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Theropod ‘semilunate’ carpal and theropod hand evolution (free pdf)

Ben Creisler

A recent paper in open access, not yet mentioned:

Xing Xu, Fenglu Han & Qi Zhao (2014)
Homologies and homeotic transformation of the theropod ‘semilunate’ carpal.
Scientific Reports 4, Article number: 6042

The homology of the ‘semilunate’ carpal, an important structure
linking non-avian and avian dinosaurs, has been controversial. Here we
describe the morphology of some theropod wrists, demonstrating that
the ‘semilunate’ carpal is not formed by the same carpal elements in
all theropods possessing this feature and that the involvement of the
lateralmost distal carpal in forming the ‘semilunate’ carpal of birds
is an inheritance from their non-avian theropod ancestors.
Optimization of relevant morphological features indicates that these
features evolved in an incremental way and the ‘semilunate’ structure
underwent a lateral shift in position during theropod evolution,
possibly as a result of selection for foldable wings in birds and
their close theropod relatives. We propose that homeotic
transformation was involved in the evolution of the ‘semilunate’
carpal. In combination with developmental data on avian wing digits,
this suggests that homeosis played a significant role in theropod hand
evolution in general.