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Developmental modularity and the marsupial-placental dichotomy
 
SVPCA Conference
 
Platform presentation (20 minutes)
Authors
 
*Anjali Goswami
 
 
Marcelo R Sánchez-Villagra
 
 
Vera Weisbecker
 
Abstract
 
The contrasting evolutionary histories of marsupials and placentals have been debated for decades. The speciose placental mammals have radiated into diverse niches, while marsupials are limited in taxonomic, ecological, and morphological diversity. This disparity has been attributed to the different reproductive modes of these clades. Marsupials give birth to altricial young with only well-developed forelimbs, to crawl to the teat, and oral apparatus to suckle. They experience most of their growth outside of the womb. Placentals develop mainly in utero, and young are relatively precocial at birth.

These differences in reproductive patterns have been tied to clear differences in sequence heterochrony between marsupials and placentals (Sánchez-Villagra, 2002; Smith, 2006). It has also been hypothesized that coordinated shifts in developmental timing occur among functionally- or developmentally-related structures, such as the forelimbs and oral apparatus in marsupials (Goswami, 2007). Here, we use new developmental sequence data for 11 marsupial and 14 placental species to assess the integration of developmental timing in the cranial and postcranial elements across mammals. Results demonstrate that marsupials and placentals differ markedly in the integration of developmental timing. Marsupials show significant modularity in the development of the postcranial skeleton, with independent forelimb and hindlimb developmental modules, while placentals show significant integration of the entire appendicular skeleton. There are few significant developmental modules in cranium, although placentals show greater integration in the facial region than marsupials. These differences in developmental modularity may relate to differences in morphological diversity between these clades and across the skeleton

London 2020