General Aspects Concerning Marine and Terrestrial Biodiversity

– is immense, and they are also the primevalscenario for the diversification of life. Thus the oldest known fossils aremarine stromatolites, laminar structures produced by the activity ofcyanobacteria, preserved in Australia and dating back 3,500 million years.Seemingly, the first animals also appeared in the sea. We know of trace fossils800 million year old, but the first fossils of “real” animals are dated later; about640 million years ago at the end of the Proterozoic period. These animalsbelong to the so-called “Ediacara” fauna of the Vendian system, a name whichrecalls the Australian locality where they were discovered, although they arealso present in other parts of the globe. They were soft-bodied organisms thatare hard to attribute to any of our modern types.In comparison, the earliest ter restrial fossil record corresponds to spores, pos-sibly of bryophytes (mosses, liverworts, etc.) and is datable to the MiddleOrdovician (about 450 million years ago). For animals, the first continentalsettlement appears to go back to the Silurian period (a bit over 400 millionyears ago), from which we have recovered remains of myriapods (centipedesand millipedes) and arachnids, although certain trace fossils, probably pro-duced by terrestrial arthropods, also date to the Ordovician period.Marine organisms have thus had more time to diversify than their terrestrialcounterparts (about double in the case of animals). And yet the oceans appar-ently harbour only 2% of the total number of known animal species. Scien-tists have resorted to different