Primitive Old World monkey from the earliest Miocene of Kenya and the evolution of cercopithecoid bilophodonty

Abstract

Old World monkeys (Cercopithecoidea) are a highly successful primate radiation, with more than 130 living species and the broadest geographic range of any extant group except humans. Although cercopithecoids are highly variable in habitat use, social behavior, and diet, a signature dental feature unites all of its extant members: bilophodonty (bi: two, loph: crest, dont: tooth), or the presence of two cross-lophs on the molars. This feature offers an adaptable Bauplan that, with small changes to its individual components, permits its members to process vastly different kinds of food. Old World monkeys diverged from apes perhaps 30 million years ago (Ma) according to molecular estimates, and the molar lophs are sometimes incompletely developed in fossil species, suggesting a mosaic origin for this key adaptation. However, critical aspects of the group’s earliest evolution remain unknown because the cercopithecoid fossil record before ∼18 Ma consists of only two isolated teeth, one from Uganda and one from Tanzania. Here we describe a primitive Old World monkey from Nakwai, Kenya, dated at ∼22 Ma, that offers direct evidence for the initial key steps in the evolution of the cercopithecoid dentition. The simple dentition and absence of bilophodonty in the Nakwai monkey indicate that the initial radiation of Old World monkeys was first characterized by a reorganization of basic molar morphology, and a reliance on cusps rather than lophs suggests frugivorous diets and perhaps hard object feeding. Bilophodonty evolved later, likely in response to the inclusion of leaves in the diet.

Widespread loss of mammalian lineage and dietary diversity in the early Oligocene of Afro-Arabia

“…Phylogenetics. The composite near-comprehensive tree of Afro-Arabian primates, anomaluroid rodents, and hystricognathous rodents combines information from multiple BTD analyses of character matrices published by Gunnell et al 22 , Rasmussen et al 60 , Dembo et al 61 , DeSilva et al 62 , Sallam and Seiffert 25 , and Marivaux et al 16 . The tree is supplemented by molecular phylogenies of extant taxa 59,63 , and grafting of several extinct taxa that were not included in any of the aforementioned phylogenetic character matrices.…”

Total evidence tip-dating phylogeny of platyrrhine primates and 27 well-justified fossil calibrations for primate divergences

“…Additional CladeAge calibration Another fossil species from Nsungwe 2B is Nsungwepithecus gunnelli, currently known from a single specimen (RRBP 11178), a left partial mandible with a lower m3 (Stevens et al, 2013). Nsungwepithecus was not included in the phylogenetic analyses by Stevens et al (2013), but they report the presence of numerous lower molar synapomorphies that are shared with "victoriapithecid" cercopithecoids ("Victoriapithecidae" is a paraphyletic assemblage of stem cercopithecoids in the phylogenetic analyses of Stevens et al (2013) and Rasmussen et al (2019)), such as deeply incised buccal clefts, a high degree of buccal flare, and the lack of a buccal cingulid. Rasmussen et al (2019) confirmed the stem cercopithecoid position of Nsungwepithecus in their phylogenetic analysis, but they argued that the phylogenetic position of Nsungwepithecus should be regarded as tentative until more material is available.…”

“…By contrast, even in the most recent morphological datasets for primate phylogenetics (at least, those focused on higher level relationships, e.g., between families), extant taxa are typically scored at the genus level, or only a single species-level representative of each genus is included (e.g. Rasmussen et al, 2019;Gilbert et al, 2020;Seiffert et al, 2020).…”

“…Jameson et al, 2011;dos Reis et al, 2018;Vanderpool et al, 2020), while primate morphological datasets typically comprise a few hundred characters (e.g. Rasmussen et al, 2019;Gilbert et al, 2020;Seiffert et al, 2020), and so combining such datasets will mean that fossil taxa (without molecular data) might end up with >99.99% missing data. The impact of such large amounts of missing data on phylogenetic inference is not fully understood, and may not be as severe as might be expected (Wiens et al, 2005;Guillerme and Cooper, 2016b), but nevertheless can still negatively affect accurate inference of topology, support values, and (crucially for the estimation of divergence times) branch lengths (Lemmon et al, 2009;Simmons, 2012Simmons, , 2014Xia, 2014).…”

Patterns and magnitudes of craniofacial covariation in extant cercopithecids

“…Cercopithecid primates evolved in Africa approximately 23 million years ago (MA; Figure 1; Frost, 2017). Although the earliest cercopithecid fossil remains are all isolated teeth dated to ~20 MA (Rasmussen et al, 2019), molecular evidence dates the divergence of Cercopithecinae and Colobinae to approximately 18 MA, after which both clades quickly diversified and expanded out of Africa and across Europe and Asia (Frost, 2017). In addition to being the most speciose primate family, and sister taxon to apes (Hominoidea), the genetics and developmental biology of cercopithecids have been well-studied in biomedical literature (VandeBerg, Williams-Blangero, & Tardif, 2009).…”