MONOTREME OSSIFICATION SEQUENCES AND THE RIDDLE OF MAMMALIAN SKELETAL DEVELOPMENT

Weisbecker, Vera (2011) MONOTREME OSSIFICATION SEQUENCES AND THE RIDDLE OF MAMMALIAN SKELETAL DEVELOPMENT. Evolution, 65 (5). pp. 1323-1335. DOI 10.1111/j.1558-5646.2011.01234.x

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Abstract

The developmental differences between marsupials, placentals, and monotremes are thought to be reflected in differing patterns of postcranial development and diversity. However, developmental polarities remain obscured by the rarity of monotreme data. Here, I present the first postcranial ossification sequences of the monotreme echidna and platypus, and compare these with published data from other mammals and amniotes. Strikingly, monotreme stylopodia (humerus, femur) ossify after the more distal zeugopodia (radius/ulna, tibia/fibula), resembling only the European mole among all amniotes assessed. European moles also share extreme humeral adaptations to rotation digging and/or swimming with monotremes, suggesting a causal relationship between adaptation and ossification heterochrony. Late femoral ossification with respect to tibia/fibula in monotremes and moles points toward developmental integration of the serially homologous fore- and hindlimb bones. Monotreme cervical ribs and coracoids ossify later than in most amniotes but are similarly timed as homologous ossifications in therians, where they are lost as independent bones. This loss may have been facilitated by a developmental delay of coracoids and cervical ribs at the base of mammals. The monotreme sequence, although highly derived, resembles placentals more than marsupials. Thus, marsupial postcranial development, and potentially related diversity constraints, may not represent the ancestral mammalian condition.

Item Type: Article
Uncontrolled Keywords: 2011AREP; IA62;
Subjects: 04 - Palaeobiology
Divisions: 04 - Palaeobiology
Journal or Publication Title: Evolution
Volume: 65
Page Range: pp. 1323-1335
Identification Number: 10.1111/j.1558-5646.2011.01234.x
Depositing User: Sarah Humbert
Date Deposited: 26 Feb 2011 12:35
Last Modified: 23 Jul 2013 10:01
URI: http://eprints.esc.cam.ac.uk/id/eprint/2010

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