The researchers discovered that the body sizes of these fishes have grown larger over the past hundred million years in conjunction with the gradual cooling of ocean temperatures.Their finding adheres to two well-known rules of evolutionary trends, Cope’s rule which states that organismal body sizes tend to increase over evolutionary time, and Bergmann’s rule which states that species reach larger sizes in cooler environments and smaller sizes in warmer environments. What was less understood, however, was how these rules relate to ectotherms, organisms that can’t regulate their internal body temperatures and are dependent on their external or environmental climates. Therefore, the authors add a caveat that many more factors could play a role in fish body size evolution. They said undoubtedly they will discover more about their body size evolution in the future.