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Multiple Functional Solutions During Flightless to Flight-Capable Transitions Provisionally accepted The final, formatted version of the article will be published soon. Â
Frontiers in Ecology and Evolution (abstract only)
doi: 10.3389/fevo.2020.573411
https://www.frontiersin.org/articles/10.3389/fevo.2020.573411/abstract

The evolution of avian flight is one of the great transformations in vertebrate history, marked by striking anatomical changes that presumably help meet the demands of aerial locomotion. These changes did not occur simultaneously, and are challenging to decipher. Although extinct theropods are most often compared to adult birds, studies show that developing birds can uniquely address certain challenges and provide powerful insights into the evolution of avian flight: unlike adults, immature birds have rudimentary, somewhat âdinosaur-likeâ flight apparatuses and can reveal relationships between form, function, performance, and behavior during flightless to flight-capable transitions. Here, we focus on the musculoskeletal apparatus and use CT scans coupled with a three-dimensional musculoskeletal modeling approach to analyze how ontogenetic changes in skeletal anatomy influence muscle size, leverage, orientation, and corresponding function during the development of flight in a precocial ground bird (Alectoris chukar). Our results demonstrate that immature and adult birds use different functional solutions to execute similar locomotor behaviors: in spite of dramatic changes in skeletal morphology, muscle paths and subsequent functions are largely maintained through ontogeny, because shifts in one bone are offset by changes in others. These findings help provide a viable mechanism for how extinct winged theropods with rudimentary pectoral skeletons might have achieved bird-like behaviors before acquiring fully bird-like anatomies. These findings also emphasize the importance of a holistic, whole-body perspective, and the need for extant validation of extinct behaviors and performance. As empirical studies on locomotor ontogeny accumulate, it is becoming apparent that traditional, isolated interpretations of skeletal anatomy mask the reality that integrated whole systems function in frequently unexpected yet effective ways. Collaborative and integrative efforts that address this challenge will surely strengthen our exploration of life and its evolutionary history.

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Sean P. Modesto (2020)
The disaster taxon Lystrosaurus: a paleontological myth Provisionally accepted The final, formatted version of the article will be published soon. Â
Frontiers in Earth Science (abstract only)
doi: 10.3389/feart.2020.610463
https://www.frontiersin.org/articles/10.3389/feart.2020.610463/abstract

The term 'disaster species' was a term originally conceived to describe marine microfossils that exhibited profound abundances in the wake of a biological crisis. The term was expanded in the 1990s to describe (as 'disaster taxa') opportunistic taxa that dominated their biota numerically ('bloomed') during the survival interval of a mass extinction event. The Permo-Triassic tetrapod genus Lystrosaurus has been cited regularly as a 'disaster taxon' of the end-Permian mass extinction. A review of the definitions that have been developed for disaster taxa, and data from recent biostratigraphic and phylogenetic studies that include species of Lystrosaurus, leads to the conclusion that the genus is not a 'disaster taxon'. Further, the known biostratigraphy and tree topologies of species of Lystrosaurus do not satisfy more recent definitions that attribute diversification to disaster species. At most, species of Lystrosaurus that form the informal 'Lystrosaurus abundant zone' in the lower Katberg Formation, Lower Triassic of South Africa, could be described as opportunistic species.

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Elke Schneebeli-Hermann (2020)
Regime shifts in an Early Triassic subtropical ecosystem
Frontiers in Earth Science (abstract only)
doi: 10.3389/feart.2020.58869
https://www.frontiersin.org/articles/10.3389/feart.2020.588696/abstract

The Early Triassic was one of the most remarkable time intervals in Earth History. To begin with, life on Earth had to face one of the largest subaerial volcanic degassing, the Siberian Traps, followed by a plethora of accompanying environmental hazards with pronounced and repeated climatic changes. These changes not only led to repeated and, for several marine nektonic clades, intense extinction events but also to significant changes in terrestrial ecosystems. The Early Triassic terrestrial ecosystems of the southern subtropical region (Pakistan) are not necessarily marked by abrupt extinction events but by extreme shifts in composition. Modern ecological theories describe such shifts as catastrophic regime shifts. Here, the applicability of modern ecological theories to these past events is tested. Abrupt shifts in ecosystems can occur when protracted changing abiotic drivers (e.g. climate) reach critical points (thresholds or tipping points) sometimes accentuated by stochastic events. Early Triassic terrestrial plant ecosystem changes stand out from the longer term paleobotanical records because changes of similar magnitude have not been observed for many millions of years before and after the Early Triassic. To date, these changes have been attributed to repeated severe environmental perturbations, but here an alternative explanation is tested: the initial environmental perturbations around the PermianâTriassic boundary interval are regarded here as a main cause for a massive loss in terrestrial ecosystem resilience with the effect that comparatively small-scale perturbations in the following ~5 Ma lead to abrupt regime shifts in terrestrial ecosystems.

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