Skeletal adaptations and phylogeny of the oldest mole Eotalpa (Talpidae,Lipotyphla, Mammalia) from the UK Eocene: the beginning of fossoriality in moles

The oldest talpid, Eotalpa, was previously known only from isolated cheek teeth from the European late Middle Eocene to earliest Oligocene. Screenwashing of Late Eocene sediments of the Hampshire Basin, UK, has yielded cranial and postcranial elements: maxilla, dentary, ulna, metacarpals, distal tibia, astragalus, calcaneum, metatarsals and phalanges. In addition to M_1–2 myotodonty, typical talpid features are as follows: ulna with long medially curved olecranon and deep abductor fossa and astragalar body with lateral process. However, Eotalpa retains certain soricid‐like primitive states (M¹ preparacrista, P⁴ with prominent mesiolingual protocone lobe, strongly angled astragalar neck and calcaneum with no space for a cuboid medial process) not found in modern talpids. Eotalpa is more derived than the most primitive living talpid Uropsilus in having lost the M^1–2 talon shelf, developed a convex radial facet on the ulna, an incipient proximal olecranon crest, relatively shorter metapodials and depressed manual unguals. Its astragalus with medial trochlear ridge taller than the lateral one and massive medial plantar process is typical of the Lipotyphla. Eotalpa lacks synostosis of tibia and fibula, found in other Talpidae, Soricidae and Erinaceidae, suggesting that synostosis in these groups has been independently acquired. Cladistic analysis places Eotalpa as stem member of the Talpidae and shows that much homoplasy arose during the early evolution of the family. Ground dwelling in Eotalpa is indicated by the following: astragalus with a medially dipping head, curved in a single plane; calcaneum with distal peroneal process and strongly overlapping ectal and sustentacular facets; and matching sized ectal and sustentacular facets on calcaneum and astragalus. These features would have restricted ankle mobility. Ungual and metatarsal shape and ulnar structure suggest a primitive stage in fossorial evolution and argue against a semiaquatic precursor stage in talpid fossoriality. Shrew‐moles may represent a reversal to surface foraging rather than an intermediate stage in fossoriality.     

The humerus of Aegyptopithecus zeuxis: a primitive anthropoid

Two complete humeri of Aegyptopithecus zeuxis have been recovered from Oligocene deposits in the Fayum Province of Egypt. These new specimens support previous interpretations of the locomotor adaptations of this species and indicate that A. zeuxis was a robust, slowly moving arboreal quadruped. While the previously described distal articular region of the humerus is virtually identical with the same region in many extant ceboids and the Miocene hominoid Pliopithecus vindobonensis, the more proximal parts of the humerus show many primitive "prosimianlike" features not found the limbs of extant anthropoids. The primitive features include the absence of a distinct deltoid plane, a broad shallow bicipital groove, a large brachialis flange, and an entepicondylar foramen. In most features, the humerus of Aegyptopithecus zeuxis is more primitive than the hypothetical last common ancestor of extant cercopithecoids and hominoids based on neontological comparisons. This supports other lines of evidence indicating that the hominoids from the Egyptian Oligocene are morphologically ancestral to both Old World monkeys and apes.     

Caudal vertebral body articular surface morphology correlates with functional tail use in anthropoid primates

Prehensile tails, capable of suspending the entire body weight of an animal, have evolved in parallel in New World monkeys (Platyrrhini): once in the Atelinae (Alouatta, Ateles, Brachyteles, Lagothrix), and once in the Cebinae (Cebus, Sapajus). Structurally, the prehensile tails of atelines and cebines share morphological features that distinguish them from nonprehensile tails, including longer proximal tail regions, well‐developed hemal processes, robust caudal vertebrae resistant to higher torsional and bending stresses, and caudal musculature capable of producing higher contractile forces. The functional significance of shape variation in the articular surfaces of caudal vertebral bodies, however, is relatively less well understood. Given that tail use differs considerably among prehensile and nonprehensile anthropoids, it is reasonable to predict that caudal vertebral body articular surface area and shape will respond to use‐specific patterns of mechanical loading. We examine the potential for intervertebral articular surface contour curvature and relative surface area to discriminate between prehensile‐tailed and nonprehensile‐tailed platyrrhines and cercopithecoids. The proximal and distal intervertebral articular surfaces of the first (Ca1), transitional and longest caudal vertebrae were examined for individuals representing 10 anthropoid taxa with differential patterns of tail‐use. Study results reveal significant morphological differences consistent with the functional demands of unique patterns of tail use for all vertebral elements sampled. Prehensile‐tailed platyrrhines that more frequently use their tails in suspension (atelines) had significantly larger and more convex intervertebral articular surfaces than all nonprehensile‐tailed anthropoids examined here, although the intervertebral articular surface contour curvatures of large, terrestrial cercopithecoids (i.e., Papio sp.) converge on the ateline condition. Prehensile‐tailed platyrrhines that more often use their tails in tripodal bracing postures (cebines) are morphologically intermediate between atelines and nonprehensile tailed anthropoids. J. Morphol. 275:1300–1311, 2014. © 2014 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.     

The ecology of oligocene African anthropoidea

African anthropoids are first recorded in Early Oligocene deposits of the Fayum Province, Egypt. Six genera and nine species are recognized. Estimated body weights for these taxa are based on the regression equation log ₁₀(B) = 2.86log ₁₀(L) + 1.37, whereB is the bodyweight in grams, and Lis the M ₂ length in millimeters. The equation is derived from 106 species of living primates. Fayum species range in body weight from about 600 g (Apidium moustafai)to about 6000 g (Aegyptopithecus zeuxis).A similar range of body weight is found among extant Cebidae. The Fayum primates are larger than any extant insectivorous primates;this fact probably rules out a predominantly insectivorous diet. Extant frugivorous hominoids can be separated from folivorous hominoids on the basis of molar morphology. Folivorous apes (gorilla and siamang) have proportionately more shearing on their molars than do frugivorous species. Based on the hominoid analogy, the molar morphology of the Fayum species is consistent with a frugivorous diet. Parapithecus grangeristands apart from other Fayum species in having better developed molar shearing, possibly indicating that it had more fiber in its diet. Terrestrial species of Old World monkeys tend to have significantly higher molar crowns than do more arboreal species. This difference may relate to an increased amount of grit in the diet of the more terrestrial species, selecting for greater resistance to wear. Oligocene primates have molar crown heights consistent with a primarily arboreal mode of existence. However, the particularly high molar crowns of Parapithecus grangerisuggest that this species may have foraged on the ground to a considerable degree. Other evidence is advanced suggesting that Apidiummay have had a diurnal activity pattern.     

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.     

Evolution and Allometry of Calcaneal Elongation in Living and Extinct Primates

Specialized acrobatic leaping has been recognized as a key adaptive trait tied to the origin and subsequent radiation of euprimates based on its observed frequency in extant primates and inferred frequency in extinct early euprimates. Hypothesized skeletal correlates include elongated tarsal elements, which would be expected to aid leaping by allowing for increased rates and durations of propulsive acceleration at takeoff. Alternatively, authors of a recent study argued that pronounced distal calcaneal elongation of euprimates (compared to other mammalian taxa) was related primarily to specialized pedal grasping. Testing for correlations between calcaneal elongation and leaping versus grasping is complicated by body size differences and associated allometric affects. We re-assess allometric constraints on, and the functional significance of, calcaneal elongation using phylogenetic comparative methods, and present an evolutionary hypothesis for the evolution of calcaneal elongation in primates using a Bayesian approach to ancestral state reconstruction (ASR). Results show that among all primates, logged ratios of distal calcaneal length to total calcaneal length are inversely correlated with logged body mass proxies derived from the area of the calcaneal facet for the cuboid. Results from phylogenetic ANOVA on residuals from this allometric line suggest that deviations are explained by degree of leaping specialization in prosimians, but not anthropoids. Results from ASR suggest that non-allometric increases in calcaneal elongation began in the primate stem lineage and continued independently in haplorhines and strepsirrhines. Anthropoid and lorisid lineages show stasis and decreasing elongation, respectively. Initial increases in calcaneal elongation in primate evolution may be related to either development of hallucal-grasping or a combination of grasping and more specialized leaping behaviors. As has been previously suggested, subsequent increases in calcaneal elongation are likely adaptations for more effective acrobatic leaping, highlighting the importance of this behavior in early euprimate evolution.     

First record of a parapithecid primate from the Oligocene of Kenya

Recent excavations in northwestern Kenya have recovered a vertebrate fauna of late early or early late Oligocene age. Among the mammal remains, a fragmentary lower jaw and an isolated upper molar have been attributed to a small primate, Lokonepithecus manai gen. et sp. nov. Lokonepithecus is a primitive member of the Parapithecidae and possibly most closely related to Apidium from the Fayum. The new primate from Kenya is the youngest parapithecid known and its occurrence in the Oligocene of Kenya suggests that sub-Saharan Africa probably played a major role in the evolutionary history of several groups of mammals.     

Patterns of astragalar fibular facet orientation in extant and fossil primates and their evolutionary implications

A laterally sloping fibular facet of the astragalus (=talus) has been proposed as one of few osteological synapomorphies of strepsirrhine primates, but the feature has never been comprehensively quantified. We describe a method for calculating fibular facet orientation on digital models of astragali as the angle between the planes of the fibular facet and the lateral tibial facet. We calculated this value in a sample that includes all major extant primate clades, a diversity of Paleogene primates, and nonprimate euarchontans (n = 304). Results show that previous characterization of a divide between extant haplorhines and strepsirrhines is accurate, with little overlap even when individual data points are considered. Fibular facet orientation is conserved in extant strepsirrhines despite major differences in locomotion and body size, while extant anthropoids are more variable (e.g., low values for catarrhines relative to non‐callitrichine platyrrhines). Euprimate outgroups exhibit a mosaic of character states with Cynocephalus having a more obtuse strepsirrhine‐like facet and sampled treeshrews and plesiadapiforms having more acute haplorhine‐like facets. Surprisingly, the earliest species of the adapiform Cantius have steep haplorhine‐like facets as well. We used a Bayesian approach to reconstruct the evolution of fibular facet orientation as a continuous character across a supertree of living and extinct primates. Mean estimates for crown Primatomorpha (97.9°), Primates (99.5°), Haplorhini (98.7°), and Strepsirrhini (108.2°) support the hypothesis that the strepsirrhine condition is derived, while lower values for crown Anthropoidea (92.8°) and Catarrhini (88.9°) are derived in the opposite direction. Am J Phys Anthropol 151:420–447, 2013.© 2013 Wiley Periodicals, Inc.     

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.     

Patterns of dental emergence in early anthropoid primates from the Fayum Depression,Egypt

Abstract

Paleontological field work in the Fayum Depression of Egypt has produced a remarkable diversity of fossil anthropoids, and this, combined with advances in genetic analyses of living anthropoids, has led to establishment of a temporal and phylogenetic framework for anthropoids that is achieving some degree of consensus. Less well understood are the evolutionary mechanisms and selective factors behind the origin and early diversification of anthropoids. One area that has remained under explored is investigation into the life history patterns of early anthropoids, a major omission given that understanding patterns of growth and development is essential for interpreting the paleobiology of fossil species. Here we detail dental emergence sequences for five species in four families of early anthropoid primates from the Fayum, and use these data to test Schultz’s Rule concerning the timing of emergence of molars versus premolars in mammals. Two important results are generated: (1) only one species had a dental eruption sequence identical to that observed among crown catarrhine primates; and (2) in all cases, the permanent canine was the last post-incisor dental element to fully erupt, a finding that may be significant for interpreting early anthropoid behavioral strategies.     

Forelimb anatomy of New World monkeys: myology and the interpretation of primitive anthropoid models

The forelimbs of 12 genera of New World monkeys, two genera of Old World monkeys, and a gibbon were dissected. Of the 54 muscles examined, 19 exhibited significant intergeneric variation. We present arguments for which morphologies are primitive and which are derived within platyrrhines and within anthropoids. We conclude that the forelimbs of Cebus apella and Callicebus moloch represent good models of the ancestral anthropoid morphology. Thus among living anthropoids they are most appropriate for comparisons with early fossil anthropoids. They are also useful for determining whether myological anomalies of human aneuploids are atavistic. Wagner tree analyses were conducted to assess the value of these myological characters in phylogenetic studies of platyrrhines. In most respects the Wagner trees were consonant with phylogenies previously proposed, although some hypothesized trees are less parsimonious than others in explaining our data. There is an unexpected number of derived features shared by Aotus and the Atelines. There are marked dissimilarities in forelimb musculature between Aotus and Callicebus.     

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.     

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.     

Diets of fossil primates from the Fayum Depression of Egypt: a quantitative analysis of molar shearing

Over the last 90 years, Eocene and Oligocene aged sediments in the Fayum Depression of Egypt have yielded at least 17 genera of fossil primates. However, of this diverse sample the diets of only four early Oligocene anthropoid genera have been previously studied using quantitative methods. Here we present dietary assessments for 11 additional Fayum primate genera based on the analysis of body mass and molar shearing crest development. These studies reveal that all late Eocene Fayum anthropoids were probably frugivorous despite marked subfamilial differences in dental morphology. By contrast, late Eocene Fayum prosimians demonstrated remarkable dietary diversity, including specialized insectivory (Anchomomys), generalized frugivory (Plesiopithecus), frugivory+insectivory (Wadilemur), and strict folivory (Aframonius). This evidence that sympatric prosimians and early anthropoids jointly occupied frugivorous niches during the late Eocene reinforces the hypothesis that changes in diet did not form the primary ecological impetus for the origin of the Anthropoidea. Early Oligocene Fayum localities differ from late Eocene Fayum localities in lacking large-bodied frugivorous and folivorous prosimians, and may document the first appearance of primate communities with trophic structures like those of extant primate communities in continental Africa. A similar change in primate community structure during the Eocene-Oligocene transition is not evident in the Asian fossil record. Putative large anthropoids from the Eocene of Asia, such as Amphipithecus mogaungensis, Pondaungia cotteri, and Siamopithecus eocaenus, share with early Oligocene Fayum anthropoids derived features of molar anatomy related to an emphasis on crushing and grinding during mastication. However, these dental specializations are not seen in late Eocene Fayum anthropoids that are broadly ancestral to the later-occurring anthropoids of the Fayum's upper sequence. This lack of resemblance to undisputed Eocene African anthropoids suggests that the "progressive" anthropoid-like dental features of some large-bodied Eocene Asian primates may be the result of dietary convergence rather than close phyletic affinity with the Anthropoidea.     

Functional morphology of the hallucal metatarsal with implications for inferring grasping ability in extinct primates

Primate evolutionary morphologists have argued that selection for life in a fine branch niche resulted in grasping specializations that are reflected in the hallucal metatarsal (Mt1) morphology of extant “prosimians”, while a transition to use of relatively larger, horizontal substrates explains the apparent loss of such characters in anthropoids. Accordingly, these morphological characters—Mt1 torsion, peroneal process length and thickness, and physiological abduction angle—have been used to reconstruct grasping ability and locomotor mode in the earliest fossil primates. Although these characters are prominently featured in debates on the origin and subsequent radiation of Primates, questions remain about their functional significance. This study examines the relationship between these morphological characters of the Mt1 and a novel metric of pedal grasping ability for a large number of extant taxa in a phylogenetic framework. Results indicate greater Mt1 torsion in taxa that engage in hallucal grasping and in those that utilize relatively small substrates more frequently. This study provides evidence that Carpolestes simpsoni has a torsion value more similar to grasping primates than to any scandentian. The results also show that taxa that habitually grasp vertical substrates are distinguished from other taxa in having relatively longer peroneal processes. Furthermore, a longer peroneal process is also correlated with calcaneal elongation, a metric previously found to reflect leaping proclivity. A more refined understanding of the functional associations between Mt1 morphology and behavior in extant primates enhances the potential for using these morphological characters to comprehend primate (locomotor) evolution. Am J Phys Anthropol 156:327–348, 2015. © 2014 Wiley Periodicals, Inc.     

Astragalar morphology of late Eocene anthropoids from the Fayum Depression (Egypt) and the origin of catarrhine primates

The phylogenetic relationships of the late Eocene anthropoids Catopithecus browni and Proteopithecus sylviae are currently a matter of debate, with opinion divided as to whether these taxa are stem or crown anthropoids. The phylogenetic position of Catopithecus is of particular interest, for, unlike the highly generalized genus Proteopithecus, this taxon shares apomorphic dental and postcranial features with more derived undoubted catarrhines that appear in the same region 1-2 Ma later. If these apomorphies are homologous and Catopithecus is a stem catarrhine, the unique combination of plesiomorphic and apomorphic features preserved in this anthropoid would have important implications for our understanding of the crown anthropoid morphotype and the pattern of morphological character transformations that occurred during the early phases of stem catarrhine evolution.Well-preserved astragali referrable to Proteopithecus, Catopithecus, and the undoubted early Oligocene stem catarrhine Aegyptopithecus have provided additional morphological evidence that allows us to further evaluate competing hypotheses of interrelationships among Eocene-Oligocene Afro-Arabian anthropoids. Qualitative observations and multivariate morphometric analyses reveal that the astragalar morphology of Proteopithecus is very similar to that of early Oligocene parapithecids and living and extinct small-bodied platyrrhines, and strengthens the hypothesis that the morphological pattern shared by these taxa is primitive within crown Anthropoidea. In contrast, Catopithecus departs markedly from the predicted crown anthropoid astragalar morphotype and shares a number of apomorphic features (e.g., deep cotylar fossa, laterally projecting fibular facet, trochlear asymmetry, mediolaterally wide astragalar head) with Aegyptopithecus and Miocene-Recent catarrhines. The evidence from the astragalus complements other independent data from the dentition, humerus and femur of Catopithecus that support this taxon's stem catarrhine status, and we continue to maintain that oligopithecines are stem catarrhines that constitute the sister group of a clade containing propliopithecines and Miocene-Recent catarrhines.     

Functional anatomy and adaptation of the third to sixth thoracic vertebrae in primates using three-dimensional geometric morphometrics

The morphology of the cranial thoracic vertebrae has long been neglected in the study of primate skeletal functional morphology. This study explored the characteristics of the third to sixth thoracic vertebrae among various positional behavioural primates. A total of 67 skeletal samples from four species of hominoids, four of cercopithecoids, and two of platyrrhines were used. Computed tomography images of the thoracic vertebrae were converted to a three-dimensional (3D) bone surface, and 104 landmarks were obtained on the 3D surface. For size-independent shape analysis, the vertebrae were scaled to the same centroid size, and the normalised landmarks were registered using the generalised Procrustes method. Principle components of shape variation among samples were clarified using the variance–covariance matrix of the Procrustes residuals. The present study revealed that the transverse processes were more dorsally positioned in hominoids compared to non-hominoids. The results showed that not only a dorsolaterally oriented but also a dorsally positioned transverse process in relation to the vertebral arch contribute to the greater dorsal depth in hominoids than in monkeys. The thoracic vertebrae of Ateles and Nasalis show relatively dorsoventrally low and craniocaudally long vertebrae with craniocaudally long zygapophyses and craniocaudally long base/short tip of the caudally oriented spinous process, accompanied by a laterally oriented and craniocaudally long base of the transverse process. Despite being phylogenetically separated, the vertebral features of Ateles (suspensory platyrrhine with its prehensile tail's aid) are similar to those of Nasalis (arboreal quadrupedal/jumping/arm-swing colobine). The morphology of the third to sixth thoracic vertebrae tends to reflect the functional adaptation in relation to positional behaviour rather than the phylogenetic characteristics of hominoids, cercopithecoids, and platyrrhines.