title: 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).
authors.affiliation: Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Barcelona, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Pina
authors.affiliation: Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Barcelona, Spain; Department of Anatomical Sciences, Stony Brook University School of Medicine, Stony Brook, New York, United States of America; NYCEP Morphometrics Group.
authors.forename: Sergio
authors.initials: S
authors.lastname: Almécija
authors.affiliation: Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Barcelona, Spain; Dipartimento di Scienze della Terra, Università degli Studi di Torino, Torino, Italy.
authors.forename: David M
authors.initials: DM
authors.lastname: Alba
authors.affiliation: Department of Anatomical Sciences, Stony Brook University School of Medicine, Stony Brook, New York, United States of America.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: O'Neill
authors.affiliation: ICREA at Institut Català de Paleontologia Miquel Crusafont and Unitat d'Antropologia Biològica (Dept. BABVE), Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Barcelona, Spain.
authors.forename: Salvador
authors.initials: S
authors.lastname: Moyà-Solà
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005260:Female; D005580:Fossils; D015186:Hominidae / Q000033:anatomy & histology*; D008297:Male; D008953:Models, Anatomic; D010329:Patella / Q000033:anatomy & histology*