Renowned 19th-century American paleontologist Edward Drinker Cope proposed "Cope's Rule," hypothesizing that animal lineages tend to increase in body size over time.

The dinosaur fossils he dug up in the American West seemed to bear this out. However, Cope was not infallible. In a mistake famed in the annals of paleontology, he published a description of the wondrous long-necked marine reptile Elasmosaurus in 1868 with its head erroneously placed at the end of the tail.

However, it appears Cope had his head on straight about body size. Scientists recently said the most comprehensive test of "Cope's rule" ever conducted, involving 17,208 different marine animal groups spanning the past 542 million years, demonstrated a clear trend toward larger size over time. The analysis went back to Earth's dawn of animal life.