Locomotor inferences in Pierolapithecus and Hispanopithecus: Reply to Deane and Begun (2008)

Paleoenvironmental inferences on the Late Miocene hominoid-bearing site of Can Llobateres (NE Iberian Peninsula): An ecometric approach based on functional dental traits

Hispanopithecus laietanus from the Late Miocene (9.8 Ma) of Can Llobateres 1 (CLL1; Vallès-Penedès Basin, NE Iberian Peninsula) represents one of the latest occurrences of fossil apes in Western mainland Europe, where they are last recorded at ∼9.5 Ma. The paleoenvironment of CLL1 is thus relevant for understanding the extinction of European hominoids. To refine paleoenvironmental inferences for CLL1, we apply ecometric models based on functional crown type (FCT) variables-a scoring scheme devised to capture macroscopic functional traits of occlusal shape and wear surfaces of herbivorous large mammal molars. Paleotemperature and paleoprecipitation estimates for CLL1 are provided based on published regional regression models linking average FCT of large herbivorous mammal communities to climatic conditions. A mapping to Whittaker's present-day biome classification is also attempted based on these estimates, as well as a case-based reasoning via canonical variate analysis of FCT variables from five relevant biomes. Estimates of mean annual temperature (25 °C) and mean annual precipitation (881 mm) classify CLL1 as a tropical seasonal forest/savanna, only in partial agreement with the canonical variate analysis results, which classify CLL1 as a tropical rainforest with a higher probability. The former biome agrees better with previous inferences derived from fossil plants and mammals, as well as preliminary isotopic data. The misclassification of CLL1 as a tropical forest is attributed to the mixture of forest-adapted taxa with others adapted to more open environments, given that faunal and plant composition indicates the presence of a dense wetland/riparian forest with more open woodlands nearby. The tested FCT ecometric approaches do not provide unambiguous biome classification for CLL1. Nevertheless, our results are consistent with those from other approaches, thus suggesting that FCT variables are potentially useful to investigate paleoenvironmental changes through time and space-including those that led to the extinction of European Miocene apes.

The reconstructed cranium of Pierolapithecus and the evolution of the great ape face

Pierolapithecus catalaunicus (~12 million years ago, northeastern Spain) is key to understanding the mosaic nature of hominid (great ape and human) evolution. Notably, its skeleton indicates that an orthograde (upright) body plan preceded suspensory adaptations in hominid evolution. However, there is ongoing debate about this species, partly because the sole known cranium, preserving a nearly complete face, suffers from taphonomic damage. We 1) carried out a micro computerized tomography (CT) based virtual reconstruction of the Pierolapithecus cranium, 2) assessed its morphological affinities using a series of two-dimensional (2D) and three-dimensional (3D) morphometric analyses, and 3) modeled the evolution of key aspects of ape face form. The reconstruction clarifies many aspects of the facial morphology of Pierolapithecus. Our results indicate that it is most similar to great apes (fossil and extant) in overall face shape and size and is morphologically distinct from other Middle Miocene apes. Crown great apes can be distinguished from other taxa in several facial metrics (e.g., low midfacial prognathism, relatively tall faces) and only some of these features are found in Pierolapithecus, which is most consistent with a stem (basal) hominid position. The inferred morphology at all ancestral nodes within the hominoid (ape and human) tree is closer to great apes than to hylobatids (gibbons and siamangs), which are convergent with other smaller anthropoids. Our analyses support a hominid ancestor that was distinct from all extant and fossil hominids in overall facial shape and shared many features with Pierolapithecus. This reconstructed ancestral morphotype represents a testable hypothesis that can be reevaluated as new fossils are discovered.

Systematics of Miocene apes: State of the art of a neverending controversy

Hominoids diverged from cercopithecoids during the Oligocene in Afro-Arabia, initially radiating in that continent and subsequently dispersing into Eurasia. From the Late Miocene onward, the geographic range of hominoids progressively shrank, except for hominins, which dispersed out of Africa during the Pleistocene. Although the overall picture of hominoid evolution is clear based on available fossil evidence, many uncertainties persist regarding the phylogeny and paleobiogeography of Miocene apes (nonhominin hominoids), owing to their sparse record, pervasive homoplasy, and the decimated current diversity of this group. We review Miocene ape systematics and evolution by focusing on the most parsimonious cladograms published during the last decade. First, we provide a historical account of the progress made in Miocene ape phylogeny and paleobiogeography, report an updated classification of Miocene apes, and provide a list of Miocene ape species-locality occurrences together with an analysis of their paleobiodiversity dynamics. Second, we discuss various critical issues of Miocene ape phylogeny and paleobiogeography (hylobatid and crown hominid origins, plus the relationships of Oreopithecus) in the light of the highly divergent results obtained from cladistic analyses of craniodental and postcranial characters separately. We conclude that cladistic efforts to disentangle Miocene ape phylogeny are potentially biased by a long-branch attraction problem caused by the numerous postcranial similarities shared between hylobatids and hominids-despite the increasingly held view that they are likely homoplastic to a large extent, as illustrated by Sivapithecus and Pierolapithecus-and further aggravated by abundant missing data owing to incomplete preservation. Finally, we argue that-besides the recovery of additional fossils, the retrieval of paleoproteomic data, and a better integration between cladistics and geometric morphometrics-Miocene ape phylogenetics should take advantage of total-evidence (tip-dating) Bayesian methods of phylogenetic inference combining morphologic, molecular, and chronostratigraphic data. This would hopefully help ascertain whether hylobatid divergence was more basal than currently supported.

Reassessment of the phylogenetic relationships of the late Miocene apes Hispanopithecus and Rudapithecus based on vestibular morphology

Late Miocene great apes are key to reconstructing the ancestral morphotype from which earliest hominins evolved. Despite consensus that the late Miocene dryopith great apes Hispanopithecus laietanus (Spain) and Rudapithecus hungaricus (Hungary) are closely related (Hominidae), ongoing debate on their phylogenetic relationships with extant apes (stem hominids, hominines, or pongines) complicates our understanding of great ape and human evolution. To clarify this question, we rely on the morphology of the inner ear semicircular canals, which has been shown to be phylogenetically informative. Based on microcomputed tomography scans, we describe the vestibular morphology of Hispanopithecus and Rudapithecus, and compare them with extant hominoids using landmark-free deformation-based three-dimensional geometric morphometric analyses. We also provide critical evidence about the evolutionary patterns of the vestibular apparatus in living and fossil hominoids under different phylogenetic assumptions for dryopiths. Our results are consistent with the distinction of Rudapithecus and Hispanopithecus at the genus rank, and further support their allocation to the Hominidae based on their derived semicircular canal volumetric proportions. Compared with extant hominids, the vestibular morphology of Hispanopithecus and Rudapithecus most closely resembles that of African apes, and differs from the derived condition of orangutans. However, the vestibular morphologies reconstructed for the last common ancestors of dryopiths, crown hominines, and crown hominids are very similar, indicating that hominines are plesiomorphic in this regard. Therefore, our results do not conclusively favor a hominine or stem hominid status for the investigated dryopiths.

Palaeoecological differences underlie rare co-occurrence of Miocene European primates

Background

The two main primate groups recorded throughout the European Miocene, hominoids and pliopithecoids, seldom co-occur. Due to both their rarity and insufficiently understood palaeoecology, it is currently unclear whether the infrequent co-occurrence of these groups is due to sampling bias or reflects different ecological preferences. Here we rely on the densely sampled primate-bearing sequence of Abocador de Can Mata (ACM) in Spain to test whether turnovers in primate assemblages are correlated with palaeoenvironmental changes. We reconstruct dietary evolution through time (ca. 12.6–11.4 Ma), and hence climate and habitat, using tooth-wear patterns and carbon and oxygen isotope compositions of enamel of the ubiquitous musk-deer Micromeryx.

Results

Our results reveal that primate species composition is strongly correlated with distinct environmental phases. Large-bodied hominoids (dryopithecines) are recorded in humid, densely-forested environments on the lowermost portion of the ACM sequence. In contrast, pliopithecoids inhabited less humid, patchy ecosystems, being replaced by dryopithecines and the small-bodied Pliobates toward the top of the series in gallery forests embedded in mosaic environments.

Conclusions

These results support the view that pliopithecoid primates preferred less humid habitats than hominoids, and reveal that differences in behavioural ecology were the main factor underpinning their rare co-occurrence during the European Miocene. Our findings further support that ACM hominoids, like Miocene apes as a whole, inhabited more seasonal environments than extant apes. Finally, this study highlights the importance of high-resolution, local investigations to complement larger-scale analyses and illustrates that continuous and densely sampled fossiliferous sequences are essential for deciphering the complex interplay between biotic and abiotic factors that shaped past diversity.

The evolution of the vestibular apparatus in apes and humans

Phylogenetic relationships among extinct hominoids (apes and humans) are controversial due to pervasive homoplasy and the incompleteness of the fossil record. The bony labyrinth might contribute to this debate, as it displays strong phylogenetic signal among other mammals. However, the potential of the vestibular apparatus for phylogenetic reconstruction among fossil apes remains understudied. Here we test and quantify the phylogenetic signal embedded in the vestibular morphology of extant anthropoids (monkeys, apes and humans) and two extinct apes (Oreopithecus and Australopithecus) as captured by a deformation-based 3D geometric morphometric analysis. We also reconstruct the ancestral morphology of various hominoid clades based on phylogenetically-informed maximum likelihood methods. Besides revealing strong phylogenetic signal in the vestibule and enabling the proposal of potential synapomorphies for various hominoid clades, our results confirm the relevance of vestibular morphology for addressing the controversial phylogenetic relationships of fossil apes.

The morphology and evolutionary history of the glenohumeral joint of hominoids: A review

The glenohumeral joint, the most mobile joint in the body of hominoids, is involved in the locomotion of all extant primates apart from humans. Over the last few decades, our knowledge of how variation in its morphological characteristics relates to different locomotor behaviors within extant primates has greatly improved, including features of the proximal humerus and the glenoid cavity of the scapula, as well as the muscles that function to move the joint (the rotator cuff muscles). The glenohumeral joint is a region with a strong morphofunctional signal, and hence, its study can shed light on the locomotor behaviors of crucial ancestral nodes in the evolutionary history of hominoids (e.g., the last common ancestor between humans and chimpanzees). Hominoids, in particular, are distinct in showing round and relatively big proximal humeri with lowered tubercles and flattened and oval glenoid cavities, morphology suited to engage in a wide range of motions, which enables the use of locomotor behaviors such as suspension. The comparison with extant taxa has enabled more informed functional interpretations of morphology in extinct primates, including hominoids, from the Early Miocene through to the emergence of hominins. Here, I review our current understanding of glenohumeral joint functional morphology and its evolution throughout the Miocene and Pleistocene, as well as highlighting the areas where a deeper study of this joint is still needed.

Can Pallars i Llobateres: A new hominoid-bearing locality from the late Miocene of the Vallès-Penedès Basin (NE Iberian Peninsula)

In the Iberian Peninsula, Miocene apes (Hominoidea) are generally rare and mostly restricted to the Vallès-Penedès Basin. Here we report a new hominoid maxillary fragment with M² from this basin. It was surface-collected in March 2017 from the site of Can Pallars i Llobateres (CPL, Sant Quirze del Vallès), where fossil apes had not been previously recorded. The locality of provenance (CPL-M), which has delivered no further fossil remains, is located very close (ca. 50 m) to previously known CPL outcrops, and not very far (ca. 500 m in NW direction) from the classical hominoid-bearing locality of Can Poncic 1. Here we describe the new fossil and, based on the size and proportions of the M², justify its taxonomic attribution to Hispanopithecus cf. laietanus, a species previously recorded from several Vallesian sites of the Vallès-Penedès Basin. Based on the associated mammalian fauna from CPL, we also provide a biochronological dating and a paleoenvironmental reconstruction for the site. The associated fauna enables an unambiguous correlation to the Cricetulodon hartenbergeri - Progonomys hispanicus interval local subzone, with an estimated age of 9.98-9.73 Ma (late Vallesian, MN10). Therefore, CPL-M is roughly coeval with the Hispanopithecus laietanus-bearing localities of Can Llobateres 1 and Can Feu 1, and minimally older than those of La Tarumba 1 and Can Llobateres 2. In contrast, CPL-M is younger than the early Vallesian (MN9) localities of Can Poncic 1 (the type locality of Hispanopithecus crusafonti) as well as Polinyà 2 (Gabarró) and Estació Depuradora d'Aigües Residuals-Riu Ripoll 13, where Hispanopithecus sp. is recorded. The associated fauna from CPL indicates a densely forested and humid paleoenvironment with nearby freshwater. This supports the view that Hispanopithecus might have been restricted to dense wetland forests soon before its extinction during the late Vallesian, due to progressive climatic deterioration. Coupled with the existence of other fossiliferous outcrops in the area, this find is most promising for the prospect of discovering additional fossil hominoid remains in the future.

Dietary specialization during the evolution of Western Eurasian hominoids and the extinction of European Great Apes

Given the central adaptive role of diet, paleodietary inference is essential for understanding the relationship between evolutionary and paleoenvironmental change. Here we rely on dental microwear analysis to investigate the role of dietary specialization in the diversification and extinction of Miocene hominoids from Western Eurasian between 14 and 7 Ma. New microwear results for five extinct taxa are analyzed together with previous data for other Western Eurasian genera. Except Pierolapithecus (that resembles hard-object feeders) and Oreopithecus (a soft-frugivore probably foraging opportunistically on other foods), most of the extinct taxa lack clear extant dietary analogues. They display some degee of sclerocarpy, which is most clearly expressed in Griphopithecus and Ouranopithecus (adapted to more open and arid environments), whereas Anoiapithecus, Dryopithecus and, especially, Hispanopithecus species apparently relied more strongly on soft-frugivory. Thus, contrasting with the prevailing sclerocarpic condition at the beginning of the Eurasian hominoid radiation, soft- and mixed-frugivory coexisted with hard-object feeding in the Late Miocene. Therefore, despite a climatic trend towards cooling and increased seasonality, a progressive dietary diversification would have occurred (probably due to competitive exclusion and increased environmental heterogeneity), although strict folivory did not evolve. Overall, our analyses support the view that the same dietary specializations that enabled Western Eurasian hominoids to face progressive climatic deterioration were the main factor ultimately leading to their extinction when more drastic paleoenvironmental changes took place.

The Middle Miocene ape Pierolapithecus catalaunicus exhibits extant great ape-like morphometric affinities on its patella: inferences on knee function and evolution

The mosaic nature of the Miocene ape postcranium hinders the reconstruction of the positional behavior and locomotion of these taxa based on isolated elements only. The fossil great ape Pierolapithecus catalaunicus (IPS 21350 skeleton; 11.9 Ma) exhibits a relatively wide and shallow thorax with moderate hand length and phalangeal curvature, dorsally-oriented metacarpophalangeal joints, and loss of ulnocarpal articulation. This evidence reveals enhanced orthograde postures without modern ape-like below-branch suspensory adaptations. Therefore, it has been proposed that natural selection enhanced vertical climbing (and not suspension per se) in Pierolapithecus catalaunicus. Although limb long bones are not available for this species, its patella (IPS 21350.37) can potentially provide insights into its knee function and thus on the complexity of its total morphological pattern. Here we provide a detailed description and morphometric analyses of IPS 21350.37, which are based on four external dimensions intended to capture the overall patellar shape. Our results reveal that the patella of Pierolapithecus is similar to that of extant great apes: proximodistally short, mediolaterally broad and anteroposteriorly thin. Previous biomechanical studies of the anthropoid knee based on the same measurements proposed that the modern great ape patella reflects a mobile knee joint while the long, narrow and thick patella of platyrrhine and especially cercopithecoid monkeys would increase the quadriceps moment arm in knee extension during walking, galloping, climbing and leaping. The patella of Pierolapithecus differs not only from that of monkeys and hylobatids, but also from that of basal hominoids (e.g., Proconsul and Nacholapithecus), which display slightly thinner patellae than extant great apes (the previously-inferred plesiomorphic hominoid condition). If patellar shape in Pierolapithecus is related to modern great ape-like knee function, our results suggest that increased knee mobility might have originally evolved in relation to enhanced climbing capabilities in great apes (such as specialized vertical climbing).

The morphology of Oreopithecus bambolii pollical distal phalanx

Oreopithecus bambolii is a Late Miocene ape from Italy, first described in the late 19th century. Its interpretation is still highly controversial, especially in reference to its hand proportions and thumb morphology. In this study, the authors provide detailed descriptions of the available Oreopithecus pollical distal phalanx (PDP) specimens, as well as bivariate and multivariate morphometric analyses in comparison with humans, extant apes, selected anthropoid monkeys, and available Miocene PDP specimens. The multivariate results reveal two opposite poles on the hominoid PDP shape spectrum: on one side, a mediolaterally broad and dorsopalmarly short human PDP, and on the other side, the narrow and "conical" PDP of chimpanzees and orangutans. The authors contend that Oreopithecus exhibits intermediate PDP proportions that are largely primitive for hominoids because it shares morphological similarities with Proconsul. Furthermore, Oreopithecus displays a mediolaterally wide tuft for a hominoid, as well as a palmarly elevated attachment for a long tendon of a flexor muscle that is associated at its proximal edge with a proximal fossa and at its distal edge with an ungual fossa. These nonmetrical traits have been associated in humans with their capability to oppose and contact the proximal pads of the thumb and fingers, that is, pad-to-pad precision grasping. These traits reinforce previous studies that indicate a human-like thumb-to-hand length ratio compatible with pad-to-pad precision grasping in Oreopithecus. Although specific hand use is still unresolved in Oreopithecus, the results suggest enhanced manipulative skills (unrelated to stone tool-making) in this taxon relative to other (extant or fossil) hominoids.

Trabecular bone structure in the primate wrist

Trabecular (or cancellous) bone has been shown to respond to mechanical loading throughout ontogeny and thus can provide unique insight into skeletal function and locomotion in comparative studies of living and fossil mammalian morphology. Trabecular bone of the hand may be particularly functionally informative because the hand has more direct contact with the substrate compared with the remainder of the forelimb during locomotion in quadrupedal mammals. This study investigates the trabecular structure within the wrist across a sample of haplorhine primates that vary in locomotor behaviour (and thus hand use) and body size. High-resolution microtomographic scans were collected of the lunate, scaphoid, and capitate in 41 individuals and eight genera (Homo, Gorilla, Pan, Papio, Pongo, Symphalangus, Hylobates, and Ateles). We predicted that particular trabecular parameters would 1) vary across suspensory, quadrupedal, and bipedal primates based on differences in hand use and load, and 2) scale with carpal size following similar allometric patterns found previously in other skeletal elements across a larger sample of mammals and primates. Analyses of variance (trabecular parameters analysed separately) and principal component analyses (trabecular parameters analysed together) revealed no clear functional signal in the trabecular structure of any of the three wrist bones. Instead, there was a large degree of variation within suspensory and quadrupedal locomotor groups, as well as high intrageneric variation within some taxa, particularly Pongo and Gorilla. However, as predicted, Homo sapiens, which rarely use their hands for locomotion and weight support, were unique in showing lower relative bone volume (BV/TV) compared with all other taxa. Furthermore, parameters used to quantify trabecular structure within the wrist scale with size generally following similar allometric patterns found in trabeculae of other mammalian skeletal elements. We discuss the challenges associated with quantifying and interpreting trabecular bone within the wrist.

The nasal and paranasal architecture of the Middle Miocene ape Pierolapithecus catalaunicus (primates: Hominidae): phylogenetic implications

The internal (nasal and paranasal) cranial anatomy of the Middle Miocene (11.9 Ma [millions of years ago]) great ape Pierolapithecus catalaunicus (Hominidae: Dryopithecini) is described on the basis of computed-tomography scans of the holotype specimen (IPS21350), with particular emphasis on its phylogenetic implications. Pierolapithecus displays the following characters: an anteriorly-restricted maxillary sinus that posteriorly spreads towards the ethmoidal area (thus resembling the pongine condition), although being situated well above the molar roots (as in kenyapithecins, other dryopithecins and pongines); lack of frontal sinus (a synapomorphy of derived pongines, independently acquired by both cercopithecoids and hylobatids); posteriorly-situated turbinals (as in Pongo); anteriorly-projecting nasolacrimal canal (as in Pongo); and probably stepped nasal floor with non-overlapping premaxillary-maxillary contact (as in dryopithecines and stem hominoids, although it cannot be conclusively shown due to bone damage). Overall, Pierolapithecus displays a mosaic of primitive hominid and derived pongine features that are inconsistent with this taxon being a hominine (as previously suggested). Two alternative phylogenetic interpretations are possible: Pierolapithecus may be a stem member of the Hominidae as previously suggested in its original description, or alternatively this taxon may be a stem member of the Ponginae s.l. (with the European dryopithecines being the sister taxon to the Asian pongines).

A partial skeleton of the fossil great ape Hispanopithecus laietanus from Can Feu and the mosaic evolution of crown-hominoid positional behaviors

The extinct dryopithecine Hispanopithecus (Primates: Hominidae), from the Late Miocene of Europe, is the oldest fossil great ape displaying an orthograde body plan coupled with unambiguous suspensory adaptations. On the basis of hand morphology, Hispanopithecus laietanus has been considered to primitively retain adaptations to above-branch quadrupedalism-thus displaying a locomotor repertoire unknown among extant or fossil hominoids, which has been considered unlikely by some researchers. Here we describe a partial skeleton of H. laietanus from the Vallesian (MN9) locality of Can Feu 1 (Vallès-Penedès Basin, NE Iberian Peninsula), with an estimated age of 10.0-9.7 Ma. It includes dentognathic and postcranial remains of a single, female adult individual, with an estimated body mass of 22-25 kg. The postcranial remains of the rib cage, shoulder girdle and forelimb show a mixture of monkey-like and modern-hominoid-like features. In turn, the proximal morphology of the ulna-most completely preserved in the Can Feu skeleton than among previously-available remains-indicates the possession of an elbow complex suitable for preserving stability along the full range of flexion/extension and enabling a broad range of pronation/supination. Such features, suitable for suspensory behaviors, are however combined with an olecranon morphology that is functionally related to quadrupedalism. Overall, when all the available postcranial evidence for H. laietanus is considered, it emerges that this taxon displayed a locomotor repertoire currently unknown among other apes (extant or extinct alike), uniquely combining suspensory-related features with primitively-retained adaptations to above-branch palmigrady. Despite phylogenetic uncertainties, Hispanopithecus is invariably considered an extinct member of the great-ape-and-human clade. Therefore, the combination of quadrupedal and suspensory adaptations in this Miocene crown hominoid clearly evidences the mosaic nature of locomotor evolution in the Hominoidea, as well as the impossibility to reconstruct the ancestral locomotor repertoires for crown hominoid subclades on the basis of extant taxa alone.

The thumb of Miocene apes: new insights from Castell de Barberà (Catalonia, Spain)

Primate hands display a major selective compromise between locomotion and manipulation. The thumb may or may not participate in locomotion, but it plays a central role in most manipulative activities. Understanding whether or not the last common ancestor of humans and Pan displayed extant-ape-like hand proportions (i.e., relatively long fingers and a short thumb) can be clarified by the analysis of Miocene ape hand remains. Here we describe new pollical remains-a complete proximal phalanx and a partial distal phalanx-from the middle/late Miocene site of Castell de Barberà (ca., 11.2-10.5 Ma, Vallès-Penedès Basin), and provide morphometric and qualitative comparisons with other available Miocene specimens as well as extant catarrhines (including humans). Our results show that all available Miocene taxa (Proconsul, Nacholapithecus, Afropithecus, Sivapithecus, Hispanopithecus, Oreopithecus, and the hominoid from Castell de Barberà) share a similar phalangeal thumb morphology: the phalanges are relatively long, and the proximal phalanges have a high degree of curvature, marked insertions for the flexor muscles, a palmarly bent trochlea and a low basal height. All these features suggest that these Miocene apes used their thumb with an emphasis on flexion, most of them to powerfully assist the fingers during above-branch, grasping arboreal locomotion. Moreover, in terms of relative proximal phalangeal length, the thumb of Miocene taxa is intermediate between the long-thumbed humans and the short-thumbed extant apes. Together with previous evidence, this suggests that a moderate-length hand with relatively long thumb-involved in locomotion-is the original hand morphotype for the Hominidae.