When a creature is advanced in size, it may develop at a smaller size; alternatively, it may maintain his original size or, if delayed, it may result in a larger sized creature. That is insufficient to understand heterochronic mechanism. Size must be combined with shape, so a creature may retain paedomorphic features if advanced in shape or present recapitulatory appearance when retarded in shape. This names are not very indicatives, as theories of development were very confusing in past.
A creature in his ontogeny may combine heterochronic features in six vectors, although Jay Gould considers that there exist some binding with growth and sexual maturation. A creature may, for example, present some neotenic features and retarded development, resulting in new features derived from an original creature only by regulatory genes. Almost of human features, when compared with proximal apes were from this nature, not implying a lot of change in structural genes, as classically was considered.
THE OLDEST HINDIID DEMOSPONGE FROM THE DARRIWILIAN (MIDDLE ORDOVICIAN) OF THE ARGENTINE PRECORDILLERA: EVOLUTIONARY IMPLICATIONS FOR THE TRICRANOCLADINES
Jul 01, 2007; ABSTRACT- The tricranocladine sponges (now assigned to the suborder Eutaxicladina) are a conservative group consisting of the...