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Secrets of a Tooth Sleuth

Scientists study woolly rhino teeth to learn what it ate

How can a scientist tell what a woolly rhino ate millions of years ago just by examining its teeth? It takes patience and technical expertise. Here's a snapshot look at how tooth detective Yingfeng Xu (Yang Wang's assistant) uses the clues in fossilized teeth to uncover what prehistoric beasts ate.

Step 1: Hand Cleaning

Xu cleans the tooth until she sees its shiny enamel. To do this, she puts her hands inside a glove box and uses a special cleaning brush. When done, she uses pressurized air to blow off dirt and dust.

Step 2: Obtaining a Sample

Using a fine, dental-like drill, she bores into the tooth enamel until she has about 3 to 10 milligrams – less than an eighth-teaspoon – of enamel powder.

Step 3: Chemical Cleaning

She pours the powder into a tiny microcentrifuge tube. Now the sample must be chemically cleaned to remove any preserved organic materials. First she uses a solution of sodium hypochlorite, then acetic acid. Then the sample (shown at left) is put in a centrifuge machine to separate the powder enamel from the liquid cleaners. During this long process, the sample is shaken, left to settle, and freeze dried.

Step 4: Spectrometer Analysis

Finally, after five days, the samples are ready to be analyzed in a machine called a stable-isotope ratio mass spectrometer. The samples (in batches of 50 to 96) are loaded into a black heating box that keeps them at an even temperature. The machine uses flashes of helium gas to rid the sample of air, then adds phosphoric acid to create a carbon-dioxide (C0₂) gas. The C0₂ gas reveals the carbon and oxygen isotopes in the enamel, which in turn reveals data about the woolly rhino's diet.

Step 5: Reviewing the Data

Xu and Wang examine the samples of tooth enamel for the amounts of ¹³C and ¹²C isotopes, which are clues to what type of plants the animal ate. The C isotopes may reveal that the animal ate mostly cool-season grasses, trees and shrubs found in cold climates and high elevations. Or the C isotopes may show that the animal ate warm-season grasses, like the ones found today in Florida.

What Is an Isotope?

Isotopes are atoms of the same element (e.g., carbon) that have the same number of protons but a different number of neutrons. The carbon isotopes ¹³C and ¹²C, for instance, share the same number of protons, but each has a different number of neutrons. Sort of like members of a family who share the same last name, but have different first names.

carbon isotopes