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Herrerasaurus is one of the oldest dinosaurs. Discovered by Victorino Herrera in 1963 in Argentina, and named after him, this dinosaur was the earliest big carnivore and perhaps one of the few fully bipedal reptile of its time. It was also an enigma for a long time. Paleontologist Osvaldo Reig first described (and named) Herrerasaurus and it was very difficult.
Why was it so enigmatic? To begin with the first specimen discovered did not have a skull. And it was strange. It has traits that are found in different groups of dinosaurs and even some non-dinosaurian beasts called the archosaurs. One example are the hips.
Herrerasaurus has hips that seem to be closer to the saurischian (lizard hipped) dinosaurs than the ornithischian (bird hipped) dinosaurs, where we now think it belongs. But where the femur and pelvis meet, the skeleton is only partially open, so it also seems to resemble some no-dinosaurian types of skeletons.
But the pelvis lacks bone in the hip socket. This was the feature that lets us recognize OwenÂfs group the Dinosauria.
But it was not only the hips that were different.
Later dinosaurs mostly had three toes. This is a common feature of many dinosaurs. But Herrerasaurus was different. It had five distinct toes. Mind you, only three were weight bearing, so they are the most important ones. But unlike many dinosaurs, five toes were distinct and easily recongizable (no reduced forms). Then there was the skull.
The skull (a skull was finally found in 1988) of this dinosaur lacked most of the specializations of later dinosaurs. It also had a flexible joint in the lower jaw. This allowed it to open its mouth quite wide and it could certainly put this to good use to give a good grasping bite. This plus the serrated teeth which could be good for cutting and slashing, and this creature made a formidable predator.
An early large carnivore that was fully bipedal, this dinosaur lived in the late Triassic. With forlimbs (arms) that could hold things, it was probably an effective hunter, although the arms were not long. It could probably run fast, as the bones in the tail were partly locked together, to prevent it from swinging wildly and absorbing energy.