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ORIGIN AND EVOLUTION OF BATS: EVALUATING A POTENTIAL STEM GROUP IN THE FOSSIL RECORD
Jones, Matthew F
Jones, Matthew F
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Abstract
This dissertation investigates the origins and early evolution of bats (Mammalia, Chiroptera) in a paleontological context. Bats are the second most diverse group of mammals on the planet, comprising more than 1,400 species that are found on all continents except Antarctica. Bats provide fundamental ecosystem services as seed dispersers and pollinators, control pests that threaten humans and many of our most important crops and are recognized reservoirs and/or vectors of potentially fatal viral diseases. The evolutionary origins of bats, however, are effectively unknown. The earliest fossil bats date to the beginning of the Eocene (~56 Ma) and are found nearly worldwide. However, these earliest fossil bats are hardly more primitive than modern bats, because all of them were capable of powered flight and most were able to echolocate. Genomic data place bats in the superorder Laurasiatheria—along with Carnivora, Pholidota, Cetartiodactyla, Eulipotyphla, and Perissodactyla—but fail to resolve relationships among these orders. The lack of resolution regarding how bats are related to other living and fossil mammals hampers our understanding of the evolutionary biology of the earliest bats. Without knowledge of the fossil or extant sister group of bats we cannot adequately reconstruct their biogeographic history, polarize morphological and genomic character states, or elucidate the evolution of such complex traits as flight and echolocation. Here I examine the potential relationship of bats to an enigmatic family of early Paleogene insectivorous mammals known as nyctitheres (Mammalia, Nyctitheriidae). Isolated dentitions of nyctitheres have commonly been mistaken for bats, and recent studies indicate that they were also members of Laurasiatheria. As small, insectivorous, early Cenozoic laurasiatherians, nyctitheres are important candidates to be a sister group of bats.This dissertation is divided into four chapters. The first describes a diverse fauna of nyctitheres from the late Paleocene of southwestern Wyoming. This fauna includes multiple new species enabling a revised diagnosis for the subfamily Placentidentinae and includes abundant material of poorly known taxa, including Wyonycteris chalix. The second chapter describes the oldest known bat fossils from Asia, which provide insight into chiropteran dental evolution and the monophyly of early bat families. In the third chapter I conduct a phylogenetic analysis of early bat relationships, providing support for the presence of three distinct stem lineages and a previously unrecognized Paleogene emballonuroid radiation. I also present evidence that many stem families and genera may be nonmonophyletic. In the fourth chapter I conduct a phylogenetic analysis interrogating the relationship of nyctitheres to bats and other laurasiatheres. I find that some nyctitheres, including Wyonycteris microtis and W. chalix, may be more closely related to Chiroptera than to other nyctitheres. I also demonstrate that Nyctitheriidae and many of its subfamilies are likely nonmonophyletic. This research will provide much needed paleontological context regarding the origins and evolution of bats and a foundation for future analyses into the evolution of specialized chiropteran morphology and ecology.
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Date
2022-08-31
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University of Kansas
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Keywords
Paleontology, Systematic biology, Evolution & development, Bat evolution, Chiroptera, Eocene, Laurasiatheria, Nyctitheriidae, Paleocene