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Reading Bones and Teeth Like a Diary

Science · Dinosaurs & Paleontology · ages 12-14

Name ______________________ Date ____________

Scientists have checked that a bone formed one growth mark each year. What does the interval between two successive marks represent?
- One day of bone growth
- One year of bone growth
- Ten years of bone growth
What can a change in stable oxygen isotope ratios between tooth samples record?
- A change in body-water chemistry while the tooth formed
- An exact age measured by radioactive decay inside the tooth
- A complete list of every plant eaten while the tooth formed
Finding fossils close together is enough to treat them as one ancient community, without checking their ages.
Circle one: True False
In an invented study, tooth samples repeatedly match Region A early each year and Region B later. The regions have distinct water signals. Local seasonal changes and burial alteration do not fit the pattern. Which explanation is best supported?
- Seasonal water changes in one region produced the early and late matches without travel between regions.
- Burial changed the tooth chemistry into a repeating pattern resembling the two regional water signals.
- The dinosaur repeatedly moved between regions while the sampled tooth material was forming.
A bone preserves 8 annual growth marks. Earlier marks may have been erased as the bone changed during life. Which age estimate fits this evidence?
- Exactly 8 years; the surviving marks cover the animal's whole life
- Fewer than 8 years; allow for erased marks by reducing the surviving count
- At least about 8 years; the animal may be older
An invented study has matching dates and settings. Tooth signals support movement after local water and burial checks. A coprolite contains fern pieces matching plants shown to have grown there. Its maker is unknown. Which reconstruction fits all three clues?
- Movement is supported; local ferns match possible food, but the dung maker is not linked to the teeth.
- Movement is supported; the fern remains link the sampled dinosaur's feeding to the region its teeth last record.
- Local feeding is supported; the fern match makes local water changes a better explanation for the tooth pattern.
For this exercise, all 12 yearly growth bands are preserved. The last 2 are narrower than all the earlier bands. Assume wider bands mean faster growth in that year. How many years had the faster growth?
Answer: ______________
Seasonal dinosaur tooth changes match those in animals that stayed nearby. Two other regions also have signals resembling the dinosaur samples. Which comparison best tests movement against a local seasonal cause?
- Compare each dinosaur sample with a regional reading, using only the local annual average as the comparison.
- Compare repeated dinosaur samples with the full local seasonal range and both regional signals.
- Compare the full local seasonal range with one dinosaur sample, then match that sample with both regions.

Answer key

For grown-ups. Fold this page away before handing over the rest.

Reading Bones and Teeth Like a Diary W1-mt_8_BxtNDrLZ-s1

One year of bone growth · The marks formed yearly in this bone. The interval from one mark to the next therefore represents about one year of growth.
A change in body-water chemistry while the tooth formed · Stable oxygen isotope ratios in teeth can record body-water chemistry during formation. Several influences affect the signal, so it does not automatically reveal location, age or a list of foods.
False · Nearby fossils can come from different ages. Check their dates and setting before combining them into a reconstruction of one community.
The dinosaur repeatedly moved between regions while the sampled tooth material was forming. · Repeated matches with distinct regional signals support movement. Local seasonal changes and burial alteration are competing explanations, but the study's checks found that neither fits this pattern. The evidence does not give a travel distance.
At least about 8 years; the animal may be older · Eight preserved annual marks record about eight years. Erased early marks would leave additional years uncounted, so the animal may have been older.
Movement is supported; local ferns match possible food, but the dung maker is not linked to the teeth. · The tooth checks support movement. Coprolite fragments match vegetation that grew there, linking possible food with habitat. The unknown dung maker prevents assigning that food to the dinosaur whose teeth were sampled.
10 · Twelve yearly bands include two narrower bands. Under the stated assumption, the remaining 12 minus 2, or 10 bands, represent faster-growth years.
Compare repeated dinosaur samples with the full local seasonal range and both regional signals. · Repeated dinosaur samples must be compared with the full local seasonal range and regional signals. A local annual average can hide seasonal changes. One dinosaur sample cannot show a repeating pattern. The matching changes in animals that stayed nearby mean a local cause still needs testing.