Sexual dimorphism in a focal trait can arise from sex-specific selection acting directly on this trait. Alternatively, it may result from sex-specific selection acting on body size, to which the focal trait is genetically correlated. Quantifying the allometric relationship between trait size and body size is therefore essential for distinguishing between these different causes of sexual dimorphism. However, body size is often estimated by proxy measurements, and the choice of these proxies can influence the results of the analysis. We illustrate these issues by estimating sexual dimorphism in three craniodental traits in four mustelid species, the Eurasian otter, the European badger, the beech marten and the stoat. Depending on the trait, 16
A new gobiconodontid eutriconodontan, Westphalodon goini gen. et sp. nov., is described based on a dentary fragment with molariforms 1–3 and an attributed edentulous dentary fragment, from the Lower Cretaceous (Barremian–Aptian) of the Balve-Beckum locality in Germany. The new taxon is unique among eutriconodontans in having two distal cusps on the lower molariform teeth: a distal cusp d, which is aligned with the main cusps a–c, and a distolingual cusp of the cingulid. Similar to Gobiconodon, Westphalodon has only two lower premolariforms, with dp2 being smaller than p1 and shed without replacement. It also has five lower molariforms that are rectangular in occlusal view and have a prominent lingual cingulid. Westphalodon differs from Gobiconodon in lacking interlock between the lower molariforms. The alveoli of the shed dp2 are plugged by bone tissue. Progressive wear on cusps c and d of the molariforms in a posterior direction suggests a more intense use of the posterior teeth for mastication or replacement of anterior molariforms.
This study reexamines a glyptodontine skull, NHMD 2045557, from Lagoa Santa, Brazil. Initially misidentified as the type of Hoplophorus euphractus by J. Reinhardt, it was later referred to Glyptodon clavipes. This identification remained unchallenged for decades. Recent comprehensive revisions of glyptodontines from northeastern and southeastern Brazil have prompted a reevaluation of the Lagoa Santa material. Currently, it is referred to as Glyptotherium sp., or tentatively, as Glyptotherium cf. cylindricum, a species originally described from Mexico that is also found in Central and North America. However, even if the generic assignment to Glyptotherium is accepted, the specific identity of the Brazilian material remains unresolved. To address this issue, we conducted an exhaustive review of the historical literature, beginning with the foundational works of Lund, Reinhardt, and Winge. We also reexamined the skull NHMD 2045557. Although Lund collected this specimen, Reinhardt first described and illustrated it in 1875 as “Schistopleurum euphractum” to replace Hoplophorus euphractus. We argue that Reinhardt misidentified the skull as the type of Hoplophorus euphractus, which invalidates the combination “Schistopleurum euphractum”. According to the ICZN, the name-bearing type of H. euphractus fixes the application of the name (Art. 70). Thus, Reinhardt’s classification constitutes a misidentification rather than a taxonomic revision of the original species. Therefore, we propose a new species of Glyptotherium for the aforementioned skull, described as Glyptotherium deuterophractum sp. nov. Comparative analyses with other glyptodont species reveal a distinctive combination of cranial, dental, tarsal, and osteodermal characteristics that distinguish the Brazilian and Venezuelan material from Glyptotherium texanum (from the Pliocene and Early Pleistocene of Central America, Mexico, and the southern United States) and from Glyptotherium cylindricum (Late Pleistocene of Panama, Guatemala, Mexico, and the southern United States).
The small-bodied stem catarrhine Pliobates cataloniae (Pliopithecoidea: Crouzeliidae), from the Miocene (11.6 Ma) of the Vallès-Penedès Basin (NE Iberian Peninsula), combines catarrhine symplesiomorphies and several crown hominoid-like features that are interpreted as convergent. The most obvious modern ape-like traits of Pliobates are found in the forelimb, particularly in the wrist and elbow joints. In the humerus, these include the lack of an entepicondylar foramen, a well-developed zona conoidea, and a globular capitulum. To quantitatively assess the degree of convergence between Pliobates and extant hominoids, we compare their distal humeral shape with a comparative sample including extant and extinct anthropoid primates. Shape is analyzed using landmark-based, 3D geometric morphometric techniques, while the locomotor repertoire of Pliobates and other extinct species is inferred using two-block partial least squares regression between shape and locomotor percentages. Our results indicate that the locomotor repertoire of Pliobates would have been dominated by orthograde behaviors such as climbing/clambering and suspension, in agreement with its ape-like humeroradial joint (which is functionally related to enhanced prono-supination). Nevertheless, the humeroulnar joint of Pliobates lacks the stabilization mechanisms that are characteristic of extant hominoids and necessary for frequently engaging in suspensory behaviors. We conclude that, while suspension was probably part of the locomotor repertoire of Pliobates, this taxon did not perform the acrobatic suspensory behaviors characteristic of the similarly-sized, extant hylobatids. Consequently, we interpret the ape-like humeroradial joint of Pliobates as an adaptation for climbing rather than modern ape-like suspensory behaviors.
The Late Miocene site of Shuitangba in southwestern China has yielded a diverse vertebrate fauna and abundant plant fossils from swamp-edge and shallow lake sediments, indicating a warm, humid climate with strong temperature and precipitation seasonality, and higher regional rainfall amounts than in modern times at the site. Subtropical, evergreen broad-leaved forest dominated the ecosystem, accompanied by aquatic vegetation, lianas, widespread grasses at woodland margins, and broad-leaved deciduous forest and evergreen trees and shrubs. This heterogeneous ecosystem formed a forest-wetland refugium in a time of global cooling and aridification, supporting water birds, crocs, fish, otters, apes, and other mammals typical of forests. Among the mammalian assemblage are the remains of the archaic stegodontid proboscidean Stegodon zhaotongensis, comprising the most complete skeletal record of basal stegodonts yet recovered. Craniodentally, St. zhaotongensis exhibits numerous plesiomorphies, some reminiscent of its stegolophodont predecessors, such as a low, broad cranium narrow across the temporal lines and extremely brachyodont molars with modest numbers of plates. Absence of lower tusks and enamel bands on upper tusks, lack of independent molar accessory conules, and possession of pentalophodont intermediate molars confirm the species to belong in Stegodon within Stegodontidae. Size and robusticity of appendicular elements show that St. zhaotongensis individuals were powerful and massive, considerably larger and heavier than extant elephants, implying an important role in the maintenance of its habitats. The morphology of this species supports the hypothesis that stegodonts are of Asian derivation from stegolophodonts, and that traits shared in common with elephants are convergences. It also corroborates the validity of the species. Despite the brachyodont condition of its molars, dental isotopic analysis shows that individuals of St. zhaotongensis had broad dietary preferences, including mixed C3/C4 browsing/grazing, suggesting a shift in feeding behavior prior to evolution of morphological adaptations as a way of coping with changing ecological circumstances.
Ontogeny describes the individual developmental history of an organism across its lifetime. Comparative ontogenetic approaches can be applied to closely related taxa and provide a powerful framework for investigating evolutionary changes in morphology, life history, and developmental timing between fossil and extant relatives. This approach is particularly informative for the fossil chevrotain Dorcatherium naui and the extant African water chevrotain Hyemoschus aquaticus, which are consistently recovered as sister taxa in phylogenetic analyses. Until recently, the fossil record of D. naui was sparse, despite the fact that this species represents the type species of one of the most frequently cited fossil tragulid genera. Here we demonstrate that the life history and ecological characteristics, as sexual maturity, sexual size dimorphism, reproduction rate and maximum life span, inferred for fossil D. naui share numerous similarities with those of extant H. aquaticus, supporting a close phylogenetic relationship between both taxa. However, we find that D. naui might have lived in more open riparian woodlands, compared to its extant relative. In addition, our results provide evidence for a paedomorphic condition of cranial ornamentation in H. aquaticus relative to D. naui. Together, these findings support the use of H. aquaticus as a suitable modern analogue for fossil tragulids in general, and for Dorcatherium in particular. Moreover, the observed similarities between both taxa are consistent with a paleobiogeographic scenario involving a dispersal event of an ancestral form morphologically similar to D. naui from Eurasia into Africa during the Late Miocene, followed by independent evolution culminating in the emergence of H. aquaticus during the Pliocene.
What is the island syndrome, and why does it emerge repeatedly across taxa on small-to-medium islands, across latitudes, and throughout geological time? The wide range of interpretations surrounding this phenomenon often obscures broader evolutionary patterns—like a forest hidden by its trees. This paper approaches the island syndrome from a bioeconomic perspective and proposes a classification of its defining traits. To guide this analysis, I draw comparisons with troglomorphism—the cave equivalent of the island syndrome—which is better understood and offers a useful structural framework. Amid the complexities of island adaptation, the extinct Balearic caprine Myotragus, with its five-million-year evolutionary history and extreme insular traits—from metabolic to sensory, locomotor, digestive and life history adaptations—serves as a valuable model. Following a brief historical overview, I examine the ecological parallels between caves and islands and explore energy use from the perspective of metabolic economy. Because organ size and function strongly influence resting metabolic rate, I investigate reductions in energetically costly structures—such as brain regions—alongside compensatory expansions in others. Changes in field metabolic rate and behavioural adaptations are also considered. By tracing these bioeconomic shifts and momentarily adopting MacArthur’s “blurry glasses” to favour general patterns over fine detail, I propose a preliminary classification of island syndrome traits, organized into the categories of reduction, enhancement, and time. This framework, inspired by studies of cave evolution, highlights the directional nature of adaptation under constraint and offers a new perspective on how energy-limited environments shape life.
Hippopotamus creutzburgi is a dwarf island hippo that lived on Crete during the Early and Middle Pleistocene. Here, we describe new material from the Katharo Plateau and compare it with extinct and extant hippopotamids. Although the species underwent a substantial body-size reduction, its skull is not a simple scaled-down model of its mainland relatives. Instead, it follows the general mammalian trend where a smaller cranial size correlates with a relatively shorter muzzle. The length of its muzzle scales down along the allometric trajectory of mainland hippos. H. creutzburgi has a muzzle with a length comparable to that of the Malagasy hippo H. madagascariensis, while its palate is proportionally narrower, similar to that of H. lemerlei. The mandible is more slender and displays pronounced sexual dimorphism, with males exhibiting a longer symphysis and enlarged canines compared to the slender morph. The upper molars of H. creutzburgi are relatively wider than those of the other hippopotamids. Wear patterns on the lower incisors indicate that it retained a limited lateral masticatory movement, similar to that of H. antiquus and the extant H. amphibius.
The early Middle Miocene (15.9 Ma) site of els Casots (Vallès-Penedès Basin, Catalonia, Spain) has yielded a rich vertebrate assemblage, including abundant carnivoran remains that mostly remain unpublished. Here we describe a new species of the amphicyonid genus Paludocyon based on a compressed cranium with well-preserved teeth and an isolated lower molar (m2) from els Casots. Paludocyon moyasolai sp. nov., included in the subfamily Amphicyoninae, is characterized by a notably enlarged M2, which is buccolingually broader than the M1, and by a the relatively large size of the M3, both traits being absent in other species of Paludocyon. A phylogenetic analysis, conducted on European and North American species assigned to Cynelos and Paludocyon, indicates that Cynelos is paraphyletic but supports the monophyly of Paludocyon, with the new species being recovered as its basal-most member.
Suines originated in Asia during the Middle Miocene and dispersed into Europe by the early Late Miocene. Their first European record, which corresponds to Propotamochoerus palaeochoerus, was formerly dated to MN7+8 but recent data have suggested an earliest MN9 age. Although P. palaeochoerus has long been known from the fossiliferous area of els Hostalets de Pierola, dating inaccuracies have precluded ascertaining its earliest appearance. In contrast, the remains from the stratigraphic sequence of Abocador de Can Mata (ACM), in the same area, are precisely dated through litho-, bio-, and magnetostratigraphic correlation, allowing us to determine its first record there. Here we describe previously unpublished remains from the Hostalets area, including 75 isolated teeth, 27 dentognathic fragments, and two crania. Qualitative and metrical comparisons support an attribution to P. palaeochoerus, while a cladistic analysis suggests close relationships between Propotamochoerus and Hippopotamodon, supporting their classification into the tribe Dicoryphochoerini. The oldest ACM record of P. palaeochoerus has an interpolated age of 11.23 Ma (subchron C5r.2r), representing the earliest securely dated record of the species in the Vallès-Penedès Basin. This predates by 50 kyr the first appearance datum of hipparionin horses in this basin at 11.18 Ma (subchron C5r.1n). Coupled with recently published evidence from Central Europe, it is suggested that P. palaeochoerus may have dispersed into Europe slightly earlier than hipparionins. However, dating uncertainties about the first appearance datum of hipparionin horses in Europe do not currently allow to discount a roughly synchronous dispersal with P. palaeochoerus, giraffids, and other eastern immigrants 11.3–11.2 Ma.
A recently discovered multituberculate skull with a nearly complete dentition from the lower Paleocene part of the Denver Formation (Corral Bluffs study area, Denver Basin, Colorado) represents a species of taeniolabidid that is smaller than Taeniolabis taoensis. We conclude that this skull, as well as an isolated upper first molar from the same study area, pertains to Kimbetopsalis simmonsae, previously known only from the Nacimiento Formation of the San Juan Basin, New Mexico. The Corral Bluffs skull includes the first lower jaw and lower dentition for the species. Based on our assessment of intraspecific variation in a large sample of T. taoensis from the Nacimiento Formation, we reevaluated all occurrences of Taeniolabis in the Western Interior of North America. We consider Kimbetopsalis a subjective junior synonym of Taeniolabis and therefore refer the species to Taeniolabis in a new combination, Taeniolabis simmonsae. Questions remain as to whether T. simmonsae is morphologically distinct from T. lamberti (Fort Union Formation, Montana). In-situ occurrences of T. simmonsae are lower than those of T. taoensis in the Corral Bluffs stratigraphic section and are in association with those of mammals characteristic of the Ectoconus/Taeniolabis taoensis Interval Zone (Pu2) of the Puercan North American Land Mammal Age, and earlier than those of mammals that characterize the Taeniolabis taoensis/Periptychus carinidens Interval Zone (Pu3). Thus, Taeniolabis, considered by some authors to be restricted to the Pu3 Interval Zone, occurs in both Pu2 and Pu3 zones, which has profound implications for early Paleocene bio- and geochronology.
Despite the fact that a well-developed frontal sinus is an apomorphy evolved only in the subfamily Caninae, important ecological factors might have played a role in the development of this paranasal cavity. Here, we present the first analysis of the 3D morphology of three fossil species of the genus Canis using an innovative deformation-based morphometric approach. Our aim was to disentangle the relative contributions of phylogenetic relationships and ecological adaptations. Based on the reconstructed morphology of the fossil species sinuses, we were able to corroborate and to better reconstruct the palaeodiet of the analysed fossil taxa. In particular, the overall structure and morphology of the frontal sinus of Canis etruscus suggests a lower proportion of meat in its diet. This species also displays the most primitive morphology among the three fossil species analysed, indicating an ancestral condition within the Canina lineage. On the other hand, the sinus shape and size of Canis mosbachensis and Canis borjgali suggest a higher proportion of meat consumption. In particular, C. borjgali closely resembles the extant wolf (Canis lupus) condition and suggests a possible hypercarnivorous group-hunting adaptation. Our results thus indicate that ecology is the primary driver of frontal sinuses shape and size, whereas phylogeny accounts for differences at higher taxonomic levels (i.e., subtribe level), highlighting how the analysis of this paranasal cavity can help in the further comprehension of both the paleoecology and phylogeny of fossil canids.
In this study, we virtually reconstruct the vertebral column of Pezosiren portelli, a four-limbed stem sirenian (Pan-Sirenia, Prorastomidae) from the Eocene of Jamaica. We used three-dimensional models of various vertebrae obtained through surface scanning of fossil remains and we applied several algorithms for virtual repair, including retrodeformation of distorted vertebrae or mirroring missing processes from their bilateral counterparts. To quantify the regional morphology of P. portelli, we digitized a set of homologous landmarks, following a standardized protocol retrieved from previous morphometric studies on the evolution of the mammalian backbone. The results reveal a cervical region with relatively long spinous processes, as well as a thoracic region subdivided into prediaphragmatic and postdiaphragmatic regions with an unspecialised lumbar region. Both aspects reveal anatomical traits typical of terrestrial mammals, suggesting that P. portelli may exhibit a mosaic evolutionary pattern, showing postcranial traits typical of terrestrial taxa but also early aquatic adaptations found in its cranial skeleton. Finally, we briefly discuss the implications of morphometric analyses of the P. portelli vertebral column for understanding the evolution of axial features in other secondarily aquatic tethytherians.
Dental disorders regularly occur in mammals. However, their identification and interpretation in the fossil record are extremely rare. Here, I report cases of dental disorders in fossils of insectivoran mammals in the permanent dentition of the endemic gymnure Galerix stehlini from La Grive-Saint-Alban (Middle Miocene, France). A supernumerary dental alveolus and several second lower premolars showing a varying degree of double-tooth anomaly (including root subdivision) are described for the first time in the fossil record of the Erinaceidae. These malformations are common in the material, suggesting an issue affecting a significant proportion of the time-averaged population. This pattern is interpreted as the result of reduced population size associated with habitat fragmentation. In addition, I report the first observation of dental anomalies in extant gymnures. Non-deleterious dental disorders are common in modern gymnures, especially hypodontia. Given the frequent parallel evolution toward mandibular shortening in erinaceid lineages, premolar hypodontia is interpreted as a repeatedly selected “anomaly”. Finally, a mandibular trauma identified in G. stehlini is described and interpreted as bite marks produced by the upper incisors of a medium-sized galericine, probably Parasorex socialis. The reconstructed bite is consistent with threat-related gaping behavior observed in extant gymnures. Overall, these results suggest that the ecomorphotype of Galerix was relatively unsuccessful by the end of the Middle Miocene.
Sloths (Folivora) display remarkable morphological diversity yet share a highly conserved dental formula, whose occasional deviations offer key insights into their evolutionary history. Among nothrotheriids, Neogene species retained upper and lower caniniforms, whereas these teeth were lost in Pleistocene genera. Here we describe, for the first time, a poorly developed alveolus interpreted as an atavistic upper caniniform alveolus in an individual of Nothrotherium maquinense from the Late Pleistocene of Bahia, Brazil. Computed tomography and X-ray imaging confirm its internal anatomy and rule out taphonomic or pathological origins. The alveolus occupies the precise position of the caniniform in Neogene nothrotheriids and exhibits similar morphology, suggesting a partial re-expression of a lost ancestral trait. Beyond its developmental implications, this observation may offer additional context for interpreting the taxonomy of Nothropus, traditionally defined based on the presence of a lower caniniform alveolus. The occurrence of similar atavistic structures in related taxa indicates that this feature alone may be insufficient for diagnosis and warrants reevaluation within a broader evolutionary framework.
Sicily, one of the largest Italian islands, was characterized by the presence of a Pleistocene insular fauna dominated by dwarf elephants and hippopotamuses. The remains of the latter, mostly attributed to Hippopotamus pentlandi, are relatively abundant and are recorded from over sixty paleontological localities. Despite its paleobiogeographic, paleoenvironmental, and evolutionary significance, there has been relatively limited focus on the hippopotamus specimens collected from Sicily, and in particular from the locality of San Ciro Cave (Palermo). This site has been known since the 16th century and preserves probably the most exceptionally rich hippopotamus assemblage of the whole island. This study presents an extensive review of the abundant postcranial remains from San Ciro Cave, which are currently stored in the Museo Geologico G. G. Gemmellaro of Palermo. Our morphological and morphometric comparisons reveal the occurrence of at least two distinct hippopotamus species in San Ciro Cave, H. pentlandi and H. amphibius. This finding suggests multiple colonization events or diachronic occurrences on the island. Peculiar morphological traits, such as robustness and enhanced cranio-caudal mobility in the distal limb bones, also reveal different environmental adaptations in the two species, suggesting a complex environmental mosaic in the area around the cave. Moreover, the body mass estimates of different hippopotamuses suggest that H. pentlandi was the heaviest insular Mediterranean species, followed by the smaller H. melitensis, H. creutzburgi, and H. minor.
The late Early Miocene site of Buluk, Kenya, has yielded a rich mammalian fauna comprised of about 30 species in 20 genera, notably including a stem cercopithecoid and a range of primitive hominoids. This temporal interval is poorly represented in Africa but is important because it coincides with the Miocene Climatic Optimum (MCO), a previous period of global warming tied to a carbon excursion. As the only late Early Miocene fossiliferous locality in eastern Africa that falls within the MCO, Buluk is of singular value to paleontological studies for increasing understanding of faunal responses to climate change and related ecological transformations. Paleobotanical, geochemical, and dental isotopic investigations indicate that Buluk was a C3-dominated woodland ecosystem with a strongly seasonal subhumid to subarid climate and overall greater rainfall than at present. Depositional circumstances are primarily channel fills associated with a large fluviatile system with water transport of vertebrates over a limited distance, probably denoting an autochthonous fauna. The most abundant large mammals in the fauna are proboscideans. Comparative morphological and metric study of the proboscidean assemblage reveals the co-occurrence of at least six genera and species from three higher taxa, Deinotheriidae and the elephantimorph families Mammutidae and Gomphotheriidae. Three of these species are new, one of them marking the earliest appearance of Protanancus. Deinotheres and archaeobelodonts are equally the most common proboscidean taxa in the assemblage. Such diversity of megaherbivores was not unusual for African Miocene sites and may have been accommodated by faunal differences from modern conditions, resource partitioning, and physical competitive displacement. The relatively diminutive size of molars of proboscideans in the assemblage, most pronounced among female elephantimorphs, may have constituted coordinated dwarfing in response to either increasing temperatures or stresses on resources caused by the MCO.
The Balearic shrew Nesiotites represents one of the most remarkable examples of insular evolution among Mediterranean mammals. While most previous studies have focused on its cranial anatomy, little attention has been paid to the postcranial skeleton and its evolutionary transformations through time. In this study, we analyze and compare postcranial elements—including humeri, ulnae, femora, tibiae, and pelves—across the entire temporal range of the Nesiotites lineage in Mallorca, from its earliest representative (Asoriculus sp., earliest Pliocene, 5.3 Ma) to the terminal species of the Holocene Nesiotites hidalgo, which survived until after 3,000 cal BC. Drawing on the most complete osteological series available for this lineage, we quantify changes in skeletal proportions and functional morphology to explore patterns of morphological differentiation and life history evolution in an insular context. Comparisons with extant Soricinae and Crocidurinae species provide additional insights into body size trends, limb allometry, and potential locomotor adaptations. We discuss these results in the framework of the “island syndrome”, evaluating the extent to which Nesiotites evolved under relaxed predation, resource limitation, and extended longevity. Our findings highlight the value of postcranial anatomy in reconstructing insular evolutionary trajectories and contribute new data to the paleobiology of extinct shrews.
Trischizolagus dumitrescuae, a representative of the Leporinae, was among the most prevalent and widely distributed leporids throughout the Pliocene. The extensive collection of postcranial remains from the newly discovered Ruscinian site Megalo Emvolon-4 (MVL) in Northern Greece yielded numerous bones, including nearly all skeletal parts. The detailed fore- and hindlimb morphology of T. dumitrescuae is presented in comparison with both extant and fossil species, showcasing a wide range of locomotor adaptations. Both the morphometrical data of the forelimb and hindlimb, along with the estimated body mass (around 2,100 to 2,200 g) and the cranial characteristics (facial tilt and fenestration), indicate an animal with features consistent with moderate leaping and agile terrestrial movement. The forelimb anatomy of T. dumitrescuae, characterized by moderate distal limb elongation and robust humeri for landing, together with the skull morphology signal agile locomotion and moderate running capability. Its hindlimb features, among them a rounded acetabulum, a moderately developed ischial tuberosity, and a calcaneus appropriate for leaping, further support adaptations for controlled, agile leaping. While its lower leg and foot bones show more developed running abilities than typical rabbits (e.g., Oryctolagus cuniculus), they lack the extreme specialization of hares (e.g., Lepus europaeus). These traits reinforce the recognition of T. dumitrescuae as an ecomorphologically intermediate taxon, filling a distinctive functional role in the late Neogene ecosystems of southeastern Europe.
