Congdon made a startling discovery: The oldest female Blanding's Turtles— more than 50 years old— had more egg clutches than younger ones, as well as more eggs per clutch. Not only that, they died at a lower rate too. "What did I do wrong?" Congdon remembers thinking to himself. "Did I make a mistake? Did I analyze it incorrectly?" He knew that adult turtles kept growing throughout their lives, and so he wondered whether the true variable might be body size rather than age. Once he ran the numbers again, controlling for body size, he was astonished to find that he got nearly identical results.

Long article, but it's interesting.