'Classic example' of sexual dimorphism in fossil record actually shows nuance between males and females

For decades, scientists have pointed to uintatheres as a classic example of sexual dimorphism in the fossil record. These large, horned animals emerged around 58 million years ago, just a few million years after the dinosaur extinction event. However, a new study from the University of Kansas challenges the notion that males and females of this species were vastly different in size and appearance.

Researchers Kevin Mulcahy and K. Christopher Beard analyzed skull measurements from the American Museum of Natural History in New York. Instead of finding a clear separation between male and female traits, they observed considerable variation within each group. This suggests that the previous interpretation of uintatheres as strong examples of sexual dimorphism may be overstated.

Mulcahy speculates that the apparent dimorphism might be due to the limitations of the measurement techniques used. He also points out the potential influence of cultural biases from the late 19th and early 20th centuries when many fossils were first described. At that time, it was common to assume that males would be larger and more aggressive than females.

The study's findings imply that other species in the fossil record might also exhibit less pronounced sexual dimorphism than previously thought. It challenges the notion that strong male-biased dimorphism is the norm among mammals. Instead, the researchers suggest that such patterns may have evolved independently in various lineages over time.