GEOL2301: Palaeoecosystems

The first part of our exercise will train you in the basics of palaeontological observations. We'll start by working with the two trilobite specimens below.

• You can enlarge the models by entering full-screen mode (Click, then type f).
• Problems with the 3D models? See suggestions.

• Quickly write down how the two fossils differ from one another morphologically.

• How easy did you find it to find differences? Was it easy to describe them verbally?

Two key skills in the palaeontologist’s toolkit are valuable aids in this process.

Sketching fossils is important not just because it allows you to remember what the fossil looked like later – a photograph could do that – but also because it forces you to observe and interpret features in the specimen. When you were just looking at the fossil, you might not have paid much attention to the number of ridges (say) or the angle between them – sketching a fossil compels you to observe such details.

Using appropriate terminology is also enormously helpful. Unfamiliar terms can be a pain to memorize, but it’s much easier and more precise to say “facial suture” than “the wiggly line that runs along the head bit”, and someone else who knows the lingo will know straight away what you mean. What is more, the vocabulary of technical terms is carefully chosen to refer to features that are homologous (i.e. equivalent, or inherited from a last common ancestor) within a group. This means that the same word can be used for different fossils within that group, and often means that the absence of such and such a feature is in itself notable. Finally, each term is something that can be described; once you know what a delthyrium is, you might notice differences in the delthyrium shape that you would otherwise have overlooked.

Grab a pencil and paper and produce labelled sketches of the two fossils you have chosen. Refer to the crib sheet to see the terms as they apply to idealized fossils, then identify the features on your own fossils. A good sketch need not be an artistic masterwork: focus on keeping your drawing as simple as possible, whilst depicting (and annotating) the key features of the fossil. Use all the available space, drawing the fossil from different angles if necessary.

• Remember to include a scale. Both these specimens are circa 80 mm from head to tail.

Once you've completed your sketches, write a new list of the morphological differences between the specimens.
• How does this differ from your previous list?

Systematic description

[15–30 minutes]

Now we’ll attempt a systematic description of a new fossil. Imagine for a moment that you have just pulled it out of a cliff face, and your expert friend tells you that it is new to science! Naturally you’ll want to describe it as a new species. Let’s work through the process of a formal description here.

Figure

No description is complete without a figure of the new taxon: people will need to see what it looks like! Making an annotated sketch now will allow you to identify the diagnostic characteristics of the fossil. Concentrate on labelling features that are important for classification.

• What features are most important for distinguishing trilobite classes?
• Key features include: size & shape of cephalon; presence of genal spines; eye shape and construction; relative size of pygidium; disposition of glabella.

Classification

Now we're ready to begin our formal description. The first step is to identify which larger group the new taxon belongs to. Use your annotations, and the classification guide on the crib sheet, to identify the phylum, class, and order of your new species.

Name

Next, you need to name your species. A binomial is the full name of a species: the name of the genus it belongs to, followed by its specific epithet (species-level name), written in italics with the name of the genus capitalized (i.e. Genus species). For example, Lingula rostrum is a species (rostrum) of brachiopod in the genus Lingula. Species names can be anything at all, so long as their binomial name is unique and pronounceable. (There are species called ‘rostrum’ in other genera, for example the gastropod snail Calliotropis rostrum; this is why the genus name is always given.) Names are commonly descriptive and Latinised. Species are often named after their discoverer, or an eminent figure in the discipline – but it is considered poor form to name a species after yourself.

• Give your species a name – be creative!

• Usage note:
  One species → many species
  One genus → many genera

Diagnosis

A diagnosis describes what makes your species unique. Ideally you would establish what makes it different from every other species in its genus (or if describing a new genus, what makes it distinct from every other genus in its family). For now, why not emphasise ways that it is different from the two fossils that you have just sketched.

Type material

Next, a single specimen must be designated the holotype. In the case of uncertainty, future fossil finds will be compared to the holotype to determine whether or not they belong to the same species. As you only have one specimen, your choice of holotype is made for you.

• If you had the choice, would the specimen make a good holotype?
• What are some properties of a bad holotype specimen?

Testing your descriptive skills

Congratulations! Now all you need to do is publish your observations in a scientific journal and you will have described your first species.

Now let’s put your descriptive skills to the test. One reason to take detailed sketches is so that you can answer new questions that might arise once you no longer have access to the original material. With the help of the crib sheet, but looking only at the notes and sketches that you’ve made, can you assign the two specimens that you sketched earlier to a phylum, class and order?

Now it's time to meet some brachiopods. You'll need to download the crib sheet.

• Problems with the 3D models? See suggestions.

• Sketch the two fossils, using the glossary sheet to annotate key features.
• Remember to include a scale bar: both specimens are circa 20 mm from left to right.
• List the similarities and differences between the two taxa in as much detail as you can manage.
• Keep an eye on the time available.
• Classify your specimens to a phylum, class and order

Identification

Use the crib sheet to familiarise yourself with the principal features of corals.

Solitary corals are difficult to identify from external features unless the growth form is very distinctive and/or details of septal arrangement can be clearly seen. Among colonial corals, tabulate corals can usually be readily distinguished from rugose corals through the much smaller corallites of the former; corallite arrangements allow most tabulate corals to be separated into suborders. Unless calical surfaces are particularly clear, detailed identification requires thin sections.

On the accompanying diagram of a generalised solitary coral, label the terms:

• List the three important orders of fossil corals, noting their stratigraphic ranges.

Search SketchFab to find a representative specimen from each order. Sketch each specimen, labelling what you consider to be the three most important morphological characteristics of each order.

Which growth forms or structural organizations did the corals you chose exhibit? Find and sketch further specimens so that you have examples of three different structures of both solitary and colonial corals.

Bryozoans are a phylum of colonial marine invertebrates, loosely related to the brachiopods. Each individual bryozoan (a ‘zooid’) is around 0.5 millimetres long, but together they form colonies that can reach several centimetres in length. They are filter feeders, sieving food particles from the water using their retractable lophophore (a basket of hair-lined tentacles). In many of the 4000 species alive today, zooids within a single colony are differentiated to perform different functions: some take care of the eating and excreting, for example; others do all the reproducing.

Almost all bryozoan species secrete mineralized skeletons, affording them an excellent fossil record that can be tracked back to the Ordovician period.

Bryozoan colonies have a range of morphologies. With reference to the papers and image gallery below, and images / 3D models you can find yourself, make sketches that summarise the variety of colony morphology. Can you find any colonies that show evidence of zooid specialization?

• Hint: Right-click images and select "Open in new tab" to view at full size

Living bryozoans feeding:

Bryozoan lifecycle:

Journal articles containing nice figures (no reading necessary!)

• doi:10.1017/jpa.2016.66
• jstor:1307046
• doi:10.5852/ejt.2016.203