Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (6 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2017)

A new species of hominid, Ardipithecus ramidus, was published in 1994 and 1995. The discovery team initially diagnosed and assigned the 4.4-million-year-old Ardipithecus ramidus to the hominid branch of the hominoid family tree based on the limited available dental, cranial, and postcranial characters exclusively shared with later hominids (i.e., all species derived in the human direction after the last common ancestor shared with chimpanzees; equivalent to “hominin”). A subsequent and limited parsimony-based cladistics analysis in 2006 again aligned Ardipithecus with later Australopithecus based on shared, derived characters of the dentition, as did other independent efforts based on the 1994 publication.

A more comprehensive exposition of the species followed in 2009 when a suite of 11 research papers comprising ~600 manuscript pages of description, data, and analysis was published in Science. The additional anatomy revealed in these publications employed the numerous additional shared derived characters observable on newly recovered fossils. These characters are spread across developmentally separate parts of the body. The combined evidence for phylogenetic placement reinforced the team’s earlier inference that Ardipithecus ramidus was a hominid exclusively related to Australopithecus and Homo. By illuminating the 4-6 Ma time period, the Ardipithecus fossils allowed practitioners to contextualize both the chronologically younger Australopithecus afarensis, despite the latter’s many derivations, and the Late Miocene common ancestor that we humans once shared with chimpanzees (CLCA).

After the 2009 publication of Ardipithecus several analysts doubted its hominid phylogenetic status based on arguments invoking the Late Miocene (8.3 - 6.7 Ma) Tusco-Sardinian hominoid Oreopithecus. These claims were based on several anatomical characters of its dentition, cranium, and postcranium that were argued to have been evolved in parallel with Ardipithecus. Such parallel acquisitions (homoplasies, or traits evolved in parallel from a last common ancestor that did not share the trait) in Oreopithecus potentially confound the recognition of phylogenetically primitive hominids, and might falsify claims of derived characters argued to exclusively link Ardipithecus with later hominids.

Since its discovery in 1872, Oreopithecus has inspired 145 years of field and laboratory research, hundreds of primary publications, and countless mentions in scientific and popular literature. This taxon has been proposed by some, since its discovery, as a mysterious member of the family Hominidae or as a distant relative ape taxon that evolved several features claimed to be hominid-like. Despite the extremely distorted and damaged condition of the fossils, many of these features were originally alleged to be synapomorphic between Oreopithecus and later hominids, but with the better resolution of the phylogenetic position of Oreopithecus, these are today widely promulgated as homoplasies.

This dissertation aims to evaluate whether features are actually shared between Oreopithecus and hominids, and if so, whether they are homoplastic (evolved in parallel), synapomorphic (shared derived), or symplesiomorphic (the shared primitive condition). Such a comprehensive examination and evaluation of claims of hominid homoplasy in Oreopithecus, conducted with

original fossils in comparison with original Ardipithecus fossils, has not been undertaken until now.

The objectives of this dissertation are to determine whether the claimed morphological features in Oreopithecus are present/observable and if so, whether the alleged characters can be diagnosed as hominid homoplasies. The following three research questions are addressed:

(1) Is the claimed morphological feature present/observable, or can it be reasonably inferred on the basis of the actual fossil evidence?

(2) If the claimed morphological feature is verified as present/observable, has the feature been accurately diagnosed in hominids (Australopithecus, Ardipithecus, and others)?

(3) Can allegedly shared characters that remain after testing per (1) and (2) be diagnosed as symplesiomorphic, synapomorphic, autapomorphic (uniquely derived), or)?

Key character complexes and their subdivided characters claimed to be hominid synapomorphies or homoplasies in Oreopithecus were examined and evaluated by comparing Ardipithecus, Australopithecus, Homo sapiens, extant hominoids, and fossil hominoids. Claims of hominid homoplasy in five (5) of the character complexes and eighteen (18) of their subdivided characters of Oreopithecus skeletal anatomy were falsified because relevant Oreopithecus anatomy is absent or has been misinterpreted. Claims of homoplasy in two (2) character complexes were falsified because the similarities in Oreopithecus and Ardipithecus anatomy are probably the primitive condition for the two taxa. The claim of homoplasy in one (1) subdivided character (vertical implantation of upper and lower incisors) of the character complex of an anteroposteriorly short face in Oreopithecus could not be falsified and represents a probable homoplasy. Of the six (6) singular characters claimed as hominid homoplasies in Oreopithecus, two (2) are revealed to have been based on Oreopithecus anatomy that is absent or has been misinterpreted and four (4) represent possible homoplasies but further fossils and outgroup analysis will be required to confirm them.

The results of this study form a foundation for future comparative work to test the potential hominid homoplasies in Oreopithecus when further fossils suffering from comparatively less distortion of relevant anatomy become available. In the meantime, future studies illuminating the underlying developmental genetic relationship of potentially homoplastic morphological characters in Hominoidea is warranted.

    Cover page: Interpretation of Homoplasies in Oreopithecus and Their Relevance for Elucidating the Chimpanzee-Human Last Common Ancestor
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2017)
    Zooarchaeologists have long relied on linear traces and pits found on the surfaces of ancient bones to infer ancient hominid behaviors such as slicing, chopping, and percussive actions during butchery of mammal carcasses. However, such claims about Plio-Pleistocene hominids rely mostly on very small assemblages of bony remains. Furthermore, recent experiments on trampling animals and biting crocodiles have shown each to be capable of producing mimics of such marks. This equifinality-the creation of similar products by different processes-makes deciphering early archaeological bone assemblages difficult. Bone modifications among Ethiopian Plio-Pleistocene hominid and faunal remains at Asa Issie, Maka, Hadar, and Bouri were reassessed in light of these findings. The results show that crocodiles were important modifiers of these bone assemblages. The relative roles of hominids, mammalian carnivores, and crocodiles in the formation of Oldowan zooarchaeological assemblages will only be accurately revealed by better bounding equifinality. Critical analysis within a consilience-based approach is identified as the pathway forward. More experimental studies and increased archaeological fieldwork aimed at generating adequate samples are now required.
      Cover page: Hominid butchers and biting crocodiles in the African Plio–Pleistocene
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2015)
      Australopithecus fossils were regularly interpreted during the late 20th century in a framework that used living African apes, especially chimpanzees, as proxies for the immediate ancestors of the human clade. Such projection is now largely nullified by the discovery of Ardipithecus. In the context of accumulating evidence from genetics, developmental biology, anatomy, ecology, biogeography, and geology, Ardipithecus alters perspectives on how our earliest hominid ancestors--and our closest living relatives--evolved.
        Cover page: Neither chimpanzee nor human, Ardipithecus reveals the surprising ancestry of both
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2014)
        The early Pliocene African hominoid Ardipithecus ramidus was diagnosed as a having a unique phylogenetic relationship with the Australopithecus + Homo clade based on nonhoning canine teeth, a foreshortened cranial base, and postcranial characters related to facultative bipedality. However, pedal and pelvic traits indicating substantial arboreality have raised arguments that this taxon may instead be an example of parallel evolution of human-like traits among apes around the time of the chimpanzee-human split. Here we investigated the basicranial morphology of Ar. ramidus for additional clues to its phylogenetic position with reference to African apes, humans, and Australopithecus. Besides a relatively anterior foramen magnum, humans differ from apes in the lateral shift of the carotid foramina, mediolateral abbreviation of the lateral tympanic, and a shortened, trapezoidal basioccipital element. These traits reflect a relative broadening of the central basicranium, a derived condition associated with changes in tympanic shape and the extent of its contact with the petrous. Ar. ramidus shares with Australopithecus each of these human-like modifications. We used the preserved morphology of ARA-VP 1/500 to estimate the missing basicranial length, drawing on consistent proportional relationships in apes and humans. Ar. ramidus is confirmed to have a relatively short basicranium, as in Australopithecus and Homo. Reorganization of the central cranial base is among the earliest morphological markers of the Ardipithecus + Australopithecus + Homo clade.
          Cover page: Ardipithecus ramidus and the evolution of the human cranial base
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2021)
          The Halibee member of the Upper Dawaitoli Formation of Ethiopia's Middle Awash study area features a wealth of Middle and Later Stone Age (MSA and LSA) paleoanthropological resources in a succession of Pleistocene sediments. We introduce these artifacts and fossils, and determine their chronostratigraphic placement via a combination of established radioisotopic methods and a recently developed dating method applied to ostrich eggshell (OES). We apply the recently developed 230Th/U burial dating of OES to bridge the temporal gap between radiocarbon (14C) and 40Ar/39Ar ages for the MSA and provide 14C ages to constrain the younger LSA archaeology and fauna to ∼24 to 21.4 ka. Paired 14C and 230Th/U burial ages of OES agree at ∼31 ka for an older LSA locality, validating the newer method, and in turn supporting its application to stratigraphically underlying MSA occurrences previously constrained only by a maximum 40Ar/39Ar age. Associated fauna, flora, and Homo sapiens fossils are thereby now fixed between 106 ± 20 ka and 96.4 ± 1.6 ka (all errors 2σ). Additional 40Ar/39 results on an underlying tuff refine its age to 158.1 ± 11.0 ka, providing a more precise minimum age for MSA lithic artifacts, fauna, and H. sapiens fossils recovered ∼9 m below it. These results demonstrate how chronological control can be obtained in tectonically active and stratigraphically complex settings to precisely calibrate crucial evidence of technological, environmental, and evolutionary changes during the African Middle and Late Pleistocene.
            Cover page: Integrative geochronology calibrates the Middle and Late Stone Ages of Ethiopia’s Afar Rift
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2018)
            The dispersal of modern humans from Africa is now well documented with genetic data that track population history, as well as gene flow between populations. Phenetic skeletal data, such as cranial and pelvic morphologies, also exhibit a dispersal-from-Africa signal, which, however, tends to be blurred by the effects of local adaptation and in vivo phenotypic plasticity, and that is often deteriorated by postmortem damage to skeletal remains. These complexities raise the question of which skeletal structures most effectively track neutral population history. The cavity system of the inner ear (the so-called bony labyrinth) is a good candidate structure for such analyses. It is already fully formed by birth, which minimizes postnatal phenotypic plasticity, and it is generally well preserved in archaeological samples. Here we use morphometric data of the bony labyrinth to show that it is a surprisingly good marker of the global dispersal of modern humans from Africa. Labyrinthine morphology tracks genetic distances and geography in accordance with an isolation-by-distance model with dispersal from Africa. Our data further indicate that the neutral-like pattern of variation is compatible with stabilizing selection on labyrinth morphology. Given the increasingly important role of the petrous bone for ancient DNA recovery from archaeological specimens, we encourage researchers to acquire 3D morphological data of the inner ear structures before any invasive sampling. Such data will constitute an important archive of phenotypic variation in present and past populations, and will permit individual-based genotype-phenotype comparisons.
              Cover page: Human bony labyrinth is an indicator of population history and dispersal from Africa
              Top