A recent groundbreaking study published in PLOS Biology, led by Dr. Robert Brocklehurst of Harvard University’s Department of Organismic and Evolutionary Biology, employs cutting-edge biomechanical analysis to unravel this intricate evolutionary narrative. The team meticulously examined the humerus — the upper arm bone — from over 60 fossil specimens of non-mammalian synapsids alongside more than 140 specimens of extant species including reptiles, amphibians, and diverse mammals. By integrating fossil data with advanced computational techniques, they reconstructed the locomotor postures and forelimb functions of these ancient species with unprecedented precision.

The researchers utilized a novel “slice-based” landmarking method, innovatively adapted from an existing R software package, to map the complex surface morphology of humeral bones. This approach enabled precise quantification of crucial anatomical traits such as bone length, mass distribution, muscle leverage, and torsion — a measure of the bone’s twist along its longitudinal axis. These parameters serve as biomechanical proxies, providing insight into muscle attachments and locomotor capabilities, thereby illuminating the postural adaptations that ancient synapsids and their descendants underwent during their evolutionary journey.

Contrary to the prevailing paradigm of a neat, stepwise evolutionary progression from sprawling to semi-sprawling and finally to upright parasagittal postures, the study revealed a more labyrinthine adaptive landscape. This landscape is characterized by multiple, distinct adaptive peaks, each corresponding to specialized functional regimes in forelimb posture and movement. Importantly, extinct synapsid lineages occupied a variety of these peaks, evincing a rich tapestry of biomechanical experimentation rather than a straightforward linear trend.

This complex evolutionary pattern suggests that mammalian ancestors engaged in repeated episodes of adaptive radiation, wherein each major group explored a spectrum of locomotor strategies. Some of these postures approximated the modern upright stance, while others represented alternative solutions fine-tuned to specific ecological contexts. Such evolutionary plasticity underscores the dynamic interplay between morphology, function, and environmental pressures throughout the mammalian lineage’s deep history.

One particularly intriguing finding relates to a fossil species closely allied to modern marsupials and placentals, which exhibited humeral features congruent with the fully upright, parasagittal posture typical of extant mammals. This discovery implies that the definitive upright gait, long assumed to be an early hallmark of mammals, actually evolved relatively late, in contrast to traditional hypotheses. These results dovetail with recent comparative studies on vertebral and hindlimb morphology, collectively reshaping our understanding of mammalian locomotor evolution.

Moreover, the study challenges the long-held assumption that early non-mammalian synapsids exhibited sprawling postures analogous to modern reptiles such as lizards and crocodilians. Rather, the forelimb biomechanics of these ancient synapsids differ substantially, indicating unique functional adaptations absent in contemporary reptiles. This finding accentuates the distinct evolutionary identity of synapsids, highlighting their departure from basal reptilian locomotor modes well before the rise of crown mammals.

The methodology employed surmounted formidable technical hurdles inherent in comparing morphological traits across a vast taxonomic and temporal spectrum. Traditional geometric morphometric techniques, often limited to homologous structures with similar shapes, proved inadequate for such a diverse dataset spanning species separated by hundreds of millions of years. By adapting and innovating analytical tools, the research team generated a robust framework capable of translating complex fossil morphology into biomechanical function, paving the way for future evolutionary biomechanical investigations.

This research builds upon a storied scientific legacy, tracing intellectual lineages back to early 20th-century pioneers like Alfred Sherwood Romer and Farish Jenkins Jr., who first grappled with the origins of mammalian posture. With contemporary tools and computational power, the team now revisits these classic questions with renewed rigor and resolution, bringing clarity to long-standing evolutionary puzzles.

Looking ahead, the research group aims to develop detailed biomechanical models of limb articulation and muscle function in select fossil taxa. Such models promise to further elucidate the functional dynamics underlying posture and locomotion during key evolutionary transitions, offering deeper insight into the anatomical and ecological contexts that shaped mammalian evolution.

In sum, this groundbreaking study reveals an intricate and nonlinear evolutionary pathway from sprawling to upright forelimb function and posture in mammals. It highlights the evolutionary plasticity and innovation that characterized the mammalian lineage, challenging simplistic narratives and enriching our understanding of vertebrate evolution. As Dr. Brocklehurst emphasizes, deciphering how mammals came to stride upright transcends mere bone morphology; it opens a window into the dynamic history of life on Earth.

Subject of Research: Evolution of forelimb posture and locomotor biomechanics in mammals and their synapsid ancestors

Article Title: Adaptive landscapes unveil the complex evolutionary path from sprawling to upright forelimb function and posture in mammals

News Publication Date: 24-Jun-2025

Web References:

• PLOS Biology Article DOI: 10.1371/journal.pbio.3003188
• Related studies on backbone and hindlimb evolution:
  • Royal Society Publishing: Mammalian backbone evolution
  • Science Advances: Hindlimb evolution

Image Credits: Magdalen Mercado

The medial prefrontal cortex has long been implicated in complex cognitive functions such as decision-making, social cognition, and impulse regulation. Yet, understanding the causal role of specific subregions within this area has remained elusive until now. By investigating a cohort of individuals with focal brain damage, researchers have been able to dissect how lesions in distinct sections—the dorsomedial and ventromedial mPFC—propel divergent behavioral outcomes related to impulsivity and social conformity.

Involving 121 participants, the study encompassed three groups: those with targeted damage localized in the medial prefrontal cortex, others with lesions in disparate brain areas, and a control group of neurologically intact individuals closely matched for age. This carefully stratified design enabled the researchers to isolate the effects of precise neural injuries on behavior. Participants were subjected to a series of temporal discounting tasks assessing their baseline impulsivity in choosing between smaller immediate rewards or larger delayed ones, followed by a social influence phase wherein they were exposed to the decisions of purported peers who displayed either impulsive or patient preferences.

Results indicated that those with mPFC damage exhibited increased impulsivity in their own choices, in line with previous findings linking this brain region to self-control mechanisms. More intriguingly, these participants were markedly more susceptible to adopting the impulsive preferences demonstrated by others, a susceptibility not mirrored when observing patient behaviors. This suggests that damage to the mPFC does not uniformly heighten social influence but selectively enhances responsiveness to impulsive social cues.

Professor Patricia Lockwood of the University of Birmingham, a senior author on the study, emphasized this nuanced interplay by explaining that our neural architecture mediates how we integrate social information into personal decision frameworks. “Our research reveals that damage to a specific section of the mPFC heightens vulnerability to social influence—but specifically from impulsive individuals, not from those exhibiting restraint,” Lockwood stated. She further clarified that adjacent yet distinct brain areas are responsible for baseline impulsivity levels independent of social context.

The team’s meticulous lesion mapping revealed that damage to the dorsomedial prefrontal cortex, situated towards the upper segment of the mPFC, predominantly modulates how individuals are influenced socially in impulsive decision scenarios. Conversely, lesions in the ventromedial prefrontal cortex, located ventrally, exert a primary effect on general impulsivity unrelated to social influence factors. These findings underscore the functional heterogeneity within the mPFC and its differential contributions to cognition and behavior.

Methodologically, the study combined sophisticated computational modeling with anatomical neuroimaging to precisely delineate lesion locations and their behavioral correlates. This integrative approach strengthens the causal inferences that can be drawn, moving beyond correlative studies to a more mechanistic understanding of brain-behavior relationships. That individuals with mPFC damage can still cognitively grasp others’ preferences yet paradoxically become more prone to acting upon impulsive social influences opens new avenues for exploring how social environments dynamically interact with neural dysfunction.

Lead author Zhilin Su from the University of Birmingham highlighted the rarity of assembling such a large and well-characterized sample of participants with selective mPFC damage. “This cohort allowed us to rigorously test the hypothesis that the medial prefrontal cortex plays a distinguished role in social susceptibility and impulsivity,” Su remarked. “Our findings suggest that interventions targeting these neural circuits might modulate impulsivity and social influence in clinical populations.”

These insights bear profound significance for understanding everyday human behaviors and the vulnerabilities associated with brain injury. The increased social susceptibility observed could inform why some individuals with prefrontal damage may fall prey more readily to peer pressure, misinformation, or maladaptive financial decisions. As impulsivity and social influence are tightly interwoven in numerous psychiatric and neurological conditions, this research paves the way for tailored therapeutic strategies that consider the neural basis of social cognition.

Moreover, the dissociation between the impact of dorsomedial and ventromedial lesions advances neuropsychological models of decision-making, suggesting that complex behaviors like patience and social conformity emerge from compartmentalized neural networks rather than monolithic brain regions. Future investigations might explore how these findings translate into real-world settings, influence rehabilitation protocols, or relate to individual differences in susceptibility to marketing or social media influence.

In summary, this study provides compelling evidence that the medial prefrontal cortex is not only central to regulating impulsivity but intricately involved in how social information modulates such tendencies. This dual influence is region-specific, deepening our grasp of the neural substrates that govern the interplay between environment, cognition, and behavior. Such knowledge is indispensable in a world increasingly shaped by social connectivity and rapid information exchange.

The implications of these findings extend beyond neuroscience, touching on disciplines such as psychology, economics, and even public policy, where understanding the mechanisms of influence could improve strategies aimed at behavioral change, misinformation mitigation, and financial decision support systems. The combination of lesion mapping and behavioral paradigms in this research epitomizes how interdisciplinary approaches can unravel complex phenomena like social influence and impulsivity, often challenging to separate in healthy individuals.

As researchers continue to probe the brain’s social circuits, this study marks a significant milestone by concretely linking discrete brain damage to altered social and impulsive behavior profiles. Such work enhances our comprehension of the human condition, emphasizing the role of neural integrity in preserving autonomy amidst the pervasive sway of social information.

Subject of Research: People
Article Title: Dorsomedial and ventromedial prefrontal cortex lesions differentially impact social influence and temporal discounting
News Publication Date: 28-Apr-2025
Web References: 10.1371/journal.pbio.3003079
Keywords: Brain damage, Social research, Prefrontal cortex, Brain lesions, Social decision making, Finance

Synovial joints are predominantly found in land vertebrates and bony fish, recognized for their unique ability to facilitate smooth movement through a lubricated cavity that allows bones to glide against one another. These joints significantly enhance mobility and stability compared to other types of joints, contributing to the evolutionary advantages seen in various species. While it was theorized that synovial joints evolved in the common ancestors of both bony fish and land vertebrates, the exact timeline of their emergence in early vertebrate evolution has remained ambiguous.

In their research, Sharma and her colleagues embarked on a meticulous examination of the anatomy and joint development in two early-branching vertebrate lineages: jawless fish, specifically sea lampreys, and cartilaginous fish, including bamboo sharks and little skates. A comprehensive analysis of these species revealed the presence of cavitated joints in cartilaginous fish, a stark contrast to the absence of such structures in jawless fish. This discovery not only highlights the diversity in joint evolution but also provides evidence that these complex structures are indeed a characteristic feature of jawed fish.

Moreover, the team discovered that the cartilaginous fish exhibited specific proteins and developmental processes that mirror those associated with synovial joints in other vertebrates. This finding points to an evolutionary connection between the joints of ancient fish and the sophisticated joint systems observed in modern species. Intriguingly, through the utilization of computed tomography (CT) scans, the researchers were able to identify similar cavitated joints in the fossilized remains of the fish species Bothriolepis, which stands as one of the earliest known examples of synovial joints.

These groundbreaking results emphasize the evolutionary journey of synovial joints, indicating that this remarkable adaptation first arose in the ancestors of jawed vertebrates. The absence of synovial joint structures in jawless fish serves as a poignant reminder of the evolutionary advancements that occurred in our lineages over 400 million years ago. Understanding the origins of these joints not only contributes to the broader narrative of vertebrate evolution but also opens avenues for investigating how the skeletal architectures of modern creatures, including humans, came to be.

Sharma and her team’s findings suggest that the evolution of mobile joints in early fish ancestors was a pivotal moment. This adaptation likely allowed them to explore new feeding strategies and diverse habitats, ultimately leading to the proliferation of vertebrate species. This evolutionary milestone highlights the critical nature of joint development and its role in shaping the anatomy and behaviors of vertebrates.

Future research endeavors may involve a closer analysis of joint morphology in various fossil fish lineages. By exploring the structural differences and evolutionary trajectories among jawed and jawless vertebrates, scientists aim to uncover additional insights into the complexities of early joint evolution. The implications of this research extend beyond just the understanding of fish anatomy; it enriches our comprehension of how joint development is intricately linked with evolutionary success and adaptation across various ecosystems.

The authors of the study underscore the importance of these findings, emphasizing that the developmental mechanisms responsible for joint formation emerged deep within the evolutionary timeline of fish. This discovery not only enhances our understanding of vertebrate anatomy but also serves as a testament to the resilience and adaptability of life forms through countless evolutionary changes.

In conclusion, the research led by Neelima Sharma sheds significant light on the evolutionary origins of synovial joints, tracing their ancestry back to jawed fish. This not only provides a deeper understanding of joint mobility and its advantages but also urges further investigations into how these ancient features have shaped the anatomical diversity of modern vertebrates. The implications of such studies are profound, as they inform our understanding of evolutionary biology and the intricate connections between form, function, and adaptation.

Examining the legacy of synovial joints allows researchers to appreciate the adaptive strategies that early vertebrates employed, paving the way for future explorations in evolutionary theory and vertebrate morphology. This fascinating glimpse into our evolutionary past holds vital implications for ongoing studies regarding joint health and functionality, bridging the gap between ancient biology and contemporary medical science.

As research continues to unveil the mysteries of vertebrate evolution, the story of our joints serves as a compelling narrative of adaptation and innovation, highlighting the remarkable paths taken by our ancestors millions of years ago. This ongoing inquiry into the origins and development of synovial joints not only enlightens us about our biological heritage but also deepens our understanding of the evolutionary processes that have shaped the diversity of life today.

Subject of Research: Evolution of synovial joints in vertebrates
Article Title: Synovial joints were present in the common ancestor of jawed fish but lacking in jawless fish
News Publication Date: February 25, 2025
Web References: PLOS Biology
References: Sharma N, Haridy Y, Shubin N (2025) Synovial joints were present in the common ancestor of jawed fish but lacking in jawless fish. PLoS Biol 23(2): e3002990.
Image Credits: Neelima Sharma, University of Chicago (CC-BY 4.0)

Keywords: synovial joints, vertebrate evolution, jawed fish, cartilaginous fish, fossil joints, joint morphology, Neelima Sharma, PLOS Biology