Many body processes operate in rhythms, often called "biological clocks." A team of researchers led by Timothy Bromage at the New York University College of Dentistry has discovered that a growth rhythm previously identified only in teeth is also present in bone, and represents a biological clock. This clock controls the incremental growth of tooth and bone layers, which relates to an organism's body mass and overall pace of life. Generally, the clock operates more quickly for smaller, shorter-lived animals and more slowly for larger, longer-lived animals. Like other biological clocks, this one appears to originate in the hypothalamus, a brain region that controls many autonomic body functions such as heart rate, temperature, and metabolism.
The rhythm, which can be measured by examining growth layers in teeth and bones using high-contrast confocal microscopes that produce three-dimensional images, is a new tool to help paleobiologists reconstruct the life histories of extinct species.