A Cambrian “Explosion” The diversity of Cambrian organisms could be interpreted as adaptive radiation in which many new ecological opportunities were made available for organisms with the capacity to evolve in diverse ways so as to occupy and exploit the changing environments. Divergence among major Cambrian lineages began in the Precambrian about 700 Mya. Modifications during the Cambrian added hard parts and mineralized skeletons that provided leverage for evolving muscles, support for body organs, enclosures for gills and filtering systems, and protective shells and spines. Causes of the Cambrian Radiation: Geological, environmental and climatic conditions Changing oxygen levels Predator-prey relationships Evolution of embryonic development and body plan specification New sources of genetic variation and changes in gene number and regulation Geological conditions: Animal fossils may be absent from Precambrian rocks because geological conditions prevented fossilization or destroyed and fossils present; the heat and pressure involved in Precambrian mountain building has been proposed as an important factor limiting fossilization. However, prokaryotic and eukaryotic organisms were preserved in the Precambrian so it is unlikely that the Cambrian discontinuity is unreal and merely the consequence of geological metamorphism or imperfect fossilization. Plate tectonics and sea level changes would also have played a role in new environments. Rising Oxygen Levels
A Cambrian “Explosion” The diversity of Cambrian organisms could be interpreted as adaptive radiation in which many new ecological opportunities were made available for organisms with the capacity to evolve in diverse ways so as to occupy and exploit the changing environments. Divergence among major Cambrian lineages began in the Precambrian about 700 Mya. Modifications during the Cambrian added hard parts and mineralized skeletons that provided leverage for evolving muscles, support for body organs, enclosures for gills and filtering systems, and protective shells and spines. Causes of the Cambrian Radiation: Geological, environmental and climatic conditions Changing oxygen levels Predator-prey relationships Evolution of embryonic development and body plan specification New sources of genetic variation and changes in gene number and regulation Geological conditions: Animal fossils may be absent from Precambrian rocks because geological conditions prevented fossilization or destroyed and fossils present; the heat and pressure involved in Precambrian mountain building has been proposed as an important factor limiting fossilization. However, prokaryotic and eukaryotic organisms were preserved in the Precambrian so it is unlikely that the Cambrian discontinuity is unreal and merely the consequence of geological metamorphism or imperfect fossilization. Plate tectonics and sea level changes would also have played a role in new environments. Rising Oxygen Levels
3330_Exam_2_Student_Review_2011.docx