Another Bad Cast for your pleasure. Here we have a pretty small cast of a trilobite. You can just make out the outline of this specimen.
Just. But it is a trilobite.
Unfortunately, as is a recurring theme with these bad casts, this specimen does not convey the true flamboyance of this type of trilobite. It is a cast from the extravagant trilobite family Thysanopeltid. Species in this family of these extinct arthropods are noted for their big gabella (which is the bulging bit in the centre of the head). They also have very elaborate pygidiums (the ‘tail’ segment): almost as long as the main body in some species.
As with all trilobites, they lived in the marine environment. With their large eyes, and relatively flat, streamlined bodies, these unusual trilobites likely lived in the shallow coastal areas where there was light. Staying close to the sandy or muddy floor, they would have scurried along feeding on the tiny organisms in the water as they went.
These were creatures of the Devonian. From around 410 to 358 million years ago, several species from this family were swimming in the warm seas. From Morrocco, North America, and South England, this was a successful family.
The land was slowly being colonised by plants in the Devonian, with some primitive insects scuttling through these alien forests. The seas were different: they were rich, full of diverse life. With giant armoured fish longer than me, coral reefs, and hundreds of different types of trilobites, this was a world owned by the marine creatures. Stepping barefoot into shallow Devononian waters, you would feel the tickle of trilobites running furiously over your feet, while others swimming would accidently bump into your legs. It was a wonderful world.
Towards the end of the Devonian the fossil record shows that there was a huge extinction event, with numerous families of trilobites, ammonites, corals, and some land animals vanishing forever. Around 22% of families had gone, and 75% of species. The causes may have been due to a meteorite impact, or the changing atmosphere due to the spread of the land plants. It was, and still is, a very fragile planet where slight changes have extremely dramatic effects.
Around half of the bad casts at the museum are trilobites. I get why. Plymouth is on very hard, tough limestone. What fossils have survived 400 million years of crushing, burial, heat and uplift, are fragments of corals or sea shells. When the museum opened, like all museums, they wanted to represent life past and present. Without real fossils to purchase, casts were the next best thing. Apparently.
Did they have to be so bad? We will never know why someone, 100 years ago, spent many shillings on so many bad casts. What is worse for this particular cast, is that species from this wonderful family, Thysanopeltid, have been found in Newton Abbot. Rocks, which are only 40 minutes away. 40 minutes away. Instead of looking for the real thing, we have ended up with this bad cast.