Modern seafloor hydrocarbon seeps are usually surrounded by an unusual macrobiota dominated by symbiont-bearing endemic bivalves and worms. Numerous species of foraminifera (shelled protists) also live around hydrocarbon seeps, but none have been found that are endemic to this environment. An extinct species of benthic foraminifera (Amphimorphinella butonensis) has been found in large numbers in a 15-m-diameter patch of siltstone surrounding a Miocene concretionary carbonate mound (inferred to be a fossil methane seep) in New Zealand. The tests exhibit highly negative δ13C values, consistent with a methane-rich environment of recrystallization on or just below the seafloor. This extremely rare species has been recorded only once before, from asphalt-impregnated Miocene muddy limestone in Indonesia, most likely also associated with hydrocarbon seepage. Is this the first record of a foraminiferal species that was specifically adapted, and endemic, to hydrocarbon seep environments?