biology

Simian shelf

Simian shelf 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 Simian shelf rather than just read about it. In short: The simian shelf is a bony thickening on the front of the ape mandible. Its function is to reinforce the jaw, though it also has the effect of considerably reducing the movement of the tongue by restricting the area available for muscles.

Key takeaways

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

Reference excerpt

The simian shelf is a bony thickening on the front of the ape mandible. Its function is to reinforce the jaw, though it also has the effect of considerably reducing the movement of the tongue by restricting the area available for muscles. Humans are the only primates to have protruding chins, though some fossils of early humans show evidence of a simian shelf.

Evolution of the simian shelf In Maboko Island (1988), the lower jaw of a Kenyapithecus was found, and it provides signs of the simian shelf evolution in modern apes. Where the simian shelf is present, the bottom teeth will be leaning forward. This happened to be a unique feature of the Kenyapithecus leading there to be a link between the two. This sign of evolution was identified as shown through the lower incisors that lean forward and are known to be used to break hard objects. The lower incisors were concluded to be an adaptive feature as it was an adaptation for "hard object feeding including... large mandible... and upper incisors". Although the forward leaning lower incisors began to show up less in apes, the simian shelf still remained: "[it] was retained by most large bodied genera and served as a preadaptation for the evolution of broad lower incisors in living great apes". The simian shelf found in chimpanzees is not found in modern humans. It was found in a study that the human chin has no true purpose because the simian shelf in chimpanzees is to protect the jaw from the stress of eating and/or chewing. The human speech mechanism also played a role in the evolution or disappearance of the simian shelf. Changes in the jaw such as "widening of the mandibular arch, loss of the simian shelf, and development of the chin" allowed for the development of the speech mechanism. This suggests that the simian shelf was no longer found in modern humans due to the changes that occurred due to the development of speech.

Study: "Fetal and infant growth patterns of the mandibular symphysis in modern humans and chimpanzees" There is a study published by Michael Coquerelle, et al. that targets the study of the mandibular symphysis in the fetal and infant growth of chimpanzees. The mandibular symphysis consists of the external portion of the mandible, and the symphysis refers to the line seen between the two bones found in the middle of the mandible that appear during the fetal and infant stages. In the fetal chimpanzees, the study showed that the mandibular symphysis is "anteriorly inclined". It then begins to have "an increasingly vertical orientation up until birth". The study has shown that the shiftings that occur are due to the simian shelf becoming repositioned. The shifting that occurs with the simian shelf may show that "the suprahyoid muscles have a significant influence on the anterior growth of the symphysis". The mandibular symphysis in this case is also compared to that of the fetal and infant humans. As stated in the study, both, the human and chimpanzee, start out with a v-shaped mandible during the fetal stages, but the chimpanzee mandible remains in that v-shape leading to the development of the simian shelf. The forming of the simian shelf occurs due to the "basal symphysis [being] modified" as a result of the v-shape being maintained past the fetal stage.

References

Worked examples

Example 1 — a first encounter with Simian shelf

Start with the simplest possible case. Write down what Simian shelf 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 Simian shelf 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 Simian shelf 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 Simian shelf

In research: Simian shelf 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 Simian shelf 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: Simian shelf is common in secondary-school and first-year university syllabi. It links to neighbouring topics Primate anatomy, Skull, so understanding it makes those chapters shorter.
In everyday life: Look for Simian shelf 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 Simian shelf in 20 minutes

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

Frequently asked questions

What is Simian shelf in simple terms?

Why does Simian shelf 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 Simian shelf?

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 Simian shelf.