BSCI392
10-5-07
Heterochrony

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Heterchrony: Subtle changes over evolutionary time in an organism's developmental timetable are a potent source of overall evolutionary change. This is an idea with a history as long as the study of evolution.

A single orgamisn can incorporate both paedomorphic and peramorphic change. Consider humans:

  • Developmental parameters:

    If this is the ancestral life history:

    Combining these developmental parameters gives us:

  • Varieties of Peramorphosis:

    Cultural "evolution": Note that paedomorphosis and peramorphosis occur in popular cultural figures.

    Fossil case study: Sabre-tooth cats - E.G.: North American Pleistocene Smilodon fatalis

    Fossil case study: Blastoids - Pentremites

    Blastoids were stalked echinoderms of the Paleozoic. Their thecae (main bodies) had upper portions, vaults and lower pelves. Blastoids tended to come in two general morphs:
    • Piriform: with vault and pelvis of roughly equal height, as in the juvenile of Pentremites concoideus
    • Godoniform: with the vault much taller than the pelvi, as in the adult of Pentremites concoideus

    In Pentremites pyriformis, a possibile descendant of P. concoideus, the adult is also pyriform.

    In Pentremites robustus, another possibile descendant of P. concoideus, the juvenile is godoniform.

    Thus: