Size and Weight:
Some dinosaur names make more sense than others. A good example is Protarchaeopteryx, which translates as "before Archaeopteryx," even though this birdlike dinosaur lived tens of millions of years after its more famous ancestor. In this case, the "pro" in the name refers to Protarchaeopteryx's supposedly less advanced features; this dino-bird seems to have been considerably less aerodynamic than Archaeopteryx, and was almost certainly incapable of flight.
If it couldn't fly, why did Protarchaeopteryx have feathers? As with other small theropods, this dinosaur’s arm and tail feathers likely evolved as a way of attracting mates, and may (secondarily) have given it some "lift" if it had to make a sudden, running leap away from larger predators.