inosaurs were the most successful terrestrial vertebrates that ever lived on this planet. According to the fossil record, they first appeared in the mid-Triassic period of the Mesozoic era, dominating the landscape for 163 million years until their extinction 66 million years ago at the end of the Cretaceous period. Why were dinosaurs so successful for such a long time? One clue may be their metabolism. Until the 1960s, most scientists assumed that dinosaurs were cold-blooded heterotherms, which are animals whose body temperature vary with the environment, similar to modern reptiles like the Komodo dragon. That view began to change in the mid-1960s with papers advocating some degree of homeothermy in dinosaurs. Homeotherms are animals that internally keep their body temperatures within a limited range. The new dinosaur physiology paradigm was based on indirect evidence such as skeletal features; the presence of fossils at high latitudes that experience long, cold winter nights; rapid evolutionary rates of some dinosaur taxa; and predator/prey ratios that indicated that carnivores ate lots of prey (1). Today, paleontologists argue about whether dinosaurs were warm-blooded, high-metabolic homeotherms, like mammals and birds; cold-blooded, low-metabolic het-
D
William J.
Showers
Reese Bar -
© MICHAEL S. YAMASHITA/CORBIS
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A new pyroly-
sis technique
provides direct
evidence that M A R C H 1 , 2 0 0 2 / A N A LY T I C A L C H E M I S T R Y
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tion in different parts of the body (e.g., head, tail, or core body). Therefore, assuming that a dinosaur’s body water was in equilibrium like animals today, the measurement of the oxygen isotopic variation between different bones can be used to calculate the relative temperature difference between different parts of the body from the slope of Equation 1 as ⌬T oC = 4.3(⌬␦18Op)
Sample yields for different types of isotopic reference material, showing that carbonates do not pyrolyze well or give reproducible yields. Standards other than carbonates or water must be used as reference material to calibrate the machine gas standard.
erotherms that could not adapt to abrupt global climate changes; or something in between (2, 3). One way to directly investigate metabolism in extinct animals is to measure the oxygen isotopic composition of phosphate in ancient dinosaur bones. In 1994, Barrick and Showers used this approach and provided direct evidence that the fearsome Tyrannosaurus rex was a homeotherm (4). Although high-precision stable isotopic analyses are routine in many areas of the natural sciences, introducing continuousflow isotopic ratio technology has resulted in a rapid expansion of new, highly precise, and fast measurement techniques. In this article, we describe a new automated pyrolysis method using continuous-flow isotopic ratio MS (CF-IRMS) to measure the oxygen isotopic composition of bone phosphate. The method is used to analyze three dinosaur fossils from the Cretaceous, Jurassic, and Triassic periods to investigate whether the metabolic results determined from fossils are real or an artifact of time.
Fossil clues Oxygen isotopic composition of bone phosphate depends on the animal’s body temperature and the isotopic composition of the water in its body according to T oC = 111.4 – 4.3 (␦18Op – ␦18Ow)
(1)
in which T oC is the body temperature in Celsius, ␦18Op is the oxygen isotopic composition of the bone phosphate, and ␦18Ow is the oxygen isotopic composition of the body water (4). We will never know the isotopic composition of the water that dinosaurs drank or that was in their bodies, but we do know from modern animals that no difference exists in the isotopic composi-
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Physiologists define homeotherms as animals that have
