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Evolutionary development in basal mammaliaforms as revealed by a docodontan

Science  13 Feb 2015:
Vol. 347, Issue 6223, pp. 760-764
DOI: 10.1126/science.1260880

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Taking advantage of new neighborhoods

Mammals are one of the most morphologically diverse organisms, with adaptation to unique ecological conditions creating a wide array of forms, from mice to whales. Two new basal mammals from the mid-Jurassic period suggest that this diversification was well under way millions of years earlier than previously thought. Luo et al. describe a burrowing species with limb and digit modifications similar to those of current burrowers and identify the likely genes and developmental pathways involved. Meng et al. describe an arboreal species with modifications for climbing and that possessed teeth clearly adapted for a herbivorous diet, including the consumption of sap.

Science, this issue p. 760, p. 764

Abstract

A new Late Jurassic docodontan shows specializations for a subterranean lifestyle. It is similar to extant subterranean golden moles in having reduced digit segments as compared to the ancestral phalangeal pattern of mammaliaforms and extant mammals. The reduction of digit segments can occur in mammals by fusion of the proximal and intermediate phalangeal precursors, a developmental process for which a gene and signaling network have been characterized in mouse and human. Docodontans show a positional shift of thoracolumbar ribs, a developmental variation that is controlled by Hox9 and Myf5 genes in extant mammals. We argue that these morphogenetic mechanisms of modern mammals were operating before the rise of modern mammals, driving the morphological disparity in the earliest mammaliaform diversification.

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