Additional mandibles of Rangwapithecus gordoni, an early Miocene catarrhine from the Tinderet localities of Western Kenya

Abstract

Two catarrhine mandibles and five isolated teeth have been discovered from Early Miocene localities in Western Kenya. One mandible comes from the well-known locality of Songhor whereas the other is from a newly discovered locality, Lower Kapurtay, located near Songhor. The mandibles both can clearly be assigned to the species Rangwapithecus gordoni based on molar morphology, which is unique among Early Miocene catarrhines. The isolated specimens can be assigned to Rangwapithecus based on their similarities in morphology to the homologues preserved in the two mandibles. These specimens provide important new information about the dentognathic morphology of Rangwapithecus, which is described in detail. The mandible from Songhor (KNM-SO 22228) represents the first definitive female mandible of Rangwapithecus. The Lower Kapurtay mandible (KNM-KT 31234) appears to be male but is much smaller than another recently described male mandible of this species (KNM-SO 17500) and the type maxilla (KNM-SO 700). These specimens enable a reassessment of the attributions of all other mandibles and isolated lower teeth of Rangwapithecus, and we present a complete hypodigm of the mandibular and lower dental material for the species. Finally, we provide some additions to the diagnosis of Rangwapithecus gordoni based on previously unknown morphology.

Additional hominoid fossils from the early Miocene of the Lothidok Formation, Kenya

“…These cristids occupy positions analogous to those that converge upon a centroconid in Oreopithecus (Hurzeler, 1949; Rook et al, 1996; Schwalbe, 1915). Similar cristids have been described in Rangwapithecus but not given names (Cote et al, 2014; Hill et al, 2013). The presence of these cristids in multiple specimens of Turkanapithecus , along with the necessity of discussing them at some length leads us to introduce a tentative terminology for them, It is possible that these cristids correspond with the distal trigonid ridges identified in hominines (Bailey et al, 2011), but we propose here a set of terms that we think more appropriate for use in hominoids.…”

“…The fourth premolar is a mesiodistally elongate tooth, like those found in other nyanzapithecines (Benefit & McCrossin, 1997;Cote et al, 2014;Harrison, 1986;Hill et al, 2013;Kunimatsu, 1997). The crown is somewhat externally rotated so that the orientation of its long axis is oblique with respect to the M 1 .…”

New Fauna from Loperot Contributes to the Understanding of Early Miocene Catarrhine Communities

“…The primates at Loperot include Rangwapithecus gordoni, previously only known from Songhor ) and the nearby and age-equivalent Lower Kapurtay locality (Cote et al 2014 ). Both sites are within the Kapurtay Agglomerates Formation of the Tinderet Sequence (Pickford and Andrews 1981 ), and all the fauna found at Lower Kapurtay are also known from Songhor (Cote et al 2014 ).…”

“…Loperot shares non-cercopithecoids with the similar-age Hiwegi fauna of Rusinga (Michel et al 2004) and with maybe even older Songhor and Lower Kapurtay (Cote et al 2014 ). The presence of a monkey at Loperot may be the result of geographical differences in the distribution of monkeys, perhaps also suggested by the lack of any monkeys in any sites near Lake Victoria.…”

A systematic revision of Proconsul with the description of a new genus of early Miocene hominoid

“…Ekembo differs from Rangwapithecus in having a broad and expansive palatal fenestration, a wider palate relative to length, a more robust mandible with well-defined superior transverse torus, broader upper and lower incisors relative to height, less buccolingually compressed canines without scimitar-shaped crowns, upper premolars with reduced cingulum and cusps positioned near the mesiodistal midpoint resulting in expanded mesial foveae and symmetric buccal profiles, a broader P 4 relative to M 1 , upper and lower molars that are buccolingually broader relative to length and have more rounded cusps and inflated occlusal crests, more squared upper molars with substantially less cingulum development, and lower molars with a more mesially placed entoconid (Andrews, 1974;Harrison, 2002Harrison, , 2010Cote et al, 2013;Hill et al, 2013).…”