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Re: the opposite of paedomorphosis?



David Peters (davidrpeters@earthlink.net) wrote:

<So, if paedomorphosis is the reduction in overall size, rostrum length and
such due to sexual maturity while in the juvenile stage, what is the term and
process for rostrum lengthening, neck elongation and overall size increase?>

  Well, paedomorphosis is actually the process by which primitive features are
retained throughout ontogeny, that is without selective change of the features,
and can result in a "juvenile" appearance of adults. Neotenic salamanders, such
as mudpuppies and hellbenders, are all paedomorphic species in that they retain
ancestral and juvenile features at and adult stage of life.

  The opposite, as Jura/Jason states, is peramorphosis, a process by which the
juvenile condition is modified from the ancestral, juvenile condition, and
juvenile traits are completely or substantially modified. Examples include
Tyrannosauridae and *Panthera*, all of which heavily modify the basal or
juvenile condition through gross reworking of the skull anatomy and processes
and proportions.

  In the fossil record, the appearance of paedomorphic taxa is usually
identified by the prevalence of "neotenic" appearing fossils without
appropriate "adults" in the same level and with smaller age "classes" showing
the same juvenile conditions as the largest preserved. Such is how neotenic
amphibians are identified. The retention of largely juvenile traits in felids
such as the domestic cat also shows that while change occurs, compared to
*Panthera* and *Neofelis*, this change is much more minor, and thus *Felis*
(and *Leptailurus*) is paedomorphic to some degree, less so *Puma*, *Acinonyx*
or *Lynx*.

  I hope this helps,

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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