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Patterns of Diversification in Early Eukaryotes Emmanuelle J Patterns of diversification in early eukaryotes Emmanuelle J. Javaux To cite this version: Emmanuelle J. Javaux. Patterns of diversification in early eukaryotes. Carnets de Geologie, Carnets de Geologie, 2007, CG2007 (M01/06), pp.38-42. hal-00168238 HAL Id: hal-00168238 https://hal.archives-ouvertes.fr/hal-00168238 Submitted on 25 Aug 2007 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Carnets de Géologie / Notebooks on Geology - Memoir 2007/01, Abstract 06 (CG2007_M01/06) Patterns of diversification in early eukaryotes [Modes de diversification des premiers Eucaryotes] Emmanuelle J. JAVAUX1 Citation: JAVAUX E.J. (2007).- Patterns of diversification in early eukaryotes. In: STEEMANS P. & JAVAUX E. (eds.), Recent Advances in Palynology.- Carnets de Géologie / Notebooks on Geology, Brest, Memoir 2007/01, Abstract 06 (CG2007_M01/06) Key Words: Proterozoic; early eukaryotes; diversification Mots-Clefs : Protérozoïque ; premiers eucaryotes ; diversification 1 - Introduction Fossils may also record ancestral forms (and steps in evolution) that might not have any The Precambrian includes: the Hadean (4.6 extant relatives. The position of the root of the to 4 Ga), the period of solar system formation tree of life is not yet understood. Within the and Earth accretion; the Archean (4 to 2.5 Ga) eukaryotic tree, the eukaryotes are divided into when life appeared, and the Proterozoic (2.5 to several supergroups whose relationships are not 0.56 Ga) subdivided into the Paleo-, Meso-, and well resolved. Lineages thought to have Neoproterozoic. During this major part of Earth branched early because they seemed to lack history (about 90%), major environmental mitochondria, actually host derived changes were registered in the geological mitochondrial organelles (EMBLEY & MARTIN, record. These events include the step-wise 2006). Nevertheless, calibration of phylogenies oxygenation of the atmosphere and oceans, using dates from fossils, biomarkers, and meteoritic impacts, supercontinent formation isotopes, shows that a major diversification of and breakup, and severe glaciations; they may extant clades occurred in the Neoproterozoic, have had a profound effect on the early preceded by a long evolution of eukaryotic evolution of the eukaryotes. Several lines of fossils starting in the late Archean -as evidence from the geological record, the fossil suggested by biomarkers- or in the late history and molecular phylogenies can be used Paleoproterozoic, when the oldest eukaryotic to decipher the early record of the domain microfossils are found (see reviews in JAVAUX, Eucarya and its evolution. 2006; KNOLL et alii, 2006; PORTER, 2004). Genetic material is rarely preserved in the Superimposing the record of biological rock record, so paleontologists have to rely on innovations and environmental changes on the other features to identify microfossils as fossil record might reveal possible explanations members of the domain Eucarya. Fossils of the pattern of diversification in the middle provide direct evidence of early cells, and Neoproterozoic, long after the origin of the document steps in biological and biochemical domain and possible early divergence of major innovations. Organisms can be preserved by a clades in the Paleo- and Mesoproterozoic when variety of processes in a range of substrates. eukaryotic fossils of unknown biological Early eukaryotic fossils include: carbonaceous affinities are preserved. compressions (the organisms are preserved as As discussed elsewhere (JAVAUX & MARSHALL, a thin film of carbon); acritarchs (organic- 2006; JAVAUX et alii, 2003, 2004; MARSHALL et walled vesicles with unknown biological alii, 2005), in order to determine the biological affinities, they can be extracted from shales affinities of these fossils at the level of domain using strong acids, or observed in thin sections or beyond, we have defined a set of criteria to of shale, chert or phosphorite); multicellular differentiate prokaryotic from eukaryotic organic-walled organisms (chert, shale); vase- microfossils and have formulated a shaped microfossils; molds and casts in methodology combining microscopy and sandstone or shale; skeletons preserved in microchemistry of single acritarchs. Fossils can carbonates or phosphorite; and phylogenetically display morphological and ultrastructural informative molecules (biomarkers and features showing a degree of complexity and/or biopolymers preserved in the rocks that provide particular features unknown in prokaryotic information about past ecosystems and the organisms, therefore pointing to a eukaryotic evolution of biosynthetic pathways). affinity. Indeed, the wall structure and Molecular phylogenies yield important ornamentation, the presence of processes that information or hypotheses about relationships extend from the vesicle wall, the presence of between clades and their order of branching. excystment structures (openings through which However paleobiological data are essential for cyst liberate their content), wall ultrastructure testing these trees and for constraining the and wall chemistry can clarify the biological (minimum age of) timing of diversification. affinities of organic-walled microfossils at the 1 Département de Géologie, Université de Liège, Allée du 6 août, B18, Sart-Tilman, 4000 Liège (Belgium) [email protected] Manuscript online since March 22, 2007 38 Carnets de Géologie / Notebooks on Geology - Memoir 2007/01, Abstract 06 (CG2007_M01/06) level of the domain, and in some cases even at - The bangiophyte red alga Bangiomorpha the level of class. Microchemical analyses such pubescens is so far the oldest taxonomically as micro infra-red and Raman spectroscopy, resolved eukaryote, and records the evolution secondary ion mass spectrometry, and other of complex multicellularity, cell differentiation, techniques applicable to very small samples and sexual reproduction, eukaryotic such as one acritarch can be used to photosynthesis, primary endosymbiosis of a characterize the chemistry of organic chloroplast ancestor by 1.2-1 Ga. Note that microfossils and might even reveal biomolecules these biological innovations are recorded in this specific to extant clades. one fossil population of bangiophyte red algae that chronostratigraphy dates at 1.2 Ga-750 One limitation of this approach is the limited Ma. Chemostratigraphy and lithostratigraphy knowledge that we have about extant indicate an age closer to 1.2 Ga. However other organisms producing fossilizable structures and multicellular photosynthetic eukaryotes also their morphological, ultrastructural and appeared around 1 Ga. chemical properties. This approach requires investigation of preservable biological - Upper Mesoproterozoic / Lower properties and comparative actualistic studies Neoproterozoic rocks (and possibly of taphonomic processes affecting diverse Paleoproterozoic rocks) have yielded organisms in diverse environments (JAVAUX & biomarkers of alveolates (which include MARSHALL, 2006). dinoflagellates and ciliates, among other groups). 2 - The fossil record of biological innovations in early eukaryotes - Palaeovaucheria, a 1 Ga xanthophyte alga, indicates the appearance of stramenopiles Fossils can inform about the evolution of (which include diatoms, xanthophytes, and biological innovations, regardless of their brown algae) and of secondary symbiosis biological affinities, as briefly summarized (involving a red alga-like endosymbiont). below (see reviews in JAVAUX, 2006; KNOLL et - The 750 Ma vase-shaped microfossils alii, 2006 and reference therein). provide a firm calibration point for the - Biomarkers in 2.7 Ga kerogens of the opisthokonts, the clade that includes animals, Fortescue Group, Australia, indicate that fungi and the amoebozoans not to mention contemporaneous cells were able to synthesize direct evidence for heterotrophic eukaryotes sterols, requiring a minimum of oxygen. and eukaryotic biomineralization, and possibly predation. Cladophorales green algae also - Paleo- and Mesoproterozoic macroscopic appeared, recording again multicellular compressions or mold and cast structures have photosynthetic eukaryotes, and implying earlier been compared to algae but this interpretation evolution and diversification of green algae, as remains controversial. clearly underlined by BUTTERFIELD et alii (1994), - The first ornamented acritarchs are KNOLL (2003) and other Precambrian populations of Valeria lophostriata recorded in paleontologists, but recently misunderstood by the Paleoproterozoic of China (~1.8 Ga) and TEYSSÈDRE (2006). Australia (+1.65 Ga). Early Mesoproterozoic - The late Neoproterozoic appearance of acritarchs Shuiyousphaeridium macro- animals preserved as calcareous skeletons reticulatum, Valeria lophostriata, Tappania forming large reefs or as possible animal plana, and Satka favosa exhibits a complexity embryos in phosphorites added another of form observed with TEM, SEM, and light dimension to ecosystems and predation microscopy that is unknown in prokaryotes. pressure. Prokaryotes can be large, they can have
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