science

Pachyrhachis

Pachyrhachis 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 Pachyrhachis rather than just read about it. In short: Pachyrhachis (from Greek: παχύς pakhús, 'thick' and Greek: ῥάχῐς rhákhis, 'spine') is an extinct genus of snake with well developed hind legs known from fossils discovered in Ein Yabrud, near Ramallah, in the central West Bank. It is a relatively small snake, measuring more than 1.5 metres (4.9 ft) long at maximum.

Key takeaways

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

Reference excerpt

Pachyrhachis (from Greek: παχύς pakhús, 'thick' and Greek: ῥάχῐς rhákhis, 'spine') is an extinct genus of snake with well developed hind legs known from fossils discovered in Ein Yabrud, near Ramallah, in the central West Bank. It is a relatively small snake, measuring more than 1.5 metres (4.9 ft) long at maximum. Pachyrhachis appears to have been an ancient marine snake; the fossils occur in a marine limestone deposit, and the thickened bone of the ribs and vertebrae would have functioned as ballast to decrease the buoyancy of the animal, allowing it to dive beneath the ancient Cretaceous seas that it once inhabited. Pachyrhachis is one of three genera of Cenomanian snakes with hindlimbs. Although many modern pythons and boas still retain remnants of legs, in the form of small spurs, the tiny legs of Pachyrhachis included a hip, knee, and ankle joint. Pachyrhachis was originally described by Haas (1979, 1980) who noted it had a puzzling melange of snake and lizard features; its status as an early snake was later confirmed (Caldwell and Lee, 1997). The position of Pachyrhachis within snakes has been debated (e.g. Lee and Scanlon 2002; Rieppel et al. 2003). Pachyrhachis is among the oldest known snakes and retains well-developed hind limbs, suggesting it represented a transitional form linking snakes to marine lizards (Lee and Scanlon 2002), though other studies place Pachyrhachis within the modern snake radiation as stem-Macrostomata (Zaher, 1998; Zaher & Rieppel, 1999).

See also

Other known fossil snakes with legs:

Eupodophis Haasiophis Najash

References

Caldwell, M.W. and Lee, M. S.Y. (1997). A snake with legs from the marine Cretaceous of the Middle East. Nature 386: 705–709. Haas, G. 1979 On a new snakelike reptile from the Lower Cenomanian of Ein Jabrud, near Jerusalem. Bull. Mus. Nat. Hist. Nat., Paris, Ser. 4, 1, 51–64. Haas, G. 1980 Pachyrhachis problematicus Haas, snakelike reptile from the Lower Cenomanian: ventral view of the skull. Bull. Mus. Nat. Hist. Nat., Paris, Ser. 4, 2:87–104. Haas, G. 1980 Remarks on a new ophiomorph reptile from the Lower Cenomanian of Ein Jabrud, Israel. In Aspects of Vertebrate History, in Honor of E.H. Colbert (ed. L.L. Jacobs), pp. 177–102. Flagstaff AZ: Museum of Northern Arizona Press. Lee, M.S.Y. and Caldwell, M.W. 1998. Anatomy and relationships of Pachyrhachis, a primitive snake with hindlimbs. Philosophical Transactions of the Royal Society of London: Biological Sciences 353: 1521–1552. Lee, M.S.Y., Scanlon, J.D. 2002. Snake phylogeny based on osteology, soft anatomy and behaviour. Biological Reviews 77: 333–401. Rieppel, Olivier et al. 2003 "The Anatomy and Relationships of Haasiophis terrasanctus, a Fossil Snake with Well-Developed Hind Limbs from the Mid-Cretaceous of the Middle East" Journal of Paleontology 77(3):536–558 Scanlon, J.D., Lee, M.S.Y., Caldwell, M.W., and Shine, R. 1999. Paleoecology of the primitive snake Pachyrhachis. Historical Biology 13: 127–152. Zaher, H. 1998. The phylogenetic position of "Pachyrhachis" within snakes (Squamata, Lepidosauria). Journal of Vertebrate Paleontology 18: 1–3. Zaher, H., Augusta, B.G., Rabinovitch, R., Polcyn, M.J., and Tafforeau, P. 2022. A review of the skull anatomy and phylogenetic affinities of marine pachyophiid snakes. In The origin and early evolutionary history of snakes (Eds. D.J. Gower and H. Zaher), pp. 180–206. Systematics Association Special Volume 90. Cambridge: Cambridge University Press.

External links Picture The Cenomanian: stage of hindlimbed snakes Archived 2010-06-29 at the Wayback Machine

Worked examples

Example 1 — a first encounter with Pachyrhachis

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

In research: Pachyrhachis 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 Pachyrhachis 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: Pachyrhachis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cretaceous snakes, Fossil taxa described in 1979, Fossils of Palestine, so understanding it makes those chapters shorter.
In everyday life: Look for Pachyrhachis 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 Pachyrhachis in 20 minutes

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

Frequently asked questions

What is Pachyrhachis in simple terms?

Why does Pachyrhachis 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 Pachyrhachis?

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 Pachyrhachis.