biology

Sisteronia

Sisteronia is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sisteronia rather than just read about it. In short: Sisteronia is an extinct genus of platypterygiine ophthalmosaurid ichthyosaur known from the 'middle' Cretaceous of southeastern England and southeastern France. It contains a single species, Sisteronia seeleyi.

Key takeaways

Sisteronia belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sisteronia to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sisteronia from memory before moving on to harder problems.

Reference excerpt

Sisteronia is an extinct genus of platypterygiine ophthalmosaurid ichthyosaur known from the 'middle' Cretaceous of southeastern England and southeastern France. It contains a single species, Sisteronia seeleyi.

Discovery Sisteronia was named by Valentin Fischer, Nathalie Bardet, Myette Guiomar and Pascal Godefroit in 2014 and the type species is Sisteronia seeleyi. The generic name honors Sisteron, a commune in the Alpes-de-Haute-Provence, southeastern France, where relatively complete specimens referable to Sisteronia were collected, including a partial articulated skeleton and at least three additional articulated specimens held in a private collection. The specific name, seeleyi, honors the renowned British paleontologist Harry Govier Seeley who cataloged thousands fragmentary ichthyosaur specimens from the Cambridge Greensand Member of the Lower Chalk Formation. Now housed in the collections of Sedgwick Museum of Earth Sciences (CAMSM), the Royal Belgian Institute of Natural Sciences (IRSNB), Hunterian Museum and Art Gallery (GLAHM), Leicester Museum & Art Gallery (LEICT) and Natural History Museum (NHMUK), most of these specimens have never been reassessed thoroughly since Seeley's publication in 1869, and include the holotype of Sisteronia. Fischer et al. (2014) designated CAMSM B58257_67 as the holotype of Sisteronia. It is one of the most complete specimens from the Cambridge Greensand member, representing an incomplete, articulated skeleton, including a partial basicranium (the inferior portion of the skull), a scapula, a humerus, and five centra.

Description Sisteronia possesses three autapomorphies, unique traits, that differentiate it from all other currently known platypterygiine ophthalmosaurids. In Sisteronia, the basioccipital possesses a raised process on the floor of foramen magnum. As observed only in a juvenile specimen of "Platypterygius" australis, the opisthotic lacks nearly completely a paroccipital process. Mature individuals of "P." australis lack this condition, unlike mature specimens of Sisteronia. The teeth of Sisteronia are rectangular in cross-section with small crown and root, the labiolingual length being usually equal to one half of the anteroposterior length. As suggested by its delicate, slender and unworn teeth, Sisteronia preyed on soft and small prey such as small fishes and neocoleoid cephalopods. Sisteronia can be also distinguished from other platypterygiines by a combination of characters. Unlike Aegirosaurus and Sveltonectes insolitus, the anterior process of its maxilla is elongated anteriorly, reaching the level of the nasal bone. As in S. insolitus, Sisteronia has prominent opisthotic facets on the basioccipital, and an expanded sacculus impression on the opisthotic, as seen in Acamptonectes and mature individuals of "P." australis. Sisteronia possesses a U-shaped supraoccipital, like "P." australis, "P." hercynicus and "Ophthalmosaurus" natans, and an anteroposteriorly shortened quadrate condyle as also present in Ophthalmosaurus icenicus and S. insolitus. Finally, the humerus of Sisteronia has a facet for a posterior accessory element, as seen in "Ophthalmosaurus" monocharactus, "P." hercynicus, "P." americanus and "P." sp. from Texas and the Northwest Territories. Fischer et al. (2013) assigned Sisteronia to Platypterygiinae as it possesses several synapomorphies of this clade and lacks the synapomorphies of ophthalmosaurine ophthalmosaurids. A yet unpublished phylogenetic analysis reportedly supports this assignment.

Phylogeny A large phylogenetic analysis performed by Fischer (2013) in his unpublished thesis found Sisteronia to be a member of Platypterygiinae. Even though variants of this analysis have been formally published, the scorings of Sisteronia are based mainly on undescribed referred material currently held in a private collection, and therefore the publication of this cladogram is pending. The following cladogram shows a possible phylogenetic position of Sisteronia in Platypterygiinae according to the analysis performed by Zverkov and Jacobs (2020).

See also List of ichthyosaurs Timeline of ichthyosaur research

References

Illustrations

Worked examples

Example 1 — a first encounter with Sisteronia

Start with the simplest possible case. Write down what Sisteronia claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sisteronia before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sisteronia ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sisteronia

In research: Sisteronia appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sisteronia in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sisteronia is common in secondary-school and first-year university syllabi. It links to neighbouring topics Albian life, Cretaceous England, Cretaceous France, so understanding it makes those chapters shorter.
In everyday life: Look for Sisteronia outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sisteronia in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sisteronia means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sisteronia out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sisteronia in simple terms?

Why does Sisteronia matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sisteronia?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sisteronia.