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

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).

Evolution of the patellar sesamoid bone in mammals

“…In contrast to the situation in humans (as well as in early hominins such as Australopithecus ), in chimpanzees and presumably many other primates (as well as other taxa such as sheep Bertollo, Pelletier & Walsh, 2012, 2013), the patella remains in tight articulation with the femur throughout the knee’s range of motion, reducing patellofemoral stresses especially when the knee is strongly flexed, as it habitually is in those non-human primates (Lovejoy, 2007). Other primates show varying degrees of specialization of patellar morphology that alter the moment arm of the patellar tendon, with great apes apparently having a patella most specialized for widely varying knee joint postures (Pina et al, 2014). It has been claimed that in hominids and ursids (bears) alike, there is an association between plantigrady (flat-footedness), increased knee range of motion and patellar mechanics (Lovejoy, 2007); that is an interesting hypothesis that could be rigorously tested.…”

“…There tends to be an inverse relationship between mechanical advantage and speed of joint motion (Hildebrand, 1998), thus a high mechanical advantage is not necessarily useful in all cases, which may in part explain the variable occurrence, size and shape of the patella in animals with different lifestyles and modes of locomotion. Biomechanical studies of primates (Lovejoy, 2007; Pina et al, 2014) and domesticated mammalian species (e.g. dogs Griffith et al, 2007; Kaiser et al, 2001, sheep Bertollo, Pelletier & Walsh, 2012, 2013, horses Schuurman, Kersten & Weijs, 2003; Wentink, 1978) have contributed some knowledge of how the patella functions in these groups, or in individual species, but a general “functional synthesis” for the patella is still lacking.…”

Knee function through finite element analysis and the role of Miocene hominoids in our understanding of the origin of antipronograde behaviours: the Pierolapithecus catalaunicus patella as a case study

“…; Pina et al . ). Moreover, the wrist displays an important synapomorphy among hominids: the lack of contact between the ulna and the triquetrum, which has been associated with vertical climbing behaviours (Moyà‐Solà et al .…”

“…; Pina et al . ). Therefore, Pierolapithecus would most likely have displayed some degree of any modern ape‐like behaviour, such as vertical climbing (Moyà‐Solà et al .…”

“…In this regard, the only complete non‐pedal hind limb element preserved for Pierolapithecus is a left patella (Pina et al . , fig. 1).…”