9:15 AM - 9:30 AM
[BPT06-02] Can speciation of early life be evidenced by morphological variation of Early Archean lenticular microfossils?
Keywords:Archean, microfossils, early life, morphology, speciation
The two fossil localities of the 3.4 Ga Strelley Pool Formation in the Goldsworthy and the Panorama greenstone belts are distinct in lithostratigraphy and trace element characteristics of fossil-bearing black cherts, suggesting that they represent different environments of habitat. Fossil-bearing black chert in the Goldsworthy greenstone belt had probably deposited in a terrestrial hydrothermal system, whereas that in the Panorama greenstone belt did in marine setting, probably intertidal to subtidal zone (Sugitani et al., 2013, 2015b). Measurement of major and minor dimensions of their polar views of over 1000 specimens indicates that lenticular microfossils from these two localities are statistically distinct in ellipticity. Although SPF lenticular microfossils are thought to have had reproduced by binary fissions, higher ellipticity of the Panorama specimens cannot be explained by vegetative growth of circular type that dominates the Goldsworthy population, because there is no correlation between ellipticities and major dimensions. Also taphonomy cannot explain the difference in ellipticity between two populations. Considering that both the elliptic and circular types have a common body plan (lenticular body and surrounding flange), the two populations of different ellipticities likely represent subgroups of the same taxon. Namely, the SPF lenticular microfossils have a common ancestor and thus could be the earliest evidence for speciation, possibly through adaptation to different environments. Although how the difference of ellipticity worked is unclear so far, we assume that it was related to different hydrodynamics of the habitats.
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