Complete primate skeleton from the Middle Eocene of Messel in Germany: morphology and paleobiology

The allometry of brain size in Euarchontoglires: clade-specific patterns and their impact on encephalization quotients

The timing and nature of evolutionary shifts in the relative brain size of Primates have been extensively studied. Less is known, however, about the scaling of the brain-to-body size in their closest living relatives, i.e., among other members of Euarchontoglires (Dermoptera, Scandentia, Lagomorpha, Rodentia). Ordinary least squares (OLS), reduced major axis (RMA), and phylogenetic generalized least squares (PGLS) regressions were fitted to the largest euarchontogliran data set of brain and body mass, comprising 715 species. Contrary to previous inferences, lagomorph brain sizes (PGLS slope = 0.465; OLS slope = 0.593) scale relative to body mass similarly to rodents (PGLS = 0.526; OLS = 0.638), and differently than primates (PGLS = 0.607; OLS = 0.794). There is a shift in the pattern of the scaling of the brain in Primates, with Strepsirrhini occupying an intermediate stage similar to Scandentia but different from Rodentia and Lagomorpha, while Haplorhini differ from all other groups in the OLS and RMA analyses. The unique brain-body scaling relationship of Primates among Euarchontoglires illustrates the need for clade-specific metrics for relative brain size (i.e., encephalization quotients; EQs) for more restricted taxonomic entities than Mammalia. We created clade-specific regular and phylogenetically adjusted EQ equations at superordinal, ordinal, and subordinal levels. When using fossils as test cases, our results show that generalized mammalian equations underestimate the encephalization of the stem lagomorph Megalagus turgidus in the context of lagomorphs, overestimate the encephalization of the stem primate Microsyops annectens and the early euprimate Necrolemur antiquus, but provide similar EQ values as our new strepsirrhine-specific EQ when applied to the early euprimate Adapis parisiensis.

Pervasive incomplete lineage sorting illuminates speciation and selection in primates

Incomplete lineage sorting (ILS) causes the phylogeny of some parts of the genome to differ from the species tree. In this work, we investigate the frequencies and determinants of ILS in 29 major ancestral nodes across the entire primate phylogeny. We find up to 64% of the genome affected by ILS at individual nodes. We exploit ILS to reconstruct speciation times and ancestral population sizes. Estimated speciation times are much more recent than genomic divergence times and are in good agreement with the fossil record. We show extensive variation of ILS along the genome, mainly driven by recombination but also by the distance to genes, highlighting a major impact of selection on variation along the genome. In many nodes, ILS is reduced more on the X chromosome compared with autosomes than expected under neutrality, which suggests higher impacts of natural selection on the X chromosome. Finally, we show an excess of ILS in genes with immune functions and a deficit of ILS in housekeeping genes. The extensive ILS in primates discovered in this study provides insights into the speciation times, ancestral population sizes, and patterns of natural selection that shape primate evolution.

Exceptional preservation of internal organs in a new fossil species of freshwater shrimp (Caridea: Palaemonoidea) from the Eocene of Messel (Germany)

A new species of extinct freshwater shrimp was discovered in the Eocene deposit of the Messel Pit Konservat-Lagerstätte. This rare find is represented by only a few specimens, one of which showing exceptionally preserved soft tissues and other internal parts like the stomach with possibly gastric ossicles in place, branchiae, the ovary, and the left mandible, never described in a fossil shrimp. The new species Bechleja brevirostris n. sp. is characterized by a short rostrum bearing 6-8 dorsal spines and one ventral tooth, and long second pereiopods with strong chelae. One additional specimen shows a slightly different morphology and might belong to a different species. The systematic position of the species among the superfamily Palaemonoidea is discussed, as well as implications for the knowledge of the paleoenvironment of Lake Messel and the paleobiogeography of the Eocene.

Visual Depictions of Our Evolutionary Past: A Broad Case Study Concerning the Need for Quantitative Methods of Soft Tissue Reconstruction and Art-Science Collaborations

Flip through scientific textbooks illustrating ideas about human evolution or visit any number of museums of natural history and you will notice an abundance of reconstructions attempting to depict the appearance of ancient hominins. Spend some time comparing reconstructions of the same specimen and notice an obvious fact: hominin reconstructions vary in appearance considerably. In this review, we summarize existing methods of reconstruction to analyze this variability. It is argued that variability between hominin reconstructions is likely the result of unreliable reconstruction methods and misinterpretation of available evidence. We also discuss the risk of disseminating erroneous ideas about human evolution through the use of unscientific reconstructions in museums and publications. The role an artist plays is also analyzed and criticized given how the aforementioned reconstructions have become readily accepted to line the halls of even the most trusted institutions. In conclusion, improved reconstruction methods hold promise for the prediction of hominin soft tissues, as well as for disseminating current scientific understandings of human evolution in the future.

Comparative dental anatomy in newborn primates: Cusp mineralization

Previous descriptive work on deciduous dentition of primates has focused disproportionately on great apes and humans. To address this bias in the literature, we studied 131 subadult nonhominoid specimens (including 110 newborns) describing deciduous tooth morphology and assessing maximum hydroxyapatite density (MHD). All specimens were CT scanned at 70 kVp and reconstructed at 20.5-39 μm voxels. Grayscale intensity from scans was converted to hydroxyapatite (HA) density (mg HA/cm3 ) using a linear conversion of grayscale values to calibration standards of known HA density (R2 = .99). Using Amira software, mineralized dental tissues were captured by segmenting the tooth cusps first and then capturing the remainder of the teeth at descending thresholds of gray levels. We assessed the relationship of MHD of selected teeth to cranial length using Pearson correlation coefficients. In monkeys, anterior teeth are more mineralized than postcanine teeth. In tarsiers and most lemurs and lorises, postcanine teeth are the most highly mineralized. This suggests that monkeys have a more prolonged process of dental mineralization that begins with incisors and canines, while mineralization of postcanine teeth is delayed. This may in part be a result of relatively late weaning in most anthropoid primates. Results also reveal that in lemurs and lorises, MHD of the mandibular first permanent molar (M1 ) negatively correlates with cranial length. In contrast, the MHD of M1 positively correlates with cranial length in monkeys. This supports the hypothesis that natural selection acts independently on dental growth as opposed to mineralization and indicates clear phylogenetic differences among primates.

Comparison of structure and composition of a fossil Champsosaurus vertebra with modern Crocodylidae vertebrae: A multi-instrumental approach

Information on the adaptation of bone structures during evolution is rare since histological data are limited. Micro- and nano-computed tomography of a fossilized vertebra from Champsosaurus sp., which has an estimated age of 70-73 million years, revealed lower porosity and higher bone density compared to modern Crocodylidae vertebrae. Mid-infrared reflectance and energy dispersive X-ray mapping excluded a petrification process, and demonstrated a typical carbonate apatite distribution, confirming histology in light- and electron microscopy of the preserved vertebra. As a consequence of this evolutionary process, the two vertebrae of modern Crocodylidae show reduced overall stiffness in the finite element analysis simulation compared to the fossilized Champsosaurus sp. vertebra, with predominant stiffness along the longitudinal z-axes.

Conserved sequences identify the closest living relatives of primates

Elucidating the closest living relatives of extant primates is essential for fully understanding important biological processes related to the genomic and phenotypic evolution of primates, especially of humans. However, the phylogenetic placement of these primate relatives remains controversial, with three primary hypotheses currently espoused based on morphological and molecular evidence. In the present study, we used two algorithms to analyze differently partitioned genomic datasets consisting of 45.4 Mb of conserved non-coding elements and 393 kb of concatenated coding sequences to test these hypotheses. We assessed different genomic histories and compared with other molecular studies found solid support for colugos being the closest living relatives of primates. Our phylogeny showed Cercopithecinae to have low levels of nucleotide divergence, especially for Papionini, and gibbons to have a high rate of divergence. The MCMCtree comprehensively updated divergence dates of early evolution of Primatomorpha and Primates.

New Eocene primate from Myanmar shares dental characters with African Eocene crown anthropoids

Recent discoveries of older and phylogenetically more primitive basal anthropoids in China and Myanmar, the eosimiiforms, support the hypothesis that Asia was the place of origins of anthropoids, rather than Africa. Similar taxa of eosimiiforms have been discovered in the late middle Eocene of Myanmar and North Africa, reflecting a colonization event that occurred during the middle Eocene. However, these eosimiiforms were probably not the closest ancestors of the African crown anthropoids. Here we describe a new primate from the middle Eocene of Myanmar that documents a new clade of Asian anthropoids. It possesses several dental characters found only among the African crown anthropoids and their nearest relatives, indicating that several of these characters have appeared within Asian clades before being recorded in Africa. This reinforces the hypothesis that the African colonization of anthropoids was the result of several dispersal events, and that it involved more derived taxa than eosimiiforms.

Phalangeal morphology of Shanghuang fossil primates

Here, we describe hundreds of isolated phalanges attributed to middle Eocene fossil primates from the Shanghuang fissure-fillings from southern Jiangsu Province, China. Extending knowledge based on previous descriptions of postcranial material from Shanghuang, this sample of primate finger and toe bones includes proximal phalanges, middle phalanges, and over three hundred nail-bearing distal phalanges. Most of the isolated proximal and middle phalanges fall within the range of small-bodied individuals, suggesting an allocation to the smaller haplorhine primates identified at Shanghuang, including eosimiids. In contrast to the proximal and middle phalanges from Shanghuang, there are a variety of shapes, sizes, and possible taxonomic allocations for the distal phalanges. Two distal phalangeal morphologies are numerically predominant at Shanghuang. The sample of larger bodied specimens is best allocated to the medium-sized adapiform Adapoides while the smaller ones are allocated to eosimiids on the basis of the commonality of dental and tarsal remains of these taxa at Shanghuang. The digit morphology of Adapoides is similar morphologically to that of notharctines and cercamoniines, while eosimiid digit morphology is unlike living anthropoids. Other primate distal phalangeal morphologies at Shanghuang include grooming "claws" as well as specimens attributable to tarsiids, tarsiiforms, the genus Macrotarsius, and a variety of adapiforms. One group of distal phalanges at Shanghuang is morphologically indistinguishable from those of living anthropoids. All of the phalanges suggest long fingers and toes for the fossil primates of Shanghaung, and their digit morphology implies arboreality with well-developed digital flexion and strong, grasping hands and feet.

Agerinia marandati sp. nov., a new early Eocene primate from the Iberian Peninsula, sheds new light on the evolution of the genus Agerinia

BACKGROUND

The Eocene was the warmest epoch of the Cenozoic and recorded the appearance of several orders of modern mammals, including the first occurrence of Euprimates. During the Eocene, Euprimates were mainly represented by two groups, adapiforms and omomyiforms, which reached great abundance and diversity in the Northern Hemisphere. Despite this relative abundance, the record of early Eocene primates from the European continent is still scarce and poorly known, preventing the observation of clear morphological trends in the evolution of the group and the establishment of phylogenetic relationships among different lineages. However, knowledge about the early Eocene primates from the Iberian Peninsula has been recently increased through the description of new material of the genus Agerinia from several fossil sites from Northeastern Spain.

METHODS

Here we present the first detailed study of the euprimate material from the locality of Masia de l'Hereuet (early Eocene, NE Spain). The described remains consist of one fragment of mandible and 15 isolated teeth. This work provides detailed descriptions, accurate measurements, high-resolution figures and thorough comparisons with other species of Agerinia as well with other Eurasian notharctids. Furthermore, the position of the different species of Agerinia has been tested with two phylogenetic analyses.

RESULTS

The new material from Masia de l'Hereuet shows several traits that were previously unknown for the genus Agerinia, such as the morphology of the upper and lower fourth deciduous premolars and the P2, and the unfused mandible. Moreover, this material clearly differs from the other described species of Agerinia, A. roselli and A. smithorum, thus allowing the erection of the new species Agerinia marandati. The phylogenetic analyses place the three species of Agerinia in a single clade, in which A. smithorum is the most primitive species of this genus.

DISCUSSION

The morphology of the upper molars reinforces the distinction of Agerinia from other notharctids like Periconodon. The analysis of the three described species of the genus, A. smithorum, A. marandati and A. roselli, reveals a progressive change in several morphological traits such as the number of roots and the position of the P1 and P2, the molarization of the P4, the reduction of the paraconid on the lower molars and the displacement of the mental foramina. These gradual modifications allow for the interpretation that these three species, described from the early Eocene of the Iberian Peninsula, are part of a single evolutionary lineage. The stratigraphical position of Masia de l'Hereuet and Casa Retjo-1 (type locality of A. smithorum) and the phylogenetic analyses developed in this work support this hypothesis.

Microchoerus hookeri nov. sp., a new late Eocene European microchoerine (Omomyidae, Primates): New insights on the evolution of the genus Microchoerus

The study of Eocene primates is crucial for understanding the evolutionary steps undergone by the earliest members of our lineage and the relationships between extinct and extant taxa. Recently, the description of new material from Spain has improved knowledge of European Paleogene primates considerably, particularly regarding microchoerines. Here we describe the remains of Microchoerus from Sossís (late Eocene, Northern Spain), consisting of more than 120 specimens and representing the richest sample of Microchoerus from Spain. This primate was first documented in Sossís during the 1960s, on the basis of scarce specimens that were ascribed to Microchoerus erinaceus. However, the studied material clearly differs from M. erinaceus at its type locality, Hordle Cliff, and shows some characters that allow the erection of a new species, Microchoerus hookeri. This new species is characterized by its medium size, moderate enamel wrinkling, generally absent mesoconid and small hypoconulid in the M₁ and M₂, single paracone in the upper molars and premolars and, particularly, by the lack of mesostyle in most M¹ and M², a trait not observed in any other species of Microchoerus. Some specimens from Eclépens B (late Eocene, Switzerland), determined previously to be Microcherus aff. erinaceus, are also ascribed to M. hookeri. M. hookeri represents the first step of a lineage that differentiated from Necrolemur antiquus and, later, gave rise to several unnamed forms of Microchoerus, such as those from Euzet and Perrière, finally leading to M. erinaceus. This discovery sheds new light on the complex evolutionary scheme of Microchoerus, indicating that it is most probably a paraphyletic group. A detailed revision of the age of the localities containing remains of Microchoerus and the description of the still unpublished material from some European localities, are necessary to clarify the phylogenetic relationships among the members of this microchoerine group.

From Correlation to Causation: What Do We Need in the Historical Sciences?

Changes in the methodology of the historical sciences make them more vulnerable to unjustifiable speculations being passed off as scientific results. The integrity of historical science is in peril due the way speculative and often unexamined causal assumptions are being used to generate data and underpin the identification of correlations in such data. A step toward a solution is to distinguish between plausible and speculative assumptions that facilitate the inference from measured and observed data to causal claims. One way to do that is by comparing these assumptions against a well-attested set of aspects of causation, such as the so-called "Bradford Hill Criteria" (BHC). The BHC do not provide a test for causation or necessary and sufficient conditions for causation but do indicate grounds for further investigation. By revising the BHC to reflect the needs and focus of historical sciences, it will be possible to assess the cogency of methods of investigation. These will be the Historical Sciences Bradford Hill Criteria (HSBHC). An application to one area in historical science is used to demonstrate the effectiveness of the HSBHC, namely biogeography. Four methods are assessed in order to show how the HSBHC can be used to examine the assumptions between our data and the causal biogeographical processes we infer.

Agerinia smithorum sp. nov., a new early Eocene primate from the Iberian Peninsula

The new species Agerinia smithorum (Adapiformes, Primates) from the early Eocene of the Iberian Peninsula is erected in this work. An emended diagnosis of the genus is provided, together with a broad description of the new species and comparisons with other samples assigned to Agerinia and other similar medium-sized cercamoniines. The new species is based on the most complete specimen of this genus published to date, a mandible preserving the alveoli of the canine and P1 , the roots of the P2 and all teeth from P3 to M3 . It was found in Casa Retjo-1, a new early Eocene locality from Northeastern Spain. The studied specimen is clearly distinguishable from other cercamoniines such as Periconodon, Darwinius, and Donrussellia, but very similar to Agerinia roselli, especially in the similar height of P3 and P4 and the general morphology of the molars, therefore allowing the allocation to the same genus. However, it is undoubtedly distinct from A. roselli, having a less molarized P4 and showing a larger paraconid in the M1 and a tiny one in the M2 , among other differences. The body mass of A. smithorum has also been estimated, ranging from 652 to 724 g, similar to that of A. roselli. The primitive traits shown by A. smithorum (moderately molarized P4 , large paraconid in the M1 and small but distinct in the M2 ) suggest that it could be the ancestor of A. roselli.

Astragalar and calcaneal morphology of the middle Eocene primate Anchomomys frontanyensis (Anchomomyini): Implications for early primate evolution

Astragali and calcanei of Anchomomys frontanyensis, a small adapiform from the middle Eocene of Sant Jaume de Frontanyà (Southern Pyrenean basins, northeastern Spain) are described in detail. Though these bones have been known for some time, they have never been carefully analyzed in a context that is comprehensively comparative, quantitative, considers sample variation (astragalus n = 4; calcaneus n = 16), and assesses the phylogenetic significance of the material in an explicit cladistic context, as we do here. Though these bones are isolated, regression analyses provide the first formal statistical support for attribution to A. frontanyensis. The astragalus presents features similar to those of the small stem strepsirrhine Djebelemur from the middle Eocene of Tunisia, while the calcaneus more closely resembles those of the basal omomyiform Teilhardina. The new phylogenetic analyses that include Anchomomys' postcranial and dental data recover anchomomyins outside of the adapiform clade, and closer to djebelemurids, azibiids, and crown strepsirrhines. The small size of A. frontanyensis allows comparison of similarly small adapiforms and omomyiforms (haplorhines) such that observed variation has more straightforward implications for function. Previous studies have demonstrated that distal calcaneal elongation is reflective of leaping proclivity when effects of body mass are appropriately accounted for; in this context, A. frontanyensis has calcaneal elongation suggesting a higher degree of leaping specialization than other adapiforms and even some early omomyiforms. Moreover, comparison to a similarly-sized early adapiform from India, Marcgodinotius (which shows no calcaneal elongation) confirms that high distal calcaneal elongation in A. frontanyensis cannot be simply explained by allometric effects of small size compared to larger adapiform taxa. This pattern is consistent with the idea that significant distal calcaneal elongation evolved at least twice in early euprimates, and that early primate niche space frequently included demands for increased leaping specialization.

Microscopical and elemental FESEM and Phenom ProX-SEM-EDS analysis of osteocyte- and blood vessel-like microstructures obtained from fossil vertebrates of the Eocene Messel Pit, Germany

The Eocene (∾48 Ma) Messel Pit in Germany is a UNESCO World Heritage Site because of its exceptionally preserved fossils, including vertebrates, invertebrates, and plants. Messel fossil vertebrates are typically characterized by their articulated state, and in some cases the skin, hair, feathers, scales and stomach contents are also preserved. Despite the exceptional macroscopic preservation of Messel fossil vertebrates, the microstructural aspect of these fossils has been poorly explored. In particular, soft tissue structures such as hair or feathers have not been chemically analyzed, nor have bone microstructures. I report here the preservation and recovery of osteocyte-like and blood vessel-like microstructures from the bone of Messel Pit specimens, including the turtles Allaeochelys crassesculpta and Neochelys franzeni, the crocodile Diplocynodon darwini, and the pangolin Eomanis krebsi. I used a Field Emission Scanning Electron Microscope (FESEM) and a Phenom ProX desktop scanning electron microscope (LOT-QuantumDesign) equipped with a thermionic CeB6 source and a high sensitivity multi-mode backscatter electron (BSE) for microscopical and elemental characterization of these bone microstructures. Osteocyte-like and blood vessel-like microstructures are constituted by a thin layer (∾50 nm thickness), external and internal mottled texture with slightly marked striations. Circular to linear marks are common on the external surface of the osteocyte-like microstructures and are interpreted as microbial troughs. Iron (Fe) is the most abundant element found in the osteocyte-like and blood vessel-like microstructures, but not in the bone matrix or collagen fibril-like microstructures. The occurrence of well-preserved soft-tissue elements (at least their physical form) establishes a promising background for future studies on preservation of biomolecules (proteins or DNA) in Messel Pit fossils.

Dental maturation, eruption, and gingival emergence in the upper jaw of newborn primates

In this report we provide data on dental eruption and tooth germ maturation at birth in a large sample constituting the broadest array of non-human primates studied to date. Over 100 perinatal primates, obtained from natural captive deaths, were screened for characteristics indicating premature birth, and were subsequently studied using a combination of histology and micro-CT. Results reveal one probable unifying characteristic of living primates: relatively advanced maturation of deciduous teeth and M1 at birth. Beyond this, there is great diversity in the status of tooth eruption and maturation (dental stage) in the newborn primate. Contrasting strategies in producing a masticatory battery are already apparent at birth in strepsirrhines and anthropoids. Results show that dental maturation and eruption schedules are potentially independently co-opted as different strategies for attaining feeding independence. The most common strategy in strepsirrhines is accelerating eruption and the maturation of the permanent dentition, including replacement teeth. Anthropoids, with only few exceptions, accelerate mineralization of the deciduous teeth, while delaying development of all permanent teeth except M1. These results also show that no living primate resembles the altricial tree shrew (Tupaia) in dental development. Our preliminary observations suggest that ecological explanations, such as diet, provide an explanation for certain morphological variations at birth. These results confirm previous work on perinatal indriids indicating that these and other primates telegraph their feeding adaptations well before masticatory anatomy is functional. Quantitative analyses are required to decipher specific dietary and other influences on dental size and maturation in the newborn primate.

Life history of the most complete fossil primate skeleton: exploring growth models for Darwinius

Darwinius is an adapoid primate from the Eocene of Germany, and its only known specimen represents the most complete fossil primate ever found. Its describers hypothesized a close relationship to Anthropoidea, and using a Saimiri model estimated its age at death. This study reconstructs the ancestral permanent dental eruption sequences for basal Euprimates, Haplorhini, Anthropoidea, and stem and crown Strepsirrhini. The results show that the ancestral sequences for the basal euprimate, haplorhine and stem strepsirrhine are identical, and similar to that of Darwinius. However, Darwinius differs from anthropoids by exhibiting early development of the lower third molars relative to the lower third and fourth premolars. The eruption of the lower second premolar marks the point of interruption of the sequence in Darwinius. The anthropoid Saimiri as a model is therefore problematic because it exhibits a delayed eruption of P2. Here, an alternative strepsirrhine model based on Eulemur and Varecia is presented. Our proposed model shows an older age at death than previously suggested (1.05-1.14 years), while the range for adult weight is entirely below the range proposed previously. This alternative model is more consistent with hypotheses supporting a stronger relationship between adapoids and strepsirrhines.

Primate tarsal bones from Egerkingen, Switzerland, attributable to the middle Eocene adapiform Caenopithecus lemuroides

The middle Eocene species Caenopithecus lemuroides, known solely from the Egerkingen fissure fillings in Switzerland, was the first Paleogene fossil primate to be correctly identified as such (by Ludwig Rütimeyer in 1862), but has long been represented only by fragmentary mandibular and maxillary remains. More recent discoveries of adapiform fossils in other parts of the world have revealed Caenopithecus to be a biogeographic enigma, as it is potentially more closely related to Eocene adapiforms from Africa, Asia, and North America than it is to any known European forms. More anatomical evidence is needed, however, to provide robust tests of such phylogenetic hypotheses. Here we describe and analyze the first postcranial remains that can be attributed to C. lemuroides-an astragalus and three calcanei held in the collections of the Naturhistorisches Museum Basel that were likely recovered from Egerkingen over a century ago. Qualitative and multivariate morphometric analyses of these elements suggest that C. lemuroides was even more loris-like than European adapines such as Adapis and Leptadapis, and was not simply an adapine with an aberrant dentition. The astragalus of Caenopithecus is similar to that of younger Afradapis from the late Eocene of Egypt, and parsimony and Bayesian phylogenetic analyses that include the new tarsal data strongly support the placement of Afradapis and Caenopithecus as sister taxa to the exclusion of all other known adapiforms, thus implying that dispersal between Europe and Africa occurred during the middle Eocene. The new tarsal evidence, combined with previously known craniodental fossils, allows us to reconstruct C. lemuroides as having been an arboreal and highly folivorous 1.5-2.5 kg primate that likely moved slowly and deliberately with little or no capacity for acrobatic leaping, presumably maintaining consistent powerful grasps on branches in both above-branch and inverted postures.

Additional postcranial elements of Teilhardina belgica: the oldest European primate

Teilhardina belgica is one of the earliest fossil primates ever recovered and the oldest fossil primate from Europe. As such, this taxon has often been hypothesized as a basal tarsiiform on the basis of its primitive dental formula with four premolars and a simplified molar cusp pattern. Until recently [see Rose et al.: Am J Phys Anthropol 146 (2011) 281-305; Gebo et al.: J Hum Evol 63 (2012) 205-218], little was known concerning its postcranial anatomy with the exception of its well-known tarsals. In this article, we describe additional postcranial elements for T. belgica and compare these with other tarsiiforms and with primitive adapiforms. The forelimb of T. belgica indicates an arboreal primate with prominent forearm musculature, good elbow rotational mobility, and a horizontal, rather than a vertical body posture. The lateral hand positions imply grasps adaptive for relatively large diameter supports given its small body size. The hand is long with very long fingers, especially the middle phalanges. The hindlimb indicates foot inversion capabilities, frequent leaping, arboreal quadrupedalism, climbing, and grasping. The long and well-muscled hallux can be coupled with long lateral phalanges to reconstruct a foot with long grasping digits. Our phyletic analysis indicates that we can identify several postcranial characteristics shared in common for stem primates as well as note several derived postcranial characters for Tarsiiformes.

Scaling of convex hull volume to body mass in modern primates, non-primate mammals and birds

The volumetric method of ‘convex hulling’ has recently been put forward as a mass prediction technique for fossil vertebrates. Convex hulling involves the calculation of minimum convex hull volumes (vol_CH) from the complete mounted skeletons of modern museum specimens, which are subsequently regressed against body mass (M_b) to derive predictive equations for extinct species. The convex hulling technique has recently been applied to estimate body mass in giant sauropods and fossil ratites, however the biomechanical signal contained within vol_CH has remained unclear. Specifically, when vol_CH scaling departs from isometry in a group of vertebrates, how might this be interpreted? Here we derive predictive equations for primates, non-primate mammals and birds and compare the scaling behaviour of M_b to vol_CH between groups. We find predictive equations to be characterised by extremely high correlation coefficients (r² = 0.97–0.99) and low mean percentage prediction error (11–20%). Results suggest non-primate mammals scale body mass to vol_CH isometrically (b = 0.92, 95%CI = 0.85–1.00, p = 0.08). Birds scale body mass to vol_CH with negative allometry (b = 0.81, 95%CI = 0.70–0.91, p = 0.011) and apparent density (vol_CH/M_b) therefore decreases with mass (r² = 0.36, p<0.05). In contrast, primates scale body mass to vol_CH with positive allometry (b = 1.07, 95%CI = 1.01–1.12, p = 0.05) and apparent density therefore increases with size (r² = 0.46, p = 0.025). We interpret such departures from isometry in the context of the ‘missing mass’ of soft tissues that are excluded from the convex hulling process. We conclude that the convex hulling technique can be justifiably applied to the fossil record when a large proportion of the skeleton is preserved. However we emphasise the need for future studies to quantify interspecific variation in the distribution of soft tissues such as muscle, integument and body fat.

A mitogenomic phylogeny of living primates

Primates, the mammalian order including our own species, comprise 480 species in 78 genera. Thus, they represent the third largest of the 18 orders of eutherian mammals. Although recent phylogenetic studies on primates are increasingly built on molecular datasets, most of these studies have focused on taxonomic subgroups within the order. Complete mitochondrial (mt) genomes have proven to be extremely useful in deciphering within-order relationships even up to deep nodes. Using 454 sequencing, we sequenced 32 new complete mt genomes adding 20 previously not represented genera to the phylogenetic reconstruction of the primate tree. With 13 new sequences, the number of complete mt genomes within the parvorder Platyrrhini was widely extended, resulting in a largely resolved branching pattern among New World monkey families. We added 10 new Strepsirrhini mt genomes to the 15 previously available ones, thus almost doubling the number of mt genomes within this clade. Our data allow precise date estimates of all nodes and offer new insights into primate evolution. One major result is a relatively young date for the most recent common ancestor of all living primates which was estimated to 66-69 million years ago, suggesting that the divergence of extant primates started close to the K/T-boundary. Although some relationships remain unclear, the large number of mt genomes used allowed us to reconstruct a robust primate phylogeny which is largely in agreement with previous publications. Finally, we show that mt genomes are a useful tool for resolving primate phylogenetic relationships on various taxonomic levels.

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.

The role of modularity in the evolution of primate postcanine dental formula: integrating jaw space with patterns of dentition

The assembly of a phenotype into modules or developmental fields, which are semiautonomous units in development and function, seems to be one of the strategies to increase the capacity to produce phenotypic variation. In mammals the upper dentition is formed on two distinct developmental units, wherein incisors are formed on the primary palate, which is derived from the embryonic frontonasal process, and the other teeth (canine, premolar, and molar) are formed on the alveolar bone, which is derived from the maxillary process (termed herein as PALATE2). The aim of the present work was to analyze the variations in size and number of premolar and molar teeth in primate dentition and to correlate these morphometrical parameters with the relative size of these tooth classes with respect to PALATE2. Furthermore, we seek to understand to what extent the changes in the relative size of premolar and molar fields can influence the size of each tooth within its respective field, and how these parameters connect with the variations in the dental formula that occurred during primate evolution. The data presented here not only indicate that premolar and molar fields can be seen as submodules of a larger and hierarchically superior module (i.e., PALATE2) but also present quantitative parameters that allow us to understand how variations in the relative size of premolar and molar teeth connect with the variations in the dental formula that occurred during primate evolution.

Species diversity and postcranial anatomy of eocene primates from Shanghuang, China

The middle Eocene Shanghuang fissure-fillings, located in southern Jiangsu Province in China near the coastal city of Shanghai (Fig. 1), contain a remarkably diverse array of fossil primates that provide a unique window into the complex role played by Asia during early primate evolution.1 Compared to contemporaneous localities in North America or Europe, the ancient primate community sampled at the Shanghuang fissure-fillings is unique in several ways. Although Shanghuang has some typical Eocene primates (Omomyidae and Adapoidea), it also contains the earliest known members of the Tarsiidae and Anthropoidea (Fig. 2), and some new taxa that are not as yet known from elsewhere. It exhibits a large number of primate species, at least 18, most of which are very small (15-500 g), including some of the smallest primates that have ever been recovered.

Morphometric analysis of cranial shape in fossil and recent euprimates

Quantitative analysis of morphology allows for identification of subtle evolutionary patterns or convergences in anatomy that can aid ecological reconstructions of extinct taxa. This study explores diversity and convergence in cranial morphology across living and fossil primates using geometric morphometrics. 33 3D landmarks were gathered from 34 genera of euprimates (382 specimens), including the Eocene adapiforms Adapis and Leptadapis and Quaternary lemurs Archaeolemur, Palaeopropithecus, and Megaladapis. Landmark data was treated with Procrustes superimposition to remove all nonshape differences and then subjected to principal components analysis and linear discriminant function analysis. Haplorhines and strepsirrhines were well separated in morphospace along the major components of variation, largely reflecting differences in relative skull length and width and facial depth. Most adapiforms fell within or close to strepsirrhine space, while Quaternary lemurs deviated from extant strepsirrhines, either exploring new regions of morphospace or converging on haplorhines. Fossil taxa significantly increased the area of morphospace occupied by strepsirrhines. However, recent haplorhines showed significantly greater cranial disparity than strepsirrhines, even with the inclusion of the unusual Quaternary lemurs, demonstrating that differences in primate cranial disparity are likely real and not simply an artefact of recent megafaunal extinctions.

Evidence for a grooming claw in a North American adapiform primate: implications for anthropoid origins

Among fossil primates, the Eocene adapiforms have been suggested as the closest relatives of living anthropoids (monkeys, apes, and humans). Central to this argument is the form of the second pedal digit. Extant strepsirrhines and tarsiers possess a grooming claw on this digit, while most anthropoids have a nail. While controversial, the possible presence of a nail in certain European adapiforms has been considered evidence for anthropoid affinities. Skeletons preserved well enough to test this idea have been lacking for North American adapiforms. Here, we document and quantitatively analyze, for the first time, a dentally associated skeleton of Notharctus tenebrosus from the early Eocene of Wyoming that preserves the complete bones of digit II in semi-articulation. Utilizing twelve shape variables, we compare the distal phalanges of Notharctus tenebrosus to those of extant primates that bear nails (n = 21), tegulae (n = 4), and grooming claws (n = 10), and those of non-primates that bear claws (n = 7). Quantitative analyses demonstrate that Notharctus tenebrosus possessed a grooming claw with a surprisingly well-developed apical tuft on its second pedal digit. The presence of a wide apical tuft on the pedal digit II of Notharctus tenebrosus may reflect intermediate morphology between a typical grooming claw and a nail, which is consistent with the recent hypothesis that loss of a grooming claw occurred in a clade containing adapiforms (e.g. Darwinius masillae) and anthropoids. However, a cladistic analysis including newly documented morphologies and thorough representation of characters acknowledged to have states constituting strepsirrhine, haplorhine, and anthropoid synapomorphies groups Notharctus tenebrosus and Darwinius masillae with extant strepsirrhines rather than haplorhines suggesting that the form of pedal digit II reflects substantial homoplasy during the course of early primate evolution.

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.

A molecular phylogeny of living primates

Comparative genomic analyses of primates offer considerable potential to define and understand the processes that mold, shape, and transform the human genome. However, primate taxonomy is both complex and controversial, with marginal unifying consensus of the evolutionary hierarchy of extant primate species. Here we provide new genomic sequence (∼8 Mb) from 186 primates representing 61 (∼90%) of the described genera, and we include outgroup species from Dermoptera, Scandentia, and Lagomorpha. The resultant phylogeny is exceptionally robust and illuminates events in primate evolution from ancient to recent, clarifying numerous taxonomic controversies and providing new data on human evolution. Ongoing speciation, reticulate evolution, ancient relic lineages, unequal rates of evolution, and disparate distributions of insertions/deletions among the reconstructed primate lineages are uncovered. Our resolution of the primate phylogeny provides an essential evolutionary framework with far-reaching applications including: human selection and adaptation, global emergence of zoonotic diseases, mammalian comparative genomics, primate taxonomy, and conservation of endangered species.

Advances in human biomedicine, including those focused on changes in genes triggered or disrupted in development, resistance/susceptibility to infectious disease, cancers, mechanisms of recombination, and genome plasticity, cannot be adequately interpreted in the absence of a precise evolutionary context or hierarchy. However, little is known about the genomes of other primate species, a situation exacerbated by a paucity of nuclear molecular sequence data necessary to resolve the complexities of primate divergence over time. We overcome this deficiency by sequencing 54 nuclear gene regions from DNA samples representing ∼90% of the diversity present in living primates. We conduct a phylogenetic analysis to determine the origin, evolution, patterns of speciation, and unique features in genome divergence among primate lineages. The resultant phylogenetic tree is remarkably robust and unambiguously resolves many long-standing issues in primate taxonomy. Our data provide a strong foundation for illuminating those genomic differences that are uniquely human and provide new insights on the breadth and richness of gene evolution across all primate lineages.

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.