| Oreopithecus Temporal range: 9–7 Million years ago | |
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| Oreopithecus bambolii fossil | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Suborder: | Haplorhini |
| Infraorder: | Simiiformes |
| Superfamily: | Hominoidea |
| Genus: | †Oreopithecus Gervais, 1872 |
| Type species | |
| Oreopithecus bambolii Gervais, 1872 | |
Oreopithecus (from the Greekὄρος,oros andπίθηκος,pithekos, meaning "hill-ape") is anextinct genus ofape from theMiocene epoch whosefossils have been found in today'sTuscany andSardinia inItaly.[1] It existed 9–7 million years ago in the Tusco-Sardinian area when this region was an isolated island in a chain of islands stretching fromcentral Europe tonorthern Africa in what was becoming theMediterranean Sea.[a]
Oreopithecus was one of many European immigrants that settled this area in theVallesian–Turolian transition and one of few hominoids, together withSivapithecus in Asia, to survive the so-calledVallesian Crisis.[2] To date, dozens of individuals have been discovered at theTuscan localities ofMontebamboli,Montemassi, Casteani,Ribolla, and, most notably, in the fossil-rich lignite mine in theBaccinello Basin,[2] making it one of the best-represented fossilapes.
Oreopithecus bambolii was first described by French paleontologistPaul Gervais in 1872,[3][4] after the discovery of a juvenile mandible in a lignite mine at Montebamboli in 1862 by Tito Nardi, who donate the specimen to ProfessorIgino Cocchi.[5] In 1890, nearly a dozen new specimens were reported by Guiseppe Ristori, among them an upper jaw.[6] In 1898, a left lower jaw was described by Felice Ottolenghi.[7] In 1907, Giuseppe Merciai reported four maxillae and a lower jaw from the Grosseto mine at Ribolla.[8] During this period there was no consensus whetherOreopithecus was a monkey or an ape.[9]
From 1949 onwards, Swiss paleontologistJohannes Hürzeler began to restudy the known material.[10][11] In 1954, 1955, 1956, and 1958, he claimedOreopithecus were a true hominin—based on its premolars, short jaws and reducedcanines, at the time considered diagnostic of the hominin family.[12][13][14] This hypothesis immediately became a hotly discussed topic among his fellow paleontolgists.[15][16][17][18][19] When he toured the world to give a series of lectures, his views generated an enormous press coverage, often being presented as a challenge to the Darwinian descent of man from apes.[20] After Hürzeler was invited to give a lecture inNew York in March 1956, theWenner-Gren Foundation decided to finance excavations in Italy, with the cooperation of the Italian paleontologistAlberto Carlo Blanc. On 2 August 1958, Hürzeler's views seemed to be confirmed when he discovered a complete skeleton inBaccinello,[21] which in 1960 he interpreted as abiped because of the shortpelvis was closer to those of hominins than those ofchimpanzees andgorillas.[22] Hominin affinities claimed forOreopithecus remained controversial for decades until new analyses in the 1990s reasserted thatOreopithecus was directly related toDryopithecus. The peculiar cranial and dental features were explained as consequences ofinsular isolation.
This new evidence confirmed thatOreopithecus was bipedal but also revealed that its peculiar form of bipedalism was much different from that ofAustralopithecus. Thehallux formed a 100° angle with the other toes, which enabled the foot to act as a tripod in erect posture, but preventedOreopithecus from developing a fast bipedal stride. When a land bridge broke the isolation of the Tusco-Sardinian area6.5 million years ago, large predators such asMachairodus andMetailurus were present among the new generation of European immigrants andOreopithecus faced quick extinction together with other endemic genera.[2][b]
Known as the "enigmatichominoid",Oreopithecus can dramatically rewrite the palaeontological map depending on whether it is a descendant of the European apeDryopithecus or an Africananthropoid.[2] Some have suggested the unique locomotory behavior ofOreopithecus requires a revision of the current consensus on the timing of bipedality in human developmental history, but there is limited agreement on this point amongpaleontologists.
Simons (1960) consideredOreopithecus closely related to the early OligoceneApidium, a small arboreal anthropoid that lived nearly 34 million years ago in Egypt.[23]Oreopithecus shows strong links to modern apes in itspostcranium and, in this respect, it is the most modern Miocene ape below the neck, with closest similarities to the postcranial elements ofDryopithecus, but its dentition is adapted to a leafy diet and a close link is uncertain. Others claim it to be either the sister taxon toCercopithecoidea or an even direct human ancestor, but it is usually placed in its own subfamily withinHominidae. It could instead be added to the same subfamily asDryopithecus, perhaps as a distinct tribe (Oreopithecini).[24] A cladistic analysis ofNyanzapithecus alesi recoversOreopithecus as a member of the proconsulid subfamilyNyanzapithecinae.[25] A 2023 phylogenetic analysis suggested found a close relationship withgibbons, though the author suggested that this was likely due to having a similar climbing lifestyle and retained plesiomorphies, rather than a real close relationship, but suggested that it was unlikely thatOreopithecus was a member of Hominidae.[26]
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Oreopithecus bambolii is estimated to have weighed 30–35 kg (66–77 lb). It possessed a relatively short snout, elevated nasal bones, small and globularneurocranium, verticalorbital plane, andgracile facial bones. The shearing crests on itsmolars suggest a diet specializing in plant leaves. The very robust lower face, with a large attachment surface for themasseter muscle and asagittal crest for attachment of thetemporal muscle, indicates a heavymasticatory apparatus.
Its teeth were small relative to body size. The lack of a diastema (gap) between the secondincisor and firstpremolar of themandible indicates thatOreopithecus hadcanines 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 lesssexual dimorphism.
Its habitat appears to have beenswampy, and notsavanna orforest. The postcranial anatomy ofOreopithecus features adaptations for suspensory arborealism. Functional traits related to suspensory locomotion include its broad thorax, short trunk, highintermembral index, long and slender digits, and extensive mobility in virtually all joints. Its fingers and arms seem to show adaptations for climbing and swinging.
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 thirdmetatarsal bone. InOreopithecus, thelateral metatarsals are permanentlyabducted so that this line falls between the first and second metatarsals instead. Furthermore, the shape of thetarsus indicate loads on the foot were transmitted to the medial side of the foot instead of the lateral, like in other primates.[27] The metatarsals are short and straight, but have a lateral orientation increase. Its foot proportions are close to the unusual proportions ofGorilla andHomo but are distinct from those found in specialized climbers. The lack of predators and the limitation of space and resources inOreopithecus' insular environment favored a locomotor system optimized for low energy expenditure rather than speed and mobility.[27]
Oreopithecus has been claimed to exhibit features that are adaptations to upright walking, such as the presence of alumbar curve, in distinction to otherwise similar species known from the same period. Since the fossils have been dated to about 8million years ago, this would represent an unusually early appearance of upright posture.[27] However, a reevaluation of the spine from a skeleton ofOreopithecus has led to the conclusion that it lacked adaptations for habitualbipedality.[28][29]
Thesemicircular 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 anendolymph-filled circuit. Hair cells in the duct'sauditory 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.
Across species, the semicircular canals of agile animals have larger arcs than those of slower ones. For example, the rapid leaperTarsius bancanus has semicircular canals much bigger than the slow-climbingNycticebus coucang. The semicircular canals of brachiatinggibbons are bigger than those of arboreal and terrestrial quadrupedalgreat apes. As a rule of thumb, arc size of the ductsdecreases with body mass and consequently slower angular head motions. Arc sizeincreases with greater agility and thus more rapid head motions. Modernhumans 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.[30]
Allometric measurements on thebony labyrinth of BAC-208, a fragmentary cranium that preserves a complete, undeformedpetrosal bone suggest thatOreopithecus moved with agility comparable to extantgreat apes. Its anterior and lateral semicircular canal sizes fall within the range for great apes.[31]Its relatively large posterior arc implies thatOreopithecus was more proficient at stabilizing angular head motion along the sagittal plane.
Oreopithecus had hominin-like hand proportions that allowed a firm, pad-to-pad precision grip. Features present in the hands of neither non-human-extant nor fossil apes include hand length, relative thumb length, a deep and large insertion for theflexor pollicis longus, and the shape of thecarpometacarpal joint between themetacarpal bone of the index finger and thecapitate bone.[32]At the base of thesecond metacarpal bone, the facet for thecapitate is oriented transversally, as in hominins. The capitate, on the other hand, lacks the waisting associated with apes and climbing, and still present inAustralopithecus.Oreopithecus share the specialised orientation at the carpometacarpal joint withA. afarenis and the marked groove for the flexor pollicis longus withA. africanus. It is thus likely that the hand morphology ofOreopithecus isderived for apes andconvergent for early hominins.[32]
Media related toOreopithecus at Wikimedia Commons
