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Thermogenic muscle hypothesis for origin of birds

From: Ben Creisler

A new online paper:

Stuart A. Newman, Nadezhda V. Mezentseva & Alexander V. Badyaev (2013)
Gene loss, thermogenesis, and the origin of birds.
Annals of the New York Academy of Sciences (advance online publication)
DOI: 10.1111/nyas.12090

Compared to related taxa, birds have exceptionally enlarged and
diversified skeletal muscles, features that are closely associated
with skeletal diversification and are commonly explained by a
diversity of avian ecological niches and locomotion types. The
thermogenic muscle hypothesis (TMH) for the origin of birds proposes
that such muscle hyperplasia and the associated skeletal innovations
are instead the consequence of the avian clade originating from an
ancestral population that underwent several successive episodes of
loss of genes associated with thermogenesis, myogenesis, and
skeletogenesis. Direct bird ancestors met this challenge with a
combination of behavioral strategies (e.g., brooding of nestlings) and
acquisition of a variety of adaptations for enhanced nonshivering
thermogenesis in skeletal muscle. The latter include specific
biochemical alterations promoting muscle heat generation and dramatic
expansion of thigh and breast muscle mass. The TMH proposes that such
muscle hyperplasia facilitated bipedality, freeing upper limbs for new
functions (e.g., flight, swimming), and, by altering the mechanical
environment of embryonic development, generated skeletal novelties,
sometimes abruptly, that became distinctive features of the avian body