Different views of the patella of Pierolapithecus catalaunicus
Pierolapithecus catalaunicus (popularly known as Pau) exhibited a wide range of movements at the knee joint, similar to those observed in extant chimpanzees, gorillas and orangutans. This finding reinforces the hypothesis that this hominid showed orthograde (upright trunk) locomotor behaviors, suitable for climbing up the trees efficiently. The research, led by the predoctoral ICP fellow Marta Pina, has been published today in the PLOS ONE journal.
Positional behavior and locomotion of the Miocene apes has always been a controversial subject. In the case of Pierolapithecus, pelvic structure is rather primitive, similar to that shown by Proconsul (an older African hominoid). This, along with the morphology of the phalanges, indicates that Pierolapithecus catalaunicus could walk over the branches on all fours, without below-branch suspension. However, other features of its anatomy, such as the structure of the thorax or the morphology of the wrist, suggest that it could adopt orhograde postural and locomotor behaviors (with the upright trunk).
Reconstruction of Pierolapithecus catalaunicus at the ICP Museum
In the article published today in PLOS ONE, Marta Pina, a predoctoral researcher at the Paleoprimatology and Human Paleontology Group of the Institut Català de Paleontologia Miquel Crusafont (ICP), in collaboration with other researchers of the center and of the Stony Brook University (New York), provides a detailed description and morphometric analyses of the patella, the only complete bone from the hind limbs among the more than 80 skeletal remains preserved of the fossil hominid Pierolapithecus catalaunicus. Due to the lack of other complete remains of the hind limbs, this knee bone becomes a very interesting remain to deduce locomotor repertoires.
In this study, the researchers analyzed the patella of several species of extant anthropoids and available fossil hominoids and found that the patella of Pierolapithecus is essentially similar to that of great apes (orangutans, gorillas and chimpanzees). It is rather broad and thin compared to that of cercopithecoids (the Old World monkeys, such as baboons and macaques), which is usually narrower and thicker. In the case of great apes, previous biomechanical studies have associated the patellar shape with increased knee mobility, a feature suitable to climb trees vertically. By contrast, in extant cercopithecoids, joint mobility is lesser and restricted to a single plane, which gives them greater stability when walking on the branches and running on all fours.
Orangutan feeding on a tree (Derek Keats, distributed under CC BY 2.0. license. http://farm1.staticflickr.com/100/290811997_d519598d37_o.jpg)
Although orangutans, gorillas and chimpanzees differ in type of locomotion (gorillas and chimpanzees are characterized by the practice of knuckle-walking, while orangutans are more arboreal, and mostly rely on below-branch suspension and clambering for traveling horizontally), they all share the ability to perform vertical climbing (upright trunk progression on tree trunks employing hind limb propulsion and hands and feet grasping). "We believe that Pierolapithecus would have also been able to climb vertically frequently. In fact, previous studies published from other parts of the postcranial skeleton corroborate these adaptations", says Marta Pina.
Pierolapithecus, the oldest orthograde hominid
Pierolapithecus catalaunicus was found in the Abocador de Can Mata (Hostalets of Pierola, Anoia, Catalonia) in 2002. With an age of 12 million years, is the oldest extinct member showing unequivocally orthograde behaviors among the great-ape-and-human clade (i.e., the Hominidae). More than 80 fossil remains were found corresponding to a single individual, popularly dubbed as Pau.
A. Reconstruction of Pierolapithecus, by Meike Köhler. B. Reconstruction of Anoiapithecus, by Marta Palmero. C. Reconstruction of Hispanopithecus, by Ramon López. Quagga.
Pierolapithecus, along with other hominoid species from the Vallès-Penedès basin, such as Hispanopithecus laietanus, Dryopithecus fontani and Anoiapithecus brevirostris, represent a unique set of taxa that provides valuable information on the evolution of apes and humans, as they combine simultaneously primitive and derived characters.
