Other features of bird of prey feet gave clues as to the functional anatomy of their ancient relatives, toe proportions of dromaeosaurids seemed more suited for grasping than running, and the metatarsus, the bones between the ankles and the toes, is more adapted for strength than speed.
A long metatarsus lets you take bigger strides to run faster; but in dromaeosaurids, the metatarsus is very short, which is odd," he said.
The study also has implications for the next closest relatives of troodontids and dromaeosaurids, the birds.
We see fully formed wings in exquisitely preserved dromaeosaurid fossils, and from biomechanical studies we can show that they were also able to perform a rudimentary flapping stroke.
The new find indicates that dromaeosaurids were far more widespread than previously recognized, says Mark A.
Dromaeosaurids had the same joint arrangement as did early birds such as Archaeopteryx, Holtz adds.
Overall, researchers have found four specimens, all far south of where any indisputable dromaeosaurid remains have ever been discovered.
Those commonalities might prompt paleontologists to move Rahonavis from the primitive-bird branch of the dinosaur family tree into the dromaeosaurid group, says Thomas R.
As one of the earliest and most complete dromaeosaurids
, Sinornithosaurus helps fill in critical information, says Wu.
Dromaeosaurids lived during the Cretaceous Period, when the southern continents were well-separated from those in the north.
The shape was different, with small curves and edges unlike those of the dromaeosaurids.
Novas concluded it was the first known example of a kind of killer dinosaur that developed in the Southern Hemisphere--one that was unrelated to dromaeosaurids of North America.
Like the dromaeosaurids, it probably used its single huge claw on each foot to slash open its prey.
Other meat-eating dinosaurs besides dromaeosaurids carry the name "raptor," including the toothless Oviraptor (OH-vuh-RAP-tur), which means "egg thief," and the dog-sized early meat eater Eoraptor (EE-oh-RAP-tur), which means "dawn thief.
Velociraptor ("fast thief") is perhaps the best known of all dromaeosaurid dinosaurs.