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The Middle Awash late Miocene faunal assemblages document diverse evolutionary trajectories for mammalian species across the Miocene-Pliocene boundary. The assemblages indicate a number of originations and extinctions in various groups adapted to different habitats. This chapter examines the biochronological and evolutionary significance of the Middle Awash faunal assemblages by looking at possible first appearance (FA) and last appearance (LA) of mammalian species. It synthesizes the information to look into faunal turnovers and their probable causes. The fact that the Middle Awash late Miocene fauna samples two time successive horizons, dated to between 5.8 Ma and 5.2 Ma, makes it ideal to look into what factors trigger evolutionary changes in a lineage.

This book addresses the geology, geochronology, paleontology, paleogeography, paleobiochronology, and paleoecology of the Middle Awash late Miocene. It synthesizes vertebrate evolution in eastern Africa during the end of the Miocene epoch, a time during which the modern African fauna started forming. The Middle Awash valley of Ethiopia is a unique natural laboratory for the study of human origins and evolution. This introductory chapter provides a historical overview of the Middle Awash research project, which was formed to conduct geological, paleoanthropological, and archaeological reconnaissance surveys in the area.

This chapter describes the Middle Awash carnivore fauna, which represents one of the most diverse in the latest Miocene of eastern Africa. At least 15 genera in seven families are recognized from the Asa Koma Member of the Adu-Asa Formation and the Kuseralee Member of the Sagantole Formation. The carnivore assemblage from the late Miocene of the Middle Awash has important implications for regional and global biogeography, and it also documents the first local appearances of some taxa that established the modern African carnivore fauna.

This chapter discusses the phylogenetic relationships among African suids. It describes cranial and dentognathic suid remains from the late Miocene of the Middle Awash study area. The available fossil suid sample has increased enormously since the 1980s with the discovery of specimens from sites such as Lothagam and the Middle Awash. The chapter suggests that these collections provide deeper insights into the systematics and diversity of African tetraconodont suids during the late Miocene and early Pliocene.

This chapter discusses the hipparionine horses of the Eurygnathohippus clade from the Middle Awash late Miocene. It presents the morphological description and statistical analysis of the Middle Awash hipparions ranging in age from 6.0 to 5.2 Ma. It examines two taxa of Middle Awash late Miocene hipparion, Eurygnathohippus feibeli, from the oldest stratigraphic levels of Jara-Borkana and an apparently slowly evolving derivative, Eurygnathohippus aff. feibeli, from the 5.7 to 5.2 Ma interval. The chapter describes the discrete morphology of skull fragments, mandibular remains, and maxillary and mandibular dentitions by stratigraphic level and locality for each of the recognized taxa.

This concluding chapter summarizes the importance of the Middle Awash late Miocene faunal assemblages in terms of their contribution toward our understanding of the diversity, evolutionary history, and evolutionary tempo and mode of eastern African late Miocene mammals. It also summarizes the results from the paleoenvironmental and paleobiogeographic analyses in relation to regional and global climatic changes and their impact on the speciation and extinction of various mammalian taxa and the formation of the modern African mammalian fauna. Finally, it addresses future plans for continued paleontological work on the late Miocene of the Middle Awash paleontological study area, highlighting the significance of the site and the need for a long-term maintenance and protection program.

This chapter conducts comparative biogeographic analyses to examine how much the Middle Awash fauna resembles faunas from other localities of similar age at the genus level. The results indicate that the Middle Awash had close biogeographic relationships with eastern and northern African, Arabian, and western Eurasian localities of similar age. The analysis of Eurasian and African late Miocene localities provides information about the first and last occurrences of the taxa considered, and the geographic areas of these recorded occurrences. It also allows us to consider hypotheses about the timing and direction of paleogeographic connections between western Eurasia and northern and eastern Africa during the late Miocene.

This chapter considers the paleoenvironment of the Middle Awash study area in the Afar Rift of Ethiopia. Different aspects of the large mammalian faunal communities from the Asa Koma and Kuseralee Members are examined. The chapter examines the community structure based on locomotor and dietary variables, relative abundances of indicator taxa, and ecomorphology. Independent verification of the results based on large mammalian fauna have been derived from fish, bird, and small mammal faunas and from geological and stable isotopic data.

This chapter discusses the systematics and paleoecology of the small mammals recovered in fossiliferous localities of the Adu-Asa Formation. The micromammalian fauna from the late Miocene of the Middle Awash is diverse and documents at least 16 taxa in eight families. The chapter also includes important new fossils from the Haradaso Member of the Sagantole Formation belonging to Alilepus, Tachyoryctes, and Thryonomys. These remains, dated to approximately 4.85 Ma, are important additions to earliest Pliocene small mammal faunas.

This chapter describes the cercopithecid fossils recovered from the late Miocene sediments of the western margin and Central Awash Complex (CAC) of the Middle Awash. Cercopithecids in the Adu-Asa Formation and the Kuseralee Member of the Sagantole Formation are rare compared to other taxa, with total specimens collected from late Miocene Middle Awash deposits constituting only 3.8 percent of the total number of collected vertebrate specimens identifiable below the family level.

This chapter examines the Mio-Pliocene volcanic materials exposed along the western margin of the Middle Awash area, with a primary focus on the late Miocene deposits of the Adu-Asa Formation. The primary goals of this chapter are to: define the different types of volcanic material preserved in the Adu-Asa Formation; present a working composite stratigraphic view of the Adu-Asa Formation volcanic horizons; present the existing geochemical data for western margin volcanic samples, including some with uncertain chronostratigraphic context; illustrate the data and observations that provided the basis for previous correlations and naming of key volcanic marker horizons; and illustrate the data and observations that provide new regional correlations and hence the establishment of newly named volcanic horizons.

This chapter describes the giraffid remains in the Middle Awash late Miocene deposits. The family Giraffidae is represented by two modern genera (Okapia and Giraffa) in Africa. Giraffids first appear in Africa south of the Sahara sometime toward the end of the middle Miocene. During the late Miocene, however, giraffines, which were also abundant in western Eurasia, dominated the giraffid community of eastern Africa.

Tubulidentata is currently represented by a single extant species—Orycteropus afer, the aardvark. They are the largest African anteaters. This chapter focuses on the identification and description of these aardvark specimens found in the Middle Awash late Miocene. Their importance for improving our knowledge of the order Tubulidentata is also discussed.

40Ar/39Ar dating has been applied extensively to volcanic units of late Miocene to Pleistocene age in the Middle Awash study area, and is the most important dating method applied to these deposits. This chapter discusses all available 40Ar/39Ar data for the Adu-Asa Formation, including some data not previously reported, plus some previously unpublished results from the nearby Central Awash Complex (CAC). The methods and facilities employed for 40Ar/39Ar dating is divided into two different approaches: incremental heating and single-crystal total fusion.

This chapter discusses the Rhinocerotid remains in the Middle Awash late Miocene. During the Miocene, fossil rhinoceroses were diverse and widespread in Africa. At least five different lineages (aceratheres, brachypotheres, iranotheres, dicerorhines, and dicerotines), comprising about eight genera and thirteen species, have been documented.

Recent discoveries of hominid remains older than 5 Ma have afforded new perspectives on the origin of the hominid clade. This chapter describes and assesses the key evidence bearing on these issues—the remains of Ardipithecus kadabba from the Middle Awash study area of the Afar Rift. It introduces the major morphological features of the known Ardipithecus kadabba specimens and also infers possible ancestral ape conditions from the morphologies shared by extant great apes and the collective late and middle Miocene fossil ape record.