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1.
Nat Ecol Evol ; 3(4): 582-589, 2019 04.
Artigo em Inglês | MEDLINE | ID: mdl-30911145

RESUMO

The soft-bodied Ediacara biota (571-541 million years ago) represents the oldest complex large organisms in the fossil record, providing a bridge between largely microbial ecosystems of the Precambrian and the animal-dominated world of the Phanerozoic, potentially holding clues about the early evolution of Metazoa. However, the nature of most Ediacaran organisms remains unresolved, partly due to their enigmatic non-actualistic preservation. Here, we show that Flinders-style fossilization of Ediacaran organisms was promoted by unusually prolonged conservation of organic matter, coupled with differences in rheological behaviour of the over- and underlying sediments. In contrast with accepted models, cementation of overlying sand was not critical for fossil preservation, which is supported by the absence of cement in unweathered White Sea specimens and observations of soft sediment deformation in South Australian specimens. The rheological model, confirmed by laboratory simulations, implies that Ediacaran fossils do not necessarily reflect the external shape of the organism, but rather the morphology of a soft external or internal organic 'skeleton'. The rheological mechanism provides new constraints on biological interpretations of the Ediacara biota.


Assuntos
Fósseis , Sedimentos Geológicos , Austrália , Biota , Oceanos e Mares , Reologia
2.
Science ; 361(6408): 1246-1249, 2018 09 21.
Artigo em Inglês | MEDLINE | ID: mdl-30237355

RESUMO

The enigmatic Ediacara biota (571 million to 541 million years ago) represents the first macroscopic complex organisms in the geological record and may hold the key to our understanding of the origin of animals. Ediacaran macrofossils are as "strange as life on another planet" and have evaded taxonomic classification, with interpretations ranging from marine animals or giant single-celled protists to terrestrial lichens. Here, we show that lipid biomarkers extracted from organically preserved Ediacaran macrofossils unambiguously clarify their phylogeny. Dickinsonia and its relatives solely produced cholesteroids, a hallmark of animals. Our results make these iconic members of the Ediacara biota the oldest confirmed macroscopic animals in the rock record, indicating that the appearance of the Ediacara biota was indeed a prelude to the Cambrian explosion of animal life.


Assuntos
Fósseis/anatomia & histologia , Invertebrados/anatomia & histologia , Invertebrados/classificação , Animais , Evolução Biológica , Biomarcadores/análise , Biota , Sedimentos Geológicos , Invertebrados/química , Paleontologia , Federação Russa , Esteroides/análise
3.
Nat Ecol Evol ; 2(3): 437-440, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29358605

RESUMO

The Ediacara biota (~575-541 million years ago) mark the emergence of large, complex organisms in the palaeontological record, preluding the radiation of modern animal phyla. However, their phylogenetic relationships, even at the domain level, remain controversial. We report the discovery of molecular fossils from organically preserved specimens of Beltanelliformis, demonstrating that they represent large spherical colonies of cyanobacteria. The conservation of molecular remains in organically preserved Ediacaran organisms opens a new path for unravelling the natures of the Ediacara biota.


Assuntos
Evolução Biológica , Cianobactérias/química , Cianobactérias/classificação , Fósseis , Biomarcadores/análise , Cianobactérias/citologia , Cromatografia Gasosa-Espectrometria de Massas , Paleontologia , Federação Russa
4.
Proc Biol Sci ; 284(1851)2017 Mar 29.
Artigo em Inglês | MEDLINE | ID: mdl-28356454

RESUMO

Why large and diverse skeletons first appeared ca 550 Ma is not well understood. Many Ediacaran skeletal biota show evidence of flexibility, and bear notably thin skeletal walls with simple, non-hierarchical microstructures of either aragonite or high-Mg calcite. We present evidence that the earliest skeletal macrobiota, found only in carbonate rocks, had close soft-bodied counterparts hosted in contemporary clastic rocks. This includes the calcareous discoidal fossil Suvorovella, similar to holdfasts of Ediacaran biota taxa previously known only as casts and moulds, as well as tubular and vase-shaped fossils. In sum, these probably represent taxa of diverse affinity including unicellular eukaryotes, total group cnidarians and problematica. Our findings support the assertion that the calcification was an independent and derived feature that appeared in diverse groups where an organic scaffold was the primitive character, which provided the framework for interactions between the extracellular matrix and mineral ions. We conclude that such skeletons may have been acquired with relative ease in the highly saturated, high alkalinity carbonate settings of the Ediacaran, where carbonate polymorph was further controlled by seawater chemistry. The trigger for Ediacaran biomineralization may have been either changing seawater Mg/Ca and/or increasing oxygen levels. By the Early Cambrian, however, biomineralization styles and the range of biominerals had significantly diversified, perhaps as an escalating defensive response to increasing predation pressure. Indeed skeletal hardparts had appeared in clastic settings by Cambrian Stage 1, suggesting independence from ambient seawater chemistry where genetic and molecular mechanisms controlled biomineralization and mineralogy had become evolutionarily constrained.


Assuntos
Calcificação Fisiológica , Carbonato de Cálcio , Fósseis , Animais , Minerais , Água do Mar
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