CORAL GABLES, Fla. — For years, the scientific community has held a theory about the bonnethead shark’s famous shovel-shaped head: that in males, the pointed snout was a badge of maturity, a sign that the shark had, as it were, grown up. A new study from the Rosenstiel School of Marine, Atmospheric, and Earth Science at the University of Miami has found that the whole thing was wrong. The heads simply get rounder as the sharks get older, in both sexes, most dramatically in females. The pointed snout, it turns out, meant nothing. And that’s fine.

The study, published this month, is the first in-depth assessment of bonnethead head shape and diet in Biscayne Bay, with additional work in Tampa Bay — a pair of bays where the sharks, according to the researchers, have been doing their own thing for decades without anyone’s permission.

Kathy Liu, the study’s lead author, who conducted the work while earning her master’s degree at Rosenstiel, put the finding in the most measured language available to a scientist whose life’s work is now, officially, “the rounder heads.” “Our findings show that the pointed head shape is not a feature that develops in males when they reach maturity,” Liu said — which is the academic way of saying that the theory had been in the field’s working files for years and was, in the words of one marine biologist who asked not to be named, “a story everyone agreed to tell.”

"Our findings show that the pointed head shape is not a feature that develops in males when they reach maturity." — Kathy Liu, lead author, on the mystery of the pointed snout

The implications, for what they’re worth, are charming. The bonnethead, it turns out, is aging with grace — the head softens, the jaw rounds, and the shark acquires what one researcher described as “a more approachable profile.” The change is most dramatic in females, which suggests that the bonnethead’s famous face was never a badge of manhood at all, but a badge of youth, in both sexes, and that the sharks have, for as long as anyone has been looking at them, been getting away with it.

The study also assessed what the sharks are eating, which is, frankly, the more important question, and found a diet that, in the words of the report, “varies by bay, season, and what the bay is having.” Biscayne Bay’s bonnetheads, the researchers noted, appear to be “selective in a way that suggests intention,” which is the highest compliment a scientist can pay to a creature that has, up until now, been defined almost entirely by the shape of its face.

THE BONNETHEAD, BY THE NUMBERS

  • Head shape, with age: rounder (both sexes; females most dramatically)
  • Pointed snout as male maturity marker: debunked (a "long-standing mystery," solved)
  • Bays assessed: 2 (Biscayne and Tampa)
  • Long-standing theories retired: 1 (the one everyone was asking)
  • Sharks consulted: 0 (the study relied on "measurements and diet samples")

The study was picked up by EurekAlert and covered by SciTechDaily, which describes the finding as “new clues to a long-standing mystery” — a phrase that, in this case, is doing double duty, because the mystery was long-standing, the clues are new, and the sharks, for their part, are neither.

At press time, the Rosenstiel School had received “a number of questions about the sharks’ feelings on the matter,” and the study team confirmed that the sharks “did not appear to have opinions, at least not expressible ones.”