Wrist morphology reveals substantial locomotor diversity among early catarrhines: an analysis of capitates from the early Miocene of Tinderet (Kenya)

Craig Wuthrich,Laura M Maclatchy,Isaiah O Nengo

doi:10.1038/s41598-019-39800-3

Craig Wuthrich, Laura M Maclatchy + Show 1 more

Open Access

https://doi.org/10.1038/s41598-019-39800-3

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Abstract

Considerable taxonomic diversity has been recognised among early Miocene catarrhines (apes, Old World monkeys, and their extinct relatives). However, locomotor diversity within this group has eluded characterization, bolstering a narrative that nearly all early catarrhines shared a primitive locomotor repertoire resembling that of the well-described arboreal quadruped Ekembo heseloni. Here we describe and analyse seven catarrhine capitates from the Tinderet Miocene sequence of Kenya, dated to ~20 Ma. 3D morphometrics derived from these specimens and a sample of extant and fossil capitates are subjected to a series of multivariate comparisons, with results suggesting a variety of locomotor repertoires were present in this early Miocene setting. One of the fossil specimens is uniquely derived among early and middle Miocene capitates, representing the earliest known instance of great ape-like wrist morphology and supporting the presence of a behaviourally advanced ape at Songhor. We suggest Rangwapithecus as this catarrhine’s identity, and posit expression of derived, ape-like features as a criterion for distinguishing this taxon from Proconsul africanus. We also introduce a procedure for quantitative estimation of locomotor diversity and find the Tinderet sample to equal or exceed large extant catarrhine groups in this metric, demonstrating greater functional diversity among early catarrhines than previously recognised.

Highlights

While catarrhines of the early Miocene are thought to have been taxonomically diverse, the range of locomotor diversity in this group has been more difficult to characterise due to a relative lack of fossil evidence
Functional morphology is assessed with positional classifiers built using linear discriminant function analysis (DFA) and glmnet, an elastic net-regularised multinomial logistic regression machine learning algorithm[47], and by quantitative estimation of locomotor proportions as well as qualitative comparisons
Among species recognised dentally at Mteitei Valley, its size comports with L. evansi and K. songhorensis

Summary

Results and Discussion

Results of this study sort the seven Tinderet capitates into four groups: small- and medium-sized arboreal quadrupeds, a small suspensory form, and a derived, medium-sized morph with great ape affinities. Estimates of arboreal proportions (QuadA and SuspA) align KNM-SO 1001 with Pongo, but total proportions (Quad and Susp) differ only slightly from those of E. heseloni (Table S12) Both specimens are relatively narrow, with low hamate facet concavity and small, radially-oriented centrale facets, features associated with suspension[49]. KNM-SO 1000’s hamate facet is discontinuous (Fig. S6), a trait typical only in brachiators of the extant sample (Ateles and the hylobatids) and otherwise found only in a minority of Pongo and Nasalis (Table S6b) This feature may relate to hypertrophy of the capitohamate interosseous ligament, potentially stabilizing this joint against sudden load transmission gradients experienced during brachiation or other acrobatic arborealism. Specimen KNM-MV 4 KNM-CA 409 KNM-SO 1000 KNM-SO 1001 KNM-SO 31245 KNM-SO 31246 KNM-SO 1002 E. heseloni (means)

QuadA Quad SuspA Susp Plausible identitya

Materials and Methods

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