science

Oncocerida

Oncocerida is a science 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 Oncocerida rather than just read about it. In short: The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian (early Carboniferous; one possible member is known from the Early Permian), in which the connecting rings are thin and siphuncle segments are variably expanded (Flower, 1950). At present the order consists of some 16 families, a few of which, such as the Oncoceratidae, Brevicoceratid…

Key takeaways

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

Reference excerpt

The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian (early Carboniferous; one possible member is known from the Early Permian), in which the connecting rings are thin and siphuncle segments are variably expanded (Flower, 1950). At present the order consists of some 16 families, a few of which, such as the Oncoceratidae, Brevicoceratidae, and Acleistoceratidae contain a fair number of genera each while others like the Trimeroceratidae and Archiacoceratidae are represented by only two or three (Sweet, 1964).

Physical characteristics The shells of oncocerids are primarily somewhat compressed cyrtoconic brevicones. More advanced forms include gyrocones, serpenticones, torticones, and elongate orthocones and cyrtocones, reflective of the different families and genera (Flower, 1950; Sweet, 1964). The siphuncle in the Oncocerida is commonly located at or near the ventral margin. Connecting rings are most commonly thin and structureless but in certain derived forms may become actinosiphonate with inwardly projecting radial lamellae. The juvenile segments in early genera are straight and tubular, with short orthochoanitic septal necks inherited from the Bassleroceratidae. Later in the mature stages of early forms and throughout in the more advanced the connecting rings are inflated with cyrtochoanitic septal necks, giving what can be described as a "beaded" or "ellipsoidal" appearance (Sweet, 1964).

Evolution and diversity The Oncocerida are thought to be derived from the Bassleroceratidae through Graciloceras as a result of a thinning of the connecting rings in the siphuncle (Flower, 1976). Oncocerids reached their greatest generic diversity in the Middle Silurian with some 43 genera representing nine families (Sweet, 1964), the most at any time. Of these 43 or so genera, about 38 were new, a recovery from a precipitous decline in the Late Ordovician and Early Silurian. A second period of greater diversity occurred in the Middle Devonian with eight families represented by some 37 genera, following a second decline after the Middle Silurian. After this the order declined until its extinction in the Early Carboniferous (Mississippian). Near the beginning of the Devonian and well before its end, the Oncocerida gave rise to the Rutoceratidae (Flower, 1976; Kümmel, 1964), which form the root stock of the Nautilida, which among its members includes the modern Nautilus and Allonautilus.

Distribution and range Oncocerids are well known as fossils from the later Ordovician, Silurian, and Devonian in North America, Europe, and Australia, and to a lesser extent from parts of Asia, after which the order declined into the Mississippian and reached its end by the Pennsylvanian (late Carboniferous) (Flower, 1976; Sweet, 1964).

Taxonomy Families in the Oncocerida, according to the Treatise on Invertebrate Paleontology, follow with the number of genera in each shown in parentheses, along with the stratigraphic range.

Graciloceratidae (4) M-U Ord Tripteroceratidae (5) M-U Ord Valcouroceratidae (8) M-U Ord Diestoceratidae (5) M-U Ord Oncoceratidae (24) M Ord - U Sil Jovellaniidae (5) ? U Ord, M Sil - L Dev. Nothoceratidae (10) L Sil - U Dev Karoceratidae (3) L - M Sil, ?L Dev Hemiphragmoceratidae (5) M-U Sil, ?M Dev Acleistoceratidae (22) M Sil - M Dev Polyelasmoceratidae (13) M Sil - U Dev Brevicoceratidae (17) M Sil - U Dev Poterioceratidae (7) L Dev - L Carb Tripleuroceratidae (2) ?L Dev, M Dev - L Carb Archiacoceratidae (3) M Dev/

Descendants According to more current thinking, e.g. Flower, Teichert, and Kümmel, the Oncocerida gave rise to the Rutoceratidae which form the root stock of the Nautilida, which after a number of iterations, ends up with the modern Nautilus and Allonautilus.

References

Flower, R.H. in Flower and Kümmel Jr 1950; A Classification of the Nautiloidea; Journal of Paleontology, Vol 24, no 5, pp 604–616, Sept 1950 Flower, R.H. 1976; Ordovician Cephalopod Faunas and Their Role in Correlation, pp 523–552 in The Ordovician System: proceedings of a Paleontological Association symposium; Bassett, M.G. Ed. Kümmel, B. 1964; Nautiloidea -Nautilida; Treatise on Invertebrate Paleontology, PartK, R.C. Moore Ed. Sweet, W.C. 1964; Nautiloidea -Oncocerida; Treatise on Invertebrate Paleontology, PartK, R.C. Moore Ed.

Illustrations

Worked examples

Example 1 — a first encounter with Oncocerida

Start with the simplest possible case. Write down what Oncocerida claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Oncocerida 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 Oncocerida 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 Oncocerida

In research: Oncocerida appears in science 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 Oncocerida 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: Oncocerida is common in secondary-school and first-year university syllabi. It links to neighbouring topics Middle Ordovician first appearances, Mississippian extinctions, Mollusc orders, so understanding it makes those chapters shorter.
In everyday life: Look for Oncocerida 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 Oncocerida in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Oncocerida 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 Oncocerida out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Oncocerida in simple terms?

Why does Oncocerida matter?

Because it connects several science 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 Oncocerida?

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 Oncocerida.