New insights into avian evolution : evidence from fossils and colorful phenotypes

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2022-08-12

Authors

Davis, Sarah N.

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Abstract

Birds (Aves) are the most species-rich terrestrial vertebrate group alive today, with a deep evolutionary history extending back to the Cretaceous and surviving through the Cretaceous-Paleogene (K/Pg) mass extinction event. To best understand the evolution of this group, a combination of insights from fossils and living taxa are needed. Studies of extant taxa provide information on how living systems function, which is necessary to continue improving deep-time evolutionary hypotheses, allowing for more accurate interpretations of the fossil record. It can be especially important to study traits such as coloration to inform targeted approaches to new methods or to constraint reconstructions of extinct animals. My research expands our understanding of avian evolution by investigating the carotenoid coloration system within living birds to better elucidate how distribution of this pigment type has evolved across tissue types within Dinosauria. Ancestral state reconstructions indicate that carotenoid-consistent color expression was possible in bare-part tissues of extinct archosaurs including dinosaurs, with likelihood increasing within Aves. Expression of carotenoids in more tissue types and regions is also associated with increased dietary carotenoid content, indicating that extinct archosaurs with certain diets would have been more likely to express these colors. In addition to phenotypic data from living birds, more fossils from age-constrained localities are needed to better understand bird evolution. The fossil record from the latest Cretaceous extinction interval to early Paleogene is still limited, and most discoveries are from the Northern Hemisphere. New localities in Chilean Patagonia and the Antarctic Peninsula have produced new avian fossils, as well as fossils of other theropods, that expand our understanding of diversity from a critical time interval. New Chilean fossils provide the southernmost record of enantiornithine birds, as well as crucial new datapoints for the presence of ornithurines during the Maastrichtian. Fossils from Seymour Island, Antarctic, add to the known diversity of Sphenisciformes during the Eocene, while also confirming previously controversial records of Gruiformes and Xenarthran mammals from this period in Antarctica. While these new fossils are an important piece of the story, they are still limited in the amount of information they provide. Altogether, this research expands our understanding of species from Southern Hemisphere localities and shows the importance of taking a truly global approach to investigating mass extinction events. Furthermore, I highlight the need for more broad-scale consideration for phenotypic traits in living groups to understand how phenotypic variation evolves in deep time.

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