The Demon’s hand

One dark, cold late October night, the wind whistled outside as a museum curator stepped into the store room. An old branch from a tired old tree raps against a window close by. The curator reaches out and grips the old wooden handle of a cupboard door. The door moaned as it was yanked open. A drawer slowly creaked as it was pulled out. The curator let out a high pitched scream as they became face to face with the most ghastly of sights.

The last thing any museum curator wants to see is a specimen which has been attacked by pests. Worst still, a cast that looks nothing like it should: that would make a grown man scream.

This week’s Bad Cast is fitting for Halloween. Not only is it horrifically bad, it looks like the cast of a demon’s hand on a door; just like something from those great 1980s horror films.

Catching a demon in the act? Nope. It’s just another awful bad cast.

A demon didn’t patiently wait while it’s evil three clawed hand held onto a terrified museum curators door. It would have been incredibly fantastic to capture a mould of a demon’s hand. But also impossible. Because you need steady hands to make moulds, and I for one know, I would be shaking like a terrified puppy. The hand would have to be pretty still too; it is much more likely that it would be clawing, scratching, and doing other really scary things to the door. Plus demons aren’t real.

It is a cast of one of the most familiar kinds of trilobites, called Calymene. (I’m sorry, it is yet another cast of a trilobite. For some unknown reason, around a third of our bad casts are of trilobites. Trilobites themselves are pretty awesome creatures. Not that you would know from these terrible reproductions. I am still trying to work out why a curator 104 years ago spent a lot of money on really freakin’ bad casts of trilobites.)

Calymene is a fairly common Genus of trilobite found in Silurian and early Devonian rocks across North america, Africa and Europe.  The oceans around 440 – 360 million years ago were full of these little invertebrates.

The name actually means ‘beautiful cresent’ in reference to the raised part in the middle of the head (called the glabella). In fact, Calymene is more familiar than you may realise, as this perfectly looking trilobite is the typical example used in illustrations of trilobite anatomy.

The perfect example of a trilobite. A gorgeous fossil of Calymene. (Image from here)

Calymene was a sweet little trilobite, and a Genus close to my heart. I have one from the Czech Republic from when I was 14, one of my first fossils I owned. Generally, they wouldn’t have been bigger than 2cm-3cm, and they could roll into little balls for protection. The hard shell you can see in the photo above was hard, and great protection for the soft vulnerable insides.

For Halloween, I am not giving you a fossil of a terrifying beast.Nor evidence of a demon. I am giving you something worse. Much worse. Something that gives me nightmares. An unbelievably bad cast of a most beautiful creature.

The trilobites arse

One of the commonest fossil parts of a trilobite which can be found is it’s arse. This bit of the trilobite, called the pygidium, is one whole piece with all the segments fused together. Like other animals with a hard exoskeleton, trilobites shed their outer shell as they grew larger. The head part, the cephalon, may  break up after shedding because it has lines of weakness which help with an otherwise complex shedding. The middle part, the thorax, sheds into many different sections as this part is made up of lots of individual segments. But the arse, it will shed whole, and if lucky, it will be buried and preserved in one piece.

 

A simple diagram illustrating the basic anatomy of a trilobite. (Image from here)

 

In my time I have seen many a trilobites arse. I remember getting a little too exciting in the beautiful bleak wilderness of southern Spain, as my hammer struck a lucky bedding plane: the sun beating on my naked back, the beads of sweat dripping from my forehead, as I opened the rock to reveal the most perfect trilobites arse I have ever seen. Another time, as the rains lashed down in wet and windy Pembrokeshire, every strike of my trusty geological hammer exposed groups of arses.

Nothing beats that moment when the hammer strikes the right bedding plane, opening a rock that has been sealed for over 400 million years and being the first eyes to see the remains of an animal that scurried along an ancient ocean that no longer exists.

This weeks bad cast is a trilobites arse. I have seen many different types of trilobites butts in my time, from the perfectly round to the elaborately frilly. Unfortunately I am no connoisseur in this area. So I sent an image to a few people who really know their arses. Experts at the Natural History Museum, London were able to identify this trilobite.

 

Just a god-damn fine looking trilobites arse.

 

This is actually a pretty interesting bad cast. It is two casts; one of the part and one of the counterpart. The part is the rock which has the fossil (the cast on the left). The counterpart is the section on the right and has the imprint of the fossils. The counterpart is important because sometimes it has some detail of the original fossil preserved. An interesting example is the counterpart slab of the dino-bird that never was, Archaeoraptor, which showed that this ‘fossil’ was a fake. Sometimes on very finely preserved fossils, feathers, hair or other fragile parts may be on the counterpart.

Our part and counterpart has clearly been put back together several times, chipping off the crude grey paint in the process. The experts identified this arse as belonging to a Genus of trilobites called Dalmanites. The pygidium of the genus has an elongated spine at its tip. These are really beautiful trilobites, with gorgeous headshields, perfectly streamlined bodies, and cute asses that end with a long spine.

 

A beautifully, perfect, Dalmanites limulurus. (Image from here)

 

The Genus of our bad cast is identified. But there were a number of different species within this genus. I found the card since the experts identified it. Scribbled in terrible old school handwriting is ‘Dalmanites rasutis‘. But I cant find this species. At least we have he Genus of a pretty awesome group of trilobites with a elongated spine at the tip of its arse. As with all trilobites, Dalmanites were marine creatures – no fossils have been found in freshwater environments. Its beautiful streamlined body indicates it was a swimmer, but stayed close to the sediment, as its large, curved eyes were stuck out from its head giving a great view for approaching predators.

We don’t know what the spine was used for, perhaps defence, or even digging in the sediment to lay eggs. What I do know is that this arse is amongst the finest in the trilobite kingdom.

A quick lesson in Trilobite anatomy

It’s back. And this time it’s badder than before. This weeks Bad Cast is one of a group of trilobite casts that were just so bad, I had to send photos of them to trilobite experts (they really do exist). The great Richard Fortey and colleagues at the Natural History Museum, London had a look at the photos for me. They actually managed to identify them  too, well not down to species level, but better than I could have done.

This bad cast belongs to an Order of trilobites called Illaenina. The cast is so bad, even world experts coudn’t get a more detailed identification.

This is a trilobite. The head part is the bulbous section on the left. The middle, you may be able to see faint segments, and the rounded bit on the right is its bottom.

 

Somewhat looking like a Scandinavian artists attempt at moulding breasts, this bad cast is actually from a mould of a real fossil. These were a funny looking group of trilobites: with massively rounded heads (cephalon) and massively rounded bottoms (pygidium). The faint ‘ribs’ in the middle (the thorax) contain only a few segments. Compared to your average trilobite, this was a very strange group indeed.

 

A classic sketch showing trilobite anatomy. (1) Cephalon (2) Thorax (3) Pygidium (4) Right pleural lobe (5) Axial lobe (6) Left pleural lobe. (Image from here)

 

Trilobites have a thick exoskeleton protecting their soft, life-giving insides. In many trilobite groups, the cephalon has many clearly defined areas: the glabella (a large bulge in the middle of the head), eyes, facial sutures (to make moulting easier). Some even had elaborate spikes protruding from the head for defence. Our little trilobite has lost clear definition of these features. All edges have merged together leaving a smooth, well rounded head. The eyes are just about visible, poking up from the head; used to spot approaching predators.

Mirroring the cephalon, the arse end (pygidium) is also smooth and rounded. Most pygidiums on trilobites end in a point. This part of the trilobite has segments, but they are all fused together, forming one solid piece. This specimen lacks any clear segments.

Generally, the middle section of trilobites (the thorax) is the longest part of the body. It is divided by pleural lobes (which look a little like the ribs). These segments are different from those on the pygidium; they are not fused together. Separate pleural lobes allow the thorax to be flexible.

Our little beauty has a tiny thorax, squished in-between by a big round head and a big round ass. Such quirky features had to have some reason.  This peculiar looking trilobite reduced segments in the thorax, merged sutures in its head, and lost the segments in the bottom, all so it could roll into the most perfect ball. Many species of trilobites rolled into balls to protect their softer undersides, similar to some species of woodlice today.  But this group of trilobites evolved the ultimate way to roll; the smooth rounded cephalon and pygidium were like two halves of a ball, and the small flexible thorax folded and held these two halves together, creating the most impenetrable ball of calcium carbonate strengthened chitin.

A real fossil from the Order Illaenina. (Image from here)

As a group, Illaenina were very successful, spanning the Ordovician Period (around 490-455 million years ago) until the Devonian (around 420-355 million years ago). These funny looking trilobites were around for around 135 million years. Scurrying in the sediment in those ancient oceans, those big eyes would have spotted a predator in enough time to roll itself into a tight ball.

For such a cool little group of trilobites, it is such a shame that we have this awful thing to represent them.

Work from a Scandinavian artist, or a cast of really cool trilobite?