The fossil evidence of anthropoid brain evolution

The endocast of Aegyptopithecus, a 27 million year old ape, reveals that its brain was advanced over that of prosimians and comparable to that of modern anthropoids in relative size and in having expanded visual cortex, reduced olfactory bulbs, and a central sulcus separating primary somatic sensory and motor cortex. The early appearance of those features suggests that they may have been among the adaptations responsible for the evolution of anthropoids from prosimian ancestors. The frontal lobe was relatively smaller in Aegyptopithecus than in modern anthropoids. An endocast of Dolichocebus, one of the oldest known New World monkeys (25–30 million years old), reveals visual cortex expanded as in modern anthropoids. The 19 million year old Napak frontal bone displays a hominoid rather than cercopithecoid sulcal pattern. An 18 million year old endocast of the ape Dryopithecus (Proconsul) was neither monkey-like nor primitive, as originally described, but rather apelike and essentially modern in all observable features. The oldest undoubted Old World monkey endocast, from nine million year old Mesopithecus, reveals that the brain was modern in sulcal pattern and proportions. The sulcal pattern was like that of modern colobines, but that appears to be the more primitive condition, from which features characteristic of modern cercopithecine brains have evolved. The brain of six million year old Libypithecus was similar to that of Mesopithecus. A two million year old endocast of “Dolichopithecus” arvernensis displays a modern cercopithecine sulcal pattern.     

New faces of Aegyptopithecus from the Oligocene of Egypt

Three recently discovered faces of Aegyptopithecus zeuxis from the Oligocene Jebel Qatrani Formation of Egypt provide new information about the shape and variation of the facial cranium, the earliest preserved for a presumed forerunner of apes and humans. Although varying considerably in details of shape and proportion, the new finds and a skull found in 1966 all appear to be of males, a conclusion based in part on the development of temporal and sagittal crests and on the large size of upper canines or their sockets (female canines are much smaller). The snouts of the three new faces all are shorter and broader than that of the earlier found skull as reconstructed. As in most later species of Anthropoidea, variation between these specimens is high.Aegyptopithecus helps define the nature of the oldest Anthropoidea and generally most resembles later-occurring apes. Many features, both derived and shared primitive, link Aegyptopithecus, the large Miocene great apes of the Proconsul group, and modern great apes. That these shared features and proportions are not direct allometric consequences of body size is indicated by Aegyptopithecus' resemblance to the large apes and its many distinctions from similar-sized Hylobates.In Aegyptopithecus brain volume scales smaller than in later catarrhines relative to facial size, the ectotympanic tube is less developed and the premaxilla is more primitive than in later higher primates. In closure of orbits and conformation of forehead, face and dentition, Aegyptopithecus closely resembles higher primates and not prosimians. Taken together, its overall cranial and dental anatomy constitutes one of the most important connecting links in primate evolutionary history.     

Femoral anatomy of Aegyptopithecus zeuxis,an early Oligocene anthropoid

Three partial femora from Quarries I and M of the early Oligocene Jebel Qatrani Formation in the Fayum of Egypt are attributed to Aegyptopithecus zeuxis on the basis of their appropriate size and anthropoid morphology. Compared with extant catarrhines, Aegyptopithecus is unusual in having a distinct gluteal tuberosity (third trochanter) and a relatively deep distal femoral articulation. In the estimated neck angle, Aegyptopithecus resembles arboreal quadrupeds rather than either leaping or suspensory primates. It seems likely that the femur of this species was relatively robust and short for its body mass. In aspects of its femoral anatomy, Aegyptopithecus is quite different from the parapithecid Apidium and more similar to Catopithecus from late Eocene deposits of the Fayum, and also to small hominoids from the Miocene of East Africa. Am J Phys Anthropol 106:413–424, 1998. © 1998 Wiley-Liss, Inc.     

A calcaneus attributable to the primitive late eocene anthropoid Proteopithecus sylviae: Phenetic affinities and phylogenetic implications

A well‐preserved calcaneus referrable to Proteopithecus sylviae from the late Eocene Quarry L‐41 in the Fayum Depression, Egypt, provides new evidence relevant to this taxon's uncertain phylogenetic position. We assess morphological affinities of the new specimen using three‐dimensional geometric morphometric analyses with a comparative sample of primate calcanei representing major extinct and extant radiations (n = 58 genera, 106 specimens). Our analyses reveal that the calcaneal morphology of Proteopithecus is most similar to that of the younger Fayum parapithecid Apidium. Principal components analysis places Apidium and Proteopithecus in an intermediate position between primitive euprimates and crown anthropoids, based primarily on landmark configurations corresponding to moderate distal elongation, a more distal position of the peroneal tubercle, and a relatively “unflexed” calcaneal body. Proteopithecus and Apidium are similar to cercopithecoids and some omomyiforms in having an ectal facet that is more tightly curved, along with a larger degree of proximal calcaneal elongation, whereas other Fayum anthropoids, platyrrhines and adapiforms have a more open facet with less proximal elongation. The similarity to cercopithecoids is most plausibly interpreted as convergence given the less tightly curved ectal facets of stem catarrhines. The primary similarities between Proteopithecus and platyrrhines are mainly in the moderate distal elongation and the more distal position of the peroneal tubercle, both of which are not unique to these groups. Proteopithecus and Apidium exhibit derived anthropoid features, but also a suite of primitive retentions. The calcaneal morphology of Proteopithecus is consistent with our cladistic analysis, which places proteopithecids as a sister group of Parapithecoidea. Am J Phys Anthropol 151:372–397, 2013.© 2013 Wiley Periodicals, Inc.     

New material of Qatrania from Egypt with comments on the phylogenetic position of the parapithecidae (primates,Anthropoidea)

New material of the early anthropoid primate Qatrania wingi and a new species of that genus are described. Several features of the dental anatomy show that Qatrania, while quite primitive relative to other anthropoids in many ways, is most likely a parapithecid primate. The new material suggests that several dental features previously thought to ally parapithecids with the catarrhine primates were actually evolved in parallel in catarrhines and some parapithecids. Furthermore, all nonparapithecid anthropoids (including platyrrhines and catarrhines) share a suite of derived dental and postcranial features not found in parapithecids. Therefore, parapithecid origins may predate the platyrrhine/catarrhine split.     

New primate first metatarsals from the Paleogene of Egypt and the origin of the anthropoid big toe

The specialized grasping feet of primates, and in particular the nature of the hallucal grasping capabilities of living strepsirrhines and tarsiers (i.e., ‘prosimians’), have played central roles in the study of primate origins. Prior comparative studies of first metatarsal (Mt1) morphology have documented specialized characters in living prosimians that are indicative of a more abducted hallux, which in turn is often inferred to be related to an increased ability for powerful grasping. These include a well-developed peroneal process and a greater angle of the proximal articular surface relative to the long axis of the diaphysis. Although known Mt1s of fossil prosimians share these characters with living non-anthropoid primates, Mt1 morphology in the earliest crown group anthropoids is not well known. Here we describe two Mt1s from the Fayum Depression of Egypt - one from the latest Eocene (from the ∼34 Ma Quarry L-41), and one from the later early Oligocene (from the ∼29-30 Ma Quarry M) - and compare them with a sample of extant and fossil primate Mt1s. Multivariate analyses of Mt1 shape variables indicate that the Fayum specimens are most similar to those of crown group anthropoids, and likely belong to the stem catarrhines Catopithecus and Aegyptopithecus specifically, based on analyses of size. Also, phylogenetic analyses with 16 newly defined Mt1 characters support the hypotheses that “prosimian”-like Mt1 features evolved along the primate stem lineage, while crown anthropoid Mt1 morphology and function is derived among primates, and likely differed from that of basal stem anthropoids. The derived loss of powerful hallucal grasping as reflected in the Mt1 morphology of crown anthropoids may reflect long-term selection for improved navigation of large-diameter, more horizontal branches at the expense of movement in smaller, more variably inclined branches in the arboreal environment.     

Evolutionary modifications of human milk composition: evidence from long-chain polyunsaturated fatty acid composition of anthropoid milks

Brain growth in mammals is associated with increased accretion of long-chain polyunsaturated fatty acids (LCPUFA) in brain phospholipids. The period of maximum accumulation is during the brain growth spurt. Humans have a perinatal brain growth spurt, selectively accumulating docosahexaenoic acid (DHA) and other LCPUFA from the third trimester through the second year of life. The emphasis on rapid postnatal brain growth and LCPUFA transfer during lactation has led to the suggestion that human milk LCPUFA composition may be unique. Our study tests this hypothesis by determining fatty acid composition for 11 species of captive anthropoids (n = 53; Callithrix jacchus, Cebus apella, Gorilla gorilla, Hylobates lar, Leontopithecus rosalia, Macaca mulatta, Pan troglodytes, Pan paniscus, Pongo pygmaeus, Saimiri boliviensis, and Symphalangus syndactylus). Results are compared to previously published data on five species of wild anthropoids (n = 28; Alouatta paliatta, Callithrix jacchus, Gorilla beringei, Leontopithecus rosalia, and Macaca sinica) and human milk fatty acid profiles. Milk LCPUFA profiles of captive anthropoids (consuming diets with a preformed source of DHA) are similar to milk from women on a Western diet, and those of wild anthropoids are similar to milk from vegan women. Collectively, the range of DHA percent composition values from nonhuman anthropoid milks (0.03–1.1) is nearly identical to that from a cross-cultural analysis of human milk (0.06–1.4). Humans do not appear to be unique in their ability to secrete LCPUFA in milk but may be unique in their access to dietary LCPUFA.     

Protoanthropoidea (Primates, Simiiformes): A New Primate Higher Taxon and a Solution to the Rooneyia Problem

As a derivative of the hypothesis that anthropoids evolved from omomyid-like primates, the enigmatic North American fossil Rooneyia viejaensis, from the latest Eocene of Texas, is placed in a new higher taxon, Protoanthropoidea, which is proposed as the sister-group of Anthropoidea. Rooneyia and anthropoids share synapomorphically a pattern of character states relating to the unique orbital morphology of higher primates, including; highly convergent and frontated orbits roofed above by an extended frontal bone; funnel-shaped orbital fossae; orbital apices that are recessed beneath the forebrain; a deep, large lateral process of the frontal bone (upper portion of the postorbital bar) that may presage closure of the orbit by an enlarged ascending process of the zygomatic. If the sister-group of anthropoids occupied North America as part of a Laurasian geographic distribution during the Paleogene, as some primate genera did, ancestral anthropoids may likewise have occurred across Laurasia, prestaging them to enter Africa and Central/South America in two independent episodes of dispersal—without having the ancestral platyrrhines crossing the daunting Atlantic Ocean.     

A mandible ofBranisella boliviana (Platyrrhini,Primates) from the oligocene of South America

A mandibular specimen from the Bolivian Early Oligocene is provisionally assigned toBranisella boliviana. The crown anatomy of the single preserved tooth, an M₂, indicates platyrrhine affinities and several details of the broken jaw are suggestive of symphyseal fusion. Like the African Oligocene parapithecids,Branisella contrasts with extant anthropoids in the relative shallowness of its mandible.Branisella is the most ancient, and seemingly the most primitive, fossil platyrrhine monkey, lacking any of the derived features of the two major clades of modern ceboids. Taxonomically, it is best regarded as family incertae sedis.     

Morphological study of the anthropoid thoracic cage: scaling of thoracic width and an analysis of rib curvature

While a relatively broad thorax and strongly curved ribs are widely regarded as common features of living hominoids, few studies have quantitatively examined these traits by methods other than calculating the chest index. The present study aims to quantify variations in thoracic cage morphology for living anthropoids. The odd-numbered ribs (first to eleventh) were articulated with the corresponding vertebrae and the cranial and lateral views subsequently photographed. Rib profiles were digitized in both views and line-fitted by a Bézier curve to create a three-dimensional morphological data set. When thoracic cage width was scaled against body mass, Hylobates (and possibly Pongo) plotted above non-hominoid anthropoids at almost all rib levels, while Pan did not differ from non-hominoid anthropoids. The overall pattern of the normalized thoracic width differed between Hylobates and other hominoids. In Hylobates, an upward convex curve was seen between the first and seventh ribs while a more linear pattern was observed in Pan and Pongo. This result quantitatively confirmed that the barrel-shaped thoracic cage in Hylobates can be distinguished from the funnel-shaped form in other hominoids. Conversely, all hominoids shared two distinct features in the upper half-thorax: (1) a pronounced dorsal protrusion of the proximal part of the rib in accordance with ventral displacement of the thoracic spine and (2) a relatively medially projecting sternal end. Although these features are likely to provide some mechanical advantage in orthograde and/or suspensory positional behaviors, they were barely present in the suspensory Ateles. An erratum to this article can be found at     

Body Mass Estimates for Eocene Eosimiid and Amphipithecid Primates Using Prosimian and Anthropoid Scaling Models

We estimated body masses for middle to late Eocene East Asian eosimiids and amphipithecids from the crown areas of cheek teeth. First, we calculated body mass estimate equations via an extant primate sample of 11 prosimian and 30 anthropoid species, and compared the reliability of the resulting body mass estimate regressions. M ^1–2 and M _1–2 are better body mass estimators, especially for fossils with few samples, because of their low intraspecific variations in dimensions. Moreover, body masses derived from M _1–2 tend to indicate lower estimate error than those from other cheek teeth. The relationships between tooth crown areas and body mass differ between prosimians and anthropoids; the estimated body mass from crown area of P ⁴ or any molar will be larger if anthropoids, instead of prosimians, are used as a reference taxon. Second, We applied the regressions to the fossil primates. The estimated body masses in kg are as follows: Eosimias centennicus, 0.16; E. sinensis, 0.14; Eosimiidae indet. from the Pondaung Formation, 0.41; Bahinia pondaungensis, 0.57; Myanmarpithecus yarshensis, 1.8; Amphipithecus mogaungensis, 6.8; Pondaungia cotteri, 5.9; Pondaungia savagei, 8.8; Siamopithecus eocaenus, 5.9. Eosimiids fit the prosimian model better than the anthropoid model. Amphipithecids do not fit one model particularly better than the other, as the estimates vary considerably according to the tooth used and the reference taxon. The anthropoid model gives smaller differences between upper- and lower-molar-based body mass estimates, but premolars are relatively much smaller in amphipithecids than in extant prosimians and anthropoids.     

Skull of early Eocene Cantius abditus (primates: Adapiformes) and its phylogenetic implications,with a reevaluation of “Hesperolemur” actius

A substantially complete skull and mandible of the primitive adapiform Cantius is reported from the Early Eocene Willwood Formation of Wyoming. The mandible contains an almost complete lower dentition in which the lower incisors are strongly inclined and have spatulate crowns, I₂ is larger than I₁, and the canine is large and projecting. The cranium shares many features with those of Notharctus and Smilodectes but differs in having nasals that broaden proximally. Presence of a prominent canine and strong sagittal crest may indicate that it represents a male. The basicranium preserves auditory structures almost identical to those in extant noncheirogaleid lemurs, including a large bony tube for the stapedial artery and a small, open sulcus for the distal portion of the promontorial artery. The dentition is sufficiently primitive to be compatible with a relationship to either strepsirrhines or anthropoids, but the anatomy of the auditory region is more consistent with either specific relationship to lemurs or, more likely, a basal position that approximates the euprimate morphotype. Certain features of the basicranium of “Hesperolemur” actius, described by Gunnell ([1995] Am. J. Phys. Anthropol. 98:447–470) as being unlike that of any other adapiform, were either misinterpreted or are apparently no longer present in the holotype. Reassessment of these and other features indicates that in fact “H.” actius differs little from Cantius and should not be separated from the latter at the genus level, although on dental grounds the species appears to be distinct (as C. actius). Am J Phys Anthropol 109:523–539, 1999. © 1999 Wiley-Liss, Inc.     

New notharctine (primates,adapiformes) skull from the Uintan (middle Eocene) of San Diego County,California

A new genus and species of notharctine primate, Hesperolemur actius, is described from Uintan (middle Eocene) aged rocks of San Diego County, California. Hesperolemur differs from all previously described adapiforms in having the anterior third of the ectotympanic anulus fused to the internal lateral wall of the auditory bulla. In this feature Hesperolemur superficially resembles extant cheirogaleids. Hesperolemur also differs from previously known adapiforms in lacking bony canals that transmit the internal carotid artery through the tympanic cavity. Hesperolemur, like the later occurring North American cercamoniine Mahgarita stevensi, appears to have lacked a stapedial artery. Evidence from newly discovered skulls of Notharctus and Smilodectes, along with Hesperolemur, Mahgarita, and Adapis, indicates that the tympanic arterial circulatory pattern of these adapiforms is characterized by stapedial arteries that are smaller than promontory arteries, a feature shared with extant tarsiers and anthropoids and one of the characteristics often used to support the existence of a haplorhine-strepsirhine dichotomy among extant primates. The existence of such a dichotomy among Eocene primates is not supported by any compelling evidence. Hesperolemur is the latest occurring notharctine primate known from North America and is the only notharctine represented among a relatively diverse primate fauna from southern California. The coastal lowlands of southern California presumably served as a refuge area for primates during the middle and later Eocene as climates deteriorated in the continental interior. Hesperolemur probably was an immigrant taxon that entered California from either the northern (Wyoming/Utah) or southern (New Mexico) western interior during the middle Eocene © 1995 Wiley-Liss, Inc.     

Human evolution

The common ancestor of modern humans and the great apes is estimated to have lived between 5 and 8 Myrs ago, but the earliest evidence in the human, or hominid, fossil record is Ardipithecus ramidus, from a 4.5 Myr Ethiopian site. This genus was succeeded by Australopithecus, within which four species are presently recognised. All combine a relatively primitive postcranial skeleton, a dentition with expanded chewing teeth and a small brain. The most primitive species in our own genus, Homo habilis and Homo rudolfensis, are little advanced over the australopithecines and with hindsight their inclusion in Homo may not be appropriate. The first species to share a substantial number of features with later Homo is Homo ergaster, or ‘early African Homo erectus’, which appears in the fossil record around 2.0 Myr. Outside Africa, fossil hominids appear as Homo erectus-like hominids, in mainland Asia and in Indonesia close to 2 Myr ago; the earliest good evidence of ‘archaic Homo’ in Europe is dated at between 600–700 Kyr before the present. Anatomically modern human, or Homo sapiens, fossils are seen first in the fossil record in Africa around 150 Kyr ago. Taken together with molecular evidence on the extent of DNA variation, this suggests that the transition from ‘archiac’ to ‘modern’ Homo may have taken place in Africa.     

Partial skeleton of Proconsul nyanzae from Mfangano Island,Kenya

A partial skeleton attributed to Proconsul nyanzae (KNM-MW 13142) is described. The fossils were found at a site on Mfangano Island, Kenya, which dates to 17.9 ± .1 million years ago. KNM-MW 13142 consists of six partial vertebrae (T12-S1), a nearly complete hipbone, most of the right femur and left femoral shaft, a fragmentary tibia and fibula, and a nearly complete talus and calcaneus. This skeleton provides the first pelvic fossil known for any East African Miocene hominoid. The new Proconsul specimen is compared to a large sample of extant anthropoids to determine its functional and phylogenetic affinities. In most aspects of its anatomy, KNM-MW 13142 closely resembles nonhominoid anthropoids. This individual had a long, flexible spine, narrow torso, and habitually pronograde posture, features characteristic of most extant monkeys. Evidence of spinal musculature suggests a generalized condition intermediate between that of cercopithecoids and hylobatids. The hindlimb of KNM-MW 13142 exhibits relatively mobile hip and ankle joints, with structural properties of the femur like those of hominoids. This mix of features implies a pattern of posture and locomotion that is unlike that of any extant primate. Many aspects of the Proconsul nyanzae locomotor skeleton may represent the primitive catarrhine condition. © 1993 Wiley-Liss, Inc.     

Significance of primate petrosal from Middle Eocene fissure-fillings at Shanghuang, Jiangsu Province, People's Republic of China

An isolated petrosal bone belonging to a diminutive primate is reported from Middle Eocene fissure-fills near Shanghuang (southern Jiangsu Province, People's Republic of China), the type locality of several newly described primates (Eosimias sinensis, a basal anthropoid; Adapoides troglodytes, a basal adapinan; Tarsius eocaenus, a congener of extant tarsiers; and Macrotarsius macrorhysis, the first Asian representative of an otherwise exclusively North American genus). Because of its fragmentary condition and unique combination of characters, the Shanghuang petrosal cannot be assigned unambiguously to any of the Shanghuang primate taxa known from dental remains. However, the possibility that the petrosal represents either an adapid or a tarsiid can be dismissed because it lacks defining basicranial apomorphines of these groups. By contrast, the element does present arterial features consistent with its being haplorhine. Deciding between the likeliest candidates for its allocation—Omomyidae and Eosimiidae—is difficult, in part because it is not known what (or even whether) basicranial characters can be used to distinguish these clades. If the Shanghuang petrosal is that of an cosimiid, as both direct and indirect evidence appears to indicate, the following implications emerge: (1) as long suspected on other grounds, anthropoids share a closer evolutionary history with Omomyidae (and Tarsiiformes) than they do with Adapidae (and Strepsirhini); (2) the specialised basicranial anatomy of extant anthropoids and their immediate cladistic relatives is derived from a primitive precursor whose otic morphology was like that of omomyids in most known respects; (3) the evolution of the defining dental and basicranial apomorphies of extant Anthropoidea has been distinctly mosaic in pattern.     

Paleobiology of the oligopithecines,the earliest known anthropoid primates

Anthropoid primates of the subfamily Oligopithecinae are late Eocene in age, and have a known distribution of Northeast Africa and the Arabian Peninsula. Body sizes of the three known oligopithecine species are estimated from allometric molar size regressions to be 700–1000 g forOligopithecus savagei, 600–900 g forCatopithecus browni, and 500 g for the least well-known and smallest species,Proteopithecus sylviae. Occlusal features of the molar teeth, considered in conjunction with body size, suggest that all three species were frugivorous and insectivorous. The orbital size ofCatopithecus indicates a diurnal activity cycle. A relatively broad interobital region in this species may indicate prosimian-like or callitrichid-like olfactory adaptations. Structural features of the crushed skull suggest thatCatopithecus had a smaller cranial capacity than those of extant anthropoids with a similar body size. Fossil plants and birds from localities yielding oligopithecines suggest a wet, warm, tropical, forested, swampy environment. These paleobiological inferences about the extinct oligopithecines are discussed in relation to questions about primate adaptations near the prosimian-anthropoid transition.     

Palaeoecological implications of the sympatric distribution of two species of Machairodus (Felidae,Machairodontinae, Homotherini) in the Late Miocene of Los Valles de Fuentidueña (Segovia,Spain)

In this paper, we study a sample of cranial, mandibular and dental remains of two species of the machairodontine felid genus Machairodus from the Early Vallesian (MN 9, around 10 Ma) site of Los Valles de Fuentidueña (Segovia, Spain): the tiger-sized Machairodus aphanistus, and the smaller and more primitive M. alberdiae; a species which is only known from this site. The fossils of these two sympatric populations are compared with the most abundant samples of M. aphanistus from the Late Vallesian (MN 10), younger sites of Batallones-1 and Batallones-3 (Torrejón de Velasco, Madrid, Spain). The results support the specific separation of M. alberdiae from M. aphanistus based on several differences in teeth size and proportions. Besides this, we observed differences among the analysed samples of M. aphanistus, indicating a differentiation between the older and more primitive form from Los Valles de Fuentidueña, and the younger and more derived one from the two Batallones sites. These differences fit well with the morphological evolution of this lineage towards the more derived Turolian Amphimachairodus giganteus. Finally, a relatively structured, patched habitat, combining the presence of open landscapes with shrubby and wooded areas, is inferred to explain the sympatric distribution of these two large machairodontines in Los Valles de Fuentidueña.     

The oldest primate endocast

The endocranial cast of Tetonius homunculus, a 55 million year old tarsioid primate, is primitive in having relatively large olfactory bulbs and small frontal lobes, but remarkably advanced for an Early Eocene mammal in its voluminous occipital and temporal lobes. Expansion of occipital and temporal cortical regions of the brain suggests improvement in visual and auditory function, which may have been an important factor in the Early Eocene radiation of the primates.