Bony Fish

By | September 9, 2016

About 400 million years ago, a new family of fish began swimming in the seas. Unlike the sharks that had ruled the waters for millions of years, the new fish had skeletons hardened with calcium to form bone, earning them the name “bony fish.”
The bony fish evolved into a huge range of new species and make up more than 95% of fish species alive today.


Key features
■ A skeleton made of bone
■ Most have ray fins (fins supported by long rays of bone that give these fish fine control of movement)
■ Swim bladders (air-filled sacs) to help these fish stay buoyant in water

Bony fish first appeared in the Devonian Period, almost 395 million years ago, and remain very common today.

Leedsichthys (LEEDS-ick-thiss)


When: 176–161 million years ago (Middle Jurassic)

Fossil location: Europe, Chile

Habitat: Oceans

Length: 30 ft (9 m)

Perhaps the largest bony fish that ever lived, Leedsichthys was bigger than a killer whale. Despite its fearsome size, it was a harmless filter feeder rather than a hunter—it gulped huge volumes of water into its mouth and then squirted it out while sifting shrimp and other tiny animals with its gills. Bite marks on one fossil show that Leedsichthys was hunted by gigantic marine reptiles called pliosaurs.

Xiphactinus (zye-FAC-tee-nus)


When: 112–70 million years ago (Middle to Late Cretaceous)

Fossil location: N. America

Habitat: Shallow waters of N. America

Length: 20 ft (6 m)

Xiphactinus was a powerful swimmer with a long, muscular body. It had a huge mouth and could swallow large prey whole. One fossil was found to contain the remains of a 7 ft (2 m) fish in its stomach—perhaps the prey was too big for Xiphactinus and killed it by thrashing around inside.

Diplomystus (DIP-low-MISS-tus)


When: 55–34 million years ago (Middle to Late Paleogene)

Fossil location: USA, Lebanon, Syria, S. America, Africa

Habitat: Lakes

Length: 26 in (65 cm)

A relative of herrings and sardines, Diplomystus lived in freshwater rivers and lakes. Many of the best preserved fossils have been found in the Green River region of Wyoming. These show that Diplomystus was a predator—a number of smaller fish have been found preserved in the stomachs. This creature had an upwardfacing mouth, suggesting that it hunted fish that swam just below the surface of the water.

Priscacara (PRISS-ca-carr-a)


When: 55–33 million years ago (Middle to Late Paleogene)

Fossil location: N. America

Habitat: Freshwater streams and lakes

Length: 6 in (15 cm)

Priscacara lived in deep lakes in North America, where its fossils formed in mud on the lake floor, preserved in beautiful detail. The stiff spines of its fins may have been defensive weapons—they would probably have stabbed the mouth of any predator that tried to swallow Priscacara.

Naso (NAY-zoe)

nasoWhen: 56–49 million years ago (Paleogene)

Fossil location: Italy

Habitat: Oceans

Length: 3 in (8 cm)

This fossil fish is a very close relative of modern unicorn fish, which are so named because they have a spike on the forehead like a unicorn’s horn. Like its modern relatives, this prehistoric species may have lived in shoals on coral reefs.

Knightia (NITE-ee-ah)


When: 55–34 million years ago (Middle to Late Paleogene)

Fossil location: USA

Habitat: Rivers and lakes of N. America

Length: 10 in (25 cm)

Scientists have discovered skeletons of Knightia in the stomachs of many larger fish. Huge shoals must have crowded the ancient seas, making them easy prey. Hundreds of well-preserved Knightia fossils have been found in the Green River region of Wyoming. The State of Wyoming declared Knightia as its state fossil in 1987.

Perca (PER-ca)


When: 55–37 million years ago (Middle to Late Paleogene)

Fossil location: USA

Habitat: Shallow waters

Length: 12 in (30 cm)

This ancient fish of the perch family looked just like its modern relative. Its body was covered in scales. On its humped back were two fins bearing sharp spines that it raised to scare away predators. Like many perches today, it may have had a striped body that helped it blend in with the reeds and bulrushes among which it hid from predators.
It moved in shoals, feeding on insects, fish eggs, and small fish.

Mioplosus (MY-oh-PLOH-sus)


When: 55–40 million years ago (Middle Paleogene)

Fossil location: USA

Habitat: Oceans

Length: 10 in (25 cm)

This incredible fossil shows a Mioplosus caught in the act of devouring its prey. The victim must have become lodged in the predator’s mouth, killing it. Mioplosus was a hunter that preyed on fish up to half its size, using pointed teeth to trap them in its jaws.


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