Additional remains of Wadilemur elegans, a primitive stem galagid from the late Eocene of Egypt

A new primate community from the earliest Oligocene of the Atlantic margin of Northwest Africa: Systematic, paleobiogeographic, and paleoenvironmental implications

We report a new Paleogene primate community discovered in the uppermost part of the Samlat Formation outcropping on the continental shore of the Rio de Oro, east of the Dakhla peninsula (in the south of Morocco, near the northern border of Mauritania). Fossils consist of isolated teeth, which were extracted by wet screening of estuarine sediments (DAK C2) dating from the earliest Oligocene (ca. 33.5 Ma). These dental remains testify to the presence of at least eight primate species, documenting distinct families, four of which are among the Anthropoidea (Oligopithecidae [Catopithecus aff. browni], Propliopithecidae [?Propliopithecus sp.], Parapithecidae [Abuqatrania cf. basiodontos], and Afrotarsiidae [Afrotarsius sp.]) and four in the Strepsirrhini (a Djebelemuridae [cf. 'Anchomomys' milleri], a Galagidae [Wadilemur cf. elegans], a possible lorisiform [Orogalago saintexuperyi gen. et sp. nov.], and a strepsirrhine of indeterminate affinities [Orolemur mermozi gen. et sp. nov.]). This record of various primates at Dakhla represents the first Oligocene primate community from Northwest Africa, especially from the Atlantic margin of that landmass. Considering primates plus rodents (especially hystricognaths), the taxonomic proximity at the generic (even specific) level between DAK C2 (Dakhla) and the famous Egyptian fossil-bearing localities of the Jebel Qatrani Formation (Fayum Depression), either dating from the latest Eocene (L-41) or from the early Oligocene, suggests the existence of an east-west 'trans-North African' environmental continuum during the latest Eocene-earliest Oligocene time interval. The particularly diverse mammal fauna from DAK C2, recorded within the time window of global climate deterioration characterizing the Eocene/Oligocene transition, suggests that this tropical region of northwest Africa was seemingly less affected, if at all, by the cooling and associated paleoenvironmental and biotic changes documented at that time or at least that the effects were delayed. The expected densely forested paleoenvironment bordering the western margin of North Africa at the beginning of the early Oligocene probably offered better tropical refugia than higher latitudes or more inland areas during the cooling episode.

Early anthropoid primates: New data and new questions

Although the evolutionary history of anthropoid primates (monkeys, apes, and humans) appears relatively well-documented, there is limited data available regarding their origins and early evolution. We review and discuss here the earliest records of anthropoid primates from Asia, Africa, and South America. New fossils provide strong support for the Asian origin of anthropoid primates. However, the earliest recorded anthropoids from Africa and South America are still subject to debate, and the early evolution and dispersal of platyrhines to South America remain unclear. Because of the rarity and incomplete nature of many stem anthropoid taxa, establishing the phylogenetic relationships among the earliest anthropoids remains challenging. Nonetheless, by examining evidence from anthropoids and other mammalian groups, we demonstrate that several dispersal events occurred between South Asia and Afro-Arabia during the middle Eocene to the early Oligocene. It is possible that a microplate situated in the middle of the Neotethys Ocean significantly reduced the distance of overseas dispersal.

A global catalog of whole-genome diversity from 233 primate species

The rich diversity of morphology and behavior displayed across primate species provides an informative context in which to study the impact of genomic diversity on fundamental biological processes. Analysis of that diversity provides insight into long-standing questions in evolutionary and conservation biology and is urgent given severe threats these species are facing. Here, we present high-coverage whole-genome data from 233 primate species representing 86% of genera and all 16 families. This dataset was used, together with fossil calibration, to create a nuclear DNA phylogeny and to reassess evolutionary divergence times among primate clades. We found within-species genetic diversity across families and geographic regions to be associated with climate and sociality, but not with extinction risk. Furthermore, mutation rates differ across species, potentially influenced by effective population sizes. Lastly, we identified extensive recurrence of missense mutations previously thought to be human specific. This study will open a wide range of research avenues for future primate genomic research.

Phylogeography and evolutionary lineage diversity in the small-eared greater galago, Otolemur garnettii (Primates: Galagidae)

Assessing the true lineage diversity in elusive nocturnal organisms is particularly challenging due to their subtle phenotypic variation in diagnostic traits. The cryptic small-eared greater galago (Otolemur garnettii) offers a great opportunity to test if currently recognized subspecies, suggested by discontinuities in coat colour pattern and geographic barriers, represent distinct evolutionary lineages. To answer this question, we conducted the first population-level phylogeographic study of the species, sampling wild specimens from across almost its entire latitudinal range, including the Zanzibar Archipelago. We applied five species-delimitation algorithms to investigate the genetic diversity and distribution pattern of mitochondrial DNA across the geographic range of three out of four subspecies. Our results suggest that far-northern populations of O. g. lasiotis potentially represent an independently evolving lineage, but populations assigned to O. g. garnettii from Zanzibar Island and of O. g panganiensis from mainland Tanzania do not constitute two independent lineages. A dated phylogeny suggests that this northern clade diverged from all remaining samples approximately 4 Mya. Such old divergence age is in line with the split between many galagid species. This northern lineage could potentially represent an incipient species; however, there is not yet enough evidence to support a new taxonomic status for this unique mitochondrial group.

Extant species fail to estimate ancestral geographical ranges at older nodes in primate phylogeny

A clade's evolutionary history is shaped, in part, by geographical range expansion, sweepstakes dispersal and local extinction. A rigorous understanding of historical biogeography may therefore yield insights into macroevolutionary dynamics such as adaptive radiation. Modern historical biogeographic analyses typically fit statistical models to molecular phylogenies, but it remains unclear whether extant species provide sufficient signal or if well-sampled phylogenies of extinct and extant taxa are necessary to produce meaningful estimates of past ranges. We investigated the historical biogeography of Primates and their euarchontan relatives using a novel meta-analytical phylogeny of over 900 extant (n= 419) and extinct (n = 483) species spanning their entire evolutionary history. Ancestral range estimates for young nodes were largely congruent with those derived from molecular phylogeny. However, node age exerts a significant effect on ancestral range estimate congruence, and the probability of congruent inference dropped below 0.5 for nodes older than the late Eocene, corresponding to the origins of higher-level clades. Discordance was not observed in analyses of extinct taxa alone. Fossils are essential for robust ancestral range inference and biogeographic analyses of extant clades originating in the deep past should be viewed with scepticism without them.

Rocks and clocks revised: New promises and challenges in dating the primate tree of life

In recent years, multiple technological and methodological advances have increased our ability to estimate phylogenies, leading to more accurate dating of the primate tree of life. Here we provide an overview of the limitations and potentials of some of these advancements and discuss how dated phylogenies provide the crucial temporal scale required to understand primate evolution. First, we review new methods, such as the total-evidence dating approach, that promise a better integration between the fossil record and molecular data. We then explore how the ever-increasing availability of genomic-level data for more primate species can impact our ability to accurately estimate timetrees. Finally, we discuss more recent applications of mutation rates to date divergence times. We highlight example studies that have applied these approaches to estimate divergence dates within primates. Our goal is to provide a critical overview of these new developments and explore the promises and challenges of their application in evolutionary anthropology.

Fossil lemurs from Egypt and Kenya suggest an African origin for Madagascar's aye-aye

In 1967 G.G. Simpson described three partial mandibles from early Miocene deposits in Kenya that he interpreted as belonging to a new strepsirrhine primate, Propotto. This interpretation was quickly challenged, with the assertion that Propotto was not a primate, but rather a pteropodid fruit bat. The latter interpretation has not been questioned for almost half a century. Here we re-evaluate the affinities of Propotto, drawing upon diverse lines of evidence to establish that this strange mammal is a strepsirrhine primate as originally suggested by Simpson. Moreover, our phylogenetic analyses support the recognition of Propotto, together with late Eocene Plesiopithecus from Egypt, as African stem chiromyiform lemurs that are exclusively related to the extant aye-aye (Daubentonia) from Madagascar. Our results challenge the long-held view that all lemurs are descended from a single ancient colonization of Madagascar, and present an intriguing alternative scenario in which two lemur lineages dispersed from Africa to Madagascar independently, possibly during the later Cenozoic.

Craniodental and humeral morphology of a new species of Masrasector (Teratodontinae, Hyaenodonta, Placentalia) from the late Eocene of Egypt and locomotor diversity in hyaenodonts

Hyaenodonta is a diverse clade of carnivorous mammals that were part of terrestrial faunas in the Paleogene of Eurasia and North America, but the oldest record for the group is Afro-Arabian, making the record there vital for understanding the evolution of this wide-spread group. Previous studies show an ancient split between two major clades of hyaenodonts that converged in hypercarnivory: Hyainailourinae and Hyaenodontinae. These clades are each supported by cranial characters. Phylogenetic analyses of hyaenodonts also support the monophyly of Teratodontinae, an Afro-Arabian clade of mesocarnivorous to hypercarnivorous hyaenodonts. Unfortunately, the cranial anatomy of teratodontines is poorly known, and aligning the clade with other lineages has been difficult. Here, a new species of the phylogenetically controversial teratodontine Masrasector is described from Locality 41 (latest Priabonian, late Eocene) from the Fayum Depression, Egypt. The hypodigm includes the most complete remains of a Paleogene teratodontine, including largely complete crania, multiple dentaries, and isolated humeri. Standard and "tip-dating" Bayesian analyses of a character-taxon matrix that samples cranial, postcranial, and dental characters support a monophyletic Masrasector within Teratodontinae, which is consistently placed as a close sister group of Hyainailouridae. The cranial morphology of Masrasector provides new support for an expanded Hyainailouroidea (Teratodontinae + Hyainailouridae), particularly characters of the nuchal crest, palate, and basicranium. A discriminant function analysis was performed using measurements of the distal humerus from a diverse sample of extant carnivorans to infer the locomotor habits of Masrasector. Masrasector was assigned to the "terrestrial" locomotor category, a result consistent with the well-defined medial trochlear ridges, and moderately developed supinator crests of the specimens. Masrasector appears to have been a fast-moving terrestrial form with a diverse diet. These specimens considerably improve our understanding of Teratodontinae, an ancient member of the Afro-Arabian mammalian fauna, and our understanding of hyaenodont diversity before the dispersal of Carnivora to the continent near the end of the Paleogene.

Contextualising primate origins--an ecomorphological framework

Ecomorphology - the characterisation of the adaptive relationship between an organism's morphology and its ecological role - has long been central to theories of the origin and early evolution of the primate order. This is exemplified by two of the most influential theories of primate origins: Matt Cartmill's Visual Predation Hypothesis, and Bob Sussman's Angiosperm Co-Evolution Hypothesis. However, the study of primate origins is constrained by the absence of data directly documenting the events under investigation, and has to rely instead on a fragmentary fossil record and the methodological assumptions inherent in phylogenetic comparative analyses of extant species. These constraints introduce particular challenges for inferring the ecomorphology of primate origins, as morphology and environmental context must first be inferred before the relationship between the two can be considered. Fossils can be integrated in comparative analyses and observations of extant model species and laboratory experiments of form-function relationships are critical for the functional interpretation of the morphology of extinct species. Recent developments have led to important advancements, including phylogenetic comparative methods based on more realistic models of evolution, and improved methods for the inference of clade divergence times, as well as an improved fossil record. This contribution will review current perspectives on the origin and early evolution of primates, paying particular attention to their phylogenetic (including cladistic relationships and character evolution) and environmental (including chronology, geography, and physical environments) contextualisation, before attempting an up-to-date ecomorphological synthesis of primate origins.

New phiomorph rodents from the latest Eocene of Egypt, and the impact of Bayesian "clock"-based phylogenetic methods on estimates of basal hystricognath relationships and biochronology

The Fayum Depression of Egypt has yielded fossils of hystricognathous rodents from multiple Eocene and Oligocene horizons that range in age from ∼37 to ∼30 Ma and document several phases in the early evolution of crown Hystricognathi and one of its major subclades, Phiomorpha. Here we describe two new genera and species of basal phiomorphs, Birkamys korai and Mubhammys vadumensis, based on rostra and maxillary and mandibular remains from the terminal Eocene (∼34 Ma) Fayum Locality 41 (L-41). Birkamys is the smallest known Paleogene hystricognath, has very simple molars, and, like derived Oligocene-to-Recent phiomorphs (but unlike contemporaneous and older taxa) apparently retained dP(4)∕4 late into life, with no evidence for P(4)∕4 eruption or formation. Mubhammys is very similar in dental morphology to Birkamys, and also shows no evidence for P(4)∕4 formation or eruption, but is considerably larger. Though parsimony analysis with all characters equally weighted places Birkamys and Mubhammys as sister taxa of extant Thryonomys to the exclusion of much younger relatives of that genus, all other methods (standard Bayesian inference, Bayesian "tip-dating," and parsimony analysis with scaled transitions between "fixed" and polymorphic states) place these species in more basal positions within Hystricognathi, as sister taxa of Oligocene-to-Recent phiomorphs. We also employ tip-dating as a means for estimating the ages of early hystricognath-bearing localities, many of which are not well-constrained by geological, geochronological, or biostratigraphic evidence. By simultaneously taking into account phylogeny, evolutionary rates, and uniform priors that appropriately encompass the range of possible ages for fossil localities, dating of tips in this Bayesian framework allows paleontologists to move beyond vague and assumption-laden "stage of evolution" arguments in biochronology to provide relatively rigorous age assessments of poorly-constrained faunas. This approach should become increasingly robust as estimates are combined from multiple independent analyses of distantly related clades, and is broadly applicable across the tree of life; as such it is deserving of paleontologists' close attention. Notably, in the example provided here, hystricognathous rodents from Libya and Namibia that are controversially considered to be of middle Eocene age are instead estimated to be of late Eocene and late Oligocene age, respectively. Finally, we reconstruct the evolution of first lower molar size among Paleogene African hystricognaths using a Bayesian approach; the results of this analysis reconstruct a rapid latest Eocene dwarfing event along the lineage leading to Birkamys.

Geomolecular Dating and the Origin of Placental Mammals

In modern evolutionary divergence analysis the role of geological information extends beyond providing a timescale, to informing molecular rate variation across the tree. Here I consider the implications of this development. I use fossil calibrations to test the accuracy of models of molecular rate evolution for placental mammals, and reveal substantial misspecification associated with life history rate correlates. Adding further calibrations to reduce dating errors at specific nodes unfortunately tends to transfer underlying rate errors to adjacent branches. Thus, tight calibration across the tree is vital to buffer against rate model errors. I argue that this must include allowing maximum bounds to be tight when good fossil records permit, otherwise divergences deep in the tree will tend to be inflated by the interaction of rate errors and asymmetric confidence in minimum and maximum bounds. In the case of placental mammals I sought to reduce the potential for transferring calibration and rate model errors across the tree by focusing on well-supported calibrations with appropriately conservative maximum bounds. The resulting divergence estimates are younger than others published recently, and provide the long-anticipated molecular signature for the placental mammal radiation observed in the fossil record near the 66 Ma Cretaceous-Paleogene extinction event.

Remarkable ancient divergences amongst neglected lorisiform primates

Lorisiform primates (Primates: Strepsirrhini: Lorisiformes) represent almost 10% of the living primate species and are widely distributed in sub-Saharan Africa and South/South-East Asia; however, their taxonomy, evolutionary history, and biogeography are still poorly understood. In this study we report the largest molecular phylogeny in terms of the number of represented taxa. We sequenced the complete mitochondrial cytochrome b gene for 86 lorisiform specimens, including ∼80% of all the species currently recognized. Our results support the monophyly of the Galagidae, but a common ancestry of the Lorisinae and Perodicticinae (family Lorisidae) was not recovered. These three lineages have early origins, with the Galagidae and the Lorisinae diverging in the Oligocene at about 30 Mya and the Perodicticinae emerging in the early Miocene. Our mitochondrial phylogeny agrees with recent studies based on nuclear data, and supports Euoticus as the oldest galagid lineage and the polyphyletic status of Galagoides. Moreover, we have elucidated phylogenetic relationships for several species never included before in a molecular phylogeny. The results obtained in this study suggest that lorisiform diversity remains substantially underestimated and that previously unnoticed cryptic diversity might be present within many lineages, thus urgently requiring a comprehensive taxonomic revision of this primate group. 

A multilocus phylogeny reveals deep lineages within African galagids (Primates: Galagidae)

BACKGROUND

Bushbabies (Galagidae) are among the most morphologically cryptic of all primates and their diversity and relationships are some of the most longstanding problems in primatology. Our knowledge of galagid evolutionary history has been limited by a lack of appropriate molecular data and a paucity of fossils. Most phylogenetic studies have produced conflicting results for many clades, and even the relationships among genera remain uncertain. To clarify galagid evolutionary history, we assembled the largest molecular dataset for galagos to date by sequencing 27 independent loci. We inferred phylogenetic relationships using concatenated maximum-likelihood and Bayesian analyses, and also coalescent-based species tree methods to account for gene tree heterogeneity due to incomplete lineage sorting.

RESULTS

The genus Euoticus was identified as sister taxon to the rest of the galagids and the genus Galagoides was not recovered as monophyletic, suggesting that a new generic name for the Zanzibar complex is required. Despite the amount of genetic data collected in this study, the monophyly of the family Lorisidae remained poorly supported, probably due to the short internode between the Lorisidae/Galagidae split and the origin of the African and Asian lorisid clades. One major result was the relatively old origin for the most recent common ancestor of all living galagids soon after the Eocene-Oligocene boundary.

CONCLUSIONS

Using a multilocus approach, our results suggest an early origin for the crown Galagidae, soon after the Eocene-Oligocene boundary, making Euoticus one of the oldest lineages within extant Primates. This result also implies that one - or possibly more - stem radiations diverged in the Late Eocene and persisted for several million years alongside members of the crown group.

Djebelemur, a tiny pre-tooth-combed primate from the Eocene of Tunisia: a glimpse into the origin of crown strepsirhines

BACKGROUND

Molecular clock estimates of crown strepsirhine origins generally advocate an ancient antiquity for Malagasy lemuriforms and Afro-Asian lorisiforms, near the onset of the Tertiary but most often extending back to the Late Cretaceous. Despite their inferred early origin, the subsequent evolutionary histories of both groups (except for the Malagasy aye-aye lineage) exhibit a vacuum of lineage diversification during most part of the Eocene, followed by a relative acceleration in diversification from the late Middle Eocene. This early evolutionary stasis was tentatively explained by the possibility of unrecorded lineage extinctions during the early Tertiary. However, this prevailing molecular view regarding the ancient origin and early diversification of crown strepsirhines must be viewed with skepticism due to the new but still scarce paleontological evidence gathered in recent years.

METHODOLOGICAL/PRINCIPAL FINDINGS

Here, we describe new fossils attributable to Djebelemur martinezi, a≈50 Ma primate from Tunisia (Djebel Chambi). This taxon was originally interpreted as a cercamoniine adapiform based on limited information from its lower dentition. The new fossils provide anatomical evidence demonstrating that Djebelemur was not an adapiform but clearly a distant relative of lemurs, lorises and galagos. Cranial, dental and postcranial remains indicate that this diminutive primate was likely nocturnal, predatory (primarily insectivorous), and engaged in a form of generalized arboreal quadrupedalism with frequent horizontal leaping. Djebelemur did not have an anterior lower dentition as specialized as that characterizing most crown strepsirhines (i.e., tooth-comb), but it clearly exhibited a transformed antemolar pattern representing an early stage of a crown strepsirhine-like adaptation ("pre-tooth-comb").

CONCLUSIONS/SIGNIFICANCE

These new fossil data suggest that the differentiation of the tooth-comb must postdate the djebelemurid divergence, a view which hence constrains the timing of crown strepsirhine origins to the Middle Eocene, and then precludes the existence of unrecorded lineage extinctions of tooth-combed primates during the earliest Tertiary.

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.

New insights into the ear region anatomy and cranial blood supply of advanced stem Strepsirhini: evidence from three primate petrosals from the Eocene of Chambi, Tunisia

We report the discovery of three isolated primate petrosal fragments from the fossiliferous locality of Chambi (Tunisia), a primate-bearing locality dating from the late early to the early middle Eocene. These fossils display a suite of anatomical characteristics otherwise found only in strepsirhines, and as such might be attributed either to Djebelemur or/and cf. Algeripithecus, the two diminutive stem strepsirhine primates recorded from this locality. Although damaged, the petrosals provide substantial information regarding the ear anatomy of these advanced stem strepsirhines (or pre-tooth-combed primates), notably the patterns of the pathway of the arterial blood supply. Using μCT-scanning techniques and digital segmentation of the structures, we show that the transpromontorial and stapedial branches of the internal carotid artery (ICA) were present (presence of bony tubes), but seemingly too small to supply enough blood to the cranium alone. This suggests that the ICA was not the main cranial blood supply in stem strepsirhines, but that the pharyngeal or vertebral artery primitively ensured a great part of this role instead, an arterial pattern that is reminiscent of modern cheirogaleid, lepilemurid lemuriforms and lorisiforms. This could explain parallel loss of the ICA functionality among these families. Specific measurements made on the cochlea indicate that the small strepsirhine primate(s) from Chambi was (were) highly sensitive to high frequencies and poorly sensitive to low frequencies. Finally, variance from orthogonality of the plane of the semicircular canals (SCs) calculated on one petrosal (CBI-1-569) suggests that Djebelemur or cf. Algeripithecus likely moved (at least its head) in a way similar to that of modern mouse lemurs.

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.

Nievesia sossisensis, a new anchomomyin (Adapiformes, Primates) from the early Late Eocene of the southern Pyrenees (Catalonia, Spain)

A new genus and species attributed to the tribe Anchomomyini is described from the early Late Eocene locality of Sossís (MP17a), one of the most important Paleogene fossil sites from the Iberian Peninsula. Nievesia sossisensis is characterized by its buccolingually compressed P(4) and its upper molars with no pericone, medium-sized hypocone, straight postcingulum and minuscule mesostyle, and the extremely reduced metacone on the M(3). Its lower dentition presents a P4 with an incipient metaconid, lower molars with no paraconid and a premetacristid closing the trigonid basin, and M3 with the trigonid wider than the talonid. Phylogenetic analyses suggest a close relationship between Nievesia and Mazateronodon, although the new genus is also related to Anchomomys and, to a lesser extent, Buxella and Periconodon. These analyses, which also include djebelemurines, no longer relate European anchomomyins with crown strepsirhines, and suggest their closer relationship with asiadapines and sivaladapids.

Early primate evolution in Afro-Arabia

The peculiar mammalian fauna that inhabited Afro-Arabia during the Paleogene first came to the attention of the scientific community in the early part of the twentieth century, when Andrews1 and Schlosser2 published their landmark descriptions of fossil mammals from the Fayum Depression in northern Egypt. Their studies revealed a highly endemic assemblage of land mammals that included the first known Paleogene records of hyraxes, proboscideans, and anthropoid primates, but which lacked ancestors of many iconic mammalian lineages that are found in Africa today, such as rhinos, zebras, bovids, giraffes, and cats. Over the course of the last century, the Afro-Arabian Paleogene has yielded fossil remains of several other endemic mammalian lineages,3 as well as a diversity of prosimian primates,4 but we are only just beginning to understand how the continent's faunal composition came to be, through ancient processes such as the movement of tectonic plates, changes in climate and sea level, and early phylogenetic splits among the major groups of placental mammals. These processes, in turn, made possible chance dispersal events that were critical in determining the competitive landscape--and, indeed, the survival--of our earliest anthropoid ancestors. Newly discovered fossils indicate that the persistence and later diversification of Anthropoidea was not an inevitable result of the clade's competitive isolation or adaptive superiority, as has often been assumed, but rather was as much due to the combined influences of serendipitous geographic conditions, global cooling, and competition with a group of distantly related extinct strepsirrhines with anthropoid-like adaptations known as adapiforms. Many of the important details of this story would not be known, and could never have been predicted, without the fossil evidence that has recently been unearthed by field paleontologists.

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.

New adapiform primate of Old World affinities from the Devil's Graveyard Formation of Texas

Most adapiform primates from North America are members of an endemic radiation of notharctines. North American notharctines flourished during the Early and early Middle Eocene, with only two genera persisting into the late Middle Eocene. Here we describe a new genus of adapiform primate from the Devil's Graveyard Formation of Texas. Mescalerolemur horneri, gen. et sp. nov., is known only from the late Middle Eocene (Uintan) Purple Bench locality. Phylogenetic analyses reveal that Mescalerolemur is more closely related to Eurasian and African adapiforms than to North American notharctines. In this respect, M. horneri is similar to its sister taxon Mahgarita stevensi from the late Duchesnean of the Devil's Graveyard Formation. The presence of both genera in the Big Bend region of Texas after notharctines had become locally extinct provides further evidence of faunal interchange between North America and East Asia during the middle Eocene. The fact that Mescalerolemur and Mahgarita are both unknown outside of Texas also supports prior hypotheses that low-latitude faunal assemblages in North America demonstrate increased endemism by the late middle Eocene.

Astragalar morphology of Afradapis, a large adapiform primate from the earliest late Eocene of Egypt

The ∼37 million-year-old Birket Qarun Locality 2 (BQ-2), in the Birket Qarun Formation of Egypt's Fayum Depression, yields evidence for a diverse primate fauna, including the earliest known lorisiforms, parapithecoid anthropoids, and Afradapis longicristatus, a large folivorous adapiform. Phylogenetic analysis has placed Afradapis as a stem strepsirrhine within a clade of caenopithecine adapiforms, contradicting the recently popularized alternative hypothesis aligning adapiforms with haplorhines or anthropoids. We describe an astragalus from BQ-2 (DPC 21445C), attributable to Afradapis on the basis of size and relative abundance. The astragalus is remarkably similar to those of extant lorises, having a low body, no posterior shelf, a broad head and neck. It is like extant strepsirrhines more generally, in having a fibular facet that slopes gently away from the lateral tibial facet, and in having a groove for the tendon of flexor fibularis that is lateral to the tibial facet. Comparisons to a sample of euarchontan astragali show the new fossil to be most similar to those of adapines and lorisids. The astragali of other adapiforms are most similar to those of lemurs, but distinctly different from those of all anthropoids. Our measurements show that in extant strepsirrhines and adapiforms the fibular facet slopes away from the lateral tibial facet at a gradual angle (112-126°), in contrast to the anthropoid fibular facet, which forms a sharper angle (87-101°). Phylogenetic analyses incorporating new information from the astragalus continue to support strepsirrhine affinities for adapiforms under varying models of character evolution.

A fossil primate of uncertain affinities from the earliest late Eocene of Egypt

Paleontological work carried out over the last 3 decades has established that three major primate groups were present in the Eocene of Africa-anthropoids, adapiforms, and advanced strepsirrhines. Here we describe isolated teeth of a previously undocumented primate from the earliest late Eocene ( approximately 37 Ma) of northern Egypt, Nosmips aenigmaticus, whose phylogenetic placement within Primates is unclear. Nosmips is smaller than the sympatric adapiform Afradapis but is considerably larger than other primate taxa known from the same paleocommunity. The species bears an odd mosaic of dental features, combining enlarged, elongate, and molariform premolars with simple upper molars that lack hypocones. Phylogenetic analysis across a series of different assumption sets variously places Nosmips as a stem anthropoid, a nonadapiform stem strepsirrhine, or even among adapiforms. This phylogenetic instability suggests to us that Nosmips likely represents a highly specialized member of a previously undocumented, and presumably quite ancient, endemic African primate lineage, the subordinal affinities of which have been obscured by its striking dental autapomorphies. Discriminant functions based on measurements of lower molar size and topography reliably classify extant prosimian primates into their correct dietary groups and identify Nosmips and Afradapis as omnivores and folivores, respectively. Although Nosmips currently defies classification, this strange and unexpected fossil primate nevertheless provides additional evidence for high primate diversity in northern Africa approximately 37 million years ago and further underscores the fact that our understanding of early primate evolution on that continent remains highly incomplete.

Deep evolutionary roots of strepsirrhine primate labyrinthine morphology

The cavity system of the inner ear of mammals is a complex three-dimensional structure that houses the organs of equilibrium and hearing. Morphological variation of the inner ear across mammals reflects differences in locomotor behaviour and hearing performance, and the good preservation of this structure in many fossil specimens permits analogous inferences. However, it is less well known to what extent the morphology of the bony labyrinth conveys information about the evolutionary history of primate taxa. We studied this question in strepsirrhine primates with the aim to assess the potential and limitations of using the inner ear as a phylogenetic marker. Geometric morphometric analysis showed that the labyrinthine morphology of extant strepsirrhines contains a mixed locomotor, allometric and phylogenetic signal. Discriminant analysis at the family level confirmed that labyrinthine shape is a good taxonomic marker. Our results support the hypothesis that evolutionary change in labyrinthine morphology is adequately described with a random walk model, i.e. random phenotypic dispersal in morphospace. Under this hypothesis, average shapes calculated for each node of the phylogenetic tree give an estimate of inner ear shapes of the respective last common ancestors (LCAs), and this information can be used to infer character state polarity. The labyrinthine morphology of the fossil Adapinae is close to the inferred basal morphology of the strepsirrhines. The inner ear of Daubentonia, one of the most derived extant strepsirrhines, is autapomorphic in many respects, but also presents unique similarities with adapine labyrinths.

Anthropoid versus strepsirhine status of the African Eocene primates Algeripithecus and Azibius: craniodental evidence

Recent fossil discoveries have demonstrated that Africa and Asia were epicentres for the origin and/or early diversification of the major living primate lineages, including both anthropoids (monkeys, apes and humans) and crown strepsirhine primates (lemurs, lorises and galagos). Competing hypotheses favouring either an African or Asian origin for anthropoids rank among the most hotly contested issues in paleoprimatology. The Afrocentric model for anthropoid origins rests heavily on the >45 Myr old fossil Algeripithecus minutus from Algeria, which is widely acknowledged to be one of the oldest known anthropoids. However, the phylogenetic position of Algeripithecus with respect to other primates has been tenuous because of the highly fragmentary fossils that have documented this primate until now. Recently recovered and more nearly complete fossils of Algeripithecus and contemporaneous relatives reveal that they are not anthropoids. New data support the idea that Algeripithecus and its sister genus Azibius are the earliest offshoots of an Afro-Arabian strepsirhine clade that embraces extant toothcombed primates and their fossil relatives. Azibius exhibits anatomical evidence for nocturnality. Algeripithecus has a long, thin and forwardly inclined lower canine alveolus, a feature that is entirely compatible with the long and procumbent lower canine included in the toothcomb of crown strepsirhines. These results strengthen an ancient African origin for crown strepsirhines and, in turn, strongly challenge the role of Africa as the ancestral homeland for anthropoids.

Evolution and Extinction of Afro-Arabian Primates Near the Eocene-Oligocene Boundary

Revised age estimates for the primate-bearing localities of the Jebel Qatrani Formation (Fayum area, northern Egypt) have provided a new perspective on primate response to early Oligocene climate change in North Africa. Environmental changes associated with early Oligocene cooling might have driven the local extinction of at least 4 strepsirrhine primate clades (adapids, djebelemurines, plesiopithecids and galagids). Contrary to previous suggestions, oligopithecid (and possibly proteopithecid) anthropoids persisted beyond the Eocene-Oligocene boundary (EOB) in the Fayum area, and the former group evidently continued to diversify through the early Oligocene at lower latitudes. Propliopithecids and parapithecine parapithecids first appear in the Jebel Qatrani Formation millions of years after the EOB, so their derived dental and gnathic features can no longer be interpreted as sudden adaptive morphological responses to earliest Oligocene climatic events. Evidence for latitudinal contraction of Afro-Arabian primate distribution through the early Oligocene suggests that the profound late Oligocene restructuring of Afro-Arabian primate communities is most likely to have occurred in equatorial and low-latitude tropical Africa.

Primate Origins: Implications of a Cretaceous Ancestry

It has long been accepted that the adaptive radiation of modern placental mammals, like that of modern birds, did not begin until after the Cretaceous/Tertiary (K/T) boundary 65 million years (Ma) ago, following the extinction of the dinosaurs. The first undoubted fossil relatives of modern primates appear in the record 55 Ma ago. However, in agreement with evidence from molecular phylogenies calibrated with dates from denser parts of the fossil record, a statistical analysis of the primate record allowing for major gaps now indicates a Cretaceous origin of euprimates 80-90 Ma ago. If this interpretation is correct, primates overlapped with dinosaurs by some 20 Ma prior to the K/T boundary, and the initial radiation of primates was probably truncated as part of the major extinction event that occurred at the end of the Cretaceous. Following a review of evidence for an early origin of primates, implications of this are discussed with respect to the likely ancestral condition for primates, including a southern continental area of origin and moderately large body size. The known early Tertiary primates are re-interpreted as northern continental offshoots of a 'second wave' of primate evolution.

Early evolution and biogeography of lorisiform strepsirrhines

This brief review summarizes new paleontological and molecular data that together support a late middle Eocene Afro-Arabian origin for crown Lorisiformes. Phylogenetic analysis indicates that late Eocene Karanisia is a possible stem lorisiform, late Eocene Saharagalago and Wadilemur and Miocene Komba are stem galagids, and early Miocene Mioeuoticus and Progalago may be crown lorisids. Character evolution along the lorisid and galagid stem lineages is reconstructed as having occurred primarily in postcranial and dental morphology, respectively. These patterns have important implications for interpreting an early lorisiform fossil record that is still composed primarily of jaws and isolated teeth.

Lemuriform origins as viewed from the fossil record

Fossils relevant to lemuriform origins are reviewed. Omanodon seems very close to the other early tooth-combed lemuriforms Karanisia, Wadilemur and Saharagalago, whereas Bugtilemur is rejected from the Lemuriformes. The Djebelemurinae, including Djebelemur and 'Anchomomys' milleri, are considered as stem lemuriforms preceding tooth comb differentiation; they are shown to be very distinct from European adapiforms. With tooth-combed lemuriforms present in Africa around 40 million years ago, and stem lemuriforms without tooth combs present on the same continent around 50-48 million years ago, a reasonable scenario can be proposed: tooth comb differentiation and lemuriform dispersal to Madagascar between 52-40 million years ago. The possible significance of Plesiopithecus for daubentoniid origins is raised. A critique of molecular dates is presented in the light of the fossil record. Azibiids are possibly early African prosimians. The timing of the dispersal of primates to Africa and the problem of strepsirhine origins are briefly examined.

Primate molecular divergence dates

With genomic data, alignments can be assembled that greatly increase the number of informative sites for analysis of molecular divergence dates. Here, we present an estimate of the molecular divergence dates for all of the major primate groups. These date estimates are based on a Bayesian analysis of approximately 59.8 kbp of genomic data from 13 primates and 6 mammalian outgroups, using a range of paleontologically supported calibration estimates. Results support a Cretaceous last common ancestor of extant primates (approximately 77 mya), an Eocene divergence between platyrrhine and catarrhine primates (approximately 43 mya), an Oligocene origin of apes and Old World monkeys (approximately 31 mya), and an early Miocene (approximately 18 mya) divergence of Asian and African great apes. These dates are examined in the context of other molecular clock studies.

Revised age estimates for the later Paleogene mammal faunas of Egypt and Oman

The Jebel Qatrani Formation of northern Egypt has produced Afro-Arabia's primary record of Paleogene mammalian evolution, including the world's most complete remains of early anthropoid primates. Recent studies of Fayum mammals have assumed that the Jebel Qatrani Formation contains a significant Eocene component ( approximately 150 of 340 m), and that most taxa from that succession are between 35.4 and 33.3 million years old (Ma), i.e., latest Eocene to earliest Oligocene in age. Reanalysis of the chronological evidence shared by later Paleogene strata exposed in Egypt and Oman (Taqah and Thaytiniti areas, Dhofar Province) reveals that this hypothesis is no longer tenable. Revised correlation of the Fayum and Dhofar magnetostratigraphies indicates that (i) only the lowest 48 m of the Jebel Qatrani Formation are likely to be Eocene in age; (ii) the youngest Fayum anthropoids, including well known species such as Aegyptopithecus zeuxis and Apidium phiomense, are probably between 30.2 and 29.5 Ma, approximately 3-4 Ma younger than previously thought; (iii) oligopithecid anthropoids did not go extinct at the Eocene-Oligocene boundary but rather persisted for at least another 2.5 Ma; (iv) propliopithecid anthropoids first appear in the Fayum area at approximately 31.5 Ma, long after the Eocene-Oligocene boundary; and (v) the youngest Fayum mammals may be only approximately 1 Ma older than the 28- to 27-Ma mammals from Chilga, Ethiopia, and not 4-5 Ma older, as previously thought. Whatever gap exists in the Oligocene record of Afro-Arabian mammal evolution is now limited primarily to a poorly sampled 27- to 23-Ma window in the latest Oligocene.

Malagasy Primate Origins: Phylogenies, Fossils, and Biogeographic Reconstructions

The geographic origin of Malagasy primates is a rich source of debate, providing a useful context for understanding effects of differing phylogenetic interpretations upon area of origin reconstructions. This study has evaluated the biogeographic implications of competing primate phylogenies in order to reconstruct the area of origin of Malagasy strepsirhines. The robusticity of biogeographic inference is examined based on sensitivity to tree topology. The results demonstrate extreme vulnerability to both out-group choice and internal tree topology, suggesting caution for area of origin interpretations from phylogenies that exclude fossil taxa. Moreover, even a single taxon can have a powerful effect upon biogeographic interpretations. Perhaps not surprisingly, it is only with greater phylogenetic resolution that a clearer understanding of the biogeographic origins of Malagasy primates will emerge.

Deep Time and the Search for Anthropoid Origins

Recent fossil discoveries, phylogenetic analyses, revised reconstructions of continental drift, and accumulating molecular evidence have all yielded new information relating to anthropoid origins within the broader context of primate evolution. There is an emerging consensus among molecular studies that four superorders of eutherian mammals can be recognized: Afrotheria, Euarchontoglires (to which primates belong), Laurasiatheria, and Xenarthra. Overall, molecular phylogenies for mammals agree with some statistical analyses of the primate fossil record in indicating an early origin for primates around 85 Ma ago, and the divergence of haplorhines and strepsirrhines at ca. 77 Ma. Such an ancient date for the origin of haplorhines is some 17 Ma prior to the first known possible primate, and some 22 Ma before the earliest fossil evidence of undoubted euprimates. Because anthropoid fossils date back at least to the late Eocene and perhaps to the middle Eocene, and given indications of an early origin for primates, it is unlikely that ancestral anthropoids arose within any other currently known clade of fossil primates (adapiforms, omomyiforms, strepsirrhines, or tarsiiforms). Implications of new molecular, morphological, and biogeographic lines of evidence are explored with respect to the likely time and place of the origin of anthropoids. Four competing, testable hypotheses are reviewed in detail: 1) the Paratethyan hypothesis, 2) the continental Asian hypothesis, 3) the Indo-Madagascar hypothesis, and 4) the African hypothesis. A case is made that current evidence best supports a relatively ancient Gondwanan origin for primates, as well as a Gondwanan (African or Indo-Madagascan) origin for anthropoids at least as old as that of any other currently documented major primate clade. Available fossil evidence at present seems to be most compatible with the African hypothesis, but it is noteworthy that primates are included not in Afrotheria but in Euarchontoglires.