“Joe” certainly was a small dinosaur, compared to adults of its kind. It was only six feet long (compared to over 25 feet long for adult duck-billed dinosaurs), so “Joe” couldn’t have been fully grown. But, could scientists get any more precise?
A little bone biology turned out to be just the ticket to aging “Joe.” Even though bones are hard, they are actually made up of a dynamic, living tissue that undergoes constant remodeling, replacement, and growth. Many animals alive today lay down yearly layers in their bones—just like tree rings! Dinosaurs were no exception. So, if you slice up a dinosaur bone and count the rings under a microscope, you can figure out how old it was when it died.
Let’s take a closer look at these yearly rings! Under a microscope, every tiny detail of the bone was revealed, even the spaces once occupied by blood vessels and bone cells.
What do Joe’s bones look like? The researchers studying “Joe” took a small sample from the shin bone, and sliced it up very, very thin.
“Joe”’s bone showed signs that it was growing very fast—lots of big blood vessels, but no yearly rings. This meant “Joe” was a very young animal—probably under a year in age! In under 12 months, “Joe” had hatched at less than the size of a human infant and grown to over six feet in length. It takes a human 15-20 years to grow that much.