The Middle Miocene Ape Pierolapithecus catalaunicus Exhibits Extant Great Ape-Like Morphometric Affinities on Its Patella: Inferences on Knee Function and Evolution

Marta Pina,David M Alba,Salvador Moyà-Solà,Matthew C O'Neill,Sergio Almécija,Lorenzo Rook

doi:10.1371/journal.pone.0091944

Abstract

The mosaic nature of the Miocene ape postcranium hinders the reconstruction of the positional behavior and locomotion of these taxa based on isolated elements only. The fossil great ape Pierolapithecus catalaunicus (IPS 21350 skeleton; 11.9 Ma) exhibits a relatively wide and shallow thorax with moderate hand length and phalangeal curvature, dorsally-oriented metacarpophalangeal joints, and loss of ulnocarpal articulation. This evidence reveals enhanced orthograde postures without modern ape-like below-branch suspensory adaptations. Therefore, it has been proposed that natural selection enhanced vertical climbing (and not suspension per se) in Pierolapithecus catalaunicus. Although limb long bones are not available for this species, its patella (IPS 21350.37) can potentially provide insights into its knee function and thus on the complexity of its total morphological pattern. Here we provide a detailed description and morphometric analyses of IPS 21350.37, which are based on four external dimensions intended to capture the overall patellar shape. Our results reveal that the patella of Pierolapithecus is similar to that of extant great apes: proximodistally short, mediolaterally broad and anteroposteriorly thin. Previous biomechanical studies of the anthropoid knee based on the same measurements proposed that the modern great ape patella reflects a mobile knee joint while the long, narrow and thick patella of platyrrhine and especially cercopithecoid monkeys would increase the quadriceps moment arm in knee extension during walking, galloping, climbing and leaping. The patella of Pierolapithecus differs not only from that of monkeys and hylobatids, but also from that of basal hominoids (e.g., Proconsul and Nacholapithecus), which display slightly thinner patellae than extant great apes (the previously-inferred plesiomorphic hominoid condition). If patellar shape in Pierolapithecus is related to modern great ape-like knee function, our results suggest that increased knee mobility might have originally evolved in relation to enhanced climbing capabilities in great apes (such as specialized vertical climbing).

Highlights

The partial hominoid skeleton IPS 21350 from the locality of Barranc de Can Vila 1 [1,2,3,4,5,6,7,8], situated in the local stratigraphic series of Abocador de Can Mata (ACM/BCV1; els Hostalets de Pierola, Valles-Penedes Basin, NE Iberian Peninsula), constitutes the holotype of Pierolapithecus catalaunicus
The combination of an orthograde body plan and the loss of ulnocarpal articulation with no specific below-branch adaptations suggests that vertical climbing—and not suspension per se—might have been the primary target of natural selection in Pierolapithecus, since it is the only other common behavior to the hominoid crown group [1,2]
Hind limb long bones of Pierolapithecus are not preserved, the morphology of its preserved patella (IPS 21350.37) can potentially provide hints of its knee function, as previous studies have shown for other Miocene taxa [18]

Summary

Introduction

The partial hominoid skeleton IPS 21350 from the locality of Barranc de Can Vila 1 [1,2,3,4,5,6,7,8], situated in the local stratigraphic series of Abocador de Can Mata (ACM/BCV1; els Hostalets de Pierola, Valles-Penedes Basin, NE Iberian Peninsula), constitutes the holotype (and so far only known individual) of Pierolapithecus catalaunicus. The hand displays only a moderate length and phalangeal curvature ([2,4,13] but see [14,15] for a different interpretation), the metacarpophalangeal joints are dorsally oriented, and the pollical distal phalanx is long and wide at the base relative to the distal phalanges of the lateral rays [4,16]. These features indicate that Pierolapithecus—as in other Miocene apes—relied significantly on above-branch palmigrady with a thumb-assisted grasping during arboreal locomotion [12,17]. The aim of this study is to shed light on the patellar morphology and inferred knee function of Pierolapithecus catalaunicus

Objectives

Methods

Results

Conclusion