[allmendream]

Does a flying squirrel need a working wing? Has it lost the use of its arm? Bats are pretty dexterous with the ‘thumbs’ on their wings as well. The change from a glider to a flier would be a gradual process if the flier experienced an advantage.

Similarly a river living mammal could easily develop a multipurpose leg that also had function as a flipper, like a seal. A seal has not lost function of its front legs, they are now better flippers than legs.

And I am not implying ‘hopeful monsters’, I am saying that any gradual deviation from a successful body plan will be weeded out by natural selection. Obviously what is “successful” will change as circumstances change, from needing to be streamlined, to being a tetra-pod, back to needing to be streamlined, as all evidence suggests marine mammals went through.

These gradual changes can be observed in short periods of time that make large changes over large periods of time no problem at all. And none of the fossil intermediates will be ‘monsters’ or some sort of half formed creature, they will be a fully formed species that was just gradually more marine than its predecessors.

[valkyry1]

Calling the creature a flying squirrel is a misnomer.

What it actually is is a gliding squirrel, and there is no indication that any of the gliding creatures (transitional or otherwise) ever developed into a flying creature.

[metmom]

http://www.northern.edu/natsource/mammals/northe1.htm

“Because walking is so awkward with the membrane between their wrists and ankles, being on the ground makes them very vulnerable to predators. Protection is found by both living in the trees and being active after dark. “

amd:”The change from a glider to a flier would be a gradual process if the flier experienced an advantage.”

In which case, the intermediate arm/wing would not be suitable for either flying or walking, leaving them vulnerable to predators, much as the flying squirrel is.

amd: “Similarly a river living mammal could easily develop a multipurpose leg that also had function as a flipper, like a seal. A seal has not lost function of its front legs, they are now better flippers than legs.”

Plenty of animals swim just fine with the legs they have.

*would be*. *could be*. It’s all speculation. Nobody knows for sure, including the scientists who propose these explanations.