The appendages of wingspanroaches and turtles are modified for creeping movements, but their internal structures are completely different from each other's. What could be the possible interpretation for this similarity?

Question

bioepic · Answer

http://en.wikipedia.org/wiki/Vestigiality

bioepic · Answer

Vestigiality refers to genetically determined structures or attributes that have apparently lost most or all of their ancestral function in a given species, but have been retained through evolution.[1] Assessment of the vestigiality must generally rely on comparison with homologous features in related species. The emergence of vestigiality occurs by normal evolutionary processes, typically by loss of function of a feature that is no longer subject to positive selection pressures when it loses its value in a changing environment. More urgently the feature may be selected against when its function becomes definitely harmful. Typical examples of both types occur in the loss of flying capability in island-dwelling species.

bioepic · Answer

Please fan/medal!

matt101 · Answer

Convergent evolution - these species probably developed from different ancestors, meaning most of their internal structures developed independently. However, they probably live in similar environments, and so developed similar adaptations for it.

Similar idea to bird wings vs bat wings - different ancestors, but same environment/function.

matt101 · Answer

@BioEpic I don't think this would be a case of vestigiality! Vestigiality requires that the structure is present but serves no useful function (e.g. the appendix in humans). The question above I think implies that both species use their creeping appendages.

bioepic · Answer

Yeah... I think @matt101 is right. Convergent evolution makes more sense to me.