“I couldn’t believe what I was seeing” – discovering the missing piece of the evolution puzzle in 130 million-year-old rocks

Pictured is a rock slab containing the oldest evidence of the presence of vertebrates in the deep sea. Fossil evidence consists of pits and passages produced by feeding fish during the Early Cretaceous. The dish-like structures are about 4 cm wide. Credit: Andrea Bacon

Scientists have discovered the missing piece of the evolutionary puzzle in 130 million-year-old rocks. This discovery comes as a result of international cooperation Faculty of Sciences, University of Lisbon (Portugal) is involved.

despite of Vertebrates Being a dominant component of contemporary deep-sea ecosystems, there has been no fossil evidence of deep-sea fish older than 50 million years. Now, the recent discovery of exceptionally rare fossils provides the oldest known evidence of deep-sea fish. This pushes the timeline for deep-sea colonization back by a staggering 80 million years.

The results were recently published in the journal Proceedings of the National Academy of Sciences.

“When I first found the fossils, I couldn’t believe what I was seeing,” says paleontologist Andrea Bacon, the leader of this study and a researcher at the University of Genova (Italy). It was he who discovered fish fossils in the northwestern Apennines, near Piacenza, Modena, and Livorno (Italy).

Red mullet produce a feeding hole on the shallow sea floor of the Ligurian Sea

Red mullet produce a feeding hole on the shallow sea floor of the Ligurian Sea. The new study reports identical structures from Cretaceous sediments in Italy’s northern Apennines. The results indicate that fossil feeding pits are the oldest evidence of deep-sea vertebrates. Credit: Andrea Bacon

The reason for this astonishment is the distant age of the fossils, which predates any other evidence of the existence of deep-sea fish by a million years. The newly discovered fossils date back to the Early Era Cretaceous period (130 million years ago). “The new fossils show fish activity on the sea floor dating back to the age of dinosaurs, which was thousands of meters deep,” adds Andrea Baucon.

Using photogrammetry, the scientists provided a photo-embellished elevation map of the craters and feeding paths of the fossils. This evidence represents the oldest evidence of deep-sea vertebrates. Credit: Girolamo Lo Russo

The newly discovered fossils are rare and unusual. They include bowl-shaped fossils produced by ancient feeding fish, as well as the winding path formed by the swimming fish’s tail, which traverses the muddy sea floor. These archaeological fossils do not include body fossils such as fish bones, but they do record ancient behavior. As such, the Apennine fossils represent a critical point in space and time. It is the point at which fish moved from the continental shelf and colonized a new harsh environment, located far from their original habitat.

Thousands of meters below the surface of the Tethys Ocean — an ancient ocean that existed between 250 and 50 million years ago and is a precursor to the present-day Mediterranean Sea — the oldest deep-sea fish faced harsh environmental conditions compared to their shallow-water origins. Total darkness, near-freezing temperatures, and enormous pressures limit the survival of these abyssal pioneers.

The video shows a chimera swimming above sediments in the Kermadec Trench (depth: 1,544 metres) and then plunging its mouth into the sediment to feed. In the new study, scientists studied the behavior of modern fish to understand behaviors associated with the oldest deep-sea vertebrate fossils. Credit: Thomas Linley, Alan Jamieson

Such extreme conditions require adaptations for life in the deep sea, evolutionary innovations as important as those that allowed the colonization of land and air, such as wings and limbs, for example.

The newly discovered fossils represent not only the oldest deep-sea fish, but also the oldest deep-sea vertebrates. The evolution of vertebrates – vertical animals – has been punctuated by habitat shifts from shallow marine origins to terrestrial, aerial and deep-sea environments. Deep-sea invasion is the least understood habitat transformation due to the low potential for fossilization associated with the deep sea.

“The new fossils shed light on a mysterious chapter in the history of life on Earth,” comments Carlos Neto de Carvalho, researcher at the Dom Luiz Institute, Faculty of Sciences of the University of Lisbon (Ciências ULisboa) (Portugal).

Elevation map of the rock slab that preserves the oldest evidence of deep-sea vertebrates

Elevation map of the rock slab above, preserving the oldest evidence of deep-sea vertebrates. Color coding is related to altitude, with warmer colors at higher altitudes. Credit: Girolamo Lo Russo

Apennine fossils are forcing scientists to reconsider the factors that may have led to the colonization of the deep sea by vertebrates. The authors suggest that the catalyst was the unprecedented input of organic matter that occurred between the Late Paleolithic Jurassic The Early Cretaceous period. The availability of food in the deep sea encourages bottom-dwelling worms, which in turn attract fish that use specific behaviors to expose them to them.

In this study, the researchers turned to current seas to understand fossil behavior and study the behavior of modern fish in their environments. Scientists have explored the depths of the Pacific Ocean to study chimeras, also known as ghost sharks, in their habitat.

The new fossils match structures produced by modern fish that feed either by scratching the sea floor or exposing their bottom-dwelling prey by suction. This is reminiscent of Neoteleostei, the group of vertebrates that includes modern jelly fishes and lizard fishes.

Chimeras swimming above sediments in the Kermadec Trench in the Pacific Ocean

Chimeras swimming above sediments in the Kermadec Trench in the Pacific Ocean (depth: 1544 m). In the new study, scientists studied the behavior of modern deep-sea fish to understand the formation mechanism of archaeological fossils from the Cretaceous period. The findings reveal the oldest evidence of deep-sea vertebrates. Credit: Thomas Linley, Alan Jamieson

“Contrary to popular belief, deep sea floor sediments are full of fossil remains of ancient life, but usually from small organisms that live higher in the water column such as phytoplankton or zooplankton,” explains Mario Cachao, co-author of this research. Study and researcher at the Dom Luís Institute, Ciências ULisboa.

“However, to discover and interpret direct evidence of the organic activity of imprinted and geologically preserved vertebrates in such deposits, after they had been tectonically deformed and exposed as the northern Apennine mountain range, and which were mostly emplaced during the Miocene and Pliocene geological times – that is, almost since “20 million years ago, this is an extremely rare find.”

The newly discovered fossils may represent the first major step in the origins of modern deep-sea vertebrate biodiversity. Modern deep-sea ecosystems have their roots in Apennine fossils, undergoing a major habitat shift in ocean history. “Our fossil discoveries reassess the situation The pace of vertebrate colonization of the deep sea. Newly discovered fossils contain key evidence About the beginnings themselves “The evolution of deep-sea vertebrates has profound implications for both Earth and life sciences,” Andrea Baucon summarizes.

Reference: “The oldest evidence for deep-sea vertebrates” by Andrea Boccone, Annalisa Ferretti, Chiara Fiorone, Luca Pandolfi, Enrico Serbagli, Armando Piccinini, Carlos Neto de Carvalho, Mario Cachao, Thomas Linley, Fernando Muñiz, Zane Belastegui, Alan Jamieson. , Girolamo Lo Russo, Filippo Guerrini, Sara Ferrando and Emantes Pride, September 5, 2023, Proceedings of the National Academy of Sciences.
doi: 10.1073/pnas.2306164120

The study resulted from the collaboration of researchers affiliated with scientific institutions from Italy (Universities of Genova, Modena and Reggio Emilia, Padova, Pisa, Parma; Natural History Museum of Piacenza; South Tyrol Natural Museum), Portugal (UNESCO Global Geopark Naturtigo; University of Lisbon), England ( University of Newcastle), Spain (Universities of Seville and Barcelona), Australia (University of Western Australia), Scotland (University of Aberdeen).

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