Dissertations, Theses, and Capstone Projects

Date of Degree

6-2024

Document Type

Dissertation

Degree Name

Ph.D.

Program

Anthropology

Advisor

Christopher C. Gilbert

Committee Members

Eric Delson

Ryan Raaum

Stephen Frost

Subject Categories

Biological and Physical Anthropology

Keywords

Leaf monkeys, Colobines, Phylogenetics, Total evidence, Functional morphology

Abstract

The Colobinae (leaf-eating monkeys) are one of two crown cercopithecoid subfamilies along with the Cercopithecinae (cheek-pouch monkeys). They are today represented by a diverse modern radiation comprising two reciprocally monophyletic geographic subtribes, the African Colobina and the Asian Presbytina, which are collectively united by shared adaptations to folivory and arboreality. In addition, the colobine fossil record documents a taxonomically and ecologically diverse, geographically widespread radiation from the late Middle Miocene onwards. Fossil colobines exhibit an array of body sizes, craniofacial morphologies, postcranial adaptations, and dental dietary signals that exceeds those of the modern radiation and are also widespread over Africa, Europe, and Asia. However, interpreting their diversity and biogeography is hampered significantly by the near absence of reliable phylogenetic hypotheses for the clade. This study represents an effort to address this gap in our understanding of cercopithecoid evolution by reassessing molecular and morphological evolution of the extant radiation, inferring the phylogenetic relationships of the fossil colobines, and evaluating competing scenarios of their biogeography, reconstructions of the ancestral colobine morphotype, and the evolution of arboreality in light of these updated phylogenetic hypotheses.

First, the phylogeny of the extant colobines is still partly uncertain particularly among the Asian colobines. A large supermatrix of molecular data is compiled and analyzed independently as well as in total-evidence analyses with a novel craniodental character matrix. The inferred generic relationships among the extant colobines are strongly supported, resolving Presbytis as sister to all other Asian colobines, a Semnopithecus + Trachypithecus clade, the monophyly of the odd-nosed colobines, and the position of Rhinopithecus as sister to the other odd-nosed colobines, as well as recovering previously supported relationships among African colobines. Evaluating the morphological evolution of the modern colobine clades provides an updated set of skeletal synapomorphies by reevaluating the valence and polarity of previously described synapomorphies as well as identifying a handful of novel diagnostic features.

Second, fossil colobines are subsequently added to the character matrix and relationships of the fossil and extant colobines are inferred with total evidence parsimony and Bayesian analyses. Strongly supported generic relationships from the extant-only analyses are applied as a molecular backbone to the parsimony analyses, and a partitioned supermatrix of molecular and morphological data are subject to non-clock and tip-dated Bayesian analyses. Topologies inferred by these analyses differ slightly but are largely congruent and identify several genera that are likely polyphyletic (species I consider generically distinct from the types of their current assignments are denoted with quotation marks around the genus name). The results consistently recover the stem colobine position of several Late Miocene taxa (including Microcolobus tugenensis, Sawecolobus lukeinoensis, “Cercopithecoides” bruneti, “Paracolobus” enkorikae, Libypithecus markgrafi, Mesopithecus pentelicus, and “Cercopithecoides” kerioensis) along with some later-occurring Plio-Pleistocene taxa (Rhinocolobus turkanaensis, “Paracolobus” mutiwa, and Dolichopithecus ruscinensis). Other species of Cercopithecoides are consistently recovered as crown colobines, and specifically as stem colobinans, while Paracolobus chemeroni, Kuseracolobus aramisi, and Kuseracolobus hafu are either recovered as stem colobinans or as stem colobines. The Asian Pliocene taxa Parapresbytis eohanuman and Kanagawapithecus leptopostorbitalis are consistently recovered with odd-nosed colobines as crown presbytinans.

Collectively, these results support several inferences of their historical biogeography, evolution of the colobine craniodental morphotype, and ecological evolution. Multiple dispersals into Eurasia are inferred for the colobines, including at least two to three independent lineages in the early Late Miocene and again at the Mio-Pliocene boundary. The facial morphology of several stem colobines inferred to be close to the base of the tree suggests that the ancestral colobine was characterized by a narrow interorbital breadth, elongate rostrum, and superoinferiorly deeper midface, most similar to some primitive-looking cercopithecines and the stem cercopithecoid Victoriapithecus macinnesi. This additionally supports the inference of the ancestral cercopithecoid as more Victoriapithecus-like than colobine- or hylobatid-like (i.e., characterized by a shortened face, large orbits, and globular neurocranium), and also suggests such a short-faced morphotype is independently derived for several other fossil catarrhine groups (e.g., dendropithecids, pliopithecoids, and nyanzapithecines).

Finally, a functional analysis of the forelimb within the context of these updated phylogenetic relationships suggests that stem colobines retained substantial ecological and locomotor flexibility throughout much of the radiation, and that crown colobines are really characterized by a committed shift to arboreality. The ancestral colobine, shortly following the split with cercopithecines, is interpreted here to have retained a substantial proportion of terrestrial locomotion in its behavioral repertoire, with implications for the ecological profile of the ancestral cercopithecoid.

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