sentences:  In order to achieve liftoff, "Archaeopteryx" would have to run faster than modern birds by a factor of three, due to its weight.Furthermore, the mass of "Archaeopteryx" versus the distance needed for minimum velocity to obtain liftoff speed is proportional, therefore, as mass increases, the energy required for takeoff increases.Other research has shown that the physics involved in cursorial flight would not make this a likely answer to the origin of avian flight.