Curated timeline

Fish Evolution

From Jawless Chordates to Teleost Kings: A chronological guide to the origins, diversification, and supreme aquatic adaptations of fishes over 530 million years of Earth history.

• Origin of Chordata (about 530 Million Years Ago)

  During the Cambrian Explosion, early chordates like Pikaia develop a notochord—a flexible rod providing structural support—laying the very first foundation for the vertebrate backbone.

• First Craniates (Vertebrata) (about 525 Million Years Ago)

  Haikouichthys and Myllokunmingia appear in the fossil record. They are among the earliest known craniates, possessing a distinct head, eyes, and primitive cartilaginous vertebrae.

• Evolution of Conodonts (about 495 Million Years Ago)

  Conodonts emerge. Long known only from their microscopic, tooth-like fossils, these eel-like jawless vertebrates are the first to evolve calcium phosphate (the mineral making up our bones and teeth).

• Rise of Ostracoderms (about 480 Million Years Ago)

  Ostracoderms, heavily armored jawless fishes, diversify in the Ordovician. Lacking paired fins, they are likely sluggish bottom-feeders using muscular pharynxes to suction food.

• Cyclostomata Divergence (about 450 Million Years Ago)

  The lineage containing modern hagfishes and lampreys (Cyclostomata) diverges. As the only surviving jawless fishes today, they retain a primitive, eel-like cartilaginous anatomy.

• Evolution of Jaws (Gnathostomata) (about 430 Million Years Ago)

  A massive evolutionary leap: the first gill arches migrate forward and hinge to form jaws. This transforms vertebrates from passive filter-feeders into active, biting predators.

• Acanthodians ('Spiny Sharks') (about 430 Million Years Ago)

  Acanthodians appear. Despite their nickname, they are not true sharks but possess features of both cartilaginous and bony fishes, with stout spines supporting their fins.

• Origin of Placodermi (about 420 Million Years Ago)

  Placoderms, jawed fishes with heavily armored heads and thoraxes, emerge in the Silurian. They will soon dominate the Devonian period.

• Entelognathus and the Modern Face (about 419 Million Years Ago)

  Entelognathus primordialis, a placoderm fossil from China, reveals the earliest known presence of maxilla, premaxilla, and dentary bones—the exact jaw bones found in modern bony fishes and humans.

• Origin of Osteichthyes (Bony Fishes) (about 419 Million Years Ago)

  The Osteichthyes originate. Characterized by an ossified (bony) internal skeleton, this superclass will eventually comprise 99% of all living fish species.

• Origin of Chondrichthyes (Cartilaginous Fishes) (about 420 Million Years Ago)

  Sharks, rays, and chimaeras diverge. They abandon heavy bone in favor of a lighter, highly flexible cartilaginous skeleton, optimizing for speed and agility.

• Sarcopterygii vs. Actinopterygii (about 415 Million Years Ago)

  Bony fishes split into two monumental lineages: Actinopterygii (ray-finned fishes, supported by bony spines) and Sarcopterygii (lobe-finned fishes, with fleshy, muscular fins).

• Evolution of Lungs and Swim Bladders (about 410 Million Years Ago)

  Early bony fishes develop an out-pocketing of the gut to gulp air in oxygen-poor waters. In lobe-finned fishes, this remains a lung; in ray-finned fishes, it evolves into a buoyancy-controlling swim bladder.

• Rise of Lungfishes (Dipnoi) (about 410 Million Years Ago)

  Lungfishes emerge and thrive. They are uniquely adapted to survive droughts by burrowing into mud and breathing atmospheric oxygen. They are the closest living relatives to all tetrapods (land vertebrates).

• Origin of Coelacanths (about 410 Million Years Ago)

  The coelacanths (Actinistia) appear. This lineage of lobe-finned fishes reaches peak diversity in the Mesozoic before seemingly vanishing from the fossil record alongside the dinosaurs.

• Eusthenopteron (about 385 Million Years Ago)

  Eusthenopteron, a pelagic lobe-finned fish, shows internal fin bone structures homologous to the humerus, ulna, and radius of future land animals.

• Palaeonisciformes Dominate (about 380 Million Years Ago)

  Early ray-finned fishes (Palaeonisciformes) begin their long ascent. They feature heavy, interlocking ganoid scales and asymmetrical, shark-like (heterocercal) tails.

• Tiktaalik: The Fishapod (about 375 Million Years Ago)

  Tiktaalik roseae bridges the gap between fish and amphibians. It has fish-like gills and scales, but a tetrapod-like neck, ribs, and wrist bones capable of bearing its weight on land.

• Cladoselache (about 370 Million Years Ago)

  Cladoselache, an early shark, swims the Devonian seas. Unlike modern sharks, it lacked scales and a rostrum, and its mouth was located at the very front of its head.

• Dunkleosteus rules the Devonian (about 360 Million Years Ago)

  Dunkleosteus, a massive predatory placoderm up to 6 meters long, becomes the apex predator of the 'Age of Fishes', equipped with self-sharpening bony jaw plates.

• Late Devonian Extinction (about 359 Million Years Ago)

  A devastating mass extinction wipes out the placoderms completely and severely curtails the lobe-finned fishes, clearing the oceans for ray-finned fishes and sharks to take over.

• Origin of Neopterygii (about 340 Million Years Ago)

  The Neopterygii ('new fins') evolve from early ray-fins. They develop a more symmetrical tail and a modified jaw that allows for rapid opening, improving feeding efficiency.

• Helicoprion (Buzzsaw Shark) (about 290 Million Years Ago)

  Helicoprion, an early cartilaginous fish closely related to chimaeras, evolves a bizarre, spiraling tooth-whorl in its lower jaw to slice through cephalopods.

• Permian-Triassic Extinction (about 252 Million Years Ago)

  The 'Great Dying' heavily impacts marine ecosystems. Cartilaginous fishes face a massive bottleneck, while bony fishes suffer but ultimately rebound with extreme diversity.

• Chondrostei Divergence (about 250 Million Years Ago)

  The lineage leading to modern sturgeons and paddlefishes (Chondrostei) diverges. They secondarily lose much of their bony skeleton, reverting to mostly cartilage.

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