All is quiet in the Jungle: too quiet. The sun is high, the small mammals that dare venture out in broad daylight are taking a siesta. But the top predator in this primeval forest are not meat eating saber-toothed cats or behemoth reptiles of a bygone age. It's a bipedal monster. And if you saw this thing coming after you, running like the wind, the last thing that would pass through your brain, aside from stark raving terror, is that you were being taken out by a raptorial dinosaur. Because this ambushing bitch is twelve-feet tall and weighs half a ton. She was vicious, from scaly clawed feet to feathered crown. Topped off with a giant serrated maw, a wicked re-curved tip, the whole head sporting the profile of an ax blade. But this is no dinosaur, they're long gone. Our ancestors are already using stone tools in Africa and about to start the first of many migrations out of the Dark Continent. This is only two-million years ago, in the rain forests of Florida, and our killer is a
Titanis walleri; a giant, flightless bird with a taste for meat. Wanna hear something really scary? She had evolved
hands ...
We have this rosy picture in our primate heads, courtesy of the endless science specials on the demise of the dinos: Small, clever mammals were hiding in our fur-lined burrows and hollowed out logs, just
waiting for our Dinosaurian Overlords to bite the cometary dust of the K-T Impact. Then we would rise gloriously from the ashes of a ruined world and claim our rightful inheritance as the new masters of the planet. It appeals deliciously to our built in bias of mammalian superiority. But this is the legend of the Phoenix: And the Phoenix was a
bird.
Truth be told, on almost every continent we hairy critters were handily beat out of the evolutionary gates after the fall of the dinosaurs by another clade of animals that would give even Stephen King nightmare sweats. Had it not been for the one continent these killer avians somehow missed, you and I wouldn't be here. In our furry stead might well be races of giant creatures with feathered bodies, clawed feet, and stiletto tipped fingers on powerful hands; the whispered vestige of their ancient raptorial ancestors of Jurassic Park echoing from ancient graves of mud and stone: These are the Terror Birds..
Birds are vertebrates of course and are further classified in the class called Aves. The term Terror Bird is not a precise taxon and includes a wide variety of birds. But they're all real big and real mean.
In a real way, all raptorial dinosaurs could be called terror birds. They had feathers and they were closely related to what we think of as birds today. And it may well be that flying birds, which are believed to have evolved from feathered dinos called Maniraptors, occasionally went the reverse evolutionary route and became flightless birds. We might see the remains of such animals in the fossil record and be unable to distinguish them from a standard dinosaur. There was tens of millions of years to work with and lots of archipelagos between Eurasia and what would be America in the Late Jurassic and Cretaceous for evolution to work its island magic. It could have happened many times, as it has since. Consider for example Caudipteryx, below.
Did this early Cretaceous Dinosaur evolve from the common ancestor of flying birds like other dinosaurs, or did it evolve from flying birds back into what we mistakenly call a dinosaur? The fossil and morphological evidence supports either scenario. And those long feathers on the arms have the features of aerodynamic remiges suggesting a possible vestigial use
But the first official terror birds arise quickly after the end of the Cretaceous. By 55 MYA the terrifying Gastornis vaults into the fossil record on powerful legs and rules the Eocene Jungle for millions of years as top predator. At this early juncture the largest mammals were rarely larger than a good sized house cat, while this fearsome ambush hunter was already six feet tall and tipped the scales at 200 lb.! It probably ate many a small mammal including our own ancestors, shredding them down tidbit sized for the ravenous chicks.
Gastornis, 50 MYA, prowling Europe. That little beastie hanging limply in her maw is an early equine, i.e., a horse! Photo courtesy Discovery Channel
Staring around 40 MYA, South America, adrift, mostly cut off from the Northern version by the Isthmus of Panama, became the home to several species of enormous birds called Phorusrhacids.
An artist's reconstruction of a Phorusrhacos longissimus in S. America circa 25 MYA. They reached three meters in height
One of the South American Terror Birds was not flightless. Argentavis Magnificens was the largest known flying bird and could have picked up a goat or an adult human in her mighty talons and flown away. Now that's a terror bird!
Argentavis Magnificens. The largest flying bird known, in reconstruction and scale
A few million years ago, North and South America joined up and the South American Terror Birds strolled right up through Mexico, Texas, and as far east as Florida. Some then evolved into the amazing T. walleri, the handy hunter I first started out with in the introduction. This creature was the closest thing to its theropod ancestors we know of and was well on the way to re-evolving hands, when the terror birds mysteriously died out in most of the world.
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Titanis walleri circa 2.5 MYA. North America showing off her arms and hands. Check out the skull on that thing in the photo on the left: The entire head was built like a gruesome, medieval weapon!
Why did the Terror Birds die off? Why are they almost entirely absent now when only a few short million years ago they were numerous and seemingly entrenched on several continents?
Well, we can never really know. But several phenomena working in concert may have knocked these magnificent animals out of the race. For whatever reason, terror birds never really caught on some places, like China. That region was often isolated from Europe by ice sheets, tundra, and desert. So the European terror Birds did not as far as we can tell, make the trek. Free of the overwhelming pressure of the killer birds, mammals in China radiated into the top predatory slots. In particular, one group called Miacids evolved and began to grow large; the forerunner of bears, dogs, and cats.
The second was the evolution of grasses and the changing climate 30 MYA which allowed huge grasslands to form and probably opened routes from Siberia to America. Large animals quickly evolved to eat grasses, the ancestors of the large herbivores we see today: Elephants, hoofed animals like bison and horses. And the miacids followed these mobile meat markets out into the open plains and started getting really big. By ten to fifteen million years ago the recognizable forerunners of great cats, bears, and wolves are thriving in North America and down to the South; right into the stronghold of the terror birds. The climate began swinging wildly about this time, and for whatever reason the mammals outcompeted the big birds.
Dinornis Gigantis. The largest species of Moa, in reconstruction and scale
There was one holdout though, way to the South in Australia and New Zealand. There, isolated from the placental mammals, several species of Moa survived until just the last few thousands years. One of them, Dinornis Gigantis, was the tallest bird known to have ever existed. Sadly, these resplendent creatures where knocked off by another mammal which arrived on the continent about 50,000 years ago; this mammal walked on two legs. Within just a few hundred years of the arrival of man, the great Moa are gone.
But don't think this planet will never see another terror bird, an emergent dino. Birds are one of the most successful vertebrate clades on earth, with an estimated ten-thousand species extant today. They can pull up stakes and fly half a world away when environmental catastrophes occur, surviving on islands and mountain tops when other animals are stuck in the middle of a wrecked biome and go the way of T. rex. They eat about anything, they breed fast and evolve quickly. That's all, apparently, one hell of a recipe for success!
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Look carefully into the eyes of the hawk, the owl, even a playful sparrow or fluttering humming bird; all sharper than early surveillance satellites. There is mind behind those gorgeous orbs. Doesn't it almost look like they're planning something? Deep inside these gaudy feathered creatures lurks the heart of a fearsome serial killer who has feasted on mammals for two-hundred million years. The ancient DNA of a one-ton Utah raptor still fresh enough to rise again, given half a chance.
They're not done, not by a long shot! They've barely begun. The evolutionary plasticity of Aves is simply astounding. The dinosaurs and the flightless terror birds are still there in vestigial form, patiently biding their time, blazing low over the blurring earth at 100 MPH, swimming through the sea under Antarctic pack ice, bounding across the savanna, and dancing through the clouds as man can only dream of, while we hairy rats have our evolutionary run. They're the greatest warm blooded survivors our world has ever known. While other species were dying in huge numbers, these marvelous creatures sailed right through the K-T Impact with nary a ruffle in their wings. Over and over again, in at least a dozen different times and places, those small flyers have grown to nightmarish sizes and savage dietary predilections.
Oh yes; the terror birds will be back, thundering across the earth in monstrous form. Neo-dinosaurs; Bigger, stronger, smarter; more deadly than ever. It's just a matter of time: Count on it.