Level 1 — Absolute Beginner

A mouse is a rodent. A rat is a rodent too. Most rodents are small animals with strong front teeth.

A very long time ago, a giant rodent lived in Thailand. It was as heavy as a big dog. It weighed about 30 kilograms.

Scientists know this from two old teeth. A woman found the teeth in a coal mine in 2004. One tooth was very big, and she did not know what it was.

Now scientists say it is a new kind of animal. They gave it a name for a princess of Thailand. They do not know what the animal looked like, because they have only two teeth.

rodent

A small animal with strong front teeth, such as a mouse or a rat.

teeth

The hard white things in your mouth that you use to eat.

giant

Very, very big.

heavy

Weighing a lot.

weighed

Was a certain number of kilograms.

coal mine

A place under the ground where people dig out black rock for fuel.

found

Saw or got something after looking for it, or by chance.

princess

The daughter of a king or queen.

Level 2 — Elementary

Scientists have identified a giant prehistoric rodent from two fossil teeth found in southern Thailand. The animal lived between 33 and 35 million years ago and probably weighed about 30 kilograms, as much as a large dog.

The teeth, a molar and part of an incisor, were discovered in 2004 at a coal mine in Krabi province by a Thai geologist, Pannipa Tian. The incisor was so large that at first she did not think it belonged to a rodent. Her supervisor later recognized what it was.

After many years of study, a team of researchers from Thailand, France and Canada has now described the animal as a new species in the journal Scientific Reports. They named it Yakamys sirindhornae in honor of Thailand's Princess Sirindhorn, who has supported science for many years.

Newspapers have called the animal a "giant rat," but it was not really a rat. It belonged to a very old family of rodents that is now extinct. Because only two teeth exist, nobody knows exactly what it looked like or what it ate.

identified

Recognized what something is and gave it a name.

prehistoric

From the time before people wrote history.

fossil

Part of an animal or plant from long ago that has turned to stone.

molar

A large tooth at the back of the mouth, used for grinding food.

incisor

A sharp tooth at the front of the mouth, used for cutting.

geologist

A scientist who studies rocks and the Earth.

species

A group of animals or plants of the same kind.

extinct

No longer existing anywhere in the world.

Level 3 — Intermediate

Two teeth that sat in a collection for two decades have revealed one of the largest rodents known from its era: an animal weighing roughly 30 kilograms that lived in what is now southern Thailand between 33 and 35 million years ago. The species, named Yakamys sirindhornae, is described in a study published in Scientific Reports.

The evidence is slim. It consists of a single lower molar and a fragment of a lower incisor, both recovered in 2004 from a coal mine in Krabi province by the Thai geologist Pannipa Tian. She initially misidentified the incisor because of its unusual size; it was her supervisor who suggested it came from an enormous rodent. The formal description was led by Yaowalak Chaimanee, a specialist in fossil mammals at France's National Center for Scientific Research, working with Thailand's Department of Mineral Resources and colleagues in Canada.

The body weight is an estimate, calculated from the size of the molar using the relationship between tooth and body size in other rodents. The comparison that impressed the researchers was with Hulgana, until now regarded as the largest Asian member of the same family. Its molars are less than half as long and half as wide as those of the new species.

Although Thai media have nicknamed the creature "Sirindhorn's giant rat," it was not a rat. It belonged to the Ischyromyidae, one of the earliest major groups of rodents, which died out long ago. The authors argue that the find shows rodents had already evolved very large bodies in Asia by the late Eocene, well before the famous giant rodents of South America appeared.

The limits are obvious. With no skull or skeleton, the animal's appearance, diet and behavior remain unknown, and claims that it lived partly in water go beyond what the paper says.

era

A long period of time in history.

slim

Small in amount; not much.

fragment

A small piece broken off something larger.

misidentified

Wrongly recognized as something else.

specialist

A person with expert knowledge of one subject.

estimate

A careful guess about a size or amount.

nicknamed

Given an informal name.

evolved

Developed gradually over many generations.

Level 4 — Advanced

Paleontology has a long tradition of extracting large conclusions from small objects, and a paper published in Scientific Reports is a textbook case. From one lower molar and a broken lower incisor, unearthed in a coal mine in Thailand's Krabi province in 2004, an international team has erected a new genus and species, Yakamys sirindhornae, and inferred an animal of about 30 kilograms: a rodent the size of a large dog, alive in the late Eocene, some 33 to 35 million years ago.

The story of the specimens is itself instructive. Pannipa Tian, the Thai geologist who collected them, did not at first take the incisor for a rodent's at all, so far did it exceed anything she expected; her supervisor made the connection. The material then waited the better part of twenty years for a full description, eventually led by Yaowalak Chaimanee of France's National Center for Scientific Research with colleagues from Thailand's Department of Mineral Resources and from Canada. The species name honors Princess Maha Chakri Sirindhorn, a longstanding patron of Thai science.

Teeth are the currency of mammal paleontology for good reason. Enamel survives where bone dissolves, and the pattern of cusps and ridges on a molar is as diagnostic as a fingerprint. Here it places the animal among the Ischyromyidae, an archaic family near the base of the rodent tree. Tooth dimensions also scale predictably with body mass, which is how the weight was derived. The largest Asian ischyromyid previously known, Hulgana, has molars less than half the length and width of the new form.

The broader claim is evolutionary. Gigantism in rodents is usually associated with South America, where later lineages produced animals as heavy as cattle and where the capybara, today's largest rodent, still lives. Yakamys suggests that an early lineage had independently grown large in tropical Asia tens of millions of years before.

How much weight two teeth can bear is a fair question. A mass estimate from a single molar carries wide uncertainty; press reports calling this the largest rodent of its period overstate what the more cautious coverage, and the authors, assert. Nothing is known of the skeleton, the diet or the habits, and the lake sediments in which the teeth lay do not show the animal was semi-aquatic. What the find establishes is narrower and still striking: something far bigger than expected was gnawing its way through the Eocene forests of Southeast Asia.

unearthed

Dug up from the ground; discovered.

genus

A group of closely related species, one level above species in scientific naming.

inferred

Reached a conclusion from evidence, not from direct observation.

patron

A person who gives support, often money or influence, to a cause.

enamel

The very hard outer layer of a tooth.

diagnostic

Serving to identify something clearly.