The features we both noted were: About four to five feet tall and ran on the two hind feet. The knees bent backward, not forward as a human’s. It made it across the road in three or four seconds. It had the body of a slim small child, not like a fat kangaroo. The arms chugged back and forth like a person running. The head had a pointed chin and a pointed top at the back like a rooster’s comb. The body looked gray or some other dark color. The thing looked to be an alien to both of us. We have never seen a picture of any [conventional] animal that resembled what we saw. It seems there have been many sightings of such a thing in the past. These are found on the Internet under Chupacabras.
Many of the features described sound distinctly bird-like:
- It is bipedal.
- Its "knees" bend "backward". (Birds' knees don't actually bend "backward"; what people mistake for knees are actually ankles. Birds have fairly short legs but very long feet, and they run on their toes.)
- The "rooster's comb" is compared by the witness himself to an avian feature.
- The "sharp chin" sounds compatible with a beak.
However, if there were a breeding population able to sustain the species through the many millenia since their last known fossil, it should have been seen much more often. If Bigfoot is unlikely, a surviving terror bird is even more unlikely. This is more a topic for fiction than an hypothesis for serious science.
In fact, a Google search shows that the idea that the "Chupacabras" might be a terror bird had already occurred to others, and in fact there is a novel (The Flock, by James Robert Smith) about terror birds surviving in central Florida. As animatronics at Epcot Center, maybe; otherwise, I'm afraid not.
So what did these people see in Texas? My guess is some other large bird. Maybe it was wounded, or maybe they so little expected to see a large bird that their brains tried to find other categories for what they glimpsed -- and remember, all they got was a glimpse. I'd be inclined to guess a sandhill crane, but it's hard to imagine its long beak being mistaken for anything other than a beak.