Two divers looking out for the sight of a lobster’s exoskeleton while hunting in the Florida Keys found a very different type: a human skull.

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The man and woman were diving for lobster Sunday under the Card Sound Bridge, which connects Florida’s mainland to North Key Largo. The divers — who were visiting from Naples, Florida, to hunt lobster for the day — exited the water and alerted a Florida Fish and Wildlife officer, according to the Monroe County Sheriff's Office. The bones were submitted to the Monroe County Medical Examiner, and the case is currently under investigation.