Mesopodial arrangements that are homoplastic are commonly encountered in studies of intrapopulational variation.
Departures from a standard mesopodial arrangement are found in Taricha, and, at least in the hind limb, alternative patterns reach a relatively high frequency.
Mesopodial morphology and phalangeal formulae were scored for all limbs.
Reductions in numbers of mesopodial elements in urodeles result from: (1) failure of an element to form during development, (2) formation of an element but a failure to separate early developmental connections (typically resulting in an enlarged "combined" element) and (3) fusion of elements that are separate developmentally.
There are 21 different mesopodial arrangements, and each variant condition is rare.
Twelve different mesopodial arrangements are observed.
There are two asymmetrical mesopodial reductions that appear elsewhere in taxa with reduced limbs (table 5).
Particular mesopodial arrangements may be subject to weak selection (such as dt 5 + m, Wake 1966) or may be selectively neutral.
Major trends in the evolution of the caudate limb are: (1) reduction in the number of mesopodials (fig.
In Ambystoma mexicanum, two major axes of development are observed: a proximodistal axis initiates at the humerus/femur, radius/tibia, ulna/fibula and extends to other mesopodials, while an anteroposterior (digital) axis arises on the anterior (preaxial) border and development of both digits and distal mesopodials progresses posteriorly (postaxially) (fig.