The history of life on Earth is marked by the emergence, evolution, and extinction of countless species, but only a few have managed to survive millions of years of transformation while maintaining traits almost identical to those of their ancestors. prehistoric fish They are authentic living witnesses of the earliest chapters of the planet's animal history. Some coexisted with the dinosaurs, and others, surprisingly, have survived to this day practically unchanged, inhabiting the depths of the sea as true creatures. living fossilsDiscover the most iconic fish of prehistory—and which of them still inhabit the oceans today—in this comprehensive tour.
What is a prehistoric fish and why are some still alive?
When we talk about prehistoric fish, we refer to those fish whose lineage dates back to remote geological eras, and which have retained primitive morphological and physiological characteristics over millennia. Many of these fish have survived mass extinctions and drastic environmental changes, while others have failed to adapt. The term living fossil It is frequently used to describe current species that show very few morphological differences from their fossil ancestors, although at the genetic level they have also undergone changes (some slow, others significant). The key to their survival lies in adaptations such as tolerance to extreme environments, long reproductive cycles and little competition in very specific ecological niches in the deep oceans. More on the threat of giant fish to ecosystems.
On our journey through time, we encounter everything from giant predators that are now extinct to small, present-day species that go unnoticed in the deep waters but carry with them the secrets of evolutionary history.
Dunkleosteus: The Devonian Colossus
One of the most impressive fish of prehistory was the Dark Osteus, a distinguished member of the family of arthrodire placoderms—the first large vertebrate fish with jawsTheir presence dominated the seas during the Devonian period, approximately between 380 and 360 million years ago.
Dunkleosteus was characterized by a massive, massive skull covered in bony plates like armor. Its jaws, equipped with sharp bony blades instead of teeth, were capable of devastating force, allowing it to easily crush the shells of other fish and large prey.
With an imposing size, up to 10 meters long and weighing more than 3 tonsThis predator occupied the top of the food chain in its oceans. Its movements, although not as swift as those of modern sharks, were extremely effective in ambushes and direct attacks.
The remains of Dunkleosteus were first found near Lake Erie, prompting numerous investigations and reconstructions, many of which have shed light on what marine life was like before the appearance of the dinosaurs.
Xiphactinus: The predator of the Cretaceous waters
El Xiphactinus It belongs to the group of teleosts and was one of the most feared carnivorous fish of the CretaceousIts name, which literally means “sword fin,” anticipates its predatory nature and amazing adaptations.
It primarily inhabited the maritime areas of the south and southwest of what is now the United States, but its range extended to regions of Central and South America. Its body was elongated, reaching a length of 4,3 and 6 meters longIts powerful fins stood out, provided with protruding bony rays that gave it great agility and maneuverability.
The head of Xiphactinus was flattened and had enormous jaws with sharp teeth, capable of swallowing prey of considerable size. Fossils found even show adult specimens with remains of young individuals inside, evidencing phenomena of cannibalism.
Some theories suggest that Xiphactinus may have lived in small groups, which would have allowed it to successfully dominate diverse habitats and exploit different trophic resources.
Cretoxyrhina: The Ginsu Shark of Prehistory
El CretoxyrhinaNicknamed the "Ginsu shark" for the sharp shape of its teeth, it was one of the great marine predators of the late Cretaceous. Its appearance and size are reminiscent of today's great white shark, to which it bears a striking morphological similarity.
Being able to reach up to 7 meters in length, the Cretoxyrhina had robust jaws armed with teeth up to 7 cm long, distributed in two rows of more than 30 pieces each. Its diet was carnivorous and varied:de peces, marine reptiles, to other smaller sharks.
Its powerful and precise bite allowed it to quickly tear through the flesh and bones of its prey. This predator's efficiency contributed to making the Cretaceous oceans highly competitive and dangerous environments.
Recent paleontological studies have confirmed the important role that Cretoxyrhina played in controlling marine populations, consolidating its position as a key player in past ecosystems.
Squalicorax: The carrion shark of prehistory
El squalicorax was another genus of shark that inhabited the oceans during the Cretaceous. Externally it was very similar to the current tiger shark, with dimensions varying between the 2 and 5 meters in lengthIts maximum height rarely exceeded 3 meters.
This shark had a mouth full of sharp, recurved teeth, perfect for both capture live prey enough to develop scavenging behavior. Fossil remains demonstrate that it had a very diverse omnivorous diet and did not disregard the remains of other dead animals.
The evolutionary success of the Squalicorax was due in part to its food versatility, which allowed them to survive in changing habitats and compete efficiently in Cretaceous marine ecosystems.
Prehistoric fish still alive today: Living fossils in our seas
Not all prehistoric species disappeared. Some extraordinary fish have managed to survive to the present day. and can be considered true living fossils. Among them are the coelacanth, the hagfish, the sturgeon, the lamprey, and other lesser-known but equally fascinating species.
- Coelacanth (Latimeria chalumnae and Latimeria menadoensis): This lobe-finned fish was considered extinct until a living specimen was found in the mid-100th century in deep waters off Africa and Indonesia. Coelacanths are enormous, measuring up to two meters and weighing almost XNUMX kg. They are distinguished by their paired fins with an internal bony structure, considered precursors of the limbs of terrestrial vertebrates. They live in underwater cavesThey are slow-moving, long-lived, and have a very low reproductive rate. Recent studies have shown that they have continued to evolve, albeit at a much slower pace than other marine species.
- hagfish (hagfish or hyperotretos): Considered among the oldest vertebrates still in existence, with more than 60 extant species. Their elongated, slimy body, lack of jaws, and suction and viscera-feeding habits make them unique. Furthermore, they can produce large amounts of mucus as a defense.
- lampreysElongated, eel-like marine parasites that have existed for over 400 million years. They attach themselves to other fish with their suction-cup mouths and feed on their blood. Their morphology has changed very little compared to their fossil ancestors.
- Sturgeon: It includes approximately 27 species that have existed for about 200 million years. Sturgeons can live for over a hundred years and reach enormous sizes. They are currently endangered due to overfishing for the caviar trade.
- Other living fossilsThe frilled shark, the Greenland shark (capable of living for several centuries), nautilus, horseshoe shrimp and crabs, some tadpole shrimp, and jellyfish represent prehistoric lineages still present.
These living fossils often inhabit deep, inaccessible environments, which contributes to their survival and the slowness of their morphological evolution.
Hagfish and lampreys: Agnathans from the past to the present
The hagfish and lampreys belong to an ancient group de peces jawless, called agnathans. They are cornerstones in the evolutionary history of vertebrates.
Hagfish have the unique ability to produce a sticky substance that they use as a defense when they feel threatened. They are very long-lived, and their feeding habits are so peculiar that they often burrow into dead or dying animals to devour them from within, using their toothed tongues.
Lampreys, on the other hand, have a cylindrical shape and a circular mouth filled with horny teeth. Many species are obligate parasites, allowing them to survive by attaching themselves to other marine species and feeding on their blood.
Lancetfish: Fierce appearance and remote origin
El lancetfish (Alepisaurus ferox) is another striking example of an ancient lineage with an unmistakably prehistoric appearance. With an elongated and compressed body, it can reach up to two meters in length. Its enormous dorsal fin, resembling a sail, and its jaws equipped with sharp teeth make it an efficient marine predator.
It feeds mainly on de peces small cephalopods and crustaceans. It usually swims at great depths and is rarely seen near the surface, except when carried by currents or accidentally stranded.
Arowana: Surprising Adaptations from the Jurassic
El ArowanaThe Osteoglossidae family is a living relic whose lineage dates back to the Jurassic. It inhabits the rivers and lakes of South America, Africa, Asia, and Australia. It is famous for its unique ability to leap up to two meters out of the water to catch prey such as birds or insects, a skill that distinguishes it among freshwater predators.
The Arowana's body is elongated and covered with large, shiny scales, which has also made it a highly valued fish in international aquaristics.
Coelacanth: The icon of living fossils
El coelacanth occupies a privileged place in the history of biology and evolution. It belongs to the group of actinistios, a lobe-finned fish that emerged more than 400 million years ago. It was thought to be extinct until its rediscovery in the XNUMXth century off the east coast of Africa and later in Indonesia. The coelacanth is one of the marine vertebrates evolutionarily closest to the first organisms to colonize land: its lobe-finned fins feature bony structures similar to the limb bones of terrestrial vertebrates.
It lives in deep caves and rarely comes close to the surface. Its metabolism is slow, it reproduces ovoviviparously, and it can live for several decades. The coelacanth has unique adaptations, such as a articulated movable jaw and a sensory system capable of detecting electrical impulses.
At least two living species have been identified: Latimeria chalumnae on the east coast of Africa, and Latimeria menadoensis in Indonesian waters. Both are considered critically endangered due to bycatch and habitat changes. Furthermore, its large, rough scales, along with its coloration (from deep blue to brown) and its large size, make the coelacanth a authentic emblem of evolutionary resistance.
Other living fossils and species with ancient lineages
The list of marine species with prehistoric origins doesn't end here. There are other organisms whose lineage and morphology have stood the test of time, such as:
- greenland sharkConsidered one of the longest-lived vertebrates on the planet. Its life expectancy could exceed four centuries. It lives in the cold waters of the North Atlantic.
- Frilled shark (Chlamydoselachus anguineus): A true living fossil with eel-like characteristics that has changed very little in over a hundred million years.
- NautilusCephalopod molluscs that have retained their traditional spiral shell shape for 500 million years.
- Shrimp and horseshoe crabArthropods with an appearance and biology almost identical to their fossil ancestors. They have survived several mass extinctions, and their physiological systems are models of evolutionary resilience.
- Tadpole ShrimpTiny crustaceans, present on Earth for over 200 million years. They adapt and survive because their eggs only hatch under favorable environmental conditions.
- Jellyfish and sponges: Among the oldest animals, with fossils dating back hundreds of millions of years, and even almost a geological millennium in some cases.
Protecting these ancient lineages is essential to preserving the planet's biodiversity and natural history.Many of these species are in serious danger due to exploitation, pollution, and climate change. Researching, understanding, and appreciating their extraordinary history is essential to inspire their conservation and to better understand how life was able to conquer and adapt to every corner of the Earth.
