The first true birds evolved during the late Jurassic period, and went on to become one of the most successful and diverse branches of vertebrate life on earth. In this slideshow, you'll find pictures and detailed profiles of over 50 prehistoric and recently extinct birds, ranging from Archaeopteryx to the Passenger Pigeon.

01 of 52 Adzebill The Adzebill (Wikimedia Commons). Name: Adzebill; pronounced ADZ-eh-bill

Adzebill; pronounced ADZ-eh-bill Habitat: Shores of New Zealand

Shores of New Zealand Historical Epoch: Pleistocene-Modern (500,000-10,000 years ago)

Pleistocene-Modern (500,000-10,000 years ago) Size and Weight: About three feet long and 40 pounds

About three feet long and 40 pounds Diet: Omnivorous

Omnivorous Distinguishing Characteristics: Small wings; sharply curved beak When it comes to the extinct birds of New Zealand, many people are familiar with the Giant Moa and the Eastern Moa, but not many can name the Adzebill (genus Aptornis), a moa-like bird that was actually more closely related to cranes and grails. In a classic case of convergent evolution, the distant ancestors of the Adzebill adapted to their island habitat by becoming large and flightless, with strong legs and sharp bills, the better to hunt the small animals (lizards, insects, and birds) of New Zealand. Like its better-known relatives, unfortunately, the Adzebill was no match for human settlers, which quickly hunted this 40-pound bird to extinction (presumably for its meat).

02 of 52 Andalgalornis Andalgalornis (Wikimedia Commons). Name: Andalgalornis (Greek for "Andalgala bird"); pronounced AND-al-gah-LORE-niss

Andalgalornis (Greek for "Andalgala bird"); pronounced AND-al-gah-LORE-niss Habitat: Woodlands of South America

Woodlands of South America Historical Epoch: Miocene (23-5 million years ago)

Miocene (23-5 million years ago) Size and Weight: About 4-5 feet tall and 100 pounds

About 4-5 feet tall and 100 pounds Diet: Meat

Meat Distinguishing Characteristics: Long legs; massive head with sharp beak As "terror birds"--the oversized, flightless apex predators of Miocene and Pliocene South America--go, Andalgalornis isn't quite as well known as Phorusrhacos or Kelenken. However, you can expect to hear more about this once-obscure predator, because a recent study about the hunting habits of terror birds employed Andalgalornis as its poster genus. It seems that Andalgalornis wielded its large, heavy, pointed beak like a hatchet, repeatedly closing in on prey, inflicting deep wounds with quick stabbing motions, then withdrawing to a safe distance as its unfortunate victim bled to death. What Andalgalornis (and other terror birds) specifically did not do was grasp prey in its jaws and shake it back and forth, which would have placed undue strain on its skeletal structure.

03 of 52 Anthropornis Anthropornis. Wikimedia Commons Name: Anthropornis (Greek for "human bird"); pronounced AN-thro-PORE-niss

Anthropornis (Greek for "human bird"); pronounced AN-thro-PORE-niss Habitat: Shores of Australia

Shores of Australia Historical Epoch: Late Eocene-Early Oligocene (45-37 million years ago)

Late Eocene-Early Oligocene (45-37 million years ago) Size and Weight: Up to six feet tall and 200 pounds

Up to six feet tall and 200 pounds Diet: Fish

Fish Distinguishing Characteristics: Large size; bent joint in wing The only prehistoric bird ever to be referenced in an H.P. Lovecraft novel--albeit indirectly, as a six-foot-tall, blind, murderous albino--Anthropornis was the largest penguin of the Eocene epoch, attaining a height of close to 6 feet and weights in the neighborhood of 200 pounds. (In this respect, this "human bird" was bigger even than the putative Giant Penguin, Icadyptes, and other plus-sized prehistoric penguin species like Inkayacu.) One odd feature of Anthropornis was its slightly bent wings, a relic of the flying ancestors from which it evolved.

04 of 52 Archaeopteryx Archaeopteryx (Alain Beneteau). It has become fashionable to identify Archaeopteryx as the first true bird, but it's important to remember that this 150-million-year-old creature also possessed some distinctly dinosaur-like features, and may have been incapable of flight. See 10 Facts About Archaeopteryx

05 of 52 Argentavis Argentavis (Wikimedia Commons). The wingspan of Argentavis was comparable to that of a small plane, and this prehistoric bird weighed a respectable 150 to 250 pounds. By these tokens, Argentavis is best compared not to other birds, but to the huge pterosaurs that preceded it by 60 million years! See an in-depth profile of Argentavis

06 of 52 Bullockornis Bullockornis (Wikimedia Commons). Name: Bullockornis (Greek for "ox bird"); pronounced BULL-ock-OR-niss

Bullockornis (Greek for "ox bird"); pronounced BULL-ock-OR-niss Habitat: Woodlands of Australia

Woodlands of Australia Historical Epoch: Middle Miocene (15 million years ago)

Middle Miocene (15 million years ago) Size and Weight: About eight feet tall and 500 pounds

About eight feet tall and 500 pounds Diet: Meat

Meat Distinguishing Characteristics: Large size; prominent beak Sometimes, all you need is a catchy nickname to propel a prehistoric bird from the musty insides of paleontology journals to the front pages of newspapers. Such is the case with Bullockornis, which an enterprising Australian publicist has dubbed the "Demon Duck of Doom." Similar to another giant, extinct Australian bird, Dromornis, the middle Miocene Bullockornis seems to have been more closely related to ducks and geese than to modern ostriches, and its heavy, prominent beak points to its having had a carnivorous diet.

07 of 52 Carolina Parakeet The Carolina Parakeet. Wiesbaden Museum The Carolina Parakeet was doomed to extinction by European settlers, who cleared much of the woodlands of eastern North America and then actively hunted this bird to keep it from raiding their crops. See an in-depth profile of the Carolina Parakeet

08 of 52 Confuciusornis Confuciusornis (Wikimedia Commons). Name: Confuciusornis (Greek for "Confucius bird"); pronounced con-FEW-shus-OR-nis

Confuciusornis (Greek for "Confucius bird"); pronounced con-FEW-shus-OR-nis Habitat: Woodlands of Asia

Woodlands of Asia Historical Period: Early Cretaceous (130-120 million years ago)

Early Cretaceous (130-120 million years ago) Size and Weight: About one foot long and less than a pound

About one foot long and less than a pound Diet: Probably seeds

Probably seeds Distinguishing Characteristics: Beak, primitive feathers, curved foot claws One of a series of spectacular Chinese fossil discoveries made over the past 20 or so years, Confuciusornis was a true find: the first identified prehistoric bird with a true beak (a subsequent discovery, of the earlier, similar Eoconfuciusornis, was made a few years later). Unlike other flying creatures of its era, Confuciusornis had no teeth--which, along with its feathers and curved claws suited for sitting high up in trees, makes it one of the most unmistakably birdlike creatures of the Cretaceous period. (This arboreal habit didn't spare it from predation, however; recently, paleontologists unearthed the fossil of a much bigger dino-bird, Sinocalliopteryx, harboring the remains of three Confuciusornis specimens in its gut!) However, just because Confuciusornis looked like a modern bird doesn't mean it's the great-great-grandfather (or grandmother) of every pigeon, eagle and owl living today. There's no reason primitive flying reptiles couldn't have independently evolved birdlike characteristics such as feathers and beaks--so the Confucius Bird may well have a been a striking "dead end" in avian evolution. (In a new development, researchers have determined--based on an analysis of preserved pigment cells--that the feathers of Confuciusornis were arranged in a mottled pattern of black, brown and white patches, a bit like a tabby cat.)

09 of 52 Copepteryx Copepteryx (Wikimedia Commons). Name: Copepteryx (Greek for "oar wing"); pronounced coe-PEP-teh-rix

Copepteryx (Greek for "oar wing"); pronounced coe-PEP-teh-rix Habitat: Shores of Japan

Shores of Japan Historical Epoch: Oligocene (28-23 million years ago)

Oligocene (28-23 million years ago) Size and Weight: About six feet long and 50 pounds

About six feet long and 50 pounds Diet: Fish

Fish Distinguishing Characteristics: Large size; penguin-like build Copepteryx is the most famous member of the obscure family of prehistoric birds known as plotopterids, large, flightless creatures that resembled penguins (to the extent that they're often cited as a prime example of convergent evolution). The Japanese Copepteryx seems to have gone extinct at about the same time (23 million years ago) as the true giant penguins of the southern hemisphere, possibly because of predation by the ancient ancestors of modern seals and dolphins.

10 of 52 Dasornis Dasornis. Senckenberg Research Institute The early Cenozoic Dasornis had a wingspan of almost 20 feet, making it much larger than the largest flying bird alive today, the albatross (though it wasn't nearly as big as the giant pterosaurs that preceded it by 20 million years). See an in-depth profile of Dasornis

11 of 52 Dodo Bird Dodo Bird. Wikimedia Commons For hundreds of thousands of years, beginning in the Pleistocene epoch, the squat, plump, flightless, turkey-sized Dodo Bird grazed contentedly on the remote island of Mauritius, unthreatened by any natural predators--until the arrival of human settlers. See 10 Facts About the Dodo Bird

12 of 52 Eastern Moa Emeus (Eastern Moa). Wikimedia Commons Name: Emeus; pronounced eh-MAY-us

Emeus; pronounced eh-MAY-us Habitat: Plains of New Zealand

Plains of New Zealand Historical Epoch: Pleistocene-Modern (2 million-500 years ago)

Pleistocene-Modern (2 million-500 years ago) Size and Weight: About six feet tall and 200 pounds

About six feet tall and 200 pounds Diet: Plants

Plants Distinguishing Characteristics: Squat body; large, broad feet Of all the oversized prehistoric birds that inhabited New Zealand during the Pleistocene epoch, Emeus was the least suited to withstand the assaults of foreign predators. Judging by its squat body and oversized feet, this must have been an unusually slow, ungainly bird, which was easily hunted to extinction by human settlers. The closest relative of Emeus was the much taller, but equally doomed Dinornis (the Giant Moa), which also vanished off the face of the earth about 500 years ago.

13 of 52 Elephant Bird Aepyornis (Elephant Bird). Wikimedia Commons Part of the reason Aepyornis, aka the Elephant Bird, was able to grow to such enormous sizes was that it didn't have any natural predators on the remote island of Madagascar. Since this bird didn't know enough to feel threatened by early humans, it was easily hunted to extinction. See 10 Facts About the Elephant Bird

14 of 52 Enantiornis Enantiornis. Wikimedia Commons Name: Enantiornis (Greek for "opposite bird"); pronounced en-ANT-ee-ORE-niss

Enantiornis (Greek for "opposite bird"); pronounced en-ANT-ee-ORE-niss Habitat: Woodlands of South America

Woodlands of South America Historical Period: Late Cretaceous (65-60 million years ago)

Late Cretaceous (65-60 million years ago) Size and Weight: About six feet long and 50 pounds

About six feet long and 50 pounds Diet: Meat

Meat Distinguishing Characteristics: Relatively large size; vulture-like profile As with many prehistoric birds of the late Cretaceous period, not a whole lot is known about Enantiornis, the name of which ("opposite bird") refers to an obscure anatomical feature, not any sort of wacky, un-bird-like behavior. Judging by its remains, Enantiornis seems to have led a vulture-like existence, either scavenging the already-dead carcasses of dinosaurs and Mesozoic mammals or, perhaps, actively hunting smaller creatures.

15 of 52 Eoconfuciusornis Eoconfuciusornis (Nobu Tamura). Name Name: Eoconfuciusornis (Greek for "dawn Confuciusornis"); pronounced EE-oh-con-FYOO-shuss-OR-niss

Eoconfuciusornis (Greek for "dawn Confuciusornis"); pronounced EE-oh-con-FYOO-shuss-OR-niss Habitat: Skies of eastern Asia

Skies of eastern Asia Historical Period: Early Cretaceous (131 million years ago)

Early Cretaceous (131 million years ago) Size and Weight: Less than one foot long and a few ounces

Less than one foot long and a few ounces Diet: Insects

Insects Distinguishing Characteristics: Small size; long legs; toothless beak The 1993 discovery of Confuciusornis, in China, was big news: this was the first identified prehistoric bird with a toothless beak, and thus bore a marked resemblance to modern birds. As is so often the case, though, Confuciusornis has since been supplanted in the record books by an even earlier toothless ancestor of the Cretaceous period, Eoconfuciusornis, which resembled a scaled-down version of its more famous relative. Like many birds recently discovered in China, the "type fossil" of Eoconfuciusornis bears evidence of feathers, though the specimen was otherwise "compressed" (the fancy word paleontologists use for "crushed.")

16 of 52 Eocypselus Eocypselus. Field Museum of Natural History Name: Eocypselus (pronounced EE-oh-KIP-sell-us)

Eocypselus (pronounced EE-oh-KIP-sell-us) Habitat: Woodlands of North America

Woodlands of North America Historical Epoch: Early Eocene (50 million years ago)

Early Eocene (50 million years ago) Size and Weight: A few inches long and less than an ounce

A few inches long and less than an ounce Diet: Insects

Insects Distinguishing Characteristics: Small size; medium-sized wings Some of the birds of the early Eocene epoch, 50 million years ago, weighed as much as medium-sized dinosaurs--but that wasn't the case with Eocypselus, a tiny, one-ounce tuft of feathers that appears to have been ancestral to both modern swifts and hummingbirds. Since swifts have fairly long wings compared to their body size, and hummingbirds possess relatively tiny wings, it makes sense that the wings of Eocypselus were somewhere in between--meaning that this prehistoric bird couldn't hover like a hummingbird, or dart like a swift, but had to content itself with awkwardly fluttering from tree to tree.

17 of 52 Eskimo Curlew Eskimo Curlew. John James Audubon The Eskimo Curlew literally had it coming and going: the single, vast flocks of this recently extinct bird were hunted by humans both during their annual journeys south (to Argentina) and their return trips north (to the Arctic tundra). See an in-depth profile of the Eskimo Curlew

18 of 52 Gansus Gansus. Carnegie Museum of Natural History The early Cretaceous Gansus may (or may not) have been the earliest known "ornithuran," a pigeon-sized, semi-aquatic prehistoric bird that behaved much like a modern duck or loon, diving beneath the water in pursuit of small fish. See an in-depth profile of Gansus

19 of 52 Gastornis (Diatryma) gastornis. Gastornis (Wikimedia Commons) Gastornis wasn't the biggest prehistoric bird that ever lived, but it was probably the most dangerous, with a tyrannosaur-like body (powerful legs and head, puny arms) that testifies to how evolution tends to fit the same body shapes into the same ecological niches. See an in-depth profile of Gastornis

20 of 52 Genyornis Genyornis. Wikimedia Commons The unusual rapidity of Genyornis' extinction, about 50,000 years, ago can be attributed to relentless hunting and egg-stealing by the early human settlers who reached the Australian continent around this time. See an in-depth profile of Genyornis

21 of 52 Giant Moa Dinornis (Heinrich Harder). The "dino" in Dinornis derives from the same Greek root as the "dino" in "dinosaur"--this "terrible bird," better known as the Giant Moa, was probably the tallest bird that ever lived, attaining towering heights of around 12 feet, or twice as tall as the average human. See an in-depth profile of the Giant Moa

22 of 52 Giant Penguin The Giant Penguin. Nobu Tamura Name: Icadyptes (Greek for "Ica diver"); pronounced ICK-ah-DIP-teez; also known as the Giant Penguin

Icadyptes (Greek for "Ica diver"); pronounced ICK-ah-DIP-teez; also known as the Giant Penguin Habitat: Shores of South America

Shores of South America Historical Epoch: Late Eocene (40-35 million years ago)

Late Eocene (40-35 million years ago) Size and Weight: About five feet tall and 50-75 pounds

About five feet tall and 50-75 pounds Diet: Fish

Fish Distinguishing Characteristics: Large size; long, pointed beak A relatively recent addition to the prehistoric bird roster, Icadyptes was "diagnosed" in 2007 based on a single, well-preserved fossil specimen. At about five feet tall, this Eocene bird was significantly larger than any modern penguin species (though it fell far short of the monster sizes of other prehistoric megafauna), and it was equipped with an unusually long, spearlike beak, which it doubtless used when hunting for fish. Beyond its size, the oddest thing about Icadyptes is that it lived in a lush, tropical, near-equatorial South American climate, a far cry from the frigid habitats of the majority of modern penguins--and a hint that prehistoric penguins adapted to temperate climates much earlier than had previously been believed. (By the way, the recent discovery of an even bigger penguin from Eocene Peru, Inkayacu, may imperil Icadyptes' size title.)

23 of 52 Great Auk Pinguinus (Great Auk). Wikimedia Commons Pinguinus (better known as the Great Auk) knew enough to stay out of the way of natural predators, but it wasn't used to dealing with the human settlers of New Zealand, who easily caught and ate this slow-moving bird upon their arrival 2,000 years ago. See 10 Facts About the Great Auk

24 of 52 Harpagornis (Giant Eagle) Harpagornis (Giant Eagle). Wikimedia Commons Harpagornis (also known as the Giant Eagle or Haast's Eagle) swooped down from the skies and carried off giant moas like Dinornis and Emeus--not full-grown adults, which would have been too heavy, but juveniles and newly hatched chicks. See an in-depth profile of Harpagornis

25 of 52 Hesperornis Hesperornis. Wikimedia Commons The prehistoric bird Hesperornis had a penguin-like build, with stubby wings and a beak suited to catching fish and squids, and it was probably an accomplished swimmer. Unlike penguins, though, this bird lived in more temperate climates of Cretaceous North America. See an in-depth profile of Hesperornis

26 of 52 Iberomesornis Iberomesornis. Wikimedia Commons Name: Iberomesornis (Greek for "intermediate Spanish bird"); pronounced EYE-beh-ro-may-SORE-niss

Iberomesornis (Greek for "intermediate Spanish bird"); pronounced EYE-beh-ro-may-SORE-niss Habitat: Woodlands of western Europe

Woodlands of western Europe Historical Period: Early Cretaceous (135-120 million years ago)

Early Cretaceous (135-120 million years ago) Size and Weight: About eight inches long and two ounces

About eight inches long and two ounces Diet: Probably insects

Probably insects Distinguishing Characteristics: Small size; toothed beak; claws on wings If you happened upon a specimen of Iberomesornis while strolling through an early Cretaceous forest, you might be forgiven for mistaking this prehistoric bird for a finch or sparrow, which it superficially resembled. However, the ancient, tiny Iberomesornis retained some distinctly reptilian characteristics from its small theropod forebears, including single claws on each of its wings and jagged teeth. Most paleontologists consider Iberomesornis to have been a true bird, albeit one that seems to have left no living descendants (modern birds probably derived from an entirely different branch of Mesozoic predecessors).

27 of 52 Ichthyornis Ichthyornis (Wikimedia Commons). Name: Ichthyornis (Greek for "fish bird"); pronounced ick-thee-OR-niss

Ichthyornis (Greek for "fish bird"); pronounced ick-thee-OR-niss Habitat: Shores of southern North America

Shores of southern North America Historical Period: Late Cretaceous (90-75 million years ago)

Late Cretaceous (90-75 million years ago) Size and Weight: About two feet long and five pounds

About two feet long and five pounds Diet: Fish

Fish Distinguishing Characteristics: Seagull-like body; sharp, reptilian teeth A true prehistoric bird of the late Cretaceous period--not a pterosaur or feathered dinosaur--Ichthyornis looked remarkably like a modern seagull, with a long beak and tapered body. However, there were some major differences: this prehistoric bird had a full set of sharp, reptilian teeth planted in a very reptile-like jaw (which is one reason why the first remains of Ichthyornis were confused with those of a marine reptile, Mosasaurus). Ichthyornis is yet another of those prehistoric creatures that was discovered ahead of its time, before paleontologists fully understood the evolutionary relationship between birds and dinosaurs: the first specimen was unearthed in 1870, and described a decade later by the famous paleontologist Othniel C. Marsh, who referred to this bird as "Odontornithes."

28 of 52 Inkayacu Inkayacu. Wikimedia Commons Name: Inkayacu (indigenous for "water king"); pronounced INK-ah-YAH-koo

Inkayacu (indigenous for "water king"); pronounced INK-ah-YAH-koo Habitat: Shorelines of South America

Shorelines of South America Historical Period: Late Eocene (36 million years ago)

Late Eocene (36 million years ago) Size and Weight: About five feet tall and 100 pounds

About five feet tall and 100 pounds Diet: Fish

Fish Distinguishing Characteristics: Large size; long bill; gray and red feathers Inkayacu isn't the first plus-sized prehistoric penguin to have been discovered in modern-day Peru; that honor belongs to Icadyptes, also known as the Giant Penguin, which may have to relinquish its title in light of its slightly larger contemporary. At five feet tall and a bit over 100 pounds, Inkayacu was about twice the size of the modern Emperor Penguin, and it was equipped with a long, narrow, dangerous-looking beak that it used to spear fish out of the tropical waters (the fact that both Icadyptes and Inkayacu prospered in the lush, tropical climate of Eocene Peru may prompt some rewriting of the penguin evolution books). Still, the most amazing thing about Inkayacu isn't its size, or its humid habitat, but the fact that the "type specimen" of this prehistoric penguin bears the unmistakable imprint of feathers--reddish-brown and gray feathers, to be precise, based on an analysis of melanosomes (pigment-bearing cells) found preserved in the fossil. The fact that Inkayacu deviated so strongly from the modern penguin black-and-white color scheme has yet more implications for penguin evolution, and may shed some light on the coloration of other prehistoric birds (and possibly even the feathered dinosaurs that preceded them by tens of millions of years)

29 of 52 Jeholornis Jeholornis (Emily Willoughby). Name: Jeholornis (Greek for "Jehol bird"); pronounced JAY-hole-OR-niss

Jeholornis (Greek for "Jehol bird"); pronounced JAY-hole-OR-niss Habitat: Woodlands of Asia

Woodlands of Asia Historical Period: Early Cretaceous (120 million years ago)

Early Cretaceous (120 million years ago) Size and Weight: Three-foot wingspan and a few pounds

Three-foot wingspan and a few pounds Diet: Probably omnivorous

Probably omnivorous Distinguishing Characteristics: Moderate size; long tail; toothed beak To judge by the fossil evidence, Jeholornis was almost certainly the biggest prehistoric bird of early Cretaceous Eurasia, attaining chicken-like sizes when most of its Mesozoic relatives (like Liaoningornis) remained relatively petite. The line dividing true birds like Jeholornis from the small, feathered dinosaurs it evolved from was very fine indeed, as witness the fact this bird is sometimes referred to as Shenzhouraptor. By the way, Jeholornis ("Jehol bird") was a very different creature from the earlier Jeholopterus ("Jehol wing"), the latter being not a true bird, or even a feathered dinosaur, but a pterosaur. Jeholopterus has also occasioned its share of controversy, as one paleontologist insists it perched on the backs of the large sauropods of the late Jurassic period and sucked their blood!

30 of 52 Kairuku Kairuku. Chris Gaskin Name: Kairuku (Maori for "diver who brings back food"); pronounced kai-ROO-koo

Kairuku (Maori for "diver who brings back food"); pronounced kai-ROO-koo Habitat: Shorelines of New Zealand

Shorelines of New Zealand Historical Period: Oligocene (27 million years ago)

Oligocene (27 million years ago) Size and Weight: About five feet tall and 130 pounds

About five feet tall and 130 pounds Diet: Fish and marine animals

Fish and marine animals Distinguishing Characteristics: Tall, slender build; narrow beak One doesn't normally cite New Zealand as one of the world's great fossil-producing countries--unless, of course, you're talking about prehistoric penguins. Not only has New Zealand yielded the remains of the earliest known penguin, the 50-million-year-old Waimanu, but these rocky islands were also home to the tallest, heaviest penguin yet discovered, Kairuku. Living during the Oligocene epoch, about 27 million years ago, Kairuku had the approximate dimensions of a shortish human being (about five feet tall and 130 pounds), and prowled the shorelines for tasty fish, small dolphins, and other marine creatures. And yes, in case you were curious, Kairuku was even bigger than the so-called Giant Penguin, Icadyptes, which lived a few million years earlier in South America.

31 of 52 Kelenken Kelenken. Wikimedia Commons Name: Kelenken (indigenous Indian for a winged deity); pronounced KELL-en-ken

Kelenken (indigenous Indian for a winged deity); pronounced KELL-en-ken Habitat: Woodlands of South America

Woodlands of South America Historical Epoch: Middle Miocene (15 million years ago)

Middle Miocene (15 million years ago) Size and Weight: About seven feet tall and 300-400 pounds

About seven feet tall and 300-400 pounds Diet: Probably meat

Probably meat Distinguishing Characteristics: Long skull and beak; long legs A close relative of Phorusrhacos--the poster genus for the family of extinct feathered carnivores known as "terror birds"--Kelenken is known only from the remains of a single, oversized skull and a handful of foot bones described in 2007. That's enough for paleontologists to have reconstructed this prehistoric bird as a mid-sized, flightless carnivore of the mid-Miocene forests of Patagonia, although it's as yet unknown why Kelenken had such a huge head and beak (probably it was another means to intimidate the mammalian megafauna of prehistoric South America).

32 of 52 Liaoningornis Liaoningornis. Wikimedia Commons Name: Liaoningornis (Greek for "Liaoning bird"); pronounced LEE-ow-ning-OR-niss

Liaoningornis (Greek for "Liaoning bird"); pronounced LEE-ow-ning-OR-niss Habitat: Woodlands of Asia

Woodlands of Asia Historical Period: Early Cretaceous (130 million years ago)

Early Cretaceous (130 million years ago) Size and Weight: About eight inches long and two ounces

About eight inches long and two ounces Diet: Probably insects

Probably insects Distinguishing Characteristics: Small size; perching feet The Liaoning fossil beds in China have yielded a rich array of dino-birds, small, feathered theropods that appear to have represented intermediate stages in the slow evolution of dinosaurs into birds. Surprisingly, this same location has yielded the only known specimen of Liaoningornis, a tiny prehistoric bird from the early Cretaceous period that looked more like a modern sparrow or pigeon than any of its more famous feathered cousins. Driving home its avian bona fides, the feet of Liaoningornis show evidence of the "locking" mechanism (or at least the long claws) that helps modern birds perch securely in the high branches of trees.

33 of 52 Longipteryx Longipteryx (Wikimedia Commons). Name: Longipteryx (Greek for "long-feathered one"); pronounced long-IP-teh-rix

Longipteryx (Greek for "long-feathered one"); pronounced long-IP-teh-rix Habitat: Shores of Asia

Shores of Asia Historical Period: Early Cretaceous (120 million years ago)

Early Cretaceous (120 million years ago) Size and Weight: About one foot long and less than a pound

About one foot long and less than a pound Diet: Probably fish and crustaceans

Probably fish and crustaceans Distinguishing Characteristics: Long wings; long, narrow bill with teeth on end Nothing gives paleontologists fits like trying to trace the evolutionary relationships of prehistoric birds. A good example is Longipteryx, a surprisingly birdy-looking bird (long, feathered wings, long bill, prominent breastbone) that doesn't quite fit in with the other avian families of the early Cretaceous period. Judging by its anatomy, Longipteryx must have been able to fly for relatively long distances and perch on the high branches of trees, and the curved teeth on the end of its beak point to a seagull-like diet of fish and crustaceans.

34 of 52 Moa-Nalo A Moa-Nalo skull fragment (Wikimedia Commons). Isolated in its Hawaiian habitat, the Moa-Nalo evolved in a very strange direction during the later Cenozic Era: a flightless, plant-eating, stocky-legged bird that vaguely resembled a goose, and that was quickly hunted to extinction by human settlers. See an in-depth profile of the Moa-Nalo

35 of 52 Mopsitta Mopsitta. David Waterhouse Name: Mopsitta (pronounced mop-SIT-ah)

Mopsitta (pronounced mop-SIT-ah) Habitat: Shores of Scandinavia

Shores of Scandinavia Historical Epoch: Late Paleocene (55 million years ago)

Late Paleocene (55 million years ago) Size and Weight: About one foot long and less than a pound

About one foot long and less than a pound Diet: Nuts, insects and/or small marine animals

Nuts, insects and/or small marine animals Distinguishing Characteristics: Small size; parrot-like humerus When they announced their find in 2008, the team behind the discovery of Mopsitta was well-prepared for the satiric backlash. After all, they were claiming that this late Paleocene parrot lived in Scandinavia, a long way from the tropical South American climes where most parrots are found today. Anticipating the inevitable joke, they nicknamed their single, isolated Mopsitta specimen "Danish Blue," after the dead parrot of the famous Monty Python sketch. Well, it turns out that the joke may have been on them. Subsequent investigation of this specimen's humerus, by another team of paleontologists, led them to conclude that this supposed new genus of parrot actually belonged to an existing genus of prehistoric bird, Rhynchaeites. Adding insult to injury, Rhynchaeites wasn't a parrot at all, but an obscure genus distantly related to modern ibises. Since 2008, there's been precious little word about Mopsitta's status; after all, you can only examine the same bone so many times!

36 of 52 Osteodontornis Osteodontornis. Wikimedia Commons Name: Osteodontornis (Greek for "bony-toothed bird"); pronounced OSS-tee-oh-don-TORE-niss

Osteodontornis (Greek for "bony-toothed bird"); pronounced OSS-tee-oh-don-TORE-niss Habitat: Shorelines of eastern Asia and western North America

Shorelines of eastern Asia and western North America Historical Epoch: Miocene (23-5 million years ago)

Miocene (23-5 million years ago) Size and Weight: Wingspan of 15 feet and about 50 pounds

Wingspan of 15 feet and about 50 pounds Diet: Fish

Fish Distinguishing Characteristics: Large size; long, narrow beak As you can guess from its name--which means "bony-toothed bird"--Osteondontornis was notable for the small, serrated "pseudo-teeth" jutting out from its upper and lower jaws, which were presumably used to snatch fish off the Pacific shoreline of eastern Asia and western North America. With some species sporting 15-foot wingspans, this was the second-biggest sea-going prehistoric bird that ever lived, after the closely related Pelagornis, which was itself second in size overall only to the truly enormous Argentavis from South America (the only flying creatures bigger than these three birds were the huge pterosaurs of the late Cretaceous period).

37 of 52 Palaelodus Palaelodus. Wikimedia Commons Name: Palaelodus; pronounced PAH-lay-LOW-duss

Palaelodus; pronounced PAH-lay-LOW-duss Habitat: Shores of Europe

Shores of Europe Historical Epoch: Miocene (23-12 million years ago)

Miocene (23-12 million years ago) Size and Weight: About five feet tall and 50 pounds

About five feet tall and 50 pounds Diet: Fish or crustaceans

Fish or crustaceans Distinguishing Characteristics: Long legs and neck; long, pointed beak Since it's a relatively recent discovery, the evolutionary relationships of the genus Palaelodus are still being worked out, as are the number of separate species it comprises. What we do know is that this shore-wading prehistoric bird seems to have been intermediate in anatomy and lifestyle between a grebe and a flamingo, and that it may have been able to swim underwater. However, it's still unclear what Palaelogus ate--that is, whether it dived for fish like a grebe, or filtered water through its beak for small crustaceans like a flamingo.

38 of 52 Passenger Pigeon Passenger Pigeon. Wikimedia Commons The Passenger Pigeon once flocked the North American skies in the billions, but unrestrained hunting annihilated the entire population by the start of the 20th century. The last remaining Passenger Pigeon died at the Cincinnati Zoo in 1914. See 10 Facts About the Passenger Pigeon

39 of 52 Patagopteryx Patagopteryx. Stephanie Abramowicz Name: Patagopteryx (Greek for "Patagotian wing"); pronounced PAT-ah-GOP-teh-rix

Patagopteryx (Greek for "Patagotian wing"); pronounced PAT-ah-GOP-teh-rix Habitat: Woodlands of South America

Woodlands of South America Historical Period: Late Cretaceous (80 million years ago)

Late Cretaceous (80 million years ago) Size and Weight: About two feet long and a few pounds

About two feet long and a few pounds Diet: Probably omnivorous

Probably omnivorous Distinguishing Characteristics: Long legs; small wings Not only did prehistoric birds coexist with dinosaurs during the Mesozoic Era, but some of these birds had already been around long enough that they'd lost the ability to fly--a good example being the "secondarily flightless" Patagopteryx, which evolved from smaller, flying birds of the early Cretaceous period. To judge by its stunted wings and lack of a wishbone, the South American Patagopteryx was clearly a land-bound bird, similar to modern chickens--and, like chickens, it seems to have pursued an omnivorous diet.

40 of 52 Pelagornis Pelagornis. National Museum of Natural History Pelagornis was over twice the size of a modern albatross, and even more intimidating, its long, pointed beak studded with tooth-like appendages--which enabled this prehistoric bird to dive into the ocean at high speeds and spear large, wriggling fish. See an in-depth profile of Pelagornis

41 of 52 Presbyornis Presbyornis. Wikimedia Commons If you crossed a duck, a flamingo and a goose, you might wind up with something like Presbyornis; this prehistoric bird was once thought to be related to flamingos, then it was classified as an early duck, then a cross between a duck and a shorebird, and finally a kind of duck again. See an in-depth profile of Presbyornis

42 of 52 Psilopterus Psilopterus. Wikimedia Commons Name: Psilopterus (Greek for "bare wing"); pronounced sigh-LOP-teh-russ

Psilopterus (Greek for "bare wing"); pronounced sigh-LOP-teh-russ Habitat: Skies of South America

Skies of South America Historical Epoch: Middle Oligocene-Late Miocene (28-10 million years ago)

Middle Oligocene-Late Miocene (28-10 million years ago) Size and Weight: About two to three feet long and 10-15 pounds

About two to three feet long and 10-15 pounds Diet: Small animals

Small animals Distinguishing Characteristics: Small size; large, powerful beak As phorusrhacids, or "terror birds," go, Psilopterus was the runt of the litter--this prehistoric bird only weighed about 10 to 15 pounds, and was a positive shrimp compared to larger, more dangerous members of the breed like Titanis, Kelenken and Phorusrhacos. Even still, the heavily beaked, stockily built, short-winged Psilopterus was capable of doing extensive damage to the smaller animals of its South American habitat; it was once thought that this petite terror bird could fly and climb trees, but it was probably as clumsy and land-bound as its fellow phorusrhacids.

43 of 52 Sapeornis Sapeornis. Wikimedia Commons Name: Sapeornis (Greek for "Society of Avian Paleontology and Evolution bird"); pronounced SAP-ee-OR-niss

Sapeornis (Greek for "Society of Avian Paleontology and Evolution bird"); pronounced SAP-ee-OR-niss Habitat: Woodlands of Asia

Woodlands of Asia Historical Period: Early Cretaceous (120 million years ago)

Early Cretaceous (120 million years ago) Size and Weight: About three feet long and 10 pounds

About three feet long and 10 pounds Diet: Probably fish

Probably fish Distinguishing Characteristics: Relatively large size; long wings Paleontologists continue to be puzzled by the profusion of early Cretaceous birds possessing surprisingly advanced characteristics. One of the best-known of these avian enigmas is Sapeornis, a seagull-sized prehistoric bird that seems to have been adapted for long bursts of soaring flight, and was almost certainly one of the biggest birds of its time and place. Like many other Mesozoic birds, Sapeornis had its share of reptilian characteristics--such as the small number of teeth on the end of its beak--but otherwise it seems to have been well advanced toward the bird, rather than the feathered dinosaur, end of the evolutionary spectrum.

44 of 52 Shanweiniao Shanweiniao. Nobu Tamura Name: Shanweiniao (Chinese for "fan-tailed bird"); pronounced shan-wine-YOW

Shanweiniao (Chinese for "fan-tailed bird"); pronounced shan-wine-YOW Habitat: Skies of eastern Asia

Skies of eastern Asia Historical Period: Early Cretaceous (130-125 million years ago)

Early Cretaceous (130-125 million years ago) Size and Weight: Undisclosed

Undisclosed Diet: Probably insects

Probably insects Distinguishing Characteristics: Long beak; fan-shaped tail The "enantiornithines" were a family of Cretaceous birds that retained some distinctly reptilian characteristics--most notably their teeth--and which went extinct at the end of the Mesozoic Era, living the field open for the parallel line of bird evolution that we see today. The importance of Shanweiniao is that it was one of the few enantiornithine birds to have possessed a fanned tail, which would have helped it to take off quickly (and consume less energy while flying) by generating the necessary lift. One of Shanweiniao's closest relatives was a fellow proto-bird of the early Cretaceous period, Longipteryx.

45 of 52 Shuvuuia Shuvuuia. Wikimedia Commons Shuvuuia seems to have been composed of an equal number of bird-like and dinosaur-like characteristics. Its head was distinctly birdy, as were its long legs and three-toed feet, but its too-short arms call to mind the stunted limbs of bipedal dinosaurs like T. Rex. See an in-depth profile of Shuvuuia

46 of 52 Stephens Island Wren Stephens Island Wren. public domain The otherwise unremarkable looking, mouse-sized, and recently extinct Stephens Island Wren was noteworthy for being completely flightless, an adaptation usually seen in larger birds like penguins and ostriches. See an in-depth profile of the Stephens Island Wren

47 of 52 Teratornis Teratornis (Wikimedia Commons). The Pleistocene condor ancestor Teratornis went extinct at the end of the last Ice Age, when the small mammals it depended on for food became increasingly scarce thanks to increasingly cold conditions and a lack of vegetation. See an in-depth profile of Teratornis

48 of 52 Terror Bird Phorusrhacos, the Terror Bird (Wikimedia Commons). Phorusrhacos, aka the Terror Bird, must have been plenty scary to its mammalian prey, considering its large size and clawed wings. Experts believe Phorusrhacos grabbed its quivering lunch with its heavy beak, then bashed it repeatedly on the ground until it was dead. See an in-depth profile of the Terror Bird

49 of 52 Thunder Bird Dromornis, the Thunder Bird (Wikimedia Commons). Name: Thunder Bird; also known as Dromornis (Greek for "thunder bird"); pronounced dro-MORN-iss

Thunder Bird; also known as Dromornis (Greek for "thunder bird"); pronounced dro-MORN-iss Habitat: Woodlands of Australia

Woodlands of Australia Historical Epoch: Miocene-Early Pliocene (15-3 million years ago)

Miocene-Early Pliocene (15-3 million years ago) Size and Weight: About 10 feet tall and 500-1,000 pounds

About 10 feet tall and 500-1,000 pounds Diet: Probably plants

Probably plants Distinguishing Characteristics: Large size; long neck Perhaps for tourism purposes, Australia has been doing its best to promote the Thunder Bird as the largest prehistoric bird that ever lived, proposing an upper-bound weight for adults of a full half a ton (which would vault Dromornis over Aepyornis in the power ratings) and suggesting that it was even taller than the Giant Moa of New Zealand. Those may be overstatements, but the fact remains that Dromornis was a huge bird, surprisingly not related as much to modern Australian ostriches as to smaller ducks and geese. Unlike these other giant birds of prehistoric times, which (because of their lack of natural defenses) succumbed to hunting by early human settlers, the Thunder Bird seems to have gone extinct all on its own--perhaps because of climatic changes during the Pliocene epoch that impacted its presumed herbivorous diet.

50 of 52 Titanis Titanis (Wikimedia Commons). Titanis was a late North American descendant of a family of South American carnivorous birds, the phorusrachids, or "terror birds"--and by the early Pleistocene epoch, it had managed to penetrate as far north as Texas and southern Florida. See an in-depth profile of Titanis

51 of 52 Vegavis Vegavis. Michael Skrepnick Name: Vegavis (Greek for "Vega Island bird"); pronounced VAY-gah-viss

Vegavis (Greek for "Vega Island bird"); pronounced VAY-gah-viss Habitat: Shores of Antarctica

Shores of Antarctica Historical Period: Late Cretaceous (65 million years ago)

Late Cretaceous (65 million years ago) Size and Weight: About two feet long and five pounds

About two feet long and five pounds Diet: Fish

Fish Distinguishing Characteristics: Medium size; duck-like profile You might think it's an open-and-shut case that the immediate ancestors of modern birds lived alongside the dinosaurs of the Mesozoic Era, but matters aren't that simple: it's still possible that most Cretaceous birds occupied a parallel, but closely related, branch of avian evolution. The importance of Vegavis, a complete specimen of which was recently discovered on Antarctica's Vega Island, is that this prehistoric bird was indisputably related to modern ducks and geese, yet coexisted with dinosaurs at the cusp of the K/T Extinction 65 million years ago. As to Vegavis' unusual habitat, it's important to remember that Antarctica was much more temperate tens of millions of years ago than it is today, and was capable of supporting a wide variety of wildlife.