science

River dolphin

River dolphin 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 River dolphin rather than just read about it. In short: River dolphins also called Freshwater dolphins, are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or even in brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea.

Key takeaways

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

Reference excerpt

River dolphins also called Freshwater dolphins, are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or even in brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. These dolphins are placed in three superfamilies, Platanistoidea (Platanistidae), Inioidea (Iniidae and Pontoporiidae) and Lipotoidea (Lipotidae). They comprise the families Platanistidae (the South Asian dolphins), the possibly extinct Lipotidae (Yangtze River dolphin), Iniidae (the Amazonian dolphins) and Pontoporiidae. There are five extant species of river dolphins. River dolphins, alongside other cetaceans, belong to the clade Artiodactyla, with even-toed ungulates, and their closest living relatives the hippopotamuses, from which they diverged about 40 million years ago. Specific types of dolphins can be pink. River dolphins are relatively small compared to other dolphins, having evolved to survive in warm, shallow waters and strong river currents. They range in size from the 5-foot (1.5 m) long South Asian river dolphin to the 8-foot (2.4 m) and 220-pound (100 kg) Amazon river dolphin. Several species exhibit sexual dimorphism, in that the females are larger than the males. They have streamlined bodies and two limbs that are modified into flippers. River dolphins use their conical-shaped teeth and long beaks to capture fast-moving preys in murky water. They have well-developed hearing that is adapted for both air and water; they do not really rely on vision since their eyes are very small and the water they swim in is usually very muddy. Instead, they tend to rely on echolocation when hunting and navigating. These species are well-adapted to living in warm, shallow waters, and, unlike other cetaceans, have little to no blubber. River dolphins are not very widely distributed; they are all restricted to certain rivers or deltas. This makes them extremely vulnerable to habitat destruction. River dolphins feed primarily on fish. Male river dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them. River dolphins produce a variety of vocalizations, usually in the form of clicks and whistles. River dolphins are rarely kept in captivity; breeding success has been poor and the animals often die within a few months of capture. As of 2020, there was only one river dolphin in captivity.

Taxonomy and evolution

Classification

Four families of river dolphins (Iniidae, Pontoporiidae, Lipotidae and Platanistidae) are currently recognized, comprising three superfamilies (Inioidea, Lipotoidea and Platanistoidea). Platanistidae, containing the two subspecies of South Asian river dolphin, is the only living family in the superfamily Platanistoidea. Previously, many taxonomists had assigned all river dolphins to a single family, Platanistidae, and treated the Ganges and Indus river dolphins as separate species. A December 2006 survey found no members of Lipotes vexillifer (commonly known as the baiji, or Chinese river dolphin) and declared the species functionally extinct. The current classification of river dolphins is as follows:

Superfamily Platanistoidea Family Platanistidae Genus Platanista South Asian river dolphin, Platanista gangetica, with two subspecies Ganges river dolphin (susu), P. g. gangetica Indus river dolphin (bhulan), P. g. minor Family †Allodelphinidae (Oligocene - Miocene) Family †Squalodelphinidae (Oligocene to Miocene) Family †Squalodontidae (Oligocene to Miocene) Family †Waipatiidae (Oligocene to Miocene) Superfamily Inioidea Family Iniidae Genus Inia Amazon river dolphin (boto), Inia geoffrensis Inia geoffrensis geoffrensis Inia geoffrensis humbotiana Araguaian river dolphin, Inia araguaiaensis Bolivian river dolphin, Inia boliviensis Genus †Meherrinia (late Miocene) Genus †Isthminia (Miocene) Family Pontoporiidae Genus †Auroracetus †Auroracetus bakerae Genus Pontoporia La Plata dolphin (Franciscana), Pontoporia blainvillei Superfamily Lipotoidea Family Lipotidae Genus Lipotes Baiji (or Chinese river dolphin), Lipotes vexillifer In 2012 the Society for Marine Mammalogy began considering the Bolivian (Inia geoffrensis boliviensis) and Amazonian (Inia geoffrensis geoffrensis) subspecies as full species Inia boliviensis and Inia geoffrensis, respectively; however, much of the scientific community, including the IUCN, continue to consider the Bolivian population to be a subspecies of Inia geoffrensis. In October 2014, the Society for Marine Mammalogy took Inia boliviensis and Inia araguaiaensis off their list of aquatic mammal species and subspecies and currently does not recognize these species-level separations.

Evolution

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with River dolphin

Start with the simplest possible case. Write down what River dolphin 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 River dolphin 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 River dolphin 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 River dolphin

In research: River dolphin 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 River dolphin 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: River dolphin is common in secondary-school and first-year university syllabi. It links to neighbouring topics Animals that use echolocation, Extant Oligocene first appearances, Mammal common names, so understanding it makes those chapters shorter.
In everyday life: Look for River dolphin 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 River dolphin in 20 minutes

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

Frequently asked questions

What is River dolphin in simple terms?

Why does River dolphin 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 River dolphin?

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 River dolphin.