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The acquisition of terrestrial, limb-based locomotion during tetrapod evolution has remained a subject of debate for more than a century 1 , 2 . Our current understanding of the locomotor transition from water to land is largely based on a few exemplar fossils such as Tiktaalik 3 , Acanthostega 4 , Ichthyostega 5 and Pederpes 6 . However, isolated bony elements may reveal hidden functional diversity, providing a more comprehensive evolutionary perspective 7 . Here we analyse 40 three-dimensionally preserved humeri from extinct tetrapodomorphs that span the fin-to-limb transition and use functionally informed ecological adaptive landscapes 8 – 10 to reconstruct the evolution of terrestrial locomotion. We show that evolutionary changes in the shape of the humerus are driven by ecology and phylogeny and are associated with functional trade-offs related to locomotor performance. Two divergent adaptive landscapes are recovered for aquatic fishes and terrestrial crown tetrapods, each of which is defined by a different combination of functional specializations. Humeri of stem tetrapods share a unique suite of functional adaptations, but do not conform to their own predicted adaptive peak. Instead, humeri of stem tetrapods fall at the base of the crown tetrapod landscape, indicating that the capacity for terrestrial locomotion occurred with the origin of limbs. Our results suggest that stem tetrapods may have used transitional gaits 5 , 11 during the initial stages of land exploration, stabilized by the opposing selective pressures of their amphibious habits. Effective limb-based locomotion did not arise until loss of the ancestral ‘L-shaped’ humerus in the crown group, setting the stage for the diversification of terrestrial tetrapods and the establishment of modern ecological niches 12 , 13 . Analysis of humeri from fossils that span the fin-to-limb transition reveal that the change in the humerus shape is driven by both ecology and phylogeny, and is associated with functional trade-offs related to locomotor performance.

Recent discoveries of Homo floresiensis and H. luzonensis raise questions regarding how extreme body size reduction occurred in some extinct Homo species in insular environments. Previous investigations at Mata Menge, Flores Island, Indonesia, suggested that the early Middle Pleistocene ancestors of H. floresiensis had even smaller jaws and teeth. Here, we report additional hominin fossils from the same deposits at Mata Menge. An adult humerus is estimated to be 9 − 16% shorter and thinner than the type specimen of H. floresiensis dated to ~60,000 years ago, and is smaller than any other Plio-Pleistocene adult hominin humeri hitherto reported. The newly recovered teeth are both exceptionally small; one of them bears closer morphological similarities to early Javanese H. erectus . The H. floresiensis lineage most likely evolved from early Asian H. erectus and was a long-lasting lineage on Flores with markedly diminutive body size since at least ~700,000 years ago. How small-bodied hominins in southeast Asia became so small ~60 thousand years ago is unclear. Here, the authors present hominin remains dated to 700 thousand years ago with even smaller body size, suggesting early evolution and maintained small size in the region.’

Hurricanes are catastrophically destructive. Beyond their toll on human life and livelihoods, hurricanes have tremendous and often long-lasting effects on ecological systems 1 , 2 . Despite many examples of mass mortality events following hurricanes 3 – 5 , hurricane-induced natural selection has not previously been demonstrated. Immediately after we finished a survey of Anolis scriptus —a common, small-bodied lizard found throughout the Turks and Caicos archipelago—our study populations were battered by Hurricanes Irma and Maria. Shortly thereafter, we revisited the populations to determine whether morphological traits related to clinging capacity had shifted in the intervening six weeks and found that populations of surviving lizards differed in body size, relative limb length and toepad size from those present before the storm. Our serendipitous study, which to our knowledge is the first to use an immediately before and after comparison 6 to investigate selection caused by hurricanes, demonstrates that hurricanes can induce phenotypic change in a population and strongly implicates natural selection as the cause. In the decades ahead, as extreme climate events are predicted to become more intense and prevalent 7 , 8 , our understanding of evolutionary dynamics needs to incorporate the effects of these potentially severe selective episodes 9 – 11 . Two populations of Anolis lizards that survived Hurricanes Irma and Maria had larger toepads, longer forelimbs and shorter hindlimbs relative to the pre-hurricane populations, which suggests hurricane-induced natural selection.

Rodents are the most species-rich order within Mammalia and have evolved disparate morphologies to accommodate numerous locomotor niches, providing an excellent opportunity to understand how locomotor innovation can drive speciation. To evaluate the connection between the evolutionary success of rodents and the diversity of rodent locomotor ecologies, we used a large dataset of proximal limb CT scans from across Myomorpha and Geomyoidea to examine internal and external limb shape. Only fossorial rodents displayed a major reworking of their proximal limbs in either internal or external morphology, with other locomotor modes plotting within a generalist morphospace. Fossorial rodents were also the only locomotor mode to consistently show increased rates of humerus/femur morphological evolution. We propose that these rodent clades were successful at spreading into ecological niches due to high behavioral plasticity and small body sizes, allowing them to modify their locomotor mode without requiring major changes to their proximal limb morphology.

The ‘sprawling-parasagittal’ postural transition is a key part of mammalian evolution, associated with sweeping reorganization of the postcranial skeleton in mammals compared to their forebears, the non-mammalian synapsids. However, disputes over forelimb function in fossil synapsids render the precise nature of the ‘sprawling-parasagittal’ transition controversial. We shed new light on the origins of mammalian posture, using evolutionary adaptive landscapes to integrate 3D humerus shape and functional performance data across a taxonomically comprehensive sample of fossil synapsids and extant comparators. We find that the earliest pelycosaur-grade synapsids had a unique mode of sprawling, intermediate between extant reptiles and monotremes. Subsequent evolution of synapsid humerus form and functional traits showed little evidence of a direct progression from sprawling pelycosaurs to parasagittal mammals. Instead, posture was evolutionarily labile, and the ecological diversification of successive synapsid radiations was accompanied by variation in humerus morphofunctional traits. Further, synapsids frequently evolve toward parasagittal postures, diverging from the reconstructed optimal evolutionary path; the optimal path only aligns with becoming increasingly mammalian in derived cynodonts. We find the earliest support for habitual parasagittal postures in stem therians, implying that synapsids evolved and radiated with distinct forelimb trait combinations for most of their recorded history.

Gestational growth and development of bone is an understudied process compared to soft tissues and has implications for lifelong health. This study investigated growth and development of human fetal limb bone trabecular architecture using 3D digital histomorphometry of microcomputed tomography data from the femora and humeri of 35 skeletons (17 female and 18 male) with gestational ages between 4 and 9 months. Ontogenetic data revealed: (i) fetal trabecular architecture is similar between sexes; (ii) the proximal femoral metaphysis is physically larger, with thicker trabeculae and greater bone volume fraction relative to the humerus, but other aspects of trabecular architecture are similar between the bones; (iii) between 4 and 9 months gestation there is no apparent sexual or limb dimorphism in patterns of growth, but the size of the humerus and femur diverges early in development. Additionally, both bones exhibit significant increases in mean trabecular thickness (and for the femur alone, bone volume fraction) but minimal trabecular reorganisation (i.e., no significant changes in degree of anisotropy, connectivity density, or fractal dimension). Overall, these data suggest that in contrast to data from the axial skeleton, prenatal growth of long bones in the limbs is characterised by size increase, without major reorganizational changes in trabecular architecture.

It is accepted that the metabolic response of bone tissue depends on the intensity of the mechanical loads, but also on the type and frequency of stress applied to it. Physical exercise such as running involves stresses which, under certain conditions, have been shown to have the best osteogenic effects. However, at high intensity, it can be deleterious for bone tissue. Consequently, there is no clear consensus as to which running modality would have the best osteogenic effects. Our objective was to compare the effects of three running modalities on morphological and micro-architectural parameters on forelimb bones. Forty male Wistar rats were randomly divided into four groups: high intensity interval training (HIIT), continuous running, combined running ((alternating HIIT and continuous modalities) and sedentary (control). The morphometry, trabecular microarchitecture and cortical porosity of the ulna, radius and humerus were analyzed using micro-tomography. All three running modalities resulted in bone adaptation, with an increase in the diaphyseal diameter of all three bones. The combined running protocol had positive effects on the trabecular thickness in the distal ulna. The HIIT protocol resulted in an increase in both medio-lateral diameter and cortical bone area over total area (Ct.Ar/Tt.Ar) at the ulnar shaft compared with sedentary condition. Moreover, the HIIT protocol decreased the mean surface area of the medulla (Ma.Ar) according to sedentary condition at the ulnar shaft. This study has shown that HIIT resulted in a decrease in trabecular bone fraction in favor of cortical bone area at the ulna.

Desmostylus is an extinct genus of large, quadrupedal, herbivorous marine mammals from the Oligocene to Miocene strata of the North Pacific. Despite abundant fossil discoveries, the taxonomic, ontogenetic, and ecological aspects of this genus remain insufficiently understood. In this study, we reexamined a previously misidentified specimen (NMNS-PV 44111) from the Miocene Chikubetsu Formation in Hokkaido, Japan. Archival records rediscovered in 2024 enabled precise documentation of the locality and its stratigraphic context. Comparative anatomical analysis of the humerus revealed that the specimen represented a juvenile Desmostylus , with a body size larger than that of early desmostylians but smaller than that of fully mature Desmostylus individuals. The growth stage suggests a rapid increase in body size during the early ontogenetic phases. Stratigraphic and paleontological evidence places the specimen within the Middle Miocene Climatic Optimum (MMCO), a period linked to marine transgression and warm conditions that may have facilitated a northward range expansion of this genus. Our findings underscore the importance of reassessing legacy specimens using updated stratigraphic and comparative frameworks to better understand the evolutionary history of marine mammals in the North Pacific.

Fractures of the humerus are common on the midshaft of the bone, often causing injury to the nutrient artery. Successful fracture repair and healing requires preservation of the blood supply to the long bones which is conveyed through the nutrient foramina (NF). The topography of long bone NF varies in different populations. These variations can affect the preservation of blood supply to long bones during fracture repair management. The current study aimed to determine the topography and morphometry of the NF of the humerus in different populations of South Africa including the South African Africans (SAA), South Africans of European descent (SAED), and South Africans of mixed ancestry (SAMA). The study examined 596 dry humerii from the three South African populations, sourced from Raymond A. Dart Collection of Modern Human Skeletons. The parameters examined included the presence, number, location, position, size and direction of the NF, and foramina index (FI). The NF were present in 97.1% of the humerii. Majority of bones (76.8%) evinced a single NF with a diameter equal to or larger than 1.27 mm. The number of NF varied across the different population groups ( p  = 0.000), with SAA having more humerii presenting with a single NF and SAED having more humerii with two NF. The position of NF varied within and across populations ( p  = 0.002). Males in SAED had a higher mean FI on both the right ( p  = 0.030) (effect size = 0.258) and left ( p  = 0.022) (effect size = 0.421) sides than females. SAED had a lower mean FI than SAMA ( p  = 0.002) (effect size = 0.384). The location of NF varied across different populations ( p  = 0.000), with SAA having more NF located on the anteromedial surface and medial border, and SAED having more NF located on the lateral border ( p  = 0.000). NF were directed towards the distal ends of the shafts in 99.8% of bones and towards the proximal end in 0.2% of bones. The topography and morphometry of the nutrient foramina of the humerus are variable in the South African populations. Knowledge of the NF variations may aid in the management of humerus fractures.

This in-vitro study sought to characterize a concept for humeral component positioning during Total Elbow Arthroplasty (TEA) with bone defects. One-hundred specimens were analysed focusing a potential side-specific consensus; anatomical and Computed Tomography (CT) agreements; age-, sex- and humeral length-dependent associations. The angle of rotational alignment was defined by measuring the relationship between the flexion-extension axis (FEA) of the elbow joint and the flat posterior surface of the distal humerus (PDH). Three independent observers determined the reliabilities. The intraclass correlation coefficients (ICC), Pearson correlation coefficients ( r ), t -tests ( r , p) , and levels of 95% confidence interval were computed. P -values ( p ) were set with 0.05. An average internal rotation angle of the FEA to the PDH from 13.0° (range 6.4–27.1) was specified. Anatomical and CT measurements exposed strong agreements ( r  = .923, p  < .001) and excellent observer agreements (ICCs > 0.900). A contralateral side consensus ( r  = .906, p  < .001) and a statistically significant sex difference (at mean: female: 15.1° versus male: 11.5°; p  < .001) was verified. No age- and humeral length-dependent correlations were observed ( r  < .300). Knowledge of these anatomical landmarks and their spatial relationships can provide an essential reference for surgeons striving to replicate native joint alignment. Additionally, assessment of the contralateral (uninjured) side via CT imaging may offer a valuable template and should be considered in the management of complex TEA cases.