The reason I have not written any articles in a while is because I have just returned from Morocco collecting samples for my dissertation. My project will be titled ‘The Taphonomy of Trilobites in Different Beds in the Alnif Area”. Taphonomy is the study of the decay of different organisms and how they become fossils. Trilobites are great to study because they would shed their exoskeletons, giving them a high preservation rate.
We began the journey by flying to Marrakech, and after staying there for a night, we took an 8 hour bus journey to Tinghir. As you can imagine, an 8 hour journey was not fun, and even after that we still had an hour car journey to Alnif. Alnif is a very small town in the desert by the Sahara and Anti-Atlas mountains. Life there is very different to that in the UK, as there are barely any shops apart from fossil shops!
However, the geology in this area is wonderful, with exposures starting from the Pre-Cambrian, ranging all the way through the Palaeozoic (apart from the Permian, as there was no sea here at that time) and then through to the Mesozoic. The Kem Kem is a great area for finding dinosaur fossils. Unfortunately, we did not visit here, as it would take a very long jeep ride and we just didn’t have enough time.
The journeys out into the desert every day were long and required a car. Walking to localities is not advised and especially at midday. The first day of field work we made the mistake of trying to walk at midday and in the desert heat I thought we were going to die- no matter how much water we drank, our heads were still spinning and we were so dehydrated. So, we made a decision that we would either go very early in the morning, or late in the afternoon. And it was a good decision; specimens were collected almost every single day. And a lot of them! We almost went over our baggage allowance!
We visited every time period in the Palaeozoic here (bar Permian of course), as trilobites ruled the seas during this time. Trilobite morphology also changes drastically throughout these time periods, which may reflect the palaeoenvironment. For example, Phacops had eyes during the Ordovician, but had lost them by the Carboniferous. Could this be because the water was getting deeper? Or could it be because they changed their lifestyle and preferred living in underwater caves and holes? It appears that, in Morocco certainly, the latter would be the case, as the seas in the Carboniferous were very shallow and then non-existent in the Permian.
Most trilobites here are found in Ordovician and Devonian rock, and are preserved in limestone and sandstone. These rocks mean the fossils are fairly easy to extract, except when the rock contains coral. Coral is a rock-building organism; when it dies it forms sedimentary structures and created a very hard baffle or bound stone. Trilobites fossils that are found settled in coral is best leaving, as a hammer will just bounce off. Photographs of these are usually adequate anyway. I found that most of the trilobite fossils were fragmented; mostly thoraxes and pygidiums were found- very few cephalons. Why, you ask? This has all to do with the fact that trilobites shed. This is called ecdysis and we see it in modern crabs, lobsters and insects today. The trilobite, when it was too big for its exoskeleton, would detach its libragena (its ‘free cheek’) from its fixigena (you guessed it- ‘fixed cheek’) and the rest of its cephalon, and wriggle out. This is why the rest of the head, apart from the glabella, is not normally found.
We also visited areas that didn’t have trilobites. This was just so we could understand the overall palaeoenvironment more. In the Silurian, there were no trilobites, but many many orthocones. Here, the locals polish this black limestone, filled with orthocones, and use it for kitchen countertops (fashionable and scientific!). A lot of them were all facing the same direction; this suggests that the current was constant. The limestone was black, indicating anoxic deep water- possibly an alluvial fan. This is supported by lack of trilobites, coral or crinoids.
Another area without trilobites was an outcrop of the Carboniferous. This was an area of alternating limestone, sandstone and shale. There were very few fossils here except for the occasional brachiopod. This was because at this time the sea was regressing so much that any dead animals would have floated down to deeper areas.
The Cambrian was definitely the deepest part of the succession, except for possibly the Silurian, and we saw a general marine regression, until there was no sea whatsoever in the Permian. And, of course, then there was a mass extinction (want to know more? Read my Top 5 Extinctions!) At which this point trilobites went extinct.
So what next for my project? Well, the samples I collected will take a lot of preparation, trying to uncover as much of the specimens as I can. I also made several logs over the trip, which will have to be put on a computer and some conclusions drawn up. Stay tuned as I will be posting pictures of my prepared fossils!