Oreopithecus

Oreopithecus Temporal range: Miocene
Oreopithecus bambolii fossil
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Primates
Superfamily:	Hominoidea
Family:	†Oreopithecidae?
Genus:	†Oreopithecus
Species:	†O. bambolii
Binomial name
†Oreopithecus bambolii Gervais, 1872

Oreopithecus is an extinct primate from the Miocene epoch whose fossils have been found in today's Tuscany and Sardinia in Italy. Oreopithecus existed 9 to 7 million years ago in the Tusco-Sardinian area when this territory was an isolated island in an arc of islands stretching from central Europe to northern Africa.^{[explain 1]} It was one of a large number of European immigrants that settled this area in the Vallesian-Turolian transition and one of few hominoids to survive the so called Vallesian Crisis together with Sivapithecus in Asia. ^[1] To date, dozens of individuals have been discovered at the Tuscan localities of Montebamboli, Montemassi, Casteani, Ribolla, and, most notably, in the fossil-rich lignite mine in the Baccinello Basin,^[1] making it one of the best-represented fossil apes.

Etymology

The scientific name Oreopithecus quickly inspired the commonly used though unofficial name for the species among paleontologists, Cookie Monster. The true etymology, however, is rather more mundane: it comes from the Greek ὄρος, oros and πίθηκος, pithekos, meaning "hill-ape".

Evolutionary history

Oreopithecus bambolii was first described by French paleontologist Paul Gervais in 1872. In the 1950s, Swiss paleontologist Johannes Hürzeler discovered a complete skeleton in Baccinello and claimed it was a true hominid — based on its short jaws and reduced canines, at the time considered diagnostic of the hominid family — and a biped — since the short pelvis was closer to those of hominids than those of chimpanzees and gorillas. However, Oreopithecus′ hominid affinities remained controversial for decades until new analyses in the 1990s reasserted Oreopithecus as directly related to Dryopithecus; the peculiar cranial and dental features explained as consequences of insular isolation. These new evidences confirmed that Oreopithecus was bipedal but also revealed that its peculiar form of bipedalism was much different from that of Australopithecus′ — the hallux formed a 100° angle with the other toes enabling the foot to act as a tripod in erect postures — and could not enable Oreopithecus to develop a fast bipedal locomotion. When a land bridge finally broke the isolation of the Tusco-Sardinian area 6.5 million years ago, truly large predators such as Machairodus and Metailurus were present among the new generation of European immigrants and Oreopithecus faced quick extinction together with other endemic genera. ^{[1] [explain 2]}

Taxonomic classification

Known as the "enigmatic hominoid", Oreopithecus can dramatically rewrite the palaeontological map depending on if it is a descendant from the European ape Dryopithecus or some African anthropoid. ^[1] Some have suggested the unique locomotory behavior of Oreopithecus requires a revision of the current consensus on the timing of bipedality in human developmental history, but there is limited agreement on this point among paleontologists.

Some researchers have related Oreopithecus to the early Oligocene Apidium, a small arboreal proto-ape that lived nearly 34 million years ago in Egypt. ^[2] It shows strong links to modern apes in its postcranium and, in this respect, it is the most modern Miocene ape below the neck with closest similarities to the postcranial elements of Dryopithecus, but its dentition is adapted to a leafy diet and a close link is uncertain. Others claim it to be either the sister taxon to Cercopithecoidea or a even direct human ancestor, but it is usually placed in its own subfamily within Hominidae. It could instead be added to the same subfamily as Dryopithecus, perhaps as a distinct tribe (Oreopithecinae). ^[3]

Physical characteristics

Oreopithecus bambolii is estimated to have weighed 30–35 kg (66–77 lb). It possessed a relatively short snout, elevated nasal bones, small and globular neurocranium, vertical orbital plane, and gracile facial bones. The shearing crests on its molars suggest a diet specializing in plant leaves. The very robust lower face, with a large attachment surface for the masseter muscle and a sagittal crest for attachment of the temporal muscle, indicates a heavy masticatory apparatus. Its teeth were small relative to body size. The lack of a diastema (gap) between the second incisor and first premolar of the mandible indicates that Oreopithecus had canines of size comparable to the rest of its dentition. In many primates, small canines correlate with reduced inter-male competition for access to mates and less sexual dimorphism.

Positional behavior

Its habitat appears to have been swampy, and not savanna or forest. The postcranial anatomy of Oreopithecus features adaptations to both suspensory arborealism and bipedalism. Functional traits related to suspensory locomotion include its broad thorax, short trunk, high intermembral index, long and slender digits, and extensive mobility in virtually all joints. At the same time, it also features adaptations to upright walking such as the presence of a lumbar curve, in distinction to otherwise similar species known from the same period. Since the fossils have been dated to about 8 million years ago, this represents an unusually early appearance of upright posture. How adapted it was for bipedal walking is not known, but its fingers and arms also seems to show adaptations for climbing and swinging.

Morphological and functional studies indicate a significant part of Oreopithecus positional behavior was bipedal. Its foot has been described as chimp-like, but is different from those of extant primates. The habitual line of leverage of the primate foot is parallel to the third metatarsal bone. In Oreopithecus, the lateral metatarsals are permanently abducted so that this line falls between the first and second metatarsals instead. Furthermore, the shape of the tarsus indicate loads on the foot were transmitted to the medial side of the foot instead of the lateral, like in other primates. The metatarsals are short and straight, but their lateral orientation increased the area of support during bipedal standing and walking. ^[4]

The lack of predators and the limitation of space and resources in Oreopithecus′ insular environment favored a locomotor system optimized for low energy expenditure rather than speed and mobility. Its peculiar feet and short legs were optimized for stable postural harvesting and bipedal shuffling rather than walking or running. The postcranial anatomy of Oreopithecus is therefore considered autapomorphic rather than synapomorphic.^{[explain 3]} Its foot proportions are close to the unusual proportions of Gorilla and Homo but are distinct from those found in specialized climbers. It is not comparable to Gorilla due to low body mass but is similar to Homo; it is not our ancestor but a key species for understanding human bipedality. ^[4]

Semicircular canals

The semicircular canals of the inner ear serves as a sense organ for balance and controls the reflex for gaze stabilization. The inner ear has three canals on each side of the head, and each of the six canals encloses a membranous duct that forms an endolymph-filled circuit. Hair cells in the duct’s auditory ampulla pick up endolymph disturbances caused by movement, which register as rotatory head movement. They respond to body sway of frequencies greater than 0.1 Hz and trigger the vestibulocollic (neck) reflex and vestibuloocular (eye) reflex to recover balance and gaze stability. The bony semicircular canals allow estimates of duct arc length and orientation with respect to the sagittal plane.

During upright walking, human head rotation frequencies range between 2–8 Hz along the sagittal and coronal planes and between 1–3 Hz along the horizontal plane. Across species, the semicircular canals of agile animals have larger arcs than those of slower ones. For example, the rapid leaper Tarsius bancanus has semicircular canals much bigger than the slow-climbing Nycticebus coucang. The semicircular canals of brachiating gibbons are bigger than those of arboreal and terrestrial quadrupedal great apes. As a rule of thumb, arc size of the ducts decreases with body mass and consequently slower angular head motions. Arc size increases with greater agility and thus more rapid head motions. Modern humans have bigger arcs on their anterior and posterior canals, which reflect greater angular motion along the sagittal plane. The lateral canal has a smaller arc size, corresponding to reduced head movement from side to side. ^[5]

Allometric measurements on the bony labyrinth of BAC-208, a fragmentary cranium that preserves a complete, undeformed petrosal bone suggest that Oreopithecus moved with agility comparable to extant great apes. Its anterior and lateral semicircular canal sizes fall within the range for great apes. ^[6] Its relatively large posterior arc implies that Oreopithecus was more proficient at stabilizing angular head motion along the sagittal plane.

Dexterity

Oreopithecus had hominid-like hand proportions that allowed a firm, pad-to-pad precision grip. Features not present in the hands of extant or fossil apes include hand length, relative thumb length, a deep and large insertion for the flexor pollicis longus, and the shape of the carpometacarpal joint between the metacarpal bone of the index finger and the capitate bone. ^[7] At the base of the second metacarpal bone, the facet for the capitate is oriented transversally, like in hominids. The capitate, on the other hand, lacks the waisting associated with apes and climbing, and still present in Australopithecus. Oreopithecus share the specialised orientation at the carpometacarpal joint with A. afarenis and the marked groove for the flexor pollicis longus with A. africanus. It is thus likely that the hand morphology of Oreopithecus is derived for apes and convergent for early hominids. ^[7]

See also

Paleontology portal

• List of fossil sites
• List of hominina (hominid) fossils

Explanations

1. ^ In what remained of the Tethys Sea or what was becoming the Mediterranean Sea; see also Geology and paleoclimatology of the Mediterranean Basin and Messinian salinity crisis
2. ^ A parallel to the Great American Interchange two million years later
3. ^ An autapomorphy is a derived trait unique to a terminal group; a synapomorphy is a derived trait shared by several taxa

Notes

1. ^ ^{a b c d} Agustí & Antón 2002, pp. Prefix ix, 174–5, 193, 197–9
2. ^ Simons 1960
3. ^ Delson, Tattersall & Van Couvering 2000, p. 465
4. ^ ^{a b} Köhler & Moyà-Solà 1997
5. ^ Spoor 2003, pp. 96–7
6. ^ Rook et al. 2004, p. 355
7. ^ ^{a b} Moyà-Solà, Köhler & Rook 1999

References

• Agustí, Jordi; Antón, Mauricio (2002). Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution in Europe. New York: Columbia University Press. ISBN 0-231-11640-3. 
• Carnieri, E. and F. Mallegni (2003). "A new specimen and dental microwear in Oreopithecus bambolii". Homo 54 (1): 29–35. doi:10.1078/0018-442X-00056. PMID 12968421. 
• Delson, Eric; Tattersall, Ian; Van Couvering, John A. (2000). "Dryopithecinae". Encyclopedia of human evolution and prehistory. Taylor & Francis. pp. 464–6. ISBN 9780815316961. http://books.google.com/books?id=E8z9YZZiKHgC&pg=PA465&dq=oreopithecus. 
• Harrison, Terry (1990). "The implications of Oreopithecus for the origins of bipedalism". In Coppens, Y; Senut, B. Origine(s) de la Bipédie chez les Hominidés. Paris: Museum National d’Histoire Naturelle. http://www.nyu.edu/gsas/dept/anthro/programs/csho/Content/Facultycvandinfo/Harrison/1991%20Harrison_Oreopithecus.pdf. 
• Köhler, Meike; Moyà-Solà, Salvador (October 14 1997). Ape-like or hominid-like? "The positional behavior of Oreopithecus bambolii reconsidered". PNAS 94 (21): 11747–11750. doi:10.1073/pnas.94.21.11747. PMC 23630. PMID 9326682. http://www.pnas.org/cgi/content/full/94/21/11747 Ape-like or hominid-like?. 
• Moyà-Solà, Salvador; Köhler, Meike; Rook, Lorenzo (January 5 1999). "Evidence of hominid-like precision grip capability in the hand of the Miocene ape Oreopithecus". PNAS 96 (1): 313–317. doi:10.1073/pnas.96.1.313. PMC 15136. PMID 9874815. http://www.pnas.org/content/96/1/313.full.pdf. 
• Rook, Lorenzo; Bondioli, Luca; Casali, Franco; Rossi, Massimo; Köhler, Meike; Moyá Solád, Salvador; Macchiarelli, Roberto (2004). "The bony labyrinth of Oreopithecus bambolii". Journal of Human Evolution 46 (3): 347–354. doi:10.1016/j.jhevol.2004.01.001. PMID 14984788. http://xraytomography.giuseppelevi.it/shared/oreopiteco.pdf. 
• Rook, Lorenzo; Bondioli, Luca; Köhler, Meike; Moyà-Solà, Salvador; Macchiarelli, Roberto (July 20 1999). "Oreopithecus was a bipedal ape after all: Evidence from the iliac cancellous architecture". PNAS 96 (15): 8795–8799. doi:10.1073/pnas.96.15.8795. PMC 17596. PMID 10411955. http://www.pnas.org/content/96/15/8795.full.pdf. 
• Rook, L.; Harrison, T.; Engesser, B. (1996). "The taxonomic status and biochronological implications of new finds of Oreopithecus from Baccinello (Tuscany, Italy)". Journal of Human Evolution (30): 3–27. http://www.nyu.edu/gsas/dept/anthro/programs/csho/Content/Facultycvandinfo/Harrison/1996_Rook_et_al.pdf. 
• Simons, Elwyn L. (June 4 1960). "Apidium and Oreopithecus". Nature 186 (186): 824–826. doi:10.1038/186824a0. 
• Spoor, Fred (2003). "The semicircular canal system and locomotor behavior, with special reference to hominin evolution". In Franzen, Jens Lorenz; Köhler, Meike; Moyà-Solà, Salvador. Walking Upright: Results of the 13th International Senckenberg Conference at the Werner Reimers Foundation. E. Schweitzerbart'sche Verlagsbuchhandlung. ISBN 3510613570. http://www.eva.mpg.de/evolution/staff/spoor/pdf/Spoor_CFI03_canals-locomotion.pdf. 

External links

Media related to Oreopithecus at Wikimedia Commons

• Fitzpatrick-Matthews, Keith. "A child’s jaw in coal?". Bad Archaeology. http://www.badarchaeology.net/data/ooparts/child_jaw.php. Retrieved November 2010.  — A photo of an Oreopithecus bamboli jaw
• "†Oreopithecidae". Mikko's Phylogeny Archive. http://www.fmnh.helsinki.fi/users/haaramo/metazoa/Deuterostoma/Chordata/Synapsida/Eutheria/Primates/Parapithecoidea/Oreopithecidae.htm. Retrieved November 2010.