When you find a snake in nature, how do you know if it's a male or a female?  For a long time, the scientific consensus was that male and female snakes usually looked nearly identical from the outside. But recent research is challenging that assumption, especially for sea snakes, a fascinating group of fully marine reptiles that have rapidly diversified in the Indo-Pacific oceans.

U-M researcher Anthony DiMeglio has spent the past two years investigating whether male and female sea snakes are more different than they first appear. Inspired by earlier papers published suggesting subtle skeletal differences, Anthony dove deeper—literally scanning the bones of sea snakes to find answers.

Using CT scans of specimens from five species, Anthony measured details like jaw shape, tooth length, and even the angle of the eyes. The results? In at least two (and possibly three) species, males and females show clear sexual dimorphism—biological differences between the sexes.

“In many snakes, the differences are subtle, like a slightly narrower head or a shifted eye angle,” explains Anthony. “But those details can affect how males and females hunt, what they eat, or how they survive in different environments.”

 

 

Diet may be the key. Evidence suggests that males and females in some sea snake species eat different prey, potentially tied to seasonal behaviors like breeding and when babies are developing before the females give birth. For example, females may reduce feeding during pregnancy, while males feed less when focused on finding mates. This could push the two sexes toward different food sources, shaping their anatomy over generations.

The work is still ongoing, but the findings are already reshaping how scientists think about sea snakes—and reminding us that even in familiar animals, there are still mysteries waiting to be uncovered.

“I think it’s exciting that we can continue asking new questions and finding answers thanks to the specimens in our collections,” said Anthony. “These discoveries are only possible because of our commitment to conservation and preservation of collections, which ensures ongoing access for generations to come. This is why we collect.”