Oreopithecus bambolii
Encyclopedia
Oreopithecus is an extinct
primate
from the Miocene
epoch whose fossil
s have been found in today's Tuscany
and Sardinia
in Italy
. Oreopithecus existed in the Tusco-Sardinian area when this territory was an isolated island in an arc of islands
stretching from central Europe to northern Africa.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
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.
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, making it one of the best-represented fossil ape
s.
. The true etymology, however, is rather more mundane: it comes from the Greek ὄρος, oros and πίθηκος, pithekos, meaning "hill-ape".
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 , 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.
A parallel to the Great American Interchange
two million years later
or some African anthropoid.
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.
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).
, 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
.
y, and not savanna
or forest
. The postcranial anatomy of Oreopithecus features adaptations to both suspensory arborealism and biped
alism. 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.
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
.An autapomorphy
is a derived trait unique to a terminal group; a synapomorphy
is a derived trait shared by several taxa
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.
-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 gibbon
s 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 human
s 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.
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.
Its relatively large posterior arc implies that Oreopithecus was more proficient at stabilizing angular head motion along the sagittal plane.
, and the shape of the carpometacarpal joint
between the metacarpal bone of the index finger and the capitate bone.
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.
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
from the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
epoch whose fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been found in today's Tuscany
Tuscany
Tuscany is a region in Italy. It has an area of about 23,000 square kilometres and a population of about 3.75 million inhabitants. The regional capital is Florence ....
and Sardinia
Sardinia
Sardinia is the second-largest island in the Mediterranean Sea . It is an autonomous region of Italy, and the nearest land masses are the French island of Corsica, the Italian Peninsula, Sicily, Tunisia and the Spanish Balearic Islands.The name Sardinia is from the pre-Roman noun *sard[],...
in Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
. Oreopithecus existed in the Tusco-Sardinian area when this territory was an isolated island in an arc of islands
Island arc
An island arc is a type of archipelago composed of a chain of volcanoes which alignment is arc-shaped, and which are situated parallel and close to a boundary between two converging tectonic plates....
stretching from central Europe to northern Africa.In what remained of the Tethys Sea or what was becoming the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
; see also Geology and paleoclimatology of the Mediterranean Basin and Messinian salinity crisis
Messinian salinity crisis
The Messinian Salinity Crisis, also referred to as the Messinian Event, and in its latest stage as the Lago Mare event, was a geological event during which the Mediterranean Sea went into a cycle of partly or nearly complete desiccation throughout the latter part of the Messinian age of the Miocene...
It was one of a large number of European immigrants that settled this area in the Vallesian
Vallesian
The Vallesian age is a period of geologic time within the Miocene used more specifically with European Land Mammal Ages. It precedes the Turolian age and follows the Astaracian age. The Turolian overlaps the Tortonian and Messinian ages....
-Turolian
Turolian
The Turolian age is a period of geologic time within the Miocene used more specifically with European Land Mammal Ages. It precedes the Ruscinian age and follows the Vallesian age. The Turolian overlaps the Tortonian and Messinian ages....
transition and one of few hominoids to survive the so called Vallesian Crisis
Vallesian
The Vallesian age is a period of geologic time within the Miocene used more specifically with European Land Mammal Ages. It precedes the Turolian age and follows the Astaracian age. The Turolian overlaps the Tortonian and Messinian ages....
together with Sivapithecus
Sivapithecus
Sivapithecus is a genus of extinct primates. Fossil remains of animals now assigned to this genus, dated from 12.5 million to 8.5 million years old in the Miocene, have been found since the 19th century in the Siwalik Hills in what is now India, Nepal, and Pakistan...
in Asia.
To date, dozens of individuals have been discovered at the Tuscan
Tuscany
Tuscany is a region in Italy. It has an area of about 23,000 square kilometres and a population of about 3.75 million inhabitants. The regional capital is Florence ....
localities of Montebamboli, Montemassi, Casteani, Ribolla, and, most notably, in the fossil-rich lignite mine in the Baccinello Basin, making it one of the best-represented fossil ape
Ape
Apes are Old World anthropoid mammals, more specifically a clade of tailless catarrhine primates, belonging to the biological superfamily Hominoidea. The apes are native to Africa and South-east Asia, although in relatively recent times humans have spread all over the world...
s.
Etymology
The scientific name Oreopithecus quickly inspired the commonly used though unofficial name for the species among paleontologists, Cookie MonsterCookie Monster
Cookie Monster is a Muppet on the children's television show Sesame Street. He is best known for his voracious appetite and his famous eating phrases: "Me want cookie!", "Me eat cookie!", and "Om nom nom nom" . He often eats anything and everything, including danishes, donuts, lettuce, apples,...
. 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 GervaisPaul Gervais
For the Canadian parliamentarian see Paul Mullins GervaisPaul Gervais full name François Louis Paul Gervaise was a French palaeontologist and entomologist.-Biography:...
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
Canine tooth
In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...
, at the time considered diagnostic of the hominid family — and a biped — since the short pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
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
Dryopithecus
Dryopithecus was a genus of apes that is known from Eastern Africa into Eurasia during the late Miocene period. The first species of Dryopithecus was discovered at the site of Saint-Gaudens, Haute-Garonne, France, in 1856...
; the peculiar cranial and dental features explained as consequences of insular
Island
An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...
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
Australopithecus
Australopithecus is a genus of hominids that is now extinct. From the evidence gathered by palaeontologists and archaeologists, it appears that the Australopithecus genus evolved in eastern Africa around 4 million years ago before spreading throughout the continent and eventually becoming extinct...
′ — the hallux
Hallux
In tetrapods, the hallux is the innermost toe of the foot. Despite its name it may not be the longest toe on the foot of some individuals...
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 , truly large predators such as Machairodus
Machairodus
Machairodus was a genus of large machairodontine saber-toothed cats that lived in Europe, Asia, Africa and North America during the Miocene through Pleistocene living from 11.6mya—126,000 years ago, existing for approximately .-Species:...
and Metailurus
Metailurus
Metailurus is a genus of false saber-toothed cat of the family Felidae, belonging to the tribe Metailurini endemic to North America, Africa, Europe, and Asia during the Miocene to Pleistocene, living from 9 Ma—11,000 years ago and existed for approximately .Metailurus was named by Zdansky...
were present among the new generation of European immigrants and Oreopithecus faced quick extinction together with other endemic genera.
A parallel to the Great American Interchange
Great American Interchange
The Great American Interchange was an important paleozoogeographic event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents...
two million years later
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 DryopithecusDryopithecus
Dryopithecus was a genus of apes that is known from Eastern Africa into Eurasia during the late Miocene period. The first species of Dryopithecus was discovered at the site of Saint-Gaudens, Haute-Garonne, France, in 1856...
or some African anthropoid.
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
Apidium
The genus Apidium is that of at least three extinct primates living in the early Oligocene, roughly 36 to 32 millions years ago. Apidium fossils are common in the Fayoum deposits of Egypt...
, a small arboreal proto-ape that lived nearly 34 million years ago in Egypt.
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
Dryopithecus
Dryopithecus was a genus of apes that is known from Eastern Africa into Eurasia during the late Miocene period. The first species of Dryopithecus was discovered at the site of Saint-Gaudens, Haute-Garonne, France, in 1856...
, 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
Hominidae
The Hominidae or include them .), as the term is used here, form a taxonomic family, including four extant genera: chimpanzees , gorillas , humans , and orangutans ....
. It could instead be added to the same subfamily as Dryopithecus, perhaps as a distinct tribe (Oreopithecinae).
Physical characteristics
Oreopithecus bambolii is estimated to have weighed 30 –. It possessed a relatively short snout, elevated nasal bones, small and globular neurocranium, vertical orbital planeMaxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
, 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
Masseter muscle
In human anatomy, the masseter is one of the muscles of mastication.In the animal kingdom, it is particularly powerful in herbivores to facilitate chewing of plant matter.-Origin and insertion of the two heads:...
and a sagittal crest
Sagittal crest
A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull of many mammalian and reptilian skulls, among others....
for attachment of the temporal muscle, indicates a heavy masticatory
Mastication
Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...
apparatus. Its teeth were small relative to body size. The lack of a diastema (gap) between the second incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
and first premolar
Premolar
The premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered as a 'transitional tooth' during chewing, or...
of the mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
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
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
.
Positional behavior
Its habitat appears to have been swampSwamp
A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...
y, and not savanna
Savanna
A savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently small or widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of C4 grasses.Some...
or forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
. The postcranial anatomy of Oreopithecus features adaptations to both suspensory arborealism and biped
Biped
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs, or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning "two feet"...
alism. 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
Lumbar
In tetrapod anatomy, lumbar is an adjective that means of or pertaining to the abdominal segment of the torso, between the diaphragm and the sacrum ...
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
Abduction (kinesiology)
Abduction, in functional anatomy, is a movement which draws a limb away from the median plane of the body. It is thus opposed to adduction.-Upper limb:* of arm at shoulder ** Supraspinatus** Deltoid* of hand at wrist...
so that this line falls between the first and second metatarsals instead. Furthermore, the shape of the tarsus
Tarsus (skeleton)
In tetrapods, the tarsus is a cluster of articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. In the foot the tarsus articulates with the bones of the metatarsus, which in turn articulate with the bones of the individual toes...
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.
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
Autapomorphy
In cladistics, an autapomorphy is a distinctive anatomical feature, known as a derived trait, that is unique to a given terminal group. That is, it is found only in one member of a clade, but not found in any others or outgroup taxa, not even those most closely related to the group...
rather than synapomorphic
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
.An autapomorphy
Autapomorphy
In cladistics, an autapomorphy is a distinctive anatomical feature, known as a derived trait, that is unique to a given terminal group. That is, it is found only in one member of a clade, but not found in any others or outgroup taxa, not even those most closely related to the group...
is a derived trait unique to a terminal group; a synapomorphy
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
is a derived trait shared by several taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
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.
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 endolymphEndolymph
Endolymph is the fluid contained in the membranous labyrinth of the inner ear. It is also called Scarpa's fluid, after Antonio Scarpa.-Composition:...
-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
Sagittal plane
Sagittal plane is a vertical plane which passes from front to rear dividing the body into right and left sections.-Variations:Examples include:...
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 gibbon
Gibbon
Gibbons are apes in the family Hylobatidae . The family is divided into four genera based on their diploid chromosome number: Hylobates , Hoolock , Nomascus , and Symphalangus . The extinct Bunopithecus sericus is a gibbon or gibbon-like ape which, until recently, was thought to be closely related...
s 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 human
Human
Humans are the only living species in the Homo genus...
s 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.
Allometric measurements on the bony labyrinth
Bony labyrinth
The Bony labyrinth or osseous labyrinth consists of three parts: the vestibule, semicircular canals, and cochlea. These are cavities hollowed out of the substance of the bone, and lined by periosteum; they contain a clear fluid, the perilymph, in which the membranous labyrinth is situated....
of BAC-208, a fragmentary cranium that preserves a complete, undeformed petrosal bone suggest that Oreopithecus moved with agility comparable to extant great apes
Great Apes
Great Apes may refer to*Great apes, species in the biological family Hominidae, including humans, chimpanzees, gorillas, and orangutans*Great Apes , a 1997 novel by Will Self...
. Its anterior and lateral semicircular canal sizes fall within the range for great apes.
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 longusFlexor pollicis longus muscle
The flexor pollicis longus is a muscle in the forearm and hand that flexes the thumb...
, and the shape of the carpometacarpal joint
Carpometacarpal joint
The carpometacarpal joints are five joints in the wrist that articulates the distal row of carpal bones and the proximal bases of the five metacarpal bones....
between the metacarpal bone of the index finger and the capitate bone.
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
Australopithecus
Australopithecus is a genus of hominids that is now extinct. From the evidence gathered by palaeontologists and archaeologists, it appears that the Australopithecus genus evolved in eastern Africa around 4 million years ago before spreading throughout the continent and eventually becoming extinct...
. Oreopithecus share the specialised orientation at the carpometacarpal joint with A. afarenis
Australopithecus afarensis
Australopithecus afarensis is an extinct hominid that lived between 3.9 and 2.9 million years ago. A. afarensis was slenderly built, like the younger Australopithecus africanus. It is thought that A...
and the marked groove for the flexor pollicis longus with A. africanus
Australopithecus africanus
Australopithecus africanus was an early hominid, an australopithecine, who lived between 2–3 million years ago in the Pliocene. In common with the older Australopithecus afarensis, A. africanus was slenderly built, or gracile, and was thought to have been a direct ancestor of modern humans. Fossil...
. It is thus likely that the hand morphology of Oreopithecus is derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
for apes and convergent
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
for early hominids.
See also
- List of fossil sites
- List of hominina (hominid) fossils