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Spore aquatic stage mod4/12/2023 ![]() ![]() The earliest acritarchs represent an innovation with profound implications for evolution: a cell wall of sporopollenin-like material enabling survival from microbial attack, in a then microbial-dominated world. Many living cysts of athecate species would be “acritarchs” if found as fossils, and many earlier acritarchs would be accepted as dinoflagellate cysts if found living. The approach proposed here, based on the more natural comparison with living cysts, includes athecate species. Traditional diagnostic criteria for dinocysts, based on morphologic comparisons with motile stages, are biased towards thecate species. ![]() ![]() A re-evaluation of the pre-Triassic record shows that many acritarchs (microfossils of uncertain affinities) are dinocysts representing “missing” fossil evidence. Molecular trees and geochemical markers suggest the divergence of dinoflagellates as early eukaryotes (~650 million years ago), but the traditional fossil record of cysts (dinocysts) starts during the Triassic (~230 million years ago). ![]()
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