Department

Biological Sciences

Document Type

Article

Publication Date

2-2014

Abstract

Serially homologous systems with high internal differentiation frequently exhibit meristic constraints, although the developmental basis for constraint is unknown. Constraints in the counts of the cervical and lumbosacral vertebral series are unique to mammals, and appeared in the Triassic, early in their history. Concurrent adaptive modifications of the mammalian respiratory and locomotor systems involved a novel source of cells for muscularization of the diaphragm from cervical somites, and the loss of ribs from lumbar vertebrae. Each of these innovations increased the modularity of the somitic mesoderm, and altered somitic and lateral plate mesodermal interactions across the lateral somitic frontier. These developmental innovations are hypothesized here to constrain the anteroposterior transposition of the limbs along the column, and thus also cervical and thoracolumbar count. Meristic constraints are therefore regarded here as the nonadaptive, secondary consequences of adaptive respiratory and locomotor traits.

Comments

This is the author's accepted manuscript of the article. The final version is published in Zoology and is available here: 10.1016/j.zool.2013.09.001

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