Paleontologists have found 130-million-year-old trace fossils from abyssal plain turbidites of the ancient Tethys Ocean. Combined with nannofossil dating, the new specimens indicate that fishes have occupied the deep seafloor since at least the Early Cretaceous epoch.
Morphology of the fish-feeding trace fossils: (A) slab containing fish-feeding trails (QUER1A, B, and H) and pits (QUER1C, D, E, and G); (B) false-color height map of the feeding trail QUER1B and the feeding pit QUER1C; (C) false-color height map of the feeding pit QUER1G; (D) paleogeographical location of the studied fossil sites. Image credit: Baucon et al., doi: 10.1073/pnas.2306164120.
The 130-million-year-old fish-feeding traces were found in the Early Cretaceous deep-sea deposits of the Palombini Shale Formation near Piacenza, Modena, and Livorno in Italy.
The fossils represent the earliest direct evidence of bottom-living vertebrates from the deep sea.
“When I first found the fossils, I can’t believe what I was seeing,” said Dr. Andrea Baucon, a paleontologist at the UNESCO Geopark Naturtejo, Portugal.
“The reason for the astonishment is the age of the fossils, which predate any other evidence of deep-sea fish by million years.”
“The newly-discovered fossils date back to the Early Cretaceous. They show the activity of fishes on a dinosaur-age seafloor that was thousands of meters deep.”
These trace fossils comprise bowl-shaped excavations produced by ancient fishes, as well as the sinuous trail formed by the tail of a swimming fish, incising the muddy seafloor.
“These fossils do not comprise fish bones, but they record ancient behavior. They mark a critical point in space and time,” Dr. Baucon said.
“It is the point at which fishes moved out of the continental shelf and colonized a new harsh environment, located far away from their original habitat.”
“The studied trace fossils are akin to the astronauts’ footprints on the Moon.”
“Behavior — that’s what the new fossils are all about,” said Dr. Girolamo Lo Russo, a researcher at the Museo di Storia Naturale di Piacenza.
Extant Chimaera monstrosa. Image credit: MAREANO / Havforskingsinstituttet / CC BY-SA 4.0.
To understand the unusal trace fossils, the scientists studied the behavior of modern chimaeras, also known as ghost sharks, in their living environment.
“The coasts of Spain and Italy have provided the key to interpreting the fossil structures,” said Dr. Zain Belaústegui, a paleontologist at the Universitat de Barcelona.
“At 1,500 m of depth, we observed a chimaera plunging its mouth into the sediment. We now know it was a glimpse into the past,” said Dr. Thomas Linley, a researcher at Newcastle University and UK’s National Centre for Subsea and Offshore Engineering.
“The new fossils are identical to structures produced by modern fishes that feed by either scratching the seafloor or exposing their bottom-dwelling prey by suction.”
“This reminds of Neoteleostei, the group of vertebrates that includes modern jellynose fishes and lizardfishes.”
“A key feature of Neoteleostei is the highly developed suction feeding apparatus, therefore, the Apennine fossils may represent a very early stage of diversification of Neoteleostei into the deep sea,” said Dr. Imants Priede, a researcher at the University of Aberdeen.
“Our fossil discoveries reassess the mode and tempo of the vertebrate colonization of the deep sea,” Dr. Baucon said.
“The newly-discovered fossils contain fundamental clues about the very beginnings of vertebrate evolution in the deep sea, having profound implications for both earth and life sciences.”
A paper on the findings was published in the Proceedings of the National Academy of Sciences.
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Andrea Baucon et al. 2023. The earliest evidence of deep-sea vertebrates. PNAS 120 (37): e2306164120; doi: 10.1073/pnas.2306164120
