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Hindlimbs form first during development of most tetrapods, and they are likely to be last to disappear, as known in snakes. The fact that hindlimbs form first and are thus often larger, may be ascribed to the narrow spacing in the caudal part of the early embryo (more below).
Ahem, hindlimbs of most tetrapods form first? Are often larger?
From: Forelimb-hindlimb developmental timing changes across tetrapod phylogeny,
Olaf RP Bininda-Emonds, Jonathan E Jeffery, Marcelo R Sánchez-Villagra, James Hanken, Matthew Colbert, Claude Pieau, Lynne Selwood, Carel ten Cate, Albert Raynaud, Casmile K Osabutey and Michael K Richardson, BMC Evolutionary Biology 2007, 7:182 doi:10.1186/1471-2148-7-182
Average event-pair scores (EPSs) plotted on a phylogeny of the taxa examined, with visual examples of forelimb (FL) and hindlimb (HL) across the tree. Plot symbols in blue and green are significantly less than and greater than one, respectively; forelimb-hindlimb synchrony, in red. The tree is derived from references 33 and 34.
And two extreme case, where:
Instead, it appears that post-chondrogenic differences in growth rate (i.e., allometric heterochrony) play a more deciding role in shaping the final adult morphology of the tetrapod limb. A cogent example are marsupials, which often display a much larger hindlimb in adults despite the extreme acceleration of forelimb development in embryos. Similarly, the bat actually displayed the least degree of forelimb acceleration among the eutherians studied, despite the forelimbs being greatly enlarged and modified as wings in the adult.
And a new tag for cteappv, BIBO