lecture 2 - variation in fossils Flashcards
(14 cards)
How were species viewed before Darwin?
As static blueprints; variation seen as imperfection.
What is Darwin’s view of variation?
Variation is the substrate for evolution via natural selection.
List four causes of fossil variation.
Ontogeny (growth/age).
Population variability (individual differences).
Postmortem distortion/breakage.
Interspecific differences.
What is ontogeny?
Embryonic + post-embryonic developmental history (e.g., growth stages).
What is the “biogenic law”?
“Ontogeny recapitulates phylogeny” (embryos show ancestral traits). Criticized as overly simplistic.
Compare accretion and molting.
Accretion: Continuous growth (e.g., corals, mollusk shells).
Molting: Shedding exoskeletons (e.g., trilobites).
Define isometric and allometric growth.
Isometric: Proportional growth (shape constant).
Allometric: Differential growth rates (e.g., human skull vs. body).
what does y = mx^n represent?
Allometric growth formula; n ≠ 1 indicates uneven growth.
Define heterochrony and its two main types.
Paedomorphosis: Adult retains juvenile traits (e.g., axolotl gills).
Peramorphosis: “Hyper-adult” traits (e.g., elongated dinosaur skulls)
What three parameters control heterochrony?
Rate of development.
Onset time of development.
Offset time of development.
How are humans paedomorphic?
Environmental-induced changes (e.g., coral morphs in shallow vs. deep water).
How can fossils be distorted after death?
Compression, breakage, transport (e.g., Miniochoerus skulls flattened in sediment).
Why might small fossils be underrepresented?
Currents remove delicate parts (e.g., Corymbograptus fragments).
How to remember paedomorphosis vs. peramorphosis?
“Paedo” = “child-like”; “Per-“ = “beyond” adult form.
