Two-phase increase in the maximum size of life over 3.5 billion years reflects biological innovation and environmental opportunity

Abstract

The maximum size of organisms has increased enormously since the initial appearance of life >3.5 billion years ago (Gya), but the pattern and timing of this size increase is poorly known. Consequently, controls underlying the size spectrum of the global biota have been difficult to evaluate. Our period-level compilation of the largest known fossil organisms demonstrates that maximum size increased by 16 orders of magnitude since life first appeared in the fossil record. The great majority of the increase is accounted for by 2 discrete steps of approximately equal magnitude: the first in the middle of the Paleoproterozoic Era (Ϸ1.9 Gya) and the second during the late Neoproterozoic and early Paleozoic eras (0.6 -0.45 Gya). Each size step required a major innovation in organismal complexity-first the eukaryotic cell and later eukaryotic multicellularity. These size steps coincide with, or slightly postdate, increases in the concentration of atmospheric oxygen, suggesting latent evolutionary potential was realized soon after environmental limitations were removed.body size ͉ Cambrian ͉ oxygen ͉ Precambrian ͉ trend D espite widespread scientific and popular fascination with the largest and smallest organisms and numerous studies of body size evolution within individual taxonomic groups (1-9), the first-order pattern of body size evolution through the history of life has not been quantified rigorously. Because size influences (and may be limited by) a broad spectrum of physiological, ecological, and evolutionary processes (10-16), detailed documentation of size trends may shed light on the constraints and innovations that have shaped life's size spectrum over evolutionary time as well as the role of the body size spectrum in structuring global ecosystems. Bonner (17) presented a figure portraying a gradual, monotonic increase in the overall maximum size of living organisms over the past 3.5 billion years. The pattern appears consistent with a simple, continuous underlying process such as diffusion (18), but could also reflect a more complex process. Bonner, for example, proposed that lineages evolve toward larger sizes to exploit unoccupied ecological niches. For decades, Bonner's has been the only attempt to quantify body size evolution over the entire history of life on Earth, but the data he presented were not tied to particular fossil specimens and were plotted without consistent controls on taxonomic scale against a nonlinear timescale. Hence, we have lacked sufficient data on the tempo and mode of maximum size change to evaluate potential first-order biotic and abiotic controls on organism size through the history of life.Here, we document the evolutionary history of body size on Earth, focusing on the upper limit to size. Use of maximum size allows us to assess constraints on the evolution of large body size and avoids the more substantial empirical difficulties in determining mean, median, or minimum size for all life or even for many individual taxa. For each era within the Archean Eon (4,000-2,500 Mya) and ...

Shifts in metabolic scaling, production, and efficiency across major evolutionary transitions of life

“…So, for example, oxygen is obtained by simple diffusion in unicellular organisms but taken up by gills or lungs and transported through vascular systems in large metazoans. It may not be coincidental, therefore, that each of these evolutionary transitions apparently coincided with major increases in the concentration of oxygen in the atmosphere and oceans (3).…”

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Proterozoic ocean redox and biogeochemical stasis

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Le microbiote intestinal à l’origine de nouvelles perspectives thérapeutiques pour les maladies métaboliques ?

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