09:15 〜 09:30
[BPT06-02] 前期太古代のレンズ状微化石における形態の多様性は初期生命の種分化の証拠か？
キーワード：太古代、微化石、初期生命、形態、種分化
Organic-walled lenticular microstructures up to 100 µm along the major dimension were discovered from Early Archean (3.4 Ga) cherts of the Strelley Pool Formation in the Pilbara Craton, Western Australia (Sugitani et al., 2010, 2013). They have been extensively studied multi-disciplinarily, including classical microscopic observation, palynology, scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectroscopy, and secondary ion mass spectroscopy (SIMS) (Lepot et al., 2013; Sugitani et al., 2015a; Williford et al., 2015). Their biogenicity is now well established and appears to be widely accepted; however, their biological affinities are still poorly understood. Here we once keep away from this issue, and focus on their morphological variation in the context of taxonomy, base on new data of lenticular microfossils from the two remote localities of the 3.4 Ga Strelley Pool Formation, one in the Goldsworthy greenstone belt and the other in the Panorama greenstone belt.
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.
Lepot, K. et al. (2013) Geochimica et Cosmochimica Acta 112, 66-86.
Sugitani, K. et al. (2010) Astrobiology 10, 899-920.
Sugitani, K. et al. (2013) Precambrian Research 226, 59-74.
Sugitani, K. et al. (2015a) Geobiology 13, 507-521.
Sugitani, K. et al. (2015b) Geobiology 13, 522-545.
Williford, K.W. et al. (2015) Astorobiology Science Conference 2015. 7275pdf.
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.
Lepot, K. et al. (2013) Geochimica et Cosmochimica Acta 112, 66-86.
Sugitani, K. et al. (2010) Astrobiology 10, 899-920.
Sugitani, K. et al. (2013) Precambrian Research 226, 59-74.
Sugitani, K. et al. (2015a) Geobiology 13, 507-521.
Sugitani, K. et al. (2015b) Geobiology 13, 522-545.
Williford, K.W. et al. (2015) Astorobiology Science Conference 2015. 7275pdf.