Mainstream science holds that birds evolved from bird-like raptors beginning sometime in the jurassic period.
In fact, it's been said often in recent years that birds ARE dinosaurs, and that raptors have very few traits distinguishing them from birds. Still, orthodoxy dictates that birds evolved from only ONE species of raptor, and that all the thousands of species of bird descend from the direct proto-bird ancestor of this one species of raptor. It has even been shown that all raptors likely had feathers or at least proto-feathers, even the famous T-rex...which has finally solved the riddle of why T-Rex arms are so small compared to the rest of it's morphology; they are not arms at all but 'wings' used for balancing.
However, there has been much debate about which raptor is the direct ancestor of birds. What's more, there is no evidence that all birds evolved from only one species of raptor. The greatest argument for a one-raptor origin is that the developement of flight likely only occurred once in avian evolution.
That may likely be the case, and I do not dispute it. However, I do dispute the idea that all birds had an ancestor who could fly; there is no reason at all for this to be so.
According to wikipedia, "Phorusrhacids, colloquially known as terror birds, are an extinct clade of large carnivorous flightless birds that were the largest species of apex predators in South America during the Cenozoic, 62–2.5 million years (Ma) ago."
62 million years ago is the time period where fossils start showing up again in abundance on the planet after the K2 event, which supposedly destroyed the dinosaurs, and not long after South America broke away from Africa.
for 10 thousand years before and after the proposed time of K2, fossils become scarce over the entire planet. However, many animals that lived before and after K2 do not have any fossils from this "blank period" of our fossil record. So we know that just because we don't find a fossil of an animal between 80 thousand and 65 thousand years ago, doesn't mean that it wasn't around. In fact scientists have found a refugium in North America where dinosaurs survived for at least several thousand years past the K2 event, and are likely to find more of these 'refugium."
About Phorusrhacids, wikipedia goes on to say,
"Phorusrhacids may have even made their way into Africa, with the genus Lavocatavis recently discovered in Algeria, although its status as a true phorusrhacid is questionable. A possible European form, Eleutherornis, has also been identified, suggesting that this group had a wider geographical range in the Paleogene."
But did they really "make their way" to Africa, or were they already there before the continental split?
We can believe that one dinosaurid raptor evolved into a proto-bird and all modern birds evolved from that one proto-bird....and then only one species of those thousands of species of birds evolved BACK into a 10 foot tall raptor on three separate continents...
OR, we can believe that Phorusrhacids evolved directly from a raptor and never flew at all.
The latter is infinitely more probable, since the differences between the the youngest bird-like raptors and birds are pretty much non-existent.
If you look at the skeleton of a terror bird, it's pretty much identical to a bird-like raptor from just before the K2 event. Terror birds show back up as soon as fossils become abundant again right after the K2 event.
But when you look at the reconstruction of a terror bird, most artist try to make it look bird-like because of their preconceived notions. Likewise, most artists still draw T-Rex without feathers on it's arms or even the spindly proto-feathers that covered it's body.
Below is a drawing of several bird-like raptors from just before the K2 event.
Utahraptor in particular looks more like a dragon than any dinosaur I've ever seen.
It may be that Phorusrhacids looked more like this artists rendition than the way it is usually portrayed (basically like a big ostritch, which it wasn't!)
Man met Phorusrhacids in South America, and may have met the beast in Africa and Europe too.
There were other giant birds to meet in Oceana, and their evolutionary track is still largely unknown.
Were terror birds raptors? Were raptors dragons?
They sure like dragons to me, and if they could jump and use those little wings to slow the descent a little bit when pouncing on their prey...it would look just like flight to a puny little man on the receiving end of predation.