The effect of long-term atmospheric changes on the macroevolution of birds

Abstract

Atmospheric conditions are critical for a range of biological functions-locomotion among others-and long-term changes in these conditions have been identified as causal for different macroevolutionary patterns. Here we examine the influence of variations in atmospheric O2 concentration (AOC), temperature (Tair), and air density (ρair) on the power efficiency, as it relates to locomotion, during the evolutionary history of birds. Specifically, our study centers on four key evolutionary events: (1) the body mass reduction of non-avian theropods prior to the rise of birds; (2) the emergence of flapping flight in the earliest birds; (3) the divergence of basal pygostylians; and (4) the diversification of modern birds. Our results suggest that a marked increase in AOC and ρair during the Middle Jurassic-coeval with a trend in miniaturization-improved the power efficiency of the dinosaurian predecessors of birds. Likewise, an increase in these conditions is hypothesized as having played a major role in the diversification of early pygostylians during the Early Cretaceous. However, our analyses do not identify any significant paleoatmospheric effects on either the emergence of flapping flight or the early cladogenesis of modern birds. Extinct birds flew within the range of atmospheric conditions in which modern birds fly but varying past conditions influenced their flight performance. Our study thus highlights the importance of considering paleoatmospheric conditions when reconstructing the flight efficiency of the forerunners of modern birds.

Palaeoatmosphere facilitates a gliding transition to powered flight in the Eocene bat, Onychonycteris finneyi

“…Here we quantitatively demonstrate a gliding transition based on the actual features of a key fossil bat with the least derived flight apparatus 3 , in the estimated hyperdense atmospheric conditions of its actual geologic time of occurrence. We suggest that evolutionary responses to high atmospheric density may have been key in the evolution of powered flight 13 , 23 , as has been suggested for Permian griffinflies (Protodonata) 44 , early Mesozoic 45 and gigantic Miocene 46 birds, and as shown here for Eocene bats.…”

Palaeoatmosphere facilitates a gliding transition to powered flight in Eocene bats

“…Here we quantitatively demonstrate a gliding transition based on the actual features of a key fossil bat with the least derived flight apparatus 3 , in the estimated hyperdense atmospheric conditions of its actual geologic time of occurrence. We suggest that evolutionary responses to high atmospheric density may have been key in the evolution of powered flight 13,23 , as has been suggested for Permian griffinflies (Protodonata) 43 , early Mesozoic 44 and gigantic Miocene 45 birds, and as shown here for Eocene bats.…”

Flight and echolocation evolved once in Chiroptera: comments on ‘The evolution of flight in bats: a novel hypothesis’

“…Therefore, our model has a larger span and related wing area than the ancestor proposed by AR. We followed the mass and wing area (W) values of Amador et al (2019), and air density was set at 1.24 kg/m 3 based on a reconstruction of the atmosphere 50 million years ago (Serrano et al 2019). We used multiple coefficient of lift (CL) values ranging from 0.53, as seen in extant flying frogs of the genus Rhacophorus (Emerson & Koehl 1990) to 2.12 from the extant flying squirrels Glaucomys volans (Bishop 2007).…”