PhanerozoicpO₂and the early evolution of terrestrial animals

Abstract

Concurrent gaps in the Late Devonian/Mississippian fossil records of insects and tetrapods (i.e. Romer's Gap) have been attributed to physiological suppression by low atmospheric O Here, updated stable isotope inputs inform a reconstruction of Phanerozoic oxygen levels that contradicts the low oxygen hypothesis (and contradicts the purported role of oxygen in the evolution of gigantic insects during the late Palaeozoic), but reconciles isotope-based calculations with other proxies, like charcoal. Furthermore, statistical analysis demonstrates that the gap between the first Devonian insect and earliest diverse insect assemblages of the Pennsylvanian (Bashkirian Stage) requires no special explanation if insects were neither diverse nor abundant prior to the evolution of wings. Rather than tracking physiological constraint, the fossil record may accurately record the transformative evolutionary impact of insect flight.

A tale of two eras: Phytoplankton composition influenced by oceanic paleochemistry

“…We acknowledge that ambient pCO 2 is probably better suited for thinking about the Cenozoic as opposed to Mesozoic Earth system. That said, models disagree on pCO 2 through time, and a recent reanalysis of Berner's well-known GEOCARBSULF model paper (Berner, 2009) shows that updated isotopic data produce results distinct from those in earlier papers (Schachat et al, 2018). We also note that CO 2 solubility decreases as temperature increases, but the solubility change for the 10°C change (between 20 and 30˚) is only about 20%, and so does not completely offset estimated variations in pCO 2 through time (Li & Tsui, 1971).…”

“…The principles and background data on which these media were designed are described in Ratti et al (2011). That said, models disagree on pCO 2 through time, and a recent reanalysis of Berner's well-known GEOCARBSULF model paper (Berner, 2009) shows that updated isotopic data produce results distinct from those in earlier papers (Schachat et al, 2018). The desired pCO 2 in the gas phase was obtained using an electronic gas mixer (Bronkhorst High-Tech B.V. E-5700, Ruurlo, the Netherlands), according to Fanesi et al (2014).…”

The engineering of the giant dragonflies of the Permian: revised body mass, power, air supply, thermoregulation and the role of air density

“…An updated reconstruction of atmospheric oxygen also questions the interpretation of Carboniferous/Permian insect body size being largely determined by the diffusional limits of atmospheric oxygen, as the supposed maximum oxygen concentration during this period does not occur in updated datasets (Schachat et al, 2018). As soon as winged insects appear in the fossil record, insect fossils become far more abundant than arachnids, but Schachat and colleagues (2018) note that no link can be made between the sudden development of winged insects and any change in P O2 (see Glossary); thus, oxygen levels might not have been the driver for evolution of the very large insects of this period.…”

“…Aerodynamic lift (normal to the relative velocity) is directly proportional to air density, so large Protodonata could have flown with less power in an atmosphere of higher density. At higher densities, viscosity (see Glossary) becomes an issue, and it would be expected that, if air density were to increase over time, evolutionary pressure would favour larger sizesas observed in the fossil record of the Permian (Schachat et al, 2018).…”

Developmental expression and evolution of hexamerin and haemocyanin fromFolsomia candida(Collembola)

“…As indicated by the molecular dating results, hexamerins originated from haemocyanins approximately 423 Ma in the late Silurian–early Devonian period, concurrent with the increase of atmospheric oxygen levels (Fig. ; Berner, ; Schachat et al , ). More oxygen could freely flow through the cuticle and even the original trachea, and the respiratory proteins may have become less important in Collembola to some extent, which may have allowed some haemocyanins to evolve.…”