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G.
Palyi, C. Zucchi, & L. Caglioti (eds) Fundamentals
of Life 219-248. Elsevier, Paris. Jerzy Dzik Abstract.
Among the recent
main contributions of palaeontology to the present understanding of the course
of evolution are discoveries of fossil organisms transitional between
basically different major groups of the living world. Thus, an almost complete
transition from round worms to arthropods was documented with Cambrian fossils.
This anticipated subsequently assembled molecular phylogenetic evidence that
the ability of shedding out the chitinous cuticle is a very ancient trait
defining the great superphylum Ecdysozoa. Another idea based on molecular
evidence, that pelagic larvae are secondary adaptations in marine animals, the
Lophotrochozoa, has found support in the Early Cambrian embryos with direct
development within the egg covers. A surprising implication of the recent
findings of chordates in the Early Cambrian is that these may represent the
basalmost deuterostomes which possibly share some archaic aspects of their
body with the nemerteans, Ediacarian dipleurozoans, and ctenophores. The
latter were in the Cambrian more anatomically complex and diverse than today,
and may have derived from the sedentary Ediacarian petalonameans. The main
weakness of the available fossil evidence is its inability to document the
common roots of animals and plants within the protists. Various Precambrian
unicellular flagellates represented by cysts and cell scales, as well as
multicellular algae, await an evolutionary interpretation. The cyanobacteria
range in the fossil record prior to the formation of oxygen-rich atmosphere
and molecular evidence suggests that they may be ancestral to all extant
prokaryotes. This would mean that most of the bacterial evolution was a
morphological simplification which followed their adaptation to heterotrophic
and parasitic modes of life; also thermophily of the archaeobacteria being
secondary. |