The deep sea, which is typically defined as depths of at least 200 feet, is home to 90% of marine fish life, but the fishes that inhabit it are poorly represented in the fossil record. Whole body fish fossils are rarely preserved in the briny depths, complicating efforts to better understand how life evolved in the Earth's largest habitat.
In a recent study, Yale researchers introduced a new way to explore the origins of deep-sea fish species that seizes on a plentiful source of evolutionary evidence: tiny, fossilized fish teeth in sediments on the ocean floor.
For the study, the researchers matched distinctive spiral striations found on the teeth of extant species of Cyclothone - the world's most numerically abundant fish genus - to striated patterns on fossilized teeth, including specimens from the Yale Peabody Museum, dating back more than 55 million years. The striations are unique to Cyclothone, appearing nowhere else in the fish tree of life.
The discovery pushes back the earliest known fossil occurrence of Cyclothone by more than 40 million years from the relatively cool middle Miocene (around 11 to 16 million years ago) to the extreme warmth of the early Eocene.
