Two paleontologists present differing hypotheses regarding the evolutionary origin of avian flight in theropod dinosaurs.
Viewpoint 1 (Arboreal Hypothesis)
Avian flight evolved from tree-dwelling (arboreal) ancestors. These small theropod dinosaurs leaped between branches and utilized feathered forelimbs to glide. Over time, selective pressure favored longer glides, leading to the evolution of powered, flapping flight. Under this model, early flight adaptations were primarily aerodynamic structures optimized for air-to-ground movement, and the claws of these organisms were adapted for climbing and grasping tree bark.
Viewpoint 2 (Cursorial Hypothesis)
Avian flight evolved from ground-dwelling (cursorial) bipeds. These active, running theropods used their feathered forelimbs for non-flight behaviors, such as capturing prey, maintaining stability, or running up steep inclines. Over time, these flapping motions generated aerodynamic forces (traction and lift) that allowed them to transition into powered flight. Under this model, early flight adaptations arose from ground-based locomotion, and their hind limbs remained optimized for running on flat ground.
A summary of the differences between the two viewpoints is shown below:
| Feature | Viewpoint 1 (Arboreal) | Viewpoint 2 (Cursorial) |
|---|---|---|
| Primary Habitat | Trees and branches | Ground and flat surfaces |
| Locomotion Origin | Gliding down from heights | Running up slopes or capturing prey |
| Limbed Adaptations | Grasping claws and perching feet | Terrestrial running limbs |
Based on the provided viewpoints, is the following statement true or false?
'A finding that early proto-birds had ankle joints and claws optimized for high-speed terrestrial running, but lacked the grasping capability required to perch on branches, would support the predictions of Viewpoint 2 rather than Viewpoint 1.'
Answer: Answer