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Values of air density (ρ air ), temperature (T air ), and O 2 concentration (AOC) during the last 180 Myr. Temperature values from Retallack (2009); AOC percent from Falkowski et al. (2005) (Fk), Ward and Berner (2011) (WB), and Glasspool and Scott (2010) (GS); ρ air was derived from these two previous variables.
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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...
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... used the equation of ideal gases (ρ air = P atm / RT air g, where P atm is the atmospheric pressure, g is gravity's acceleration, and R is the universal gas constant) to calculate ρ air values at 10-Myr-intervals, which provided an air density curve spanning the last 180 Myr (Table 2). Values of past P atm were calculated using molecular masses and concentration of O 2 and N 2 relative to modern values (the contribution of other gases to present atmospheric pressure is negligible; Supplementary Table 1). ...Context 2
... the case of non-avian theropods, we estimated their V O2 values from Eq. (2), which was derived from running cursorial birds (Butler, 1991), using the M b of the nodes recovered by Lee et al. (2014) for the 180-160 Myr interval (Supplementary Table 2). ...Context 3
... cursorial theropods, we tested the differences concerning massspecific available power (i.e., P av /BM) between the nodes included in the range 180-170 Myr (N = 10) and those included in 170-160 Myr interval (N = 24) (see Supplementary Table 2). This was performed for the three AOC models included in this study (i.e., Fk, WB and GS). ...Context 4
... the absolute values of the three AOC models show significant discrepancies that are most likely the result of methodological differences (see Methods), several long-term trends (increment or decrement) are congruent among these models ( Fig. 1; Table 2). All models document an increase in AOC from 180 to 160 Myr, although the net values were more pronounced in the Fk model (+49.6%) ...Context 5
... 3 Dataset of extinct and extant birds used in this study. Values of body mass (M b ), wingspan (B), and wing area (S L ) for extinct birds were obtained from multiple regressions using anatomical measures from modern birds (see Serrano et al., 2015 show that ρ air increased between 1 and 6% (depending on the model) during the Early-Middle Jurassic (Table 2). During the Late Jurassic and at the beginning of the Cretaceous (i.e., 160 to 140 Myr), the three models show a decrease in AOC (net values: Fk, −14.1%; ...Context 6
... −5.8%), which implies a reduction of ρ air ranging from 0.3% to 2.5% depending on the model ( (Fig. 1). Consequently, our calculations of ρ air for the Early Cretaceous indicate an increase of 5.5% (GS), 6.9% (WB), or negligible (Fk) depending on the model (Table 2). During the Late Cretaceous, the three models show relatively stable AOC, despite that the actual concentrations differ from one another (Fig. 1); due to significant swings in T air , values of ρ air during this period vary significantly, with a marked peak at around 80 Myr ago ( Fig. 1; Table 2). ...Context 7
... our calculations of ρ air for the Early Cretaceous indicate an increase of 5.5% (GS), 6.9% (WB), or negligible (Fk) depending on the model (Table 2). During the Late Cretaceous, the three models show relatively stable AOC, despite that the actual concentrations differ from one another (Fig. 1); due to significant swings in T air , values of ρ air during this period vary significantly, with a marked peak at around 80 Myr ago ( Fig. 1; Table 2). Following the K-P mass extinction (~65 Myr), the WB model predicts AOC values that remain close to present atmospheric levels throughout the Cenozoic; however, there is a noticeable increase in values between 50 and 30 Myr ago (5.7% ...Context 8
... Fk model also predicts a steep rise in AOC during the early Cenozoic (21% increase between 50 and 30 Myr); consequently, ρ air estimates under this model show a major increase, moving from below today's levels to above these levels. In contrast to these two models, the GS model shows a significant drop in AOC (i.e., −18.5%) during the early-mid Paleogene (i.e., 60 to 40 Myr), oscillating slightly below modern values until present time ( Fig. 1; Table 2). Fig. 2. Power curves calculated for a herring gull, Larus argentatus (UWBM 56577), at different conditions of AOC and ρ air . ...Context 9
... this period, the reduction in body mass would have allowed a large number of non-avian theropod lineages to increase their mass-specific P av (i.e. P av /M b ) by 3.6 times (using Lee et al.'s, 2014 data, P av mean value calculated for clade nodes at 160 Myr is 3.6 times greater than the value at 179-180 Myr; Supplementary Table 2). If the effects of the increase in AOC values are also accounted, the mass-specific P av of these animals would have risen even further, between 4.7 times (according to the WB model) and 6.4 times (according to the Fk model) (Fig. 3B). ...Citations
... 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 ) to 2.12 from the extant flying squirrels Glaucomys volans (Bishop 2007). ...
Anderson and Ruxton (Mammal Review, 2020) reviewed the evolution of powered flight and laryngeal echolocation in bats. They hypothesised that powered
flight and laryngeal echolocation evolved in separate lineages of handwing gliders.
We note fossil, character evolution, and developmental evidence contradict their
hypothesis, and we test their handwing gliding model, finding it aerodynamically
implausible. We conclude that the traditional view of bat evolution (that flight
and laryngeal echolocation evolved in the common ancestor of all bats, with
the latter being lost in pteropodids) is more plausible than the proposed novel
hypothesis.
... We also chose to follow the methodology of for other Mesozoic gliding taxa: Vg=(2mg/pSCl) 1/2 Where p is the density of air (1.23 kgm -3 ) and Cl is the coefficient of lift. Recent work has documented long term atmospheric changes in air density across the Mesozoic and commented on how it could alter flight capacity (Serrano, Chiappe et al. 2019). We have incorporated thise as a separate permutation using the values from (Serrano, Chiappe et al. 2019). ...
... Recent work has documented long term atmospheric changes in air density across the Mesozoic and commented on how it could alter flight capacity (Serrano, Chiappe et al. 2019). We have incorporated thise as a separate permutation using the values from (Serrano, Chiappe et al. 2019). For Yi and Ambopteryx this means air density was set to the estimated value 160 MYA (1.171 kgm -3 ). ...
The bizarre scansoriopterygid theropods Yi and Ambopteryx had skin stretched between elongate fingers that form a potential membranous wing. This wing is thought to have been used in aerial locomotion, but this has never been tested. Using laser-stimulated fluorescence imaging, we re-evaluate their anatomy and perform aerodynamic calculations covering flight potential, other wing-based behaviors, and gliding capabilities. We find that Yi and Ambopteryx were likely arboreal, highly unlikely to have any form of powered flight, and had significant deficiencies in flapping-based locomotion and limited gliding abilities. Our results show that Scansoriopterygidae are not models for the early evolution of bird flight, and their structurally distinct wings differed greatly from contemporaneous paravians, supporting multiple independent origins of flight. We propose that Scansoriopterygidae represents a unique but failed flight architecture of non-avialan theropods and that the evolutionary race to capture vertebrate aerial morphospace in the Middle to Late Jurassic was dynamic and complex.
... Values of P av for STM 15-15 were adjusted to the O 2 atmospheric levels at 120 Myr, the estimated time of deposition for the fossil (Ward and Berner, 2011), through the percentage of variation between concentrations today and in the past (Serrano et al., 2019), calculated using Equation 3 (where AOC is atmospheric O 2 concentration): ...
... We took the ρ air at 120 Myr (i.e., 1.209 kgm -3 ; Serrano et al., 2019), while the dynamic viscosity of the air, μ, was assumed at modern standard conditions (i.e., 1 atm, 20° C). Under this approach C Db varies with Re b , and this Re b is dependent on Vt. ...
Unseen and difficult-to-see soft tissues of fossil birds revealed by laser-stimulated fluorescence (LSF) shed light on their functional morphology. Here we study a well-preserved specimen of the early pygostylian Sapeornis chaoyangensis under LSF and use the newly observed soft-tissue data to refine previous modeling of its aerial performance and to test its proposed thermal soaring capabilities. Under LSF, the body's lateral outline is observed, permitting direct estimates of the body's disc surface that generates drag during flight (Sb). This surface and the body drag coefficient-which is better estimated knowing S bare influential parameters in modeling flight dynamics. In particular, we focus on two aspects of flight dynamics: the calculation of the power margin during flapping flight (power curve), and the sinking speed during gliding (glide polar). Results from revised models using our direct soft-tissue measurements support the notion that Sapeornis was a thermal soarer that glided for long periods. LSF also confirms the absence of a true alula in Sapeornis. While the deployment of the alular digit could have enhanced control during slow flight, the position of this digit along the handwing (distal part of the wing) suggests limited maneuverability. This study demonstrates how soft-tissue preservation can be incorporated into modeling of flight dynamics in light of ever-improving palaeontological imaging techniques.
... In the long-term evolution of nature, the unique structure of bird feathers has developed to meet the needs of flight. Feather is the most complex outer skin derivative found in all vertebrates (Brusatte et al., 2015;Field et al., 2018;Lingham-Soliar, 2013;Serrano et al., 2019) and is distinguished by its unusual structure. The flight feathers of birds are keratinised appendages that achieve optimal mechanical properties with minimal weight. ...
The feathers of the seagull Larus argentatus are lightweight but can withstand high alternating stresses and exhibit excellent stiffness and strength. The shaft is an important part of the feather, with the functions of body protection and supporting flight. In this study, the microstructure properties of L. argentatus feather rachis were analysed by scanning electron microscopy (SEM). These analysis methods enabled the configuration, structure and compression properties of the rachis to be investigated. The results indicated that the rachis was composed of the outer cortex and the inner medulla. The cortex had a continuous layered nano-fibre composite structure, which bears, transmits, absorbs and disperses the compression force. The medulla had bubble-like cells with a porous-fibre structure, which rapidly absorbs, transmits and consumes compression force and is a suitably lightweight material for flight. Axial compression tests showed that the rachis from primary feathers had the best energy absorption and that from secondary feathers had the best compressive strength. The compressive strength might have something to do with the ratio of cortical area to medullary area. When the moisture content in the rachis increased, the compressive strength of feather rachis in different parts would decrease. These results indicate that the L. argentatus feather rachis have excellent compression resistance properties, deriving from structural factor.
The evolutionary transition to powered flight remains controversial in bats, the only flying mammals. We applied aerodynamic modeling to reconstruct flight in the oldest complete fossil bat, the archaic Onychonycteris finneyi from the early Eocene of North America. Results indicate that Onychonycteris was capable of both gliding and powered flight either in a standard normodense aerial medium or in the hyperdense atmosphere that we estimate for the Eocene from two independent palaeogeochemical proxies. Aerodynamic continuity across a morphological gradient is further demonstrated by modeled intermediate forms with increasing aspect ratio (AR) produced by digital elongation based on chiropteran developmental data. Here a gliding performance gradient emerged of decreasing sink rate with increasing AR that eventually allowed applying available muscle power to achieve level flight using flapping, which is greatly facilitated in hyperdense air. This gradient strongly supports a gliding (trees-down) transition to powered flight in bats.
Bats are the only flying mammals but their transition to flight remains poorly understood and controversial. We applied aerodynamic modeling to reconstruct flight in the oldest complete fossil bat, the archaic Onychonycteris finneyi from the early Eocene of North America, under paleo-atmospheric conditions. Results indicate that Onychonycteris was capable of both gliding and powered flight either in a standard normodense aerial medium or in a hyperdense atmosphere estimated for the Eocene from two independent paleogeochemical proxies. Aerodynamic continuity across a morphological gradient is demonstrated by modeled intermediate forms with increasing aspect ratio (AR) produced by gradual digital elongation, such as indicated by chiropteran developmental data. Here a performance gradient emerged of decreasing sink rate with increasing AR that eventually allowed available muscle power to achieve level flight using flapping, a process greatly facilitated under elevated atmospheric densities. This gradient strongly supports a gliding (trees-down) transition to powered flight in bats.
