Question

Why Order Urodela is anticipated to be LESS adapted to terrestrial environmental compared to frogs （Order Anura） based on the skeletal feature

Answer 1

Urodela includes lizard like amphibians with a distinct tail. And it has 2 pairs of limbs which is weak and almost equal. It has a generalized tadpole body plan. They move by bending bodies from side to side called lateral undulation in a fish like manner. Majority of them are lungless and respiration occurs through the skin or through external gills. This make them more suitable for aquatic living.
Frogs belongs to order Anura without tail in adults. Hind limbs usually adopted for leaping and swimming. Adults are without gills or gill openings. Eyelids are well formed. Anurans have a body plan that is more specialized for movements. The frogs skeleton is highly specialized for jumping locomotion. It looks unlike any other vertebrae. The body is made shorter and more reducing the number of vertebrae. The tail vertebrae are not recognizable, instead they have fused and been incorporated into pelvis as urostyle, a rod like bone that allows for attachment of muscle on it. The limbs are also modified. The humerus and femur, the radius and ulna have fused into the epipodial bone and the tibia and fibula have fused into the compound bone. The ankle, in the limb is elongate and often consist of two bones. The hind limbs are much longer and more robust than the front limb. This enables frogs for easy locomotion in land.

Considering all these it is clear that urodela is less adapted to terrestrial environment compared to frogs.