Level 1 — Absolute Beginner
Scientists found a very old animal in the Gobi Desert in Mongolia. It looked a bit like a rabbit.
The animal was small. It was only 6 to 7 inches long from head to tail. It had long back legs.
It lived when dinosaurs lived. Scientists call its group zhelestids. For almost 40 years, they did not know what these animals looked like.
Now they know. The new animal is called Tamirkhan balcarceli. It shows that zhelestids were not early cousins of animals like us.
- fossil
- The old remains of a plant or animal in rock.
- desert
- A very dry place with little rain.
- mammal
- An animal that feeds milk to its babies.
- rabbit
- A small animal with long ears.
- species
- A kind of animal or plant.
- dinosaur
- A very old, large reptile.
- mystery
- Something that people cannot explain yet.
- scientist
- A person who studies nature.
Level 2 — Elementary
A beautifully kept fossil from Mongolia's Gobi Desert has solved a puzzle that troubled scientists for almost 40 years. The study was published in the journal Nature.
The animal is called Tamirkhan balcarceli. It is the most complete fossil ever found of a group called zhelestids. It was small, about 6 to 7 inches from head to tail, and its long back legs made it look a little like a rabbit.
A student named Andres Giallombardo found the fossil in 2004 during a museum expedition. Scientists from several universities and the American Museum of Natural History studied it for years.
Before this, many experts thought zhelestids were early relatives of modern placental mammals, the group that includes humans, dogs and whales. The new fossil shows they were a separate branch of small mammals from the Cretaceous period.
- expedition
- A trip made to explore or search.
- complete
- Having all its parts.
- placental mammals
- Mammals whose babies grow inside the mother.
- relatives
- Members of the same family or group.
- branch
- A part of a family tree that grows apart.
- Cretaceous
- The last age of the dinosaurs.
- journal
- A magazine where scientists publish their work.
- puzzle
- A problem that is hard to solve.
Level 3 — Intermediate
A remarkably well preserved fossil from Mongolia's Gobi Desert has resolved a puzzle that had frustrated paleontologists for nearly four decades. Described in the journal Nature by researchers from the American Museum of Natural History, Stony Brook University, the University of Arizona and Arcadia University, the specimen belongs to a new species named Tamirkhan balcarceli.
Lead author Andres Giallombardo collected the fossil in the eastern Gobi in 2004 as a graduate student on a museum expedition. It is the most complete zhelestid yet found, and it finally reveals what these animals looked like: a creature only six to seven inches long, with unusually elongated hind limbs that gave it a somewhat rabbit like appearance.
The discovery overturns a long standing assumption. Because zhelestid teeth resembled those of early placental mammals, many scientists placed them on the branch of the family tree that leads to modern placentals. The new skeleton shows they were in fact a distinct lineage of small Cretaceous mammals.
The finding matters beyond one species. It shows how easily teeth alone can mislead, and how a single well preserved skeleton can rewrite a chapter of mammal evolution.
- preserved
- Kept in good condition over a long time.
- paleontologist
- A scientist who studies ancient life through fossils.
- specimen
- A single example of something used for study.
- elongated
- Made longer than usual.
- hind limbs
- The back legs of an animal.
- lineage
- A line of descent from a common ancestor.
- resemble
- To look like something else.
- assumption
- Something believed without proof.
Level 4 — Advanced
A strikingly well preserved skeleton from Mongolia's Gobi Desert has settled a question that had bedevilled paleontologists for the better part of four decades. Reported in Nature by a team drawn from the American Museum of Natural History, Stony Brook University, the University of Arizona and Arcadia University, the specimen represents a new species, Tamirkhan balcarceli.
Andres Giallombardo, the study's lead author, recovered the fossil in the eastern Gobi in 2004, while still a graduate student on a museum sponsored expedition. It remains the most complete zhelestid on record, and it discloses at last what these animals actually looked like: a diminutive creature of six to seven inches, its hind limbs conspicuously elongated, lending it a faintly lagomorph silhouette.
The implications are taxonomic as much as anatomical. Zhelestid dentition so closely echoed that of early placental mammals that many researchers assigned the group to the placental stem. The new skeleton dismantles that inference, placing zhelestids instead in a separate lineage of small Cretaceous mammals that evolved alongside, rather than toward, the modern placentals.
The episode is a caution against reading too much into isolated teeth, and a reminder that a decades old fossil, patiently recovered and carefully prepared, can still overturn a settled chapter of evolutionary history.
- bedevil
- To trouble or confuse for a long time.
- diminutive
- Extremely small.
- conspicuously
- In a way that is easy to notice.
- lagomorph
- A member of the rabbit and hare family.
- taxonomic
- Relating to the classification of living things.
- dentition
- The arrangement and type of teeth.
- dismantle
- To take apart or break down.
- inference
- A conclusion drawn from evidence.
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