biology

Xuanhanosaurus

Xuanhanosaurus 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 Xuanhanosaurus rather than just read about it. In short: Xuanhanosaurus (meaning "Xuanhan lizard") is a genus of theropod dinosaur that lived during the Middle Jurassic (Bathonian) of the Sichuan Basin, China, around 166 million years ago. This taxon represents one of the various non-coelurosaurian tetanuran taxa found on the Middle Jurassic of the region, uncovered in the Lower Shaximiao Formation.

Key takeaways

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

Reference excerpt

Xuanhanosaurus (meaning "Xuanhan lizard") is a genus of theropod dinosaur that lived during the Middle Jurassic (Bathonian) of the Sichuan Basin, China, around 166 million years ago. This taxon represents one of the various non-coelurosaurian tetanuran taxa found on the Middle Jurassic of the region, uncovered in the Lower Shaximiao Formation. Although it has been known for more than 40 years, this taxon has been the subject of very few studies, although most seem to agree that it is a tetanuran, possibly a basal allosauroid, highlighting the fact that it has a vestigial fourth metacarpal.

Discovery

The type species Xuanhanosaurus qilixiaensis was named by Dong Zhiming in 1984. The generic name refers to Xuanhan County in Sichuan, while the specific name is derived from the town of Qilixia. The specimen was recovered in 1979, when the author was conducting a Dinosaurian Fossil survey in Sichuan Province, when was guided by Liu Yawen and the 137th team to examine the Qilixia section, where they recovered the holotype of this new taxon at the southern flank of the Qili Dorsal Slope. The holotype specimen, IVPP V.6729, was found in China's Lower Shaximiao Formation. It consists of a partial skeleton without a skull, namely a scapula missing the posterior end, coracoid, a possible sternum, humerus, radius, ulna, manus, as well a few fragmentary dorsal vertebrae.

Description

Xuanhanosaurus, originally thought to be around 6 m long, was approximately 4.8 meters (16 ft) in length, with a weight of 265 kilograms (585 lb). Xuanhanosaurus had powerful forelimbs, over 65 cm long; this, along with the retention of the fourth metacarpal in the hand, led Dong to suggest that Xuanhanosaurus might have walked on all four legs. If so, it would be the only known four-legged meat-eater among dinosaurs. Later paleontologists have not agreed with Dong's original assessment. They think this dinosaur walked on its hind legs as other theropods did, pronation of the lower arm being impossible. The strong arms could instead have been useful in catching prey. The retention of the 4th metarcarpal is the most notorious feature of this taxon, yet the presence of a convex proximal surface on the distal carpal 2 has been used to argue it represents a second stage in the evolution of the "semilunate" carpal. Some recent work have notified that beyond the 4th metarcarpal, Xuanhanosaurus also retains ceratosaurian-like short phalanges II-1, similar in length to the ones recovered on Saltriovenator. The scapula was found to be bulkier than in Allosaurus. The distal humerus is enlarged laterally, forming a one-inch step. The vertebrae are posteriorly concave and anteriorly protruding, with cervical centra having flat anterior articular surfaces, also seen in Condorraptor, Piatnitzkysaurus and "Szechuanosaurus" zigongensis, yet lacking posterior pneumatic foramen or fossa, which is seen on the first 2 genera.

Phylogeny Originally, Xuanhanosaurus was assigned by Dong to the Megalosauridae, when this group was meant to include a larger amount of taxa, and was argued to be in the middle stage of the evolution of the Tetanurae due to its vestigial fourth metacarpals. Latter it was found by Roger Benson in 2009 to belong to a primitive lineage of the Megalosauroidea. A more recent study by Benson and colleagues in 2010 found that it was more likely to be the most primitive known member of the Metriacanthosauridae family. In 2018, based on several conditions such as the length and retention of the vestigial 4th metacarpal, it was argued that this taxon and "Szechuanosaurus" zigongensis belong to early-diverging branches of the ceratosaurian-tetanuran node. In 2019, Rauhut and Pol recovered Xuanhanosaurus outside of Metriacanthosauridae, as the basalmost member of Allosauroidea.

References

Illustrations

Worked examples

Example 1 — a first encounter with Xuanhanosaurus

Start with the simplest possible case. Write down what Xuanhanosaurus 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 Xuanhanosaurus 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 Xuanhanosaurus 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 Xuanhanosaurus

In research: Xuanhanosaurus 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 Xuanhanosaurus 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: Xuanhanosaurus is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bathonian dinosaurs, Carnosauria, Dinosaur genera, so understanding it makes those chapters shorter.
In everyday life: Look for Xuanhanosaurus 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 Xuanhanosaurus in 20 minutes

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

Frequently asked questions

What is Xuanhanosaurus in simple terms?

Why does Xuanhanosaurus 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 Xuanhanosaurus?

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 Xuanhanosaurus.