was also
discovered relatively late in Yorkshire.
I’m pretty sure it really is a H. soloniacense : So the list of ammonites for the book just got another entry longer…
 AndyS

A steep learning curve or Artwork for the book

I’m currently on a steeeeep learning curve for producing artwork for the book – I’d like to include some symbolic drawings for every ammonite, so it was time for a graphics program, in this case Adobe Illustrator, to get drawing.
I would call my computer skills “advanced” without having to blush, but this is a hugely powerful and complex program and it took me the better part of a weekend to get into how this thing works in principle (and I’m sure I barely scratched the surface…) and to produce some simple graphics.  I prefer learning a new program this way, I just need a meaningful, yet simple enough project to get started.

Every ammonite species in the book will have a symbol showing which type of ribbing the ammonite shows and what a whorl section to expect.
These are important diagnostic features that will be shown (apart from on the actual picture of the fossil) in a simplified graphic :

 

Whorl section and rib diagrams for the book

Whorl section and rib diagrams for the book

If you noticed the little stylized ammonite in the lower right corner – in the book you’ll see a lot more of it – have a guess what for !

 

Abundance (or rarity...) indicators for the book

Abundance (or rarity…) indicators for the book

 

Every species page will show a set of these, indicating the abundance (or rarity) of the species.
This of course can only be an estimation from experience – even after 24 years there can be beds I have not found yet where a seemingly rare ammonite
occurs in abundance…

 

To keep your withdrawal symptoms at bay, I will shortly post more about “real” ammonites from my spring collecting trip.

 

AndyS

Happy 1st birthday or I listen to what you search for

Aegoceras (Androgynoceras) maculatum, 7 cm

Aegoceras (Androgynoceras) maculatum, 7 cm

(Disclaimer : No ammonite has been permanently damaged in the process of making this picture)

 

It does not seem like it, but it´s to the day one year and 44 (including the first) blog posts since I´ve started it…

so Happy 1st Birthday, Blog ! 

The folks from WordPress do provide some nice statistics, and I must admit I do look at it frequently to see who´s looking for what…
There have been over 15000 views from visitors coming from 65 countries – that´s still some way from world domination 🙂 ,
but I continue to be amazed by the reach of this tool called the internet…

 

Countries with more than 10 visits

Countries with more than 10 visits

 

There is some statistics at what people look at when they´ve reached my blog, unsurprisingly the home page is at the top, being the main landing page.
Almost 600 people (or some repeatedly…) wanted to know a little bit about me, but clearly the most visited ammonite post by far is the one about
the Arnioceras species – it is a very popular ammonite, being sold often on auction websites, and I hope I could provide some help in identifying them.

 

Top visited pages of the blog

Top visited pages of the blog

Of course it does also interest me what people look for when they reach my blog through the use of search engines.
The top 20 list tells me that some people use search engines as a bookmark replacement (it´s andysfossils.com, guys ;-)), but also
that Holderness ammonites and again Arnioceras are very popular topics. Some Amaltheus species, Amauroceras, Gagaticeras also feature highly
and I think I´ve covered these well; Psiloceras, Aegoceras, Pleuroceras are still to be done and I know you´re waiting for those probably just as
much as for the second part of the Dactylioceras post (allthough there most probably will be an intermediate step before I cover the upper liassic Dactylioceratidae).
Somewhat unintentionally (but in hindsight not unwelcome), the wants lists do create some kind of an attraction point for the blog since they provide a search engine
target for all the rare ammonites that I still would like to photograph.

 

Top searches in search engines that led to my blog

Top searches in search engines that led to my blog

 

Some people have asked for the estimated completion of the book, I´m hoping to complete it in 2014, coinciding with the 25th anniversary of our first visit
to Robin Hoods Bay. It´s still some way to go, I´m currently working on getting my layout template finished in Adobe Indesign, so that I can truly begin writing pages of the book.

 

AndyS

Twice bought and three times found or Why finding the fossil yourself is best…

Amaltheus gibbosus (SCHLOTHEIM 1820), Prince Charles Cave, Isle of Skye, 8.5 cm

Amaltheus gibbosus (SCHLOTHEIM 1820), Prince Charles Cave, Isle of Skye, 8.5 cm

In my Amaltheidae post (link) I had shown you a very nice small specimen of Amaltheus gibbosus, that I had purchased from Mike Forster via Mike Marshall´s shop.

Quite recently, I had to succumb to temptation again ;-), when Mike offered a larger calcite preserved Amaltheus gibbosus from Skye – Amaltheus gibbosus according to literature is not common on the Yorkshire coast so I had basically given up finding one myself.
I was grateful to be able to plug that hole in my collection with these beautiful specimen, but why is it just not the same as finding one yourself ?
Some of the better finds start inconspicuous – and it was just like that with the following find I´d like to present you now.
When picked it up as a beach pebble at Hawsker it was then just showing a whorl cross section on the surface, and I usually investigate to see if there´s more of it…
I tried to split the rock at the ammonite, but another piece of rock broke off and showed the cross section of a second ammonite – time to bag all the pieces and take a better look during preparation !
Specimen as found with section of whorls on both pieces, oolitic structure can be seen

Specimen as found with section of whorls on both pieces, oolitic structure can be seen

Now when I removed the matrix plug in the umbilicus  of the first ammonite I knew it was something special:  There are characteristic spines on the inner whorls – It´s an Amaltheus gibbosus !

Amaltheus gibbosus (SCHLOTHEIM 1820), Hawsker Bottoms, inner whorl, width of view ca. 2.5 cm

Amaltheus gibbosus (SCHLOTHEIM 1820), Hawsker Bottoms, inner whorl, width of view ca. 2.5 cm

With this one I found after prep (I had to remove some of the remnants of the badly crushed body chamber) that it does show a bit of what is thought to be similar to the black wrinkle layer on a nautilus : A bit of specially formed shell secreted on the outer side of the inner whorl to prepare for buildup of a new bit of body chamber and supposedly helping the animal to get a better “grip” of the mantel on the shell. QUENSTEDT in 1885 called them “Bauchstreifen”  (belly stripes) since with the Amaltheidae they are consisting of spiral stripes in the dorsal overlap of the outermost whorl with the inner whorl.
Amaltheus gibbosus (SCHLOTHEIM 1820), max. width 9 cm, remnanst of wrinkle layer marked

Amaltheus gibbosus (SCHLOTHEIM 1820), max. width 9 cm, remnants of wrinkle layer marked

What would the second one that I had broken in two during my splitting attempt be ?
I quickly glued back together the pieces…
Preparation was not easy, it is never with spiny specimen. Luckily the matrix  was just soft enough so I could air abrade the inner whorl and the keel with high pressure, revealing this second, even nicer specimen of Amaltheus gibbosus.
Amaltheus gibbosus (SCHLOTHEIM 1820), Hawsker Bottoms, 6 cm diameter

Amaltheus gibbosus (SCHLOTHEIM 1820), Hawsker Bottoms, 6 cm diameter

There was something else about this rock that I somehow remembered from an earlier find : The matrix is oolitic, i.e. there are many small calcareous, sphaerical grains made up of thin concentric layers embedded in the rock, characteristic for some of the ironstone seams on the coast, in this case I think it must be the Raisdale seam.
I knew I had seen this before on the underside of an Amaltheus fragment that I had found at Staithes in 1994 and labeled as Amaltheus margaritatus. When I looked at it again in the drawer now, I realized it is also an Amatheus gibbosus, the spiny inner whorls had just been badly eroded which had made recognition difficult ! I  must have subconciously known it was something special though, since I held on to it for such a long time even though it´s just a fragment…
Amaltheus gibbosus (SCHLOTHEIM 1820), Staithes, width of fragment 5 cm

Amaltheus gibbosus (SCHLOTHEIM 1820), Staithes, width of fragment 5 cm

These 3 specimen really show that you learn so much more when you try to find an ammonite species yourself : First of all PATIENCE but secondly a lot more about the lithology of the beds you´re likely to find the ammonite in…

And then there´s the story behind the find, the memories and the “relationship” (I put this in quotes – it somehow sounds so nerdy) you build up when prepping the fossil.

I´m sure both Mike Marshall and Mike Forster did have the same sort of feelings when finding and prepping the fossils they´ve sold to me, since it shows in the quality of their prepwork. But this does not translate in any other way – memories can´t be sold – that´s why finding the fossil yourself is best, you just look at it differently, because you know it´s history from  when it just was a pebble on the beach to the final state when you put it in your drawer or display (or your blog…).

AndyS

No new species this time or Ammonite pathologies

Dactylioceras semipolitum, 6 cm, showing both sides

Hildoceras semipolitum, 6 cm, showing both sides

From time to time you might come across ammonites that look like a known species but then again they are different.
Just like the above ammonite. I had been looking at it when I was selecting the ammonites for one of the previous posts (it´s a Hildoceras semipolitum),
but something just wasn´t right :
It has a steep smooth (apart from growth lines) umbilical wall with a sharply angled edge. The ammonite is like that as far as one can see down the umbilicus.
I was looking through my books to see what it could be – H. semipolitum does not have such a sharply angled umbilical edge – until I realized it is “just” a pathology
when I turned the ammonite to the other side : There it´s just like a normal H. semipolitum should be.
Some pathologies are just like that, only a small change, a missing rib, a slight change in ribbing pattern on the body chamber, a healed fracture etc, but overall the species is still recogizable. For others the change is more drastic: a missing keel, a complete change in ribbing pattern starting very early in the shell, a completely asymmetric shell etc. leading authors in previous centuries to create new species for them, examples are Hildoceras walcotti, Monestieria errata .
"Monestieria errata", 4 cm, a Cleviceras sp. forma aegra circumdata

“Monestieria errata”, 4 cm, a Cleviceras sp. forma aegra circumdata HÖLDER 1956

Complete loss of keel or any other structural elements on the keel.

Today it is generally being recognized that these changes in the ammonite shell might have been caused by predators, parasites, diseases or interaction with other
hard-ground settling organisms like bivalves or tube worms and have set up so called “forma aegra” or “sick form” types, describing the pathologies as what they are.
“Sick” forms sometimes offer interesting glimpses into how ammonite shell growth worked and how amazingly adaptable these animals really were.
We may never fully know what caused them in all cases , only where an external cause like a settling oyster, is still preserved with the ammonite, the cause becomes obvious.
Androgynoceras lataecosta with "hook", overgrown bivalve or worm,  6 cm

Androgynoceras lataecosta with “hook”, overgrown bivalve or worm, 6 cm

A relatively common pathology : A bivalve or worm settled on the shell and was overgrown by the ammonite – a typical “bend” is created.

I´d like to show some that I have accumulated over the years, either found myself or bought from known fossil dealers.
They do represent only a portion of the described pathology types, I may add additional ones when I should find them…

forma aegra juxtacarinata HÖLDER 1956

Asteroceras sp. forma aegra juxtacarinata, cast, 5 cm

Asteroceras sp. forma aegra juxtacarinata, cast, 5 cm

Keel drawn out and relocated to the flank – it seems like the keel producing tissue was stretched to the flank and produced the keel there.
This specimen is a cast kindly given to me by my friend Klaus.

forma aegra cicatricocarinata HELLER 1964

Pleuroceras paucicostatum forma aegra cicatricocarinata HELLER 1964, 7 cm

Pleuroceras paucicostatum forma aegra cicatricocarinata HELLER 1964, 7 cm

Keel, visible on the right side, “inversed” on the left side – the exact part of the shell where it happened is eroded…

forma aegra substructa HÖLDER 1973

Catacoeloceras sp. forma aegra substructa HÖLDER 1973, 4 cm

Catacoeloceras sp. forma aegra substructa HÖLDER 1973, 4 cm

Broken out shell underlaid with new shell, bulbous shell growth at break point

forma aegra excentrica HÖLDER 1956

Zugodactylites braunianus forma aegra excentrica, 4.5 cm

Zugodactylites braunianus forma aegra excentrica, 4.5 cm, top side concave

Zugodactylites braunianus forma aegra excentrica, 4.5 cm, underside convex

Zugodactylites braunianus forma aegra excentrica, 4.5 cm, underside convex

Dactylioceras sp. forma aegra excentrica, 8 cm, showing the bowl shape from the side

Dactylioceras sp. forma aegra excentrica, 8 cm, showing the bowl shape from the side

Growth out of the normal shell symmetry into a bowl shaped form, presumably to correct a shell imbalance

forma aegra verticata HÖLDER 1956

Peronoceras fibulatum forma aegra verticata, 7 cm

Peronoceras fibulatum forma aegra verticata, 7 cm

A punctate permanent injury of the shell secreting part of the mantle probably caused by something like a lobster’s pinch with its claws creates a continuous groove across the ribs as the shell continues to be generated.

forma aegra pseudocarinata FERNÁNDEZ-LÓPEZ

Dactylioceras sp. forma aegra pseudocarinata, 7 cm

Dactylioceras sp. forma aegra pseudocarinata, 7 cm

Special form of forma aegra verticata, the adjoining ribs forming a keel like sculpture by themselves

forma aegra concreta HENGSBACH 1996

Dactylioceras sp. forma aegra concreta, pearl 2 mm diameter

Dactylioceras sp. forma aegra concreta, pearl 2 mm diameter

Pearl growth on the inside of the shell, probably similar to what happens with pearls in bivalves.

forma aegra inflata KEUPP 1976

Dactylioceras sp. forma aegra inflata, 4 cm

Dactylioceras sp. forma aegra inflata, 4 cm

Bulbous shell growth to heal a larger hole in the shell – this specimen even has septae build into the “bulb” as the animal continued to grow !

forma aegra undaticarinata HELLER 1958

Pleuroceras sp. forma aegra undaticarinata, 3 cm

Pleuroceras sp. forma aegra undaticarinata, 3 cm

Swinging keel, most often seen with Pleuroceras.

Left/right “hybrid”

Hildoceras bifrons, 12 cm  showing a strong difference between the sides

Hildoceras bifrons, 12 cm
showing a strong difference between the sides

One of the most intriguing types of pathologies : One side shows a normal Hildoceras sculpture, while on the other the spriral grove is completely missing, it looks like a bit like a Grammoceras.
This is of course no real hybrid, but the pathological side came to be through loss/damage/sickness of the spiral grove producing part of the mantle.

forma aegra undatispirata KEUPP & ILG 1992

Dactylioceras sp. forma aegra undatispirata, 6 cm (Col. D. Groocock)

Dactylioceras sp. forma aegra undatispirata, 6 cm
(Col. D. Groocock)

Dactylioceras sp. forma aegra undatispirata, 6 cm
(Col. D. Groocock)
Dactylioceras sp. forma aegra undatispirata, 6 cm (Col. D. Groocock), keel view

Dactylioceras sp. forma aegra undatispirata, 6 cm
(Col. D. Groocock), keel view

Swinging whorl, apparently to equalize an imbalance in the shell caused by e.g. an oyster settling on the shell

The mystery…

Amaltheus stokesi without keel, 11 cm

Amaltheus stokesi without keel, 11 cm

Amaltheus stokesi without keel, 11 cm, keel view

Amaltheus stokesi without keel, 11 cm, keel view

This pathology is still a mystery. What is hidden on the other side, still in the rock ?
Is is a forma aegra juxtacarinata, i.e. the keel has been dislocated to the (invisible) flank ?
Or is it a forma aegra circumdata, i.e. the keel is just not there ?
One of these days I will prep a window into the back of the matrix and see for myself…

AndyS

Literature :

Helmut Keupp : Atlas zur Paläopathologie der Cephalopoden, Berliner Paläobiologische Abhandlungen Band 12 – Berlin 2012

What´s in the egg ?

"Boiling" sea in Robin Hoods Bay - March 23,2013

“Boiling” sea in Robin Hoods Bay – March 23,2013

I know this is kind of silly and it´s also a little late, but the opportunity is just so tempting…

We´ve just returned home from a fortnight’s holiday on the Yorkshire coast,  and most of the time it was bitterly cold and the sea looked
just like on the picture above. This usually is good for fossil hunting, since it turns the beaches around and exposes fresh material,
but can be a little problem at times, when a strong easterly wind keeps you from getting to the locations you want to go, even at low tide.

Anyway, on one of these days I found this little nodule at Bay Ness :

Egg shaped nodule as found with an ammonite just showing, height = 9 cm / 3.5 "

Egg shaped nodule as found with an ammonite just showing, height = 9 cm / 3.5 “

There are some nodules, in which the fossil is just under the surface and some exposure to seas like shown above,
where the nodule is frequently and violently bashed against other rocks, will sometimes break out a little window
showing the fossil inside.

Now when I unpacked my finds yesterday, that little egg of a nodule had to be made into an Easter greeting :

Aegoceras (Androgynoceras) maculatum (YOUNG & BIRD, 1822) , 4.5 cm / 1.75 " diameter

Aegoceras (Androgynoceras) maculatum (YOUNG & BIRD, 1822) , 4.5 cm / 1.75 ” diameter

Happy Easter !

AndyS

 

 

 

 

Common as Dacs, Part 1 or A short digression into species theory

Drawer with various Dactylioceras (Orthodactylites) sp.

Drawer with various Dactylioceras (Orthodactylites) sp.

One of the most collected and most left behind,  most loved and most hated ammonites of the Yorkshire lias must be the genus Dactylioceras, also known as the “common Dac”. It is indeed one of the most common ammonites, at least at genus level, the seas of toarcian times  must have been teeming with these animals, considering that what we find today is probably only the small fraction that made it to preservation.

In the 1970s to 1990s there have been heated scientific discussions on the classification of the Dactylioceratidae e.g. between HOWARTH and GUEX.
The following articles follow the publications by M.K. Howarth who in my humble opinion provided a framework for classification grounded in solid stratigraphy and
statistics that is very consistent to what can be observed  on the Yorkshire coast.

This is the first part of what will most probably become a multipart post showing the surprising variety, and exploring the difficulty in identification of these fossils that comes with it…

Here I will cover the Grey Shales species
Dactylioceras (Orthodactylites) semicelatum (SIMPSON)
Dactylioceras (Orthodactylites) tenuicostatum (YOUNG & BIRD)
Dactylioceras (Orthodactylites) clevelandicum HOWARTH
Dactylioceras (Orthodactylites) crosbeyi (SIMPSON)
With a little care when splitting the nodules (and taking the negative with you for a transfer of torn off whorl sections if need be) ,
a lot of the specimen can be preserved with intact mouth borders. When I do find these nodules nowadays, I tend to just
carefully investigate if an ammonite is present in the nodule without splitting the nodule horizontally which raises the rate of success
in preserving the ammonite in its entirety.
Dacytlioceras (O.) semicelatum nodule, as found, with the negative taken home as well

Dacytlioceras (O.) semicelatum nodule, as found, with the negative taken home as well

Dactylioceras (Orthodactylites) semicelatum (SIMPSON)

Dactylioceras (Orthodactylites) cf. crosbeyi, 7 cm, from Yorkshire Coast Fossils

Dactylioceras (Orthodactylites) semicelatum, coronate form, 7 cm, from Yorkshire Coast Fossils

Dactylioceras (O.) semicelatum, thick form, with coronate inner whorls, 9 cm

Dactylioceras (O.) semicelatum, thick form, with coronate inner whorls, 9 cm

Dactylioceras (O.) semicelatum, slender form, 8 cm

Dactylioceras (O.) semicelatum, slender form, 8 cm

Dactylioceras (Orthodactylites) semicelatum (SIMPSON) is the youngest of the group, found at the top of the Grey shales, beds 28 to 32 (HOWARTH 1973),
which of course corresponds to the semicelatum subzone of the lower toarcian.
The 3 specimen pictured above perfectly show what is amazing about this species : The amount of variation in the shell forms exhibited may lead a collector who looks at these 3 specimen in isolation to think these are different species, yet when viewed in the context of all the specimen found in the above mentioned beds (HOWARTH examined more than 100 specimen for his “Grey Shales” paper) , it becomes apparent that there is continuous variation between the different forms.
(If you read my blog very carefully, you might have noticed that I had previously labeled the coronate form of D. semicelatum as D. cf. crosbeyi – but after reading Howarth´s paper completely and discussing the
location of the find with Mike Marshall, I´ve come to the conclusion that it´s really a D. semicelatum)

Now that of course leads to the questions : What is a species ? When is a morphological difference enough to call it a different species ?

For living organisms this is much easier to answer than for fossils : “A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring” (from Wikipedia http://en.wikipedia.org/wiki/Species).  This is something that can be observed in the wild, today we even have genetics to measure the amount of differences in the genes. No such luck with fossils, we only have the rock and the impression and/or the petrified remains of the animal to judge from.

Thus the species definition for fossil material is not comparable to the biospecies definition, it is only based on morphological similarities, also called a morphospecies.
With a large enough population of fossils, you can quantify the variation in the fossils in measurements such as number of ribs / whorl @ diameter, whorl breadth, whorl height etc.  (see previous post ) as a statistical population variance. Comparing variances of different groups of fossils then helps to separate different morphospecies from each other. That brings us back to the semicelatum problem : When you find within that within a certain timeframe (a restricted number of beds) there is continuous variation of the fossil forms found within these beds, it is safe to assign it to the same species, then also called a chronospecies (see also Wikipedia http://en.wikipedia.org/wiki/Chronospecies, and http://www.mun.ca/biology/scarr/Evolutionary_vs_Chronospecies.htm )
But back to showing the practical differences for the collector :
To quote HOWARTH 1973 (it just hits the nail on the head, I just could not write it any better in a single sentence) :
“D. (O.) semicelatum is more involute and has higher whorls than either tenuicostatum or clevelandicum.” Ribs per whorl can vary from 45 to 80 at 70 mm diameter.
The typical semicelatum nodule usually has some pyrite content.

Dactylioceras (Orthodactylites) tenuicostatum (YOUNG & BIRD)

Dactylioceras (O.) tenuicostatum, 7.5 cm

Dactylioceras (O.) tenuicostatum, 7.5 cm

The zonal ammonite Dactylioceras (Orthodactylites) tenuicostatum (YOUNG & BIRD) (beds 20-26) has a more round whorl section,
can have a lot more ribs/whorl (between 90 and 140 ! at 70 mm) than any of the other species
(allthough there is overlap at the bottom of the range, average ribs/whorl also increase from bed 20 to 22).
The largest specimen of D. tenuicostatum seem to be smaller than the largest specimen of D. semicelatum and D. clevelandicum.
tenuicostatum-nodules are usually a bit softer than semicelatum nodules.

Dactylioceras (Orthodactylites) clevelandicum HOWARTH

Dactylioceras (O.) clevelandicum, 9 cm

Dactylioceras (O.) clevelandicum, 9 cm

Dactylioceras (Orthodactylites) clevelandicum HOWARTH (bed 19b) is more similar to D. tenuicostatum than to D. semicelatum or D. crosbeyi in being more evolute and having  a round whorl section (on the outer whorl), differences are mainly that D. clevelandicum has less ribs / whorl than D. tenuicostatum (70 at 70 mm for D. clevelandicum vs. about 100 for D. tenuicostatum) and much more robust inner whorls, usually with spines. The rate of growth in whorl breadth is higher than in D. tenuicostatum, thus the umbilicus looks deeper than in D. tenuicostatum and at same diameter, whorl breadth is greater i.e. the whorl is thicker.

Dactylioceras (Orthodactylites) crosbeyi (SIMPSON)

Dactylioceras (O.) crosbeyi, 8 cm, Mulroy collection

Dactylioceras (O.) crosbeyi, 8 cm, Mulroy collection

Dactylioceras (Orthodactylites) crosbeyi (SIMPSON) is the oldest ammonite of the group, occurring only in bed 18 of the Grey Shales.
It is a quite rare, most of the time preserved only fragmentary as body chamber with crushed inner whorls.
D. crosbeyi is similar in appearance to D. semicelatum, just slightly more involute, but whorls are a higher and a lot thicker, ribs /whorl (about 70 at 80mm) at are usually lower than on similarly sized D. semicelatum.
This first part covered the lower toarcian Dactylioceratidae that can be found on the Yorkshire coast. As you might have seen from the notes in which beds the ammonites can be found, for the lower toarcian “Dacs” it is sometimes helpful to know which bed they came from – for the upper toarcian “Dacs”, this is most of the times essential to be able to properly identify them.

The next post will not be Part II as the  continuation of this one, I have another post waiting about pathological ammonites and the following picture is just the ideal transition:

Double nodule of D.(O.) tenuicostatum, one with pathology, both about 7 cm, purchased from Yorkshire Coast Fossils / Mike Marshall

Double nodule of D.(O.) tenuicostatum, one with pathology, both about 7 cm, purchased from Yorkshire Coast Fossils / Mike Marshall

AndyS
Literature : M.K. Howarth : The Stratigraphy and Ammonite Fauna of the Upper Liassic Grey Shales of the Yorkshire Coast.
Bulletin of The British Museum (Natural History), Geology series, Vol. 24 No 4. London 1973

Recent prep results and What´s in the queue ?

Recent prep results, numbers see text

Recent prep results, numbers see text

You might have noticed, I´ve deviated from my usual schedule of posting an article about every 2-3 weeks…
There are a couple of reasons, none bad, which have kept me from posting.
Reason number 1 is that commitments from my daytime job have kept me unusually busy for January and February and this will stay that way at least until mid march,
so you´ll have to wait for  a new full article until about 3-4 weeks time.

Reason number 2 is I´ve been working on several full articles, but due to my perfectionism I was not satisfied with what I could have posted…

In the “unfinished posts” queue is the first part of the Dactylioceras article, dealing with the lower toarcian Dactylioceras species.
When looking at some of the ammonites I was photographing (every little prep fault  somehow gets exaggerated when you look through a lens…),
I found that most of them needed some form of re-prep to comply to the same standard I´ve been trying to adhere to for the book.
This is for example the reason why #7 in the photograph, a Dactylioceras (Orthodactylites) clevelandicum,  went back to the top of my prep queue :
The inner whorls needed some more attention with the fine air pen and the air abrader – it had been found in 2002 and basically went straight to the drawer at that time.

Reason number 3 is I need to clean up my prep slate before I go for my traditional spring collection tour to make space for potential new finds,
so the proportion of time prepping was higher that the one on writing…
All of the ammonites (and other fossils) have been prepped last weekend, in case you´re wondering what they are here´s the list :

  1. Dactylioceras (Orthodactylites) tenuicostatum,  7 cm
  2. Double of Dacytlioceras commune, 5 & 4 cm, thanks to Dr. Mike Howarth for helping to correct my inital thoughts on this one…
  3. A Plagiostoma sp. bivalve, 6 cm,  from the apyrenum subzone of the middle lias, a “first” for me, I´ve never seen one before from the Yorkshire lias…
  4. A combo of Amaltheus stokesi (5.5 cm) , Amaltheus bifurcus (2.5 cm) , Amaltheus wertheri (2 & 1 cm)
  5. Pleuroceras hawskerense, 6 cm
  6. Dactylioceras (Orthodactylites) semicelatum, 5 cm
  7. Dactylioceras (Orthodactylites) clevelandicum, 9 cm

Another article that´s in the “unfinished posts” queue for a long time already is about pathologies on Yorkshire coast liassic ammonites, for the simple reason that
literature about pathologies was somewhat thinly spread across a wide range of publications, most of the time with few pictures (so important for the amateur collector !).
But thanks to Prof. Dr. Keupp from FU Berlin this has now changed (http://www.geo.fu-berlin.de/geol/fachrichtungen/pal/eigenproduktion/Band_12/index.html) :
A brand new copy of his almost 400 page thick, large format, just released new atlas on cephalopod palaeopathologies has landed on my desk, I had only very little time to study it yet, but what I´ve seen so far is
spectacular (pictures galore !) and will surely set the scientific standard on this topic for years to come (unfortunately it is currently only available in german).
So through this new publication my “sick ammonites from Yorkshire” post will take a giant leap forward and will be published after the first part of the Dac post…

AndyS

 

 

 

 

 

 

 

 

 

Lytoceras or Visitors from the deep

Lytoceras ceratophagum (16 cm) and half a Cleviceras exaratum (9 cm), both pyritized

Lytoceras ceratophagum (16 cm) and half a Cleviceras exaratum (9 cm), both pyritized

In the Yorkshire lias another relatively rare family of ammonites is the Lytoceratidae – finding a Lytoceras always makes a day a great collection day, the evolute shell shape reminiscent of  a “horn of plenty” and the complex suture make the ammonites very appealing.

Lytoceras is a rather “conservative” genus that remained relatively unchanged from the lower lias up to the upper cretaceous, its rarity in Yorkshire having something to do with the water depth : Lytoceras is considered a deep water genus that only occasionally strayed into the relatively shallow waters of the Cleveland basin.

Lytoceras seems to get more common during toarcian times, this may have to do with a temporary high in water levels that also allowed tethyan species like Frechiella to migrate in.

All of the liassic species that occur in Yorkshire have a more or less round whorl section, and have more or less evolute shells where the whorls hardly touch each other. The ribs on the shell generally show a typical fimbriation – a fringing of the ribs that leads to a characteristic shell pattern. A feature of the shell that is rarely preserved due to its fragilty (both during times of embedding and during preparation…) are the so-called flares – ribs that have developed into thin collar-like extensions of the shell.

Finding a Lytoceras with preserved flares is a real highlight – prepping it a real challenge, for the thin calcite flares almost break if you look at them – preparation is only possible in softer matrices where low impact prep methods (e.g. air abrasion) can be utilized.

One thing I did not know before reading newer literature about the topic (HOFFMANN 2010) for this post was that a pronounced sexual dimorphism has been
recognized in the Lytoceratidae, with relevant macroconch / microconch pairs so far published being

Lytoceras cornucopia  /  Lytoceras (Trachylytoceras) annulosum

Lytoceras ceratophagum / Lytoceras (Trachylytoceras) nitidum

I am aware of the following liassic members of the Lytoceratidae family from Yorkshire :

Lytoceras fimbriatum (SOWERBY) 

(luridum, maculatum, stokesi subzones)

Lytoceras fimbriatum (10.5 cm) from the maculatum subzone, with preserved flares

Lytoceras fimbriatum (10.5 cm) from the maculatum subzone, with preserved flares

This is a specimen from the maculatum subzone, which is relatively rare. L. fimbriatum is more common in the luridum subzone, but rarely well-preserved.

Lytoceras cornucopia (YOUNG & BIRD)

(bifrons zone)

Lytoceras cornucopia (8 cm)

Lytoceras cornucopia (8 cm)

This specimen has no shell on the inner whorls, thus showing the beautiful suture and constrictions on the innermost whorls.
The firmbriate ribbing on the outer whorl is just visible.

Perilytoceras jurense (ZIETEN)

(thourarsense zone)

Perilytoceras jurense (4 cm)

Perilytoceras jurense (4 cm)

Perilytoceras jurense (syn. Lytoceras jurense) has an oval whorl section.
 

Lytoceras ceratophagum (QUENSTEDT)

(falcifer zone)

 see title picture
Lytoceras ceratophagum and Lytoceras cornucopia are very similar, L. ceratophagum has more radial ribbing whereas L. cornucopia has slightly rursiradiate ribbing.

Lytoceras sublineatum (OPPEL)

(bifrons, variabilis zones)

Lytoceras sublineatum (5 cm)

Lytoceras sublineatum (5 cm)

Lytoceras sublineatum differs from the other species in having a more compressed whorl section.

Lytoceras (Trachylytoceras) nitidum 

(falcifer zone)

Lytoceras (Trachylytoceras) nitidum (3 cm)

Lytoceras (Trachylytoceras) nitidum (3 cm)

This is the tiny microconch of the macroconch Lytoceras ceratophagum.
The Whitby museum type specimen list also mention the three following :
Pachylytoceras gubernator
Pachylytoceras ? peregrinum
Trachylytoceras fasciatum
Allthough HOWARTH mentions the first two in his “The Yorkshire Type Ammonites And Nautiloids of Young and Bird, Phillips and Martin Simpson” paper as holotypes,
there is no further record of them in later literature.
Both OPPEL and WRIGHT had “Ammonites gubernator” as a synonym for Lytoceras jurense (now Perilytoceras jurense), which is assumed here as well.
BUCKMAN pictures the Whitby specimen of SIMPSON´s Ammonites peregrinum as Alocolytoceras peregrinus, but this is not mentioned later, either.
Due to the fragmentary nature of this specimen, this is not followed any further.
Trachylytoceras fasciatum is considered by HOWARTH as a potential synonym of Trachylytoceras nitidum, now Lytoceras (Trachylytoceras) nitidum.
AndyS

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