Prehistoric Fish Pictures and Profiles

Meet the Fish of the Paleozoic, Mesozoic and Cenozoic Eras

The first vertebrates on the planet, prehistoric fish lay at the root of hundreds of millions of years of animal evolution. On the following slides, you'll find pictures and detailed profiles of over 30 different fossil fish, ranging from Acanthodes to Xiphactinus.

Acanthodes

Despite its designation as a "spiny shark," the prehistoric fish Acanthodes had no teeth. This can be explained by the "missing link" status of this late Carboniferous vertebrate, which possessed characteristics of both cartilaginous and bony fish. See an in-depth profile of Acanthodes

Arandaspis

Name:

Arandaspis (Greek for "Aranda shield"); pronounced AH-ran-DASS-pis

Habitat:

Shallow seas of Australia

Historical Period:

Early Ordovician (480-470 million years ago)

Size and Weight:

About six inches long and a few ounces

Diet:

Small marine organisms

Distinguishing Characteristics:

Small size; flat, finless body

One of the first vertebrates (i.e., animals with backbones) ever to evolve on earth, almost 500 million years ago toward the start of the Ordovician period, Arandaspis wasn't much to look at by the standards of modern fish: with its small size, flat body and complete lack of fins, this prehistoric fish was more reminiscent of a giant tadpole than a small tuna. Arandaspis had no jaws, only movable plates in its mouth that it probably used to bottom-feed on ocean waste and single-celled organisms, and it was lightly armored (tough scales along the length of its body and about a dozen small, hard, interlocking plates protecting its oversized head).

Aspidorhynchus

Name:

Aspidorhynchus (Greek for "shield snout"); pronounced ASP-id-oh-RINK-us

Habitat:

Shallow seas of Europe

Historical Period:

Late Jurassic (150 million years ago)

Size and Weight:

About two feet long and a few pounds

Diet:

Fish

Distinguishing Characteristics:

Long, pointed snout; symmetrical tail

Judging by the number of its fossils, Aspidorhynchus must have been a particularly successful prehistoric fish of the late Jurassic period. With its sleek body and long, pointed snout, this ray-finned fish resembled a scaled-down version of a modern swordfish, to which it was only distantly related (the similarity is probably due to convergent evolution, the tendency for creatures that inhabit the same ecosystems to evolve roughly the same appearance). In any case, it's unclear if Aspidorhynchus used its formidable snout to hunt smaller fish or to keep larger predators at bay.

Astraspis

Name:

Astraspis (Greek for "star shield"); pronounced as-TRASS-pis

Habitat:

Shores of North America

Historical Period:

Late Ordovocian (450-440 million years ago)

Size and Weight:

About six inches long and a few ounces

Diet:

Small marine organisms

Distinguishing Characteristics:

Small size; lack of fins; thick plates on head

Like other prehistoric fish of the Ordovician period--the first true vertebrates to appear on earth--Astraspis looked like a giant tadpole, with an oversized head, flat body, wriggling tail and lack of fins. However, Astraspis seems to have been better-armored than its contemporaries, with distinctive plates along its head, and its eyes were set on either side of its skull rather than directly in front. This ancient creature's name, Greek for "star shield," derives from the characteristic shape of the tough proteins that composed its armored plates.

Bonnerichthys

Name:

Bonnerichthys (Greek for "Bonner's fish"); pronounced BONN-er-ICK-thiss

Habitat:

Shallow seas of North America

Historical Period:

Middle Cretaceous (100 million years ago)

Size and Weight:

About 20 feet long and 500-1,000 pounds

Diet:

Plankton

Distinguishing Characteristics:

Large eyes; wide-opening mouth

As so often happens in paleontology, the fossil of Bonnerichthys (preserved on a huge, unwieldy slab of rock extracted from a Kansas fossil site) had been stashed unnoticed for years until an enterprising researcher took a closer look at it and made an amazing discovery. What he found was a large (20 foot long) prehistoric fish that fed not on its fellow fish, but on plankton--the first filter-feeding bony fish to be identified from the Mesozoic Era. Like many other fossil fish (not to mention aquatic reptiles like plesiosaurs and mosasaurs), Bonnerichthys thrived not in the deep ocean, but the relatively shallow Western Interior Sea that covered much of North America during the Cretaceous period.

Bothriolepis

Some paleontologists speculate that Bothriolepis was the Devonian equivalent of a modern salmon, spending most of its life in saltwater oceans but returning to freshwater streams and rivers in order to breed. See an in-depth profile of Bothriolepis

Cephalaspis

Name:

Cephalaspis (Greek for "head shield"); pronounced SEFF-ah-LASS-pis

Habitat:

Shallow waters of Eurasia

Historical Period:

Early Devonian (400 million years ago)

Size and Weight:

About six inches long and a few ounces

Diet:

Small marine organisms

Distinguishing Characteristics:

Small size; armored plating

Yet another "-aspis" prehistoric fish of the Devonian period (others include Arandaspis and Astraspis), Cephalaspis was a small, big-headed, well-armored bottom feeder that probably fed on aquatic microorganisms and the waste of other marine creatures. This prehistoric fish is well-known enough to have been featured in an episode of the BBC's Walking with Monsters, though the scenarios presented (of Cephalaspis being pursued by the giant bug Brontoscorpio and migrating upstream to spawn) seem to have been concocted out of thin air.

Ceratodus

Name:

Ceratodus (Greek for "horned tooth"); pronounced SEH-rah-TOE-duss

Habitat:

Shallow waters worldwide

Historical Period:

Middle Triassic-Late Cretaceous (230-70 million years ago)

Size and Weight:

About two feet long and a few pounds

Diet:

Small marine organisms

Distinguishing Characteristics:

Small, stubby fins; primitive lungs

As obscure as it is to most people, Ceratodus was a big winner in the evolutionary sweepstakes: this small, inoffensive, prehistoric lungfish achieved worldwide distribution during the 150 million years or so of its existence, from the middle Triassic to the late Cretaceous periods, and is represented in the fossil record by almost a dozen species. As common as Ceratodus was in prehistoric times, though, its closest living relative today is the Queensland lungfish of Australia (whose genus name, Neoceratodus, pays homage to its widespread ancestor).

Cheirolepis

Name:

Cheirolepis (Greek for "hand fin"); pronounced CARE-oh-LEP-iss

Habitat:

Lakes of the northern hemisphere

Historical Period:

Middle Devonian (380 million years ago)

Size and Weight:

About two feet long and a few pounds

Diet:

Other fish

Distinguishing Characteristics:

Diamond-shaped scales; sharp teeth

The actinopterygii, or "ray-finned fish," are characterized by the ray-like skeletal structures supporting their fins, and account for the vast majority of fish in modern seas and lakes (including herring, carp and catfish). As far as paleontologists can tell, Cheirolepis lay at the base of the actinopterygii family tree; this prehistoric fish was distinguished by its tough, close-fitting, diamond-shaped scales, numerous sharp teeth, and voracious diet (which occasionally included members of its own species). The Devonian Cheirolepis could also open its jaws extremely wide, allowing it to swallow fish up to two-thirds of its own size.

Coccosteus

Name:

Coccosteus (Greek for "seed bone"); pronounced coc-SOSS-tee-us

Habitat:

Shallow waters of Europe and North America

Historical Period:

Middle-Late Devonian (390-360 million years ago)

Size and Weight:

About 8-16 inches long and one pound

Diet:

Small marine organisms

Distinguishing Characteristics:

Armored head; large, beaked mouth

Yet another of the prehistoric fish that prowled the rivers and oceans of the Devonian period, Coccosteus had a well-armored head and (even more important from a competitive standpoint) a beaked mouth that opened wider than that of other fish, allowing Coccosteus to consume a wider variety of larger prey. Unbelievably, this smallish fish was a close relative of the biggest vertebrate of the Devonian period, the huge (about 30 feet long and 3 to 4 ton) Dunkleosteus.

The Coelacanth

Coelacanths were thought to have gone extinct 100 million years ago, during the Cretaceous period, until a live specimen of the genus Latimeria was caught off the coast of Africa in 1938, and another Latimeria species in 1998 near Indonesia. See 10 Facts About Coelacanths

Diplomystus

Name:

Diplomystus (Greek for "double whiskers"); pronounced DIP-low-MY-stuss

Habitat:

Lakes and rivers of North America

Historical Epoch:

Early Eocene (50 million years ago)

Size and Weight:

1 to 2 feet long and a few pounds

Diet:

Fish

Distinguishing Characteristics:

Medium size; upward-pointing mouth

For all practical purposes, the 50-million-year-old prehistoric fish Diplomystus can be considered a larger relative of Knightia, thousands of fossils of which have been discovered in Wyoming's Green River Formation. (These relatives didn't necessarily get along; specimens of Diplomystus have been found with specimens of Knightia in their stomachs!) Although its fossils aren't as common as those of Knightia, it's possible to buy a small Diplomystus impression for a surprisingly small amount of money, sometimes as little as a hundred dollars.

Dipterus

Name:

Dipterus (Greek for "two wings"); pronounced DIP-teh-russ

Habitat:

Rivers and lakes worldwide

Historical Period:

Middle-Late Devonian (400-360 million years ago)

Size and Weight:

About a foot long and one or two pounds

Diet:

Small crustaceans

Distinguishing Characteristics:

Primitive lungs; bony plates on head

Lungfish--fish equipped with rudimentary lungs in addition to their gills--occupy a side branch of fish evolution, reaching a peak of diversity during the late Devonian period, about 350 million years ago, and then dwindling in importance (today there are only a handful of lungfish species). In the Paleozoic Era, lungfish were able to survive long periods of desiccation by gulping down air with their lungs, then reverted to an aquatic, gill-powered lifestyle when the freshwater rivers and lakes they lived in filled up again with water. (Oddly, the lungfish of the Devonian period weren't directly ancestral to the first tetrapods, which evolved from a related family of lobe-finned fish.)

As with many other prehistoric fish of the Devonian period (such as the gigantic, heavily armored Dunkleosteus), the head of Dipterus was protected from predators by tough, bony armor, and the "tooth plates" in its upper and lower jaws were adapted to crushing shellfish. Unlike modern lungfish, the gills of which are practically useless, Dipterus seems to have relied on its gills and its lungs in equal measure, which means it probably spent more of its time underwater than any of its modern descendants.

Doryaspis

Name

Doryaspis (Greek for "dart shield"); pronounced DOOR-ee-ASP-iss

Habitat

Oceans of Europe

Historical Period

Early Devonian (400 million years ago)

Size and Weight

About one foot long and one pound

Diet

Small marine organisms

Distinguishing Characteristics

Pointed rostrum; armor plating; small size

First things first: the name Doryaspis has nothing to do with the adorable, dim-witted Dory of Finding Nemo (and if anything, Dory was the smarter of the two!) Rather, this "dart shield" was a strange, jawless fish of the early Devonian period, about 400 million years ago, characterized by its armor plating, pointy fins and tail, and (most notably) the elongated "rostrum" that protruded from the front of its head and that was probably used to stir up sediments on the ocean bottom for food. Doryaspis was just one of many "-aspis" fish early in the line of fish evolution, other, better-known genera including Astraspis and Arandaspis.

Drepanaspis

Name:

Drepanaspis (Greek for "sickle shield"); pronounced dreh-pan-ASP-iss

Habitat:

Shallow seas of Eurasia

Historical Period:

Late Devonian (380-360 million years ago)

Size and Weight:

About 6 inches long and a few ounces

Diet:

Small marine organisms

Distinguishing Characteristics:

Small size; paddle-shaped head

Drepanaspis differed from other prehistoric fish of the Devonian period--such as Astraspis and Arandaspis--thanks to its flat, paddle-shaped head, not to mention the fact that its jawless mouth faced upwards rather than downwards, which makes its feeding habits something of a mystery. Based on its flat shape, though, it's clear that Drepanaspis was some kind of bottom-feeder of the Devonian seas, broadly similar to a modern flounder (though probably not quite as tasty).

Dunkleosteus

We have evidence that Dunkleosteus individuals occasionally cannibalized each other when prey fish ran low, and analysis of its jaw demonstrates that this enormous fish could bite with an impressive force of 8,000 pounds per square inch. See an in-depth profile of Dunkleosteus

Enchodus

The otherwise unremarkable Enchodus stood out from other prehistoric fish thanks to its sharp, oversized fangs, which have earned it the nickname the "saber-toothed herring" (although Enchodus was more closely related to salmon than herring). See an in-depth profile of Enchodus

Entelognathus

Name:

Entelognathus (Greek for "perfect jaw"); pronounced EN-tell-OG-nah-thuss

Habitat:

Oceans of Asia

Historical Period:

Late Silurian (420 million years ago)

Size and Weight:

About one foot long and one pound

Diet:

Marine organisms

Distinguishing Characteristics:

Small size; armor plating; primitive jaws

The Ordovician and Silurian periods, over 400 million years ago, were the heyday of the jawless fishes--small, mostly harmless bottom-feeders like Astraspis and Arandaspis. The importance of the late Silurian Entelognathus, announced to the world in September of 2013, is that it's the earliest placoderm (armored fish) yet identified in the fossil record, and it possessed primitive jaws that made it a more efficient predator. In fact, the jaws of Entelognathus may turn out to be a kind of paleontological "Rosetta Stone" that allows experts to reframe the evolution of jawed fish, the ultimate ancestors of all the world's terrestrial vertebrates.

Euphanerops

The jawless prehistoric fish Euphanerops dates from the late Devonian period (about 370 million years ago), and what makes it so remarkable is that it possessed paired "anal fins" on the far end of its body, a feature seen in few other fish of its time. See an in-depth profile of Euphanerops

Gyrodus

Name:

Gyrodus (Greek for "turning teeth"); pronounced GUY-roe-duss

Habitat:

Oceans worldwide

Historical Period:

Late Jurassic-Early Cretaceous (150-140 million years ago)

Size and Weight:

About one foot long and one pound

Diet:

Crustaceans and corals

Distinguishing Characteristics:

Circular body; round teeth

The prehistoric fish Gyrodus is best known not for its almost comically circular body--which was covered by rectangular scales and supported by an unusually fine network of small bones--but for its rounded teeth, which point to its having had a crunchy diet of small crustaceans or corals. Gyrodus is also notable for having been found (among other places) in the famous Solnhofen fossil beds of Germany, in sediments that also contain the dino-bird Archaeopteryx.

Haikouichthys

Whether or not Haikouichthys was technically a prehistoric fish is still a subject of debate. It was certainly one of the earliest craniates (organisms with skulls), but lacking any definitive fossil evidence, it may have had a primitive "notochord" running down its back rather than a true backbone. See an in-depth profile of Haikouichthys

Heliobatis

Name:

Heliobatis (Greek for "sun ray"); pronounced HEEL-ee-oh-BAT-iss

Habitat:

Shallow seas of North America

Historical Epoch:

Early Eocene (55-50 million years ago)

Size and Weight:

About one foot long and one pound

Diet:

Small crustaceans

Distinguishing Characteristics:

Disc-shaped body; long tail

One of the few prehistoric rays in the fossil record, Heliobatis was an unlikely combatant in the 19th century "Bone Wars," the decades-long feud between paleontologists Othniel C. Marsh and Edward Drinker Cope (Marsh was the first to describe this prehistoric fish, and Cope then attempted to one-up his rival with a more complete analysis). The smallish, round-bodied Heliobatis made its living by lying near the bottom of the shallow lakes and rivers of early Eocene North America, digging up crustaceans while its long, stinging, presumably poisonous tail kept larger predators at bay.

Hypsocormus

Name

Hypsocormus (Greek for "high stem"); pronounced HIP-so-CORE-muss

Habitat

Oceans of Europe

Historical Period

Middle Triassic-Late Jurassic (230-145 million years ago)

Size and Weight

About three feet long and 20-25 pounds

Diet

Fish

Distinguishing Characteristics

Armored scales; forked tail fin; fast pursuit speed

If there had been such a thing as sports fishing 200 million years ago, specimens of Hypsocormus would have been mounted in plenty of Mesozoic living rooms. With its forked tail and mackerel-like build, Hypsocormus was one of the speediest of all prehistoric fish, and its powerful bite would have made it unlikely to wriggle off a fishing line; considering its overall agility, it may have made its living by pursuing and disrupting schools of smaller fish. Still, it's important not to oversell Hypsocormus' credentials compared to, say, a modern bluefin tuna: it was still a relatively primitive "teleost" fish, as evidenced by its armored, and comparatively inflexible, scales.

Ischyodus

Name:

Ischyodus; pronounced ISS-kee-OH-duss

Habitat:

Oceans worldwide

Historical Period:

Middle Jurassic (180-160 million years ago)

Size and Weight:

About five feet long and 10-20 pounds

Diet:

Crustaceans

Distinguishing Characteristics:

Large eyes; whip-like tail; protruding dental plates

For all intents and purposes, Ischyodus was the Jurassic equivalent of modern rabbitfish and ratfish, which are characterized by their "buck-toothed" appearance (actually, protruding dental plates used to crush mollusks and crustaceans). Like its modern descendants, this prehistoric fish had unusually big eyes, a long, whiplike tail, and a spike on its dorsal fin that was probably used to intimidate predators. In addition, Ischyodus males had a strange appendage jutting out from their foreheads, clearly a sexually selected characteristic.

Knightia

The reason there are so many Knightia fossils today is that there were so many Knightia--this herring-like fish plied the lakes and rivers of North America in vast schools, and lay near the bottom of the marine food chain during the Eocene epoch. See an in-depth profile of Knightia

Leedsichthys

The gigantic Leedsichthys was equipped with a whopping 40,000 teeth, which it used not to prey on the larger fish and aquatic reptiles of the middle to late Jurassic period, but to filter-feed plankton like a modern baleen whale. See an in-depth profile of Leedsichthys

Lepidotes

Name:

Lepidotes; pronounced LEPP-ih-DOE-teez

Habitat:

Lakes of the northern hemisphere

Historical Period:

Late Jurassic-Early Cretaceous (160-140 million years ago)

Size and Weight:

About one to 6 feet long and a few to 25 pounds

Diet:

Mollusks

Distinguishing Characteristics:

Thick, diamond-shaped scales; peglike teeth

To most dinosaur fans, Lepidotes' claim to fame is that its fossilized remains have been found in the stomach of Baryonyx, a predatory, fish-eating theropod. However, this prehistoric fish was interesting in its own right, with an advanced feeding system (it could shape its jaws into the rough shape of a tube and suck in prey from a short distance away) and rows upon rows of peg-shaped teeth, called "toadstones" in medieval times, with which it ground down the shells of mollusks. Lepidotes is one of the ancestors of the modern carp, which feeds in the same, vaguely repellent way.

Macropoma

Name:

Macropoma (Greek for "big apple"); pronounced MACK-roe-POE-ma

Habitat:

Shallow seas of Europe

Historical Period:

Late Cretaceous (100-65 million years ago)

Size and Weight:

About two feet long and a few pounds

Diet:

Small marine organisms

Distinguishing Characteristics:

Moderate size; large head and eyes

Most people use the word "coelacanth" to refer to the presumably extinct fish that, as it turns out, still lurks in the depths of the Indian Ocean. In fact, coelacanths comprise a wide range of fish, some of which are still living and some of which are long gone. The late Cretaceous Macropoma was technically a coelacanth, and in most respects it was similar to the living representative of the breed, Latimeria. Macropoma was characterized by its larger-than-average head and eyes and its calcified swim bladder, which helped it to float near the surface of shallow lakes and rivers. (How this prehistoric fish received its name--Greek for "big apple"--remains a mystery!)

Materpiscis

The late Devonian Materpiscis is the earliest viviparous vertebrate yet identified, meaning that this prehistoric fish gave birth to live young rather than laying eggs, unlike the vast majority of viviparous (egg-laying) fish. See an in-depth profile of Materpiscis

Megapiranha

You may be disappointed to learn that the 10-million-year old Megapiranha "only" weighed about 20 to 25 pounds, but you have to bear in mind that modern piranhas tip the scale at two or three pounds, max! See an in-depth profile of Megapiranha

Myllokunmingia

Name:

Myllokunmingia (Greek for "Kunming millstone"); pronounced ME-loh-kun-MIN-gee-ah

Habitat:

Shallow seas of Asia

Historical Period:

Early Cambrian (530 million years ago)

Size and Weight:

About one inch long and less than an ounce

Diet:

Small marine organisms

Distinguishing Characteristics:

Tiny size; pouched gills

Along with Haikouichthys and Pikaia, Myllokunmingia was one of the first "almost-vertebrates" of the Cambrian period, a span of time that's more popularly associated with a profusion of bizarre invertebrate life forms. Essentially, Myllokunmingia resembled a bulkier, less streamlined Haikouichthys; it had a single fin running along its back, and there's some fossil evidence of fishlike, V-shaped muscles and pouched gills (whereas the gills of Haikouichthys seem to have been completely unadorned).

Was Myllokunmingia really a prehistoric fish? Technically, probably not: this creature likely had a primitive "notochord" rather than a true backbone, and its skull (another anatomical feature that characterizes all true vertebrates) was cartilaginous rather than solid. Still, with its fish-like shape, bilateral symmetry and forward-facing eyes, Myllokunmingia can certainly be considered an "honorary" fish, and it was probably ancestral to all the fish (and all the vertebrates) of succeeding geologic eras.

Pholidophorus

Name

Pholidophorus (Greek for "scale bearer"); pronounced FOE-lih-doe-FOR-us

Habitat

Oceans worldwide

Historical Period

Middle Triassic-Early Cretaceous (240-140 million years ago)

Size and Weight

About two feet long and a few pounds

Diet

Marine organisms

Distinguishing Characteristics

Moderate size; herring-like appearance

It's one of the ironies of paleontology that short-lived, bizarre-looking creatures get all the press, while boring genera that persist for tens of millions of years are often overlooked. Pholidophorus fits into the latter category: various species of this prehistoric fish managed to survive all the way from the middle Triassic through the early Cretaceous periods, a stretch of 100 million years, while dozens of less-well-adapted fish flourished and quickly went extinct. The importance of Pholidophorus is that it was one of the first "teleosts," an important class of ray-finned fishes that evolved during the early Mesozoic Era.

Pikaia

It's stretching things a bit to describe Pikaia as a prehistoric fish; rather, this inoffensive ocean dweller of the Cambrian period may have been the first true chordate (that is, an animal with a "notochord" running down its back, rather than a backbone). See an in-depth profile of Pikaia

Priscacara

Name:

Priscacara (Greek for "primitive head"); pronounced PRISS-cah-CAR-ah

Habitat:

Rivers and lakes of North America

Historical Epoch:

Early Eocene (50 million years ago)

Size and Weight:

About six inches long and a few ounces

Diet:

Small crustaceans

Distinguishing Characteristics:

Small, round body; protruding lower jaw

Along with Knightia, Priscacara is one of the most common fossil fish from Wyoming's famous Green River formation, the sediments of which date to the early Eocene epoch (about 50 million years ago). Closely related to the modern perch, this prehistoric fish had a fairly small, round body with an unforked tail and a protruding lower jaw, the better to suck up unwary snails and crustaceans from the bottom of rivers and lakes. Since there are so many preserved specimens, Priscacara fossils are fairly affordable, selling for as little as a few hundred dollars apiece.

Pteraspis

Name:

Pteraspis (Greek for "wing shield"); pronounced teh-RASS-pis

Habitat:

Shallow waters of North America and Western Europe

Historical Period:

Early Devonian (420-400 million years ago)

Size and Weight:

About one foot long and less than a pound

Diet:

Small marine organisms

Distinguishing Characteristics:

Sleek body; armored head; stiff protrusions over gills

For all practical purposes, Pteraspis displays the evolutionary improvements made by the "-aspis" fishes of the Ordovician period (Astraspis, Arandaspis, etc.) as they swam their way into the Devonian. This prehistoric fish retained the armored plating of its ancestors, but its body was significantly more hydrodynamic, and it had strange, winglike structures jutting out of the back of its gills that probably helped it to swim farther and faster than most fish of the time. It's unknown whether Pteraspis was a bottom-feeder like its ancestors; it may well have subsisted on plankton hovering near the water's surface.

Rebellatrix

Name

Rebellatrix (Greek for "rebel coelacanth"); pronounced reh-BELL-ah-trix

Habitat

Oceans of North America

Historical Period

Early Triassic (250 million years ago)

Size and Weight

About 4-5 feet long and 100 pounds

Diet

Marine organisms

Distinguishing Characteristics

Large size; forked tail

There's a reason the discovery of a living coelacanth in 1938 caused such a sensation--these primitive, lobe-finned fish swam the earth's seas during the early Mesozoic Era, over 200 million years ago, and the odds seemed slim that any could have survived down to the present day. One coelacanth genus that apparently didn't make it was Rebellatrix, an early Triassic fish that (to judge by its unusual forked tail) must have been a fairly speedy predator. In fact, Rebellatrix may well have competed with prehistoric sharks in the world's northern oceans, one of the first fish ever to invade this ecological niche.

Saurichthys

Name:

Saurichthys (Greek for "lizard fish"); pronounced sore-ICK-thiss

Habitat:

Oceans worldwide

Historical Period:

Triassic (250-200 million years ago)

Size and Weight:

About three feet long and 20-30 pounds

Diet:

Fish

Distinguishing Characteristics:

Barracuda-like body; long snout

First things first: Saurichthys ("lizard fish") was an entirely different creature from Ichthyosaurus ("fish lizard"). These were both top aquatic predators of their time, but Saurichthys was an early ray-finned fish, while Ichthyosaurus (which lived a few million years later) was a marine reptile (technically, an ichthyosaur) well-adapted to an aquatic lifestyle. Now that that's out of the way, Saurichthys seems to have been the Triassic equivalent of a modern sturgeon (the fish to which it's most closely related) or barracuda, with a narrow, hydrodynamic build and a pointed snout that accounted for a large proportion of its three-foot length. This was clearly a fast, powerful swimmer, which may or may not have hunted down its prey in swarming packs.

Titanichthys

Name:

Titanichthys (Greek for "giant fish"); pronounced TIE-tan-ICK-thiss

Habitat:

Shallow seas worldwide

Historical Period:

Late Devonian (380-360 million years ago)

Size and Weight:

About 20 feet long and 500-1,000 pounds

Diet:

Small crustaceans

Distinguishing Characteristics:

Large size; dull plates in mouth

It seems that every historical period features an oversized, undersea predator that feeds not on comparably sized fish, but much smaller aquatic life (witness the modern whale shark and its plankton diet). In the late Devonian period, about 370 million years ago, that ecological niche was filled by the 20-foot-long prehistoric fish Titanichthys, which was one of the largest vertebrates of its time (outclassed only by the truly gigantic Dunkleosteus) yet seems to have subsisted on the tiniest fish and single-celled organisms. How do we know this? By the dull-edged plates in this fish's large mouth, which only make sense as a kind of prehistoric filter-feeding apparatus.

Xiphactinus

The most famous fossil specimen of Xiphactinus contains the almost-intact remains of an obscure, 10-foot-long Cretaceous fish. The Xiphactinus died right after its meal, possibly because its still-wriggling prey managed to puncture its stomach! See an in-depth profile of Xiphactinus