All posts in category Other fossils

Who bit my ammonite ?

I showed you this 12.5 cm specimen of an Angulaticeras in the previous post,
but cunningly only from one side, stating it has these peculiar holes in what is left of the shell.
This specimen is wholly septate, the body chamber is completely missing, as is a part of the outer whorl.

Here now both sides of the specimen, with the location of the holes marked in different
colours for the different sides.

Both sides of ammonite shown with bite marks shown in red and blue, also possible sratch marks and tear-outs

Both sides of ammonite shown with bite marks shown in red and blue, also possible sratch marks and tear-outs

Interestingly, there seem to be roughly corresponding holes on both sides of the shell,
although this is hard to see side by side.

After a bit of Photoshop magic, making the above pictures slightly transparent and carefully
aligning the layers over each other, a more interpretable picture emerges :
Picture overlay of both sides of the ammonite, showing the bite marks. Green dots showing a potential jaw alingnment

Picture overlay of both sides of the ammonite, showing the bite marks. Green dots showing a potential jaw alignment

Tentative alignment of the holes has been added in green dots in form of a triangular jaw
geometry (and this is of course not the only possible interpretation, as we shall see),
which would indicate the application of at least 3 bites of a marine predator
e.g. Ichthyosaur, plesiosaur, crocodile, large fish !
If one follows this interpretation, the first two possible bites probably were softer bites
to grab the ammonite, stop it from escaping while the third bite targeted the juicy
content of the body chamber, biting it off thus separating meat from shell.

Diameters of the single holes on each of the sides vary between 4 and 8 mm,
there appear to be several combined holes from the consecutive overlapping
bites. There are no visible rims around the edges of the holes, and no apparent
shell material in the holes, but the holes seem to be fully sediment filled and could
be explored more by further preparation.

Single, double and triple bite marks

Single, double and triple bite marks

Detail of shell with double bite mark, scratch mark and bitten off shell line

Detail of shell with double bite mark, scratch mark and bitten off shell line

Detail of bite mark with tear-out

Detail of bite mark with tear-out

Now there’s some very interesting literature about cretaceous ammonites showing
potential mosasaur bite marks, and some also very interesting literature showing
that these marks could also be crushed-in resting scars of patellid limpets
(literature references see below).

Kase, Seilacher et al had 1998 offered a convincing alternative explanation for the
holes to be limpet resting scars punched through by sedimentary pressure.
They had even found limpet scraping traces and limpet shells to underpin their theory,
so some significant doubt was cast over the mosasaur bite hypothesis,
as tests performed by them on nautilus shells also showed that shells were more
likely to disintegrate  than be punctured when bitten.

In 2001, the mosasaur bite hypothesis was defended again (Tsujita & Westermann),
by examining a larger number of bitten shells and coming to the conclusion that,
given the rarity of limpet shells in the cretaceous Bearpaw formation of Alberta,
the mosasaur bite explanation was more likely.

In 2009, as part of an MSC thesis (D.S.King), experiments again performed on nautilus
shells,  showed that punctures were very possible on the nautilus phragmocone,
that certain double holes could result from crooked teeth and that indentations
do no always necessarily have to be on both sides of a shell.

In this case however, the limpet hypothesis seems very unlikely, the holes are
relatively small, they are on the phragmocone, and there are also roughly
corresponding holes on the other side of the ammonite.

The dense lobes on this entirely septate part of the shell would probably
have provided enough structural integrity to stop this part of the ammonite
shell being broken apart in contrast to the tests having been conducted the
nautilus shells, which caused the nautilus shells to split entirely.
Other tests (King 2009) showed that holes punched into she shell are even
possible on a nautilus shell, and that it is possible that not all teeth need to
leave a mark on the shell, when the predator only administered a less powerful bite.

Interpretation as bite marks is always more interesting and headline-grabbing,
but I think in this case probability for this theory to be true is very high.

As for the question in the title of the post (who actually bit the ammonite),
I guess we can only speculate.
The bite is relatively small, the angle would probably favour a slender snout.
We know that ichthyosaurs were around, less fossil remains are known of
plesiosaurs or crocodiles in the Yorkshire lower lias.
Diameter of the holes would probably not rule out any of the predators,
so unless somebody more knowledgeable in the diagnosis of bite marks comes
up with a clever idea, the question has to remain unanswered.

The whole appearance of the Angulaticeras is extraordinarily similar to what
Kaufmann & Kesling 1960 described from cretaceous Placenticeras,
albeit this one is about 100 million years older and of course mosasaurs
did not exist then.
In my opinion this is a very likely example of reptilian bite marks on a
lower liassic ammonite and  generally the oxycone shell of these types
of ammonites offers a favourable chance of preservation of these bite marks.

I had initially intended to also provide a 3D image of the ammonite,
but due to my limited spare time at the moment and the requirements
of the method (100+ pictures…) this will have to wait until a later time –
I did not want to hold posting of this blog post for much longer.

If you do have similar ammonites or want to provide feedback on this
blog post, please use the e-mail address provided in the “About me”
section of this blog.

The ammonite shown is not for sale, and my intention is to donate it to a
suitable UK museum in the future.

AndyS

Literature : (links were checked at time of posting but are not guaranteed to be functional for any length of time)

  • Mosasaur bites and limpet scrapes – Wired April 11, 2012
  • The Abilty of Mosasaurs to produce unique puncture marks on ammonite shells, MSC thesis Daniel Steven King, Bowling Green State University 2009
by andysfossils on September 30, 2018  •  Permalink
Posted in Ammonites, Literature, Other fossils
Tagged

Posted by andysfossils on September 30, 2018

https://andysfossils.com/2018/09/30/who-bit-my-ammonite/

Crinoid and starfish travel for a prep and a loan

Crinoid unprepped, picture courtesy of R. taylor

Crinoid unprepped, picture courtesy of R. Taylor

Another fossil travel story – but this time a crinoid and some associated starfish.

The story began when Robert posted a picture of a crinoid he found on the Yorkshire coast
in the Yorkshire Fossil Collectors facebook group. It looked very large and quite interesting,
so I asked him if we could meet when I would come to Yorkshire for our summer holidays
and take a “live” look. We agreed on a date and Robert came visiting with his crinoid,
see a pre-prep picture of it above.

Robert had protected the surface of the fossil with a thin coat of paraloid, but I could
instantly see the potential of this fossil, and also that there might be more in the rock –
starfish !

The surface of the slab was relatively soft, I could scratch it with a fingernail, which is a
good sign that this fossil can be easily prepared using an air abrader with iron powder
as an abrasive. I offered to prep it for Robert without charge and give it back to him on
our next visit to Yorkshire.

Now don’t get me wrong here – I neither do preparation as a business, nor do I encourage
readers to ask me to prep something for them -if I see a fossil that I see potential in and
I’m sure I can prep it well, I will offer to do so. So don’t ask me, I will ask you…

Anyway, Robert agreed to my offer and I took the fossil home to Germany with me at the
end of our holidays.Preparation commenced relatively soon after our return from
Yorkshire and it was as simple as I had hoped, the matrix covering the fossil melted
like butter under the low pressure stream of the abrasive.

When I first directed the abrasive across the crinoid remains, I was somewhat taken
aback because the crinoid arms suddenly appeared in a creamy white when the matrix
and the paraloid covering it were removed – I feared they would be soft crystallized
calcite, but they turned out to be stable and just fine.
Crinoid and starfish prepped
Crinoid and starfish prepped
Additionally, as suspected, the slab also contain the remnants of up to 6 starfish, with
two very decayed ones on top of the crinoid and 4 on the side of it. When most of the
matrix and paraloid was removed, which took about 4 hours of prep time,
I sent some pictures to Robert.

In September, Robert went to the Scarborough Fossil Festival at the Rotunda and
showed the pictures to Dr. Timothy Ewin, senior curator for Echinoderms at the
London Natural History Museum, who, in Robert’s words, got “very exited” seeing
the pictures and asked if he could see more detailed pictures of the crinoid and
of the starfish.

The Rotunda in Scarborough

The Rotunda in Scarborough

I sent some more pictures and an e-mail discussion between the 3 of us ensued with
the result that the crinoid has tentatively been identified as a large Isocrinus robustus
and the starfish needing a detailed inspection on the “live” specimen to identify them.

Since my family and I had planned a visit in London in October anyway,
I offered (of course conditional on Robert’s agreement to do so) to take the specimen
to London for Dr Ewin to see it.

Robert and Dr. Ewin agreed, so I finished the preparation of the specimen in an
additional 2 hours and packaged it very safely for the journey
(I luckily still had some foam left from the Ichthyosaur donation…)

Packaging material
Packaging material
Crinoid ready to go
Crinoid ready to go

The transport was relatively straightforward, of course you get the
“what the heck have you got in there ?” question from the x-ray folks at the airport,
but after opening the case and allowing a swab for explosives,the crinoid went
on the flight to London.

Natural History Museum, London
Natural History Museum, London

Later in the week, we met with Dr. Tim Ewin in the Natural History Museum, and after
a quick inspection we agreed that this was indeed a very complete and large
Isocrinus robustus, and the starfish were not Tropidaster, but maybe Uraster or
something similar but that would require further detailed inspection.

The material is surprisingly similar to the legendary Mickleton tunnel fossils,
which I could see later on in the collections.
Specimen will be on loan to NHM and be given back to Robert, maybe on occasion of the
next Fossil festival ? According to Dr Ewin, there’s  a good chance you might see this
specimen pictured in the upcoming Yorkshire Lias guide…

 

Many many thanks to Robert for entrusting  me with his crinoid, both for the preparation
and the transport to the NHM, it was a pure pleasure to prep. Many thanks to
Dr. Timothy Ewin for keeping the important contact with us collectors and of course
for the tour of the NHM crinoid and starfish collections 🙂

And the next post will again be an ammonite one, I promise 🙂

AndyS

by andysfossils on November 1, 2015  •  Permalink
Posted in Other fossils, Preparation

Posted by andysfossils on November 1, 2015

https://andysfossils.com/2015/11/01/crinoid-and-starfish-travel-for-a-prep-and-a-loan/

An ichthyosaur travels…and finds a new home

Ichthyosaur paddle bones laid out on a piece of foam for taking measure

Ichthyosaur paddle bones laid out on a piece of foam for taking measure

It was in March 1995, Klaus and I were searching the lower lias reefs at Robin Hoods Bay
for ammonites when I stumbled across something exposed at the surface of the shale that
looked like a hand… it turned out to be an Ichthyosaur paddle.

We spent a few hours excavating the mostly disarticulated bones, before the upcoming tide
chased us away. Unfortunately I do not have a picture of how the bones looked like when in
situ – this was pre-digital, and my wife had the camera with her…and we did not want to
wait another day to return with the camera, risking we would not find the bones again.
In hindsight that probably was a good decision – there was a bit of a storm the night and we
barely found the place again next day for checking if we had left any bones !

In the end there was one mostly complete paddle, a few vertebrae, some jaw sections partly
with teeth, some isolated teeth and an isolated hind fin femur.

Ichthyosaur paddle fitted in to a box and the piece of foam

Ichthyosaur paddle fitted in to a box and the piece of foam

A cover of bubble wrap for additional protection

A cover of bubble wrap for additional protection

A sheet of foam on top ...

A sheet of foam on top …

...and a lid on top and this one´s ready to travel !

…and a lid on top and this one´s ready to travel !

The ichthyosaur remains stayed mostly unprepped, only the paddle and two jaw sections
(I gave one to Klaus for his help salvaging the bones) were prepped.
The preparation was somewhat tricky since it could only be done mechanically – the bones
are not embedded in any kind of nodule and are relatively soft, so no air abrasion was
possible.

Ichthyosaur jaw parts and teeth laid out waiting to be packed...

Ichthyosaur jaw parts and teeth laid out waiting to be packed…

Fast forward almost exactly 20 years (doesn´t time fly ?)…

Discussing bones in the Yorkshire Fossil Collectors Facebook group, I mentioned the
finds we made in 1995 and was persuaded by a collector specialized on bones
(that´s you, Mark !) to post a few pictures.
Dean Lomax and Nigel Larkin expressed an interest in the fossils due to their rarity
(ichthyosaur material from the lower lias is a lot rarer in Yorkshire than from the
upper lias), so I mentioned that I would be happy to donate these (I´m really more
of an ammonite collector, you might have guessed), if they could come up with a
museum which would take them.

Contact was made with Sarah King, curator at the Yorkshire museum in York and
after a few e-mails back-and-forth a meeting on August 24 was arranged to hand
the fossils over to Sarah.

Klaus kindly donated his jaw section back to me, so the bones were again complete
as found.

...laid out on a thick sheet of foam for getting measured...

…laid out on a thick sheet of foam for getting measured…

To get the fragile ichthyosaur bones back to Yorkshire (talk about carrying owls to Athens…)
boxes were fitted with several layers of foam, one at the bottom for cushioning, one with a
cut-out of the fossils shape in the middle, and one at the top to cover.

...foam is being cut out ...

…foam is being cut out …

...the jaw parts fitted in (and you know the rest)

…the jaw parts fitted in (and you know the rest)

An afternoon of cutting foam later, the bones were safely packaged up in four boxes and
one bag (for associated bits of shale without bones).
To be able to carry the bulky (though not heavy) boxes, two large blue bags from a well
known swedish furniture chain were utilized.

All ready in the box & ready to go !

All ready in the box & ready to go !

On August 24, the bags were packed into our car and the bones made their journey to
the Yorkshire museum at York.  Sarah was met in her office, I gave her a bit of a tour
of the boxes with the bones and she in turn gave us a tour of the fossil collection
rooms in the museum.

Final hurdle was a donation panel decision in September and that was positive as well,
so everything was set.
The museum catalog number for the ichthyosaur remains is  :
YORM : 2015.618, just in case anyone needs to look it up…

Yorkshire Museum in York

Yorkshire Museum in York

Although I´m really specialized in ammonites, I can´t help myself from finding
other “stuff” 🙂 from time to time. These days, if I´d find something rare like this again,
I´d probably engage the help of Pro´s like Mike Marshall or Mark Smith to
professionally collect the bones – these guys are much better equipped and experienced
to deal with finds like this.

I´m letting this find go with one crying and one laughing eye.

One crying eye because of course one gets attached to a rare find – but it´s much better
to give it to someone much more suited to take care of this find properly and provide
access for scientific study.

One laughing eye because this frees up two large drawers for more ammonites !

Thanks to Dean Lomax and Nigel Larkin for providing the contact , to Sarah King and
the Yorkshire museum for taking care of this find and of course to the members of the
Yorkshire fossil collectors Facebook group for the many good discussions…

AndyS

by andysfossils on August 8, 2015  •  Permalink
Posted in Other fossils, Uncategorized

Posted by andysfossils on August 8, 2015

https://andysfossils.com/2015/08/08/an-ichthyosaur-travels-and-finds-a-new-home/

A moment frozen in time, part III, or A sun star by any other name would be as rare…

Plumaster ophiuroides, 11 cm with small Tropidaster pectinatus

Plumaster ophiuroides, 11 cm with small Tropidaster pectinatus

In part 2 I showed you what I then thought was a fragment of a Luidia murchisoni sun star –
well it turns out I´ve been wrong again…

In one of the fossil forums I visit, fellow collector Tarquin Bolton recently showed a fabulous
fragment of another starfish that made me re-assess my specimen and another acquisition
of a complete specimen from an old collection that I have treated myself to in 2012, shown
above.

The specimen painstakingly prepped by Tarquin, with great patience & skill removing grain
by grain of matrix with a prep needle and a modified dental descaler in about 150 hours,
shows an amazing fine structure of small ossicles similar to regular echinoids and enables
the specimen to be attributed to the genus Plumaster, more specifically to the species
Plumaster ophiuroides WRIGHT 1863, which has also been written about by
Prof. Andrew Gale (Portsmouth University) in a 2010 paper.

Fragment of Plumaster sp as found, specimen Bolton collection, picture by kind permission
Fragment of Plumaster sp as found, specimen Bolton collection, picture by kind permission
Fragment of Plumaster sp with dental descaler used for preparation, specimen Bolton collection, picture by kind permission
Fragment of Plumaster sp with dental descaler used for preparation, specimen Bolton collection, picture by kind permission
Beautiful fine ossicle structure of Plumaster arems, specimen Bolton collection, picture by kind permission
Beautiful fine ossicle structure of Plumaster arems, specimen Bolton collection, picture by kind permission

Sure enough, when I looked at the complete specimen above under magnification, I also
saw these structures, and thus it is not a Luidia, but also a Plumaster and so is the fragment
I had shown earlier.

It seems now that Plumaster is much more “common” (relatively speaking, they are still
extremely rare in absolute terms !) than Luidia, and is also quite often associated with
Tropidaster, as is the specimen shown at the top.

Plumaster is in fact, unlike Luidia (which Hans Hess placed in Solaster in 1955), not a
“true” sun star belonging to the Solasteridae family of starfish, but belongs to the
Plumasteridae, a family erected by Andrew Gale as recently as 2011.

 

Whatever their name & family , these fossil starfish are some of the rarest fossils on
the Yorkshire coast due to their fragility, both at time of fossilisation and when they are
exposed again – as so often a collector needs to be there right time & place to rescue
them from the elements and it also takes a skilled preparator like Tarquin to bring them
“to life” again properly.

 

AndyS
by andysfossils on January 24, 2015  •  Permalink
Posted in Other fossils, Preparation, Uncategorized
Tagged

Posted by andysfossils on January 24, 2015

https://andysfossils.com/2015/01/24/a-moment-frozen-in-time-part-iii-or-a-sun-star-by-any-other-name-would-be-as-rare/

Caught in the act – Xenomorphism

Xenomorphic oyster on a crushed Arietites - diameter of the Arietites 6.5 cm

Xenomorphic oyster on a crushed Arietites – diameter of the Arietites 6.5 cm

Every once in a while isolated fossil oyster shells turn up that look like ammonites, sometimes the imitation is so perfect that you take them for the real thing.
This is called xenomorphism – a shell that looks like a positive image of an other animal, e.g. ammonite, brachiopod etc.
The above pictured oyster on a flattened Arietites from Redcar (bought via eBay – Many thanks,  Dave !) is a perfect example, and this time it is not isolated from its previous settlement ground but still attached to the ammonite – caught in the act – and is complete with both shells :
Xenomorphic oyster on a crushed Arietites - side view

Xenomorphic oyster on a crushed Arietites – side view

Xenomorphic oyster on a crushed Arietites - detail of the oyster

Xenomorphic oyster on a crushed Arietites – detail of the oyster

The lower shell is attached to the ammonite shell and copies the ribbing of the ammonite. The upper, unattached shell then creates a positive image of the lower, attached shell in an attempt to create a proper closing between both bivalve shells.

 

Detail of xenomorphic oyster on brachiopod - with ribbing of the brachiopod replicated on oyster

Detail of xenomorphic oyster on brachiopod – with ribbing of the brachiopod replicated on oyster

The same thing happened with this Oyster that settled on a brachiopod : there is a faint copy of the ribbing of the brachiopod on the unattached shell of the oyster.
Oysters on brachiopods on Androgynoceras - width of specimen 6 cm

Oysters on brachiopods on Androgynoceras – width of specimen 6 cm

It seems with this specimen that hardgrounds to settle on at the time were extremely difficult to come by, this could actually be a settlement of brachiopods on an Androgynoceras ammonite, and on almost every brachiopod, there´s an oyster…

While this post quite literally was only indirectly about ammonites, the following posts will be about “the real thing” again:
The next one will be about the Phyllocerataceae (text is ready, photos still to be done), and I still need to continue with the Harpoceratinae, which will
begin with an erratum on one of the previous posts – did you spot it ?

 

AndyS
by andysfossils on September 21, 2014  •  Permalink
Posted in Ammonites, Other fossils

Posted by andysfossils on September 21, 2014

https://andysfossils.com/2014/09/21/caught-in-the-act-xenomorphism/

A moment frozen in time, part II

In the first part of this blog post I described the Yorkshire liassic crinoids, now´s the time to show you the starfish.
It feels like starfish are even a bit more rare than crinoids – at least with crinoids you get the obvious isolated segments (ossicles) in most sediments.
Disarticulated starfish remains are less obvious, though I guess they must be there as well, most Yorkshire lias sediments are just difficult to prepare for microfossil analysis.
Most articulated starfish remains in my collection are from the figulinum – stokesi subzones of the Yorkshire coast, as are the first three.

Palaeocoma milleri (PHILLIPS,1829)
This is the most “common” brittle star from the Yorkshire coast and can reach considerable size – my largest specimen has an arm length of 6″ / 15 cm –
 “Yorkshire” seas also fed the brittle stars better 😉 – Dorset specimen of the same species are usually considerably smaller.
(In his 1964 revision of the brittle stars of the british jurassic (“Die Ophiuren des Englischen Jura”) HESS sums some davoei/margaritazus zone
Palaeocoma species  (P. egertoni, P. gaveyi) under one species P. milleri.)
Palaecoma milleri, 9 cm diameter

Palaecoma milleri, 9 cm diameter

This one was found in a fresh cliff fall on a block of softer sediment, sensitive to both drying out/cracking and falling apart when subjected to water.
Mike Marshall kindly dry-cut the block to size and stabilized it with some epoxy putty. Having thus safely arrived home, a couple of minutes of
air abrading brought the winding arms of the 9 cm diameter brittle star to light.
Palaecoma milleri, width of view = 24 cm

Palaecoma milleri, width of view = 24 cm

Palaecoma milleri, detail of center

Palaecoma milleri, detail of center

This is the said large specimen of Palaeocoma with the arm length of 15 cm (stretched out)  and an “arm span” (as embedded) of more than 22 cm.
The long arms sink deep into the thinly bedded sandstone with harder and softer layers, with the very tips less than 0.5 mm thick.
This fossil was prepped with alternating runs of air pen (for breaking through the harder layers) and air abrader (for the detailed work around the fossil).
There is a little curiosity at the missing arm (5 o´clock position) : There is a small very thin little arm seemingly coming out of the stump, it is tempting to assume
it could be a replacement arm (allthough it looks too small for it).
I have not seen any pictures of what replacement arms with brittle stars look like, I you have, please let me know…
Palaecoma milleri, block as found

Palaecoma milleri, block as found

Palaecoma milleri, width of block 22 cm

Palaecoma milleri, width of block 22 cm

This starfish was found in March this year. It sits in a little block about 23 cm wide and was again prepped with air pen / air abrader.
The central disc is about 3.5 cm wide – the arms must have really been long on this one, if they had been preserved…
While prepping it I mistakenly thought the arm in the 4 o´clock position was connected to the end coming up in the 5 o´clock position – they are not,
as I had to notice when finding that the arm in the 5 o´clock position grew thinner while it was going down, instead of thicker to connect with the other arm…
The embedding rock seems to originate from beds around the oyster bed, showing some oysters as well.
Palaecoma milleri, width of view approx. 20 cm

Palaecoma milleri, width of view approx. 20 cm

Recent brittle stars are known to gather where there is a large supply of nutrients, i.e. in the deep sea on decaying whale carcasses.
This picture shows a section of a larger slab that contains such a fossilized gathering – the reason for it is not known (I can safely say it wasn´t a whale, though…)
The slab was found in 1999 on the way back from a long day out at Hawsker (I told you, it always happens to me like this…);
as the tide came in already, it had to be left on the beach and was hidden in a secretively marked spot.
After a very restless night and anxiously awaiting the next low tide, the 40 kg slab was carried back to Robin Hoods Bay in a large Rucksack and carried up the hill in a fishermen´s box with the help of my friend Klaus…
The reddish covering sediment was found to be preppable using potassium hydroxide (KOH) pellets, and over the course of some months
it was treated in a large cement tub. It is now awaiting finishing touches in a big enough air abrading chamber (planned for 2013…)
The slab had an eroded Amaltheus stokesi on the back, so it must originate from the stokesi subzone.

Tropidaster pectinatus FORBES, 1850
Tropidaster pectinatus, 4 cm wide

Tropidaster pectinatus, 4 cm wide

This small starfish sits on the same slab as the Palaeocoma specimen of the last picture. It is only relatively small (4 cm diameter) and very fragile.
While looking at some photographs of the slab some time ago, I notied a second Tropidaster specimen on the slab as well which I had not seen when looking at it with the “naked” eye…

Luidia murchisoni (WILLIAMSON, 1836)
This is the elusive sun starfish. I have only ever found one specimen myself, but could not salvage it without risk (huge block, last day of the holiday…)
I notified a local collector who had it cut out of the block with a diamond still saw and had it prepped professionally ,it is now on public display in a shop in Robin Hoods Bay.
Luidia murchisoni in situ (center), to the right the snout of dear beach dog Lucy

Luidia murchisoni in situ (center), to the right the snout of dear beach dog Lucy

As a surrogate, here´s an eroded specimen I got off Mike Marshall :
Luidia murchisoni, 10 cm diameter

Luidia murchisoni, 10 cm diameter


?Sinosura sp.
 
Bilder kl. brittle stars
The small brittle stars associated with the Hispidocrinus scalaris crinoid I showed you in the previous post are just too small to be identified – a little over 1 cm diameter.
I have tentatively put them towards Sinosura, since larger specimen of Sinosura have been found with these crinoids.
?Sinosura sp., 1 cm diameter

?Sinosura sp., 1 cm diameter

?Sinosura sp., 1 cm diameter

?Sinosura sp., 1 cm diameter

These tiny little brittle stars are preserved so life-like, with even some of the finest hairs still attached, truly a moment frozen in time.

Addendum November 25, 2012 :

I´ve recently had the opportunity to prep a beautifully preserved P. milleri which is, unlike all the other P. milleri shown here before (did you notice ?) not prepped in oral aspect (from the underside),
but in aboral aspect (like you would see it crawling around in and over the sediment). It is perfectly preserved and could be teased out of the relatively soft shale with low air abrader pressure in about 45 minutes.
Congratulations to the finder (D. Clark) and thanks again for letting me picture it here !

Brittle star Palaeocoma milleri, width approx. 20 cm, collection D. Clark

Brittle star Palaeocoma milleri, width approx. 20 cm, collection D. Clark

AndyS

by andysfossils on November 4, 2012  •  Permalink
Posted in Other fossils, Preparation

Posted by andysfossils on November 4, 2012

https://andysfossils.com/2012/11/04/a-moment-frozen-in-time-part-ii/

A moment frozen in time, part I

Hispidocrinus scalaris, showing crown from underside, width = 6 cm

Hispidocrinus scalaris, showing crown from underside, width = 6 cm

The title of this blog says it already : “…and other fossils”…, so now’s the time to introduce you to (for a change) my other fossil passion :
echinoderms, more specifically starfish and crinoids. It really came more as a by-product of hunting for ammonites, mostly when my rucksack was already full on the way back, tiredly stumbling across the large blocks while taking a different route across the boulder strewn beach on the way home. It also happens that I pick up rocks with crinoid or starfish content when I´m frustrated because there is nothing else (meaning decent ammonites) to find – almost as if you have to be in a certain state of mind to notice these fossils, when your attention is no longer focused on other fossils, similar to when you start hearing strange sounds in the dark night when your visual sense becomes useless…
This of course has to do something with the difference in the “search mode” when your looking for ammonites vs. starfish / crinoids : With ammonites, on the Yorkshire coast you´re mostly looking for concretions, while with starfish / crinoids you´re carefully surveying the surfaces of (potentially large) fallen blocks – this also explains the of course totally unobjective observation that I tend to find crinoids / starfish mostly on the return from a location : I tend to use the easier way across the large blocks, and it´s usually later in the day, which makes for nice low angled light and better chances to see the delicate fossils…

For intact, articulated preservation, fragile animals like starfish and crinoids need fast embedding, because decay sets in quickly, e.g. for brittle stars, already after half a day. Brittle stars cannot free themselves when they´re suddenly covered by more than 5 cm of sediment – most of the brittle star fossils on the Yorkshire coast have probably been created by rapid burial in sediment, like a sediment avalanche – truly a moment frozen in time.
Some of the crinoids that can be found articulated are thought to have been deposited in scour troughs.
In Yorkshire, subzones where the liklihood of finding articulated crinoids or starfish are greatest are in my experience :
  • taylori
  • obtusum
  • oxynotum
  • maculatum
  • figulinum
  • stokesi
  • tenuicostatum
  • falciferum
Still – “greatest liklihood” does not mean they’re common fossils, finding an articulated crinoid or starfish remains a great rarity. The falciferum zone is the odd one out here, since benthic conditions were mostly anoxic during this time (very little oxygen at the bottom) – so there are no starfish, and crinoids that occur were usually attached to drifting logs at the surface of the sea.
So the crinoids and starfish I’m showing you here now really represent more than 20 years collecting – please do not get the impression that fossils like these can be found on a day’s trip to the coast – unless of course you are extremely lucky !
Some of these have been purchased, some reside in collections other than my own and are pictured here by kind permission of their respective owners – you will see that in the notes for the fossils.
Generally preparation of starfish and crinoids most of the time is a difficult and time consuming task.
Their delicate structures are usually firmly embedded in the sediments and can only be retrieved if there is a difference between the surrounding matrix and the fossils which are usually preserved as calcite or pyrite. This difference can either be a difference in hardness, when the fossils are harder than the matrix – these fossils can be prepared mechanically, i.e. needles, airpens or – you might have guessed – air abrader. If there is no difference in hardness, there can also be the option of chemical preparation – when the fossils are more resistant to certain chemicals like acids or alkaline solutions than the matrix. In rare cases, the environment (or rather what we put into it – sulphur dioxide / nitrogen dioxide from burning fossil fuels reacting with water to form sulfurous/sulfuric resp. nitric/nitrous acid) or certain naturally occuring humic acids can do the job for us – but that is only really the exception.
This first part will be about the Yorkshire liassic crinoids, so without much further ado, here they are :

Eocomatula interbrachiatus (BLAKE, 1876)
Eocomatula interbrachiatus, width = 13 cm

Eocomatula interbrachiatus, width = 13 cm

This is one of the first more or less articulated crinoid crowns I´ve found on the Yorkshire coast.
Eocomatula interbrachiatus with Oistoceras ammonite

Eocomatula interbrachiatus with Oistoceras ammonite

Another specimen found by Keeley and Adrian which they kindly let me prep and photograph shows the crown in association
with an Oistoceras ammonite, which places the crinoid in the figulinum subzone of the lower Pliensbachian.
Eocomatula interbrachiatus as found, width = 24 cm

Eocomatula interbrachiatus as found, width = 24 cm

Eocomatula interbrachiatus prepared, height of detail = 12 cm

Eocomatula interbrachiatus prepared, height of detail = 12 cm

These crinoids only have a very short stem (only a few segments), which I´ve never found preserved so far.

Hispidocrinus scalaris (GOLDFUSS, 1831)

Hispidocrinus scalaris, slab as found, width = 30 cm

Hispidocrinus scalaris, slab as found, width = 30 cm

Hispidocrinus scalaris, prepped, width = 22 cm

Hispidocrinus scalaris, prepped, width = 22 cm

Hispidocrinus scalaris, detail with crown and small brittle stars

Hispidocrinus scalaris, detail with crown and small brittle stars

This is the crinoid specimen that really got me seriously started to try and collect all the known Yorkshire liassic crinoids. It was found on a very warm summers day in July 2007 when I was out collecting with friends and had found nothing at all up to this point – I picked up this 30 x 20 cm slab with some faint crinoid traces and put it in my bag so it at least felt like I had found something… At home I started prepping it with an air abrader (iron powder) and followed the visible arms of the crinoid into the rock. To my amazement more and more stems and arms appeared until after about 60 hours of prep work almost the whole slab showed a deathbed of multiple Hispidocrinus crinoids in an early state of decay. When looking carefully at the slab, you can even notice tiny little brittlestars that have either fed on the decaying crinoid or had used the crinoid to achieve a higher up filter feeding position or even benefit from the crinoids´excretions and got embedded with it.
Hispidocrinus scalaris, slab as found, width = 15 cm

Hispidocrinus scalaris, slab as found, width = 15 cm

Hispidocrinus scalaris, prepped

Hispidocrinus scalaris, prepped

Another specimen was found in a small 12 x 15 cm which was initially split after finding it since the outside did only show very faint crinoid traces.
As the split showed a crinoid inside, it was glued back together again and air abraded in about 20 hours.
It shows two crowns, with the larger one having all it´s arms folded unto itself. And of course there´s another small brittlestar (5 o´clock position at the bottom) …

Seirocrinus subangularis (MILLER, 1821)

Seirocrinus subangularis lens with ossicles, width = 18 cm

Seirocrinus subangularis lens with ossicles, width = 18 cm

Seirocrinus subangularis, detail of lens cross section

Seirocrinus subangularis, detail of lens cross section

This lens comes from the tenuicostatum zone of the lower Toarcian and shows remains of Seirocrinus subangularis and was prepared using an air abrader.
On the inside, this lens consists of almost 100% of crinoid ossicles amalgamated into a solid calcitic core.
Seirocrinus subangularis, crown on lens, width = 15 cm

Seirocrinus subangularis, crown on lens, width = 15 cm

Other side of lens with ammonite Dactylioceras tenuicostatum, width = 15 cm

Other side of lens with ammonite Dactylioceras tenuicostatum, width = 15 cm

Another specimen showing a beautiful crown of Seirocrinus was found by my friend Klaus, who paintakingly prepared this
specimen using potassium hydroxide pellets over the course of a couple of weeks, the final touchers were again made with an air abrader.
This specimen also handily shows a Dactylioceras tenuicostatum ammonite on the back of the nodule which tremendously helps dating it !

Isocrinus robustus (WRIGHT, 1858)

Isocrinus robustus, oxynotum subzone, 9 cm

Isocrinus robustus, oxynotum subzone, 9 cm

Isocrinus robustus, stem detail

Isocrinus robustus, stem detail

This crinoid was a surprise find on my birthday this year ! It sat neatly on the edge of a fallen rock most likely of oxynotum zone age and when found I had thought it was a Hispidocrinus in an unusual, almost 3D preservation. The surprise came at home when I prepped it using the air abrader and noticed that it did not have the characteristic spines of a Hispidocrinus. Dr Mike Simms kindly identified it as an early Isocrinus robustus.

Pentacrinites dichotomus (MCCOY, 1848)

Pentacrinites dichotomus, width of colony 20 cm

Pentacrinites dichotomus, width of colony 20 cm

This beautiful colony of Pentacrinites dichotomus from the Jet Rock in the Whitby area was found by Mike Marshall who prepared it by stabilizing the exposed weathered side of the thin fragile slab with a layer of epoxy putty and prepared it from the other side using an air abrader. The colony is nicely set into a slab of top jet dogger to stabilize it.

Jet with juvenile ?Pentacrinites

Small juvenile ?Pentacrinites crinoid on jet, width = 6 cm

Small juvenile ?Pentacrinites crinoid on jet, width = 6 cm

This beautiful section of a piece of solid black jet with a juvenile crinoid anchored to it was kindly given to me by a friend. It gives more evidence to the observation that some crinoids have used floating logs for anchoring themselves to during their lifetime and filter fed in the surface waters.

Balanocrinus gracilis (CHARLESWORTH, 1847)

Balanocrinus gracilis, ossicles with juvenile Amaltheus (1 cm diameter) ammonites

Balanocrinus gracilis, ossicles with juvenile Amaltheus (1 cm diameter) ammonites

Have you spotted the crinoid remains on this picture ? – don´t get distracted by the associated juvenile (~1 cm ) Amaltheus ammonites !
Of this one I yet have to find a crown. Disarticulated ossicles are no rarity in the stokesi and maculatum subzones, but sometimes extraction can be impossible.
The second part describing the starfish will be published next.
AndyS
by andysfossils on October 20, 2012  •  Permalink
Posted in Other fossils, Preparation

Posted by andysfossils on October 20, 2012

https://andysfossils.com/2012/10/20/a-moment-frozen-in-time-part-1/