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These are the modern dinosaurs, and the most biomechanically efficient still-living vertebrates, able to fly at 120 mph and to go around the world with amazing ease. In short, the worthy dinosaur descendants. Here we'll talk about those which range from being slightly older than Archaeopteryx to nearly as young as modern day. On the other hand, we'll not talk about historically extinct birds such as the Dodo or the Elephant-Bird: they have nothing to do with only-prehistoric beasts, and they'll deserve a Useful Notes Page on their own.
When dinosaurs went up trees: Scansoriopterygids
- Scansoriopterygids were pigeon-sized animals from either the Late Jurassic or Early Cretaceous (their exact age is uncertain). They had a body-plan apt for climbing, similar to Microraptor, or rather, even more specialized; they had forelimbs longer than their hindlimbs. First discovered in 2002 in Liaoning, they were found with feather prints around their body like many other Liaoning coelurosaurs, but their placement within the phylogenetic tree is fairly uncertain (avialian or non-avialian theropods?). Recent studies suggest were proto-birds, closer to house sparrows than Archaeopteryx was (this could change, and they may be close to the deinonychosaur-bird split, or even early oviraptorosaurs). Unluckily, only juvenile specimens are known from the few species of scansoriopterygids described, and some of their peculiar traits might just be juvenile-related and were lost in adults. The tiny Epidexipteryx (which once contended the “smallest non-avian dinosaur” record with Anchiornis), and the namesake Scansoripteryx, are the only two species recognized today: a third genus, "Epidendrosaurus", has been synonymized with Scansoriopteryx (and there are those who still prefer that name).
- Confuciusornis lived in Early Cretaceous and was from the same famous Chinese Liaoning site in which the popular feathered dinosaur fossils come from. This animal had some evolved traits, for example had already lost its teeth (convergently from modern birds) and shortened its tail, but still retained an old legacy: three-clawed wings. As is easy to think from a Liaoning animal, the Confucius-bird has also preserved prints of feathers, which show two very elongated tail-feathers rather peacock-like. Another basal bird, Jeholornis from the same age and habitat, is also known as "Shenzhouraptor".
The Mirror Universe birds: Enantiornithines
- The most successful Late Cretaceous birds were the Enantiornithes, whose name means "mirror birds". Why? Because of some skeletal features which appear specular compared to modern fliers. They were a sort of middle-ways between the aforementioned Early Cretaceous birds and modern feathered guys, and were very diversified among each other. The Zerg Rush birds in the Walking with Dinosaurs episode about pterosaurs were enantiorns, as well as, arguably, those mentioned in the last episode which made the "omnipresent chorus" from the trees. The Mirror Universe birds went extinct along with non-avian dinos only after the comet/asteroid.
Toothy seabird 1: Hesperornis
- Hesperornis and Ichthyornis are the two most famous Dinosaur Age-related birds (not counting Archaeopteryx), both from Late Cretaceous North America. Since hespero is far cooler, here we'll mention it first. Hesperornis lived in the same habitat in which Pteranodonts, Mosasaurs, Elasmosaurs and Archelons roamed: the shallow inland sea which used to cover US Midwest at that time, dividing North America in two parallel stripes of land running from Arctic down to the south. Despite its earliness, Hesperornis was already a very derived bird. 6 ft long (the size of a human), it was flightless, with vestigial wings, short splayed legs for swimming, a long neck, and a long beak with small true teeth. It spent most of its life in water, but returned on land to lay its eggs. Once, the hesperorn was shown as a sort of proto-penguin with an erect pose; we know now its legs were too weak to well-substain its body, and the animal is now portrayed more similar to modern grebes and loons. We still don’t know if it had palmated feet like a loon, or lobed like a grebe.
Toothy seabird 2: Ichthyornis
- The much smaller, far less striking Ichthyornis lived in the same age and habitat of the former, but this time we're coping with a sorta toothed, long-billed proto-seagull. The ichthyorn's lifestyle was arguably similar to modern flying sea birds, catching fishes in flight or maybe diving under the sea to pursue them like modern boobies. Both birds sometimes fell preys of large marine reptiles, as shown by stomach-remains. Ichthyornis and Hesperornis were (almost) full-birdies at that point, and if alive today, they'll be taken for components of modern avifauna. In some artistic works, both Hesperornis and Ichthyornis are depicted black and white like modern gulls or penguins, but their real coloration is totally unknown.
The first full-birdies: Prehistoric neornithines
- Neornithes (meaning new birds) or colloquially "Neorns", is the name indicating the last common ancestor of all modern birds and all its descendents. Neornithes were the only Cretaceous birds which managed to overcome the mass-extinction and to make their way in the Cenozoic, the Mammal Age. It's worth noting that their descendants, our modern birdies, have much, much more species today than mammals: thus, one can comfortably say dinosaurs still rule the world. Some ornithologists could even say "the Mammal Era" should be renamed "Bird Era" and considered a simple extension of the "Dinosaur Era"... But we humans will always be too proud to be mammals to accept this alternative view. Most Cenozoic "new birds" were very similar to their descendants: some were rather generic-looking, while others were more specialized, but still not too different to modern avians. Furthermore, their fossil record is extremely scant, maybe the scantiest of all Vertebrates; thus, evolution of the single modern-bird lineages is mostly unknown even today, and their phylogenetic tree is full of question marks. But don't worry...there were also many exceptions to this rule: we're going to talk about these.
When birds ruled the world: Gastornis (once called "Diatryma")
- Long-standing paleo-fans will remember for sure the name "Diatryma": that large, flightless, large-headed predatory bird who used to hunt the small "horse" Eohippus in so many paleo-artistic depictions. Well, now poor Diatryma seems having definitively disappeared... but luckily, it's not such: it has simply changed identity. Now we have to call it Gastornis (a far less awesome name, we've to admit, but...never mind.) Whatever name should be used, this is actually one of the most enigmatic extinct birds. It might not even be carnivorous at all: its strong beak wasn't hooked like an eagle's, and its body frame was stocky, seemingly slow-moving. Maybe it only was an omnivore who used its bill to crack nuts, cut vegetation, and sometimes, tear flesh from its prey (but it was more probable it swallowed its eohipps whole, like most modern non-raptorian birds). Anyway, it was a real giant in its forestal world, 40 million years ago: while mammals were still small, some birds grew to large size, creating a sort of Bizarro Universe in which mammals could be lower-ranking in the food pyramid.
- With Phorusrhacids (grassland-dwelling non-fliers), we have no doubts this time: thanks to their light weight and slender running legs, they were active hunter of small mammals. Not only that, with their strongly hooked, very eagle-like bill, they did not swallow their prey whole. It has recently been discovered they had even one clawed finger protruding from each of their tiny wings , for uncertain purpose. Perhaps the most amazing-looking among all prehistoric birds, they have recently nicknamed terror-birds in pop- documentaries (for example, Prehistoric Park.) Originary from South America, they have left a legacy in our modern world as well: the closely-related Seriema is a medium-sized South American bird whose shape and habits resemble a miniaturized "terrorbird". Even though is also nicknamed "terrorbird" sometimes, Gastornis/Diatryma was not related to Phorusrhacids: it has left any descendant since 40 million years. The prototypical South American Phorusrhacos (often misspelled "Phororhacos") and the recently-discovered North American Titanis (first-originated in South America as well) are the two stock species of the family.
- Dromornithids were among the largest birds that ever lived (they varied in size from about as big as a cassowary to the largest and Trope Namer of the group, Dromornis stirtoni, 3 meters tall and half a ton in weight); and yet, they've not gained much consideration in popular media, unlike their American contemporary counterparts, the phorusrhacids. It's probably because they likely weren't, fast, vicious killers. Instead, the 'thunderbirds', with their vast bulk, thick, robust bones, hoof-like toes and strong, crushing beaks were browsing and grazing herbivores, slowly plodding across a wetter, more wooded ancient Australian outback. Typical of Australian things, they've been given many nicknames: "thunderbirds" obviously refers to their huge bulk and robust bones; "demon ducks of doom" refers to their closest living relative being the Australian magpie goose, and other waterfowl, and an old debate as to whether they were carnivores. A recent addition to the list is "Mihirung", from an Aboriginal story that might mention them as the "mihirung paringmal" or Giant Emu: it is a certainty that the first people to arrive in Australia encountered them, and possibly drove them extinct (though the jury's still out on that score).
Deadly feast: Teratornis
- We leave (almost) definitively the flighless bird's world and start to watch more traditional fliers. Among prehistoric flying birds, the most depicted (and most striking) are the Teratorns. They were very vulture-like animals, but were actually more related to storks than to bird-of-prey: just like modern condors and North-american vultures. The namesake Teratornis is one of the most abundant birds in fossil record, and has been found in huge numbers in the famous Californian tar-pits in which mammalian sabretooths, giant wolves, mastodons and ground sloths have also been found. Arguably, they went to feed on the carcasses of these mammals, and remained stuck in tar just the same.
A feathered airplane: Argentavis
- The aforementioned Teratornis had an earlier relative, which lived in South America 8 million years before: Argentavis (its name means "argentinian bird"). Why should we mention it separately? Well... simply because, along with giant pterosaurs, it deserves the Giant Flyer title more than every other prehistoric creature. Its wingspan was 25 ft, as much as Pteranodon; its weight 80 kg, as much as the two-times-wider-winged Quetzalcoatlus. Imagine a giant condor with a ostrich-sized body, huge roc-like wings, a sharp uncinated beak, and a love for carrion (and maybe even an occasional hunting attitude). With no doubt, the largest flying bird ever discovered. And yet, Argentavis has yet to appear in fiction. And **heck**, it has actually had one single apparition in documentaries to date: "Paleoworld", as a side-note of Phorusrhacids! Since Walking With Beasts producers did recreate Argentavis world (the Sabretooth episode)... they wasted a perfectly good opportunity.
Toothy seabird 3: Osteodontornis
- However, Argentavis wasn't the only Giant Flyer in the Cenozoic: we have to add the Pelagorns. These were rather albatross-like or pelican-like marine birds, but they had two cool traits: their wingspan reached 20 ft (a bit less than Argentavis) and their beak was toothed, seemingly revealing the trope Toothy Bird being a Real Life thing in the past. Sadly, this is not true: these "teeth" weren't real teeth, but their bill had an ondulating, pseudo-toothed edge, just like one modern bird, the duck-like Merganser. The only Real Life toothy-birds were those living alongside non-avian dinosaurs, such as Archaeopteryx, Hesperornis, and Ichthyornis (which weren't even typical "birds"). Pelagorns were the new feathered version of Pteranodon, almost as large as it, and went extinct only 1 million years ago. Osteodontornis is the typical member of the group.
Everything's even better with giant penguins: Anthropornis
- When Hesperornis went eventually extinct at the end of the Mesozoic, a new kind of birds took soon its niche: but this time we're talking about much, much familiar-looking creatures: penguins. Giant penguins. The largest of them, Anthropornis, was nearly as tall as a fully-grown human and weighed 200 kg, more than a modern ostrich; but it probably was as nice-looking as modern penguins are. Giant penguins swum in the southern seas for million years, until they were outcompeted 20 million years ago by a new group of large marine animals, their mammalian equivalents: seals and sea-lions.