Jun 24, 2025 07:29 PM
(This post was last modified: Jun 24, 2025 07:30 PM by C C.)
New study reveals the surprising and twisty path our ancestors took to develop an upright stance
https://www.eurekalert.org/news-releases/1087834
INTRO: For over a century, scientists have puzzled over a fundamental mystery in our evolutionary history: how did mammals go from sprawling like lizards to striding like cats and dogs? This transition—from a sprawled stance (like a lizard) to an upright (parasagittal) posture—marked a pivotal moment in mammal evolution. While the earliest non-mammalian synapsids, the ancestors of living mammals, had a sprawling posture, researchers debated when and how the upright postures of modern mammals evolved.
Now, a groundbreaking study in PLOS Biology led by Dr. Robert Brocklehurst, a former postdoctoral fellow in the Department of Organismic and Evolutionary Biology (OEB) at Harvard University, offers a surprising answer: the path to upright posture wasn’t linear, but full of unexpected detours, evolutionary experimentation, and dramatic anatomical upheaval.
“The evolution of mammals has previously been characterized as a series of steps from sprawling, to semi-sprawling, to upright,” said Brocklehurst. “However, what we discovered was a more nonlinear evolutionary progression throughout mammalian history.” (MORE - details, no ads)
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The evolution from reptile-like to upright posture in mammals was highly dynamic and complex
https://www.eurekalert.org/news-releases/1087581
INTRO: The transition from sprawling (reptile-like) to more upright (parasagittal) posture and locomotion was a transformative event in mammalian evolution. A study published June 24th in the open-access journal PLOS Biology by Dr. Robert Brocklehurst and Professor Stephanie Pierce at Harvard University, USA and colleagues suggests that parasagittal posture evolved via an indirect, dynamic, and radiating process.
Non-mammalian synapsids (tetrapod vertebrates), the ancestors of extant mammals, underwent major musculoskeletal reorganization, including modifications to the forelimbs. However, when and how these anatomical transformations translated into mammal-like limb posture and upright locomotion is unknown. Prior research based on qualitative observations of the fossil record had hypothesized the evolutionary transition from sprawling to upright as a direct progression with discrete postural stages.
In order to better understand the origins and evolutionary pathway of mammalian posture, researchers analyzed humerus bone from over 200 species of tetrapods. They compared fossilized synapsid humeri to an array of extant salamander, reptile, monotreme and upright therian mammal humeri, examining humeral length, torsion, muscle leverage, bending strength, and radius of gyration. The researchers then computationally modeled the relationship between bone shape, function, and posture to visualize different evolutionary scenarios for how therian mammal upright posture evolved.
The researchers found that ancestral synapsids had a sprawling posture, but their anatomy and movement were distinct from extant sprawlers. The upright posture of modern-day mammals involved a fundamental reorganization of the musculoskeletal system and expansion of differences in forelimb function, suggesting that mammals started walking upright later than previously thought. The study had several limitations, such as uncertainty around phylogenic branch lengths and estimated dates of taxa divergence. Future studies are needed to develop greater specificity and certainty around limb posture in different taxa... (MORE - details, no ads)
An evolutionary trade-off has limited how fish catch their prey
https://www.eurekalert.org/news-releases/1087683
INTRO: A trade-off between tooth size and jaw mobility has restricted fish evolution, Nick Peoples at the University of California Davis, US, and colleagues report June 24th in the open-access journal PLOS Biology.
Ray-finned fish are a diverse and widespread group, representing 99% of living fish species. Two key adaptations have helped them thrive: large teeth and extendible jaws. Fish with larger teeth can access a wider range of food sources, while the ability to rapidly extend the upper jaw allows fish to hunt fast-swimming prey by using suction forces to pull them closer.
However, these two innovations are rarely found in the same fish species. To find out why, researchers captured high-speed videos of the feeding behavior of 161 species of ray-finned fish. They analyzed how different strategies for capturing prey had evolved alongside tooth size across the evolutionary tree.
They found that small-toothed fishes used a wider variety of methods to capture prey, including extending their jaw to create suction. In contrast, fishes with larger teeth were more likely to use rapid bursts of swimming to close-in on their prey, and fish with the largest teeth exclusively used this strategy. The researchers calculated that the optimum tooth size for fish that use jaw extension to capture prey was 4 times smaller than for fish that use rapid swimming.
The results indicate that large teeth and a highly extendible upper jaw are incompatible adaptations, creating a trade-off in the evolution of fish feeding behavior... (MORE - details, no ads)
https://www.eurekalert.org/news-releases/1087834
INTRO: For over a century, scientists have puzzled over a fundamental mystery in our evolutionary history: how did mammals go from sprawling like lizards to striding like cats and dogs? This transition—from a sprawled stance (like a lizard) to an upright (parasagittal) posture—marked a pivotal moment in mammal evolution. While the earliest non-mammalian synapsids, the ancestors of living mammals, had a sprawling posture, researchers debated when and how the upright postures of modern mammals evolved.
Now, a groundbreaking study in PLOS Biology led by Dr. Robert Brocklehurst, a former postdoctoral fellow in the Department of Organismic and Evolutionary Biology (OEB) at Harvard University, offers a surprising answer: the path to upright posture wasn’t linear, but full of unexpected detours, evolutionary experimentation, and dramatic anatomical upheaval.
“The evolution of mammals has previously been characterized as a series of steps from sprawling, to semi-sprawling, to upright,” said Brocklehurst. “However, what we discovered was a more nonlinear evolutionary progression throughout mammalian history.” (MORE - details, no ads)
- - - - - - - - - - - - - -
The evolution from reptile-like to upright posture in mammals was highly dynamic and complex
https://www.eurekalert.org/news-releases/1087581
INTRO: The transition from sprawling (reptile-like) to more upright (parasagittal) posture and locomotion was a transformative event in mammalian evolution. A study published June 24th in the open-access journal PLOS Biology by Dr. Robert Brocklehurst and Professor Stephanie Pierce at Harvard University, USA and colleagues suggests that parasagittal posture evolved via an indirect, dynamic, and radiating process.
Non-mammalian synapsids (tetrapod vertebrates), the ancestors of extant mammals, underwent major musculoskeletal reorganization, including modifications to the forelimbs. However, when and how these anatomical transformations translated into mammal-like limb posture and upright locomotion is unknown. Prior research based on qualitative observations of the fossil record had hypothesized the evolutionary transition from sprawling to upright as a direct progression with discrete postural stages.
In order to better understand the origins and evolutionary pathway of mammalian posture, researchers analyzed humerus bone from over 200 species of tetrapods. They compared fossilized synapsid humeri to an array of extant salamander, reptile, monotreme and upright therian mammal humeri, examining humeral length, torsion, muscle leverage, bending strength, and radius of gyration. The researchers then computationally modeled the relationship between bone shape, function, and posture to visualize different evolutionary scenarios for how therian mammal upright posture evolved.
The researchers found that ancestral synapsids had a sprawling posture, but their anatomy and movement were distinct from extant sprawlers. The upright posture of modern-day mammals involved a fundamental reorganization of the musculoskeletal system and expansion of differences in forelimb function, suggesting that mammals started walking upright later than previously thought. The study had several limitations, such as uncertainty around phylogenic branch lengths and estimated dates of taxa divergence. Future studies are needed to develop greater specificity and certainty around limb posture in different taxa... (MORE - details, no ads)
An evolutionary trade-off has limited how fish catch their prey
https://www.eurekalert.org/news-releases/1087683
INTRO: A trade-off between tooth size and jaw mobility has restricted fish evolution, Nick Peoples at the University of California Davis, US, and colleagues report June 24th in the open-access journal PLOS Biology.
Ray-finned fish are a diverse and widespread group, representing 99% of living fish species. Two key adaptations have helped them thrive: large teeth and extendible jaws. Fish with larger teeth can access a wider range of food sources, while the ability to rapidly extend the upper jaw allows fish to hunt fast-swimming prey by using suction forces to pull them closer.
However, these two innovations are rarely found in the same fish species. To find out why, researchers captured high-speed videos of the feeding behavior of 161 species of ray-finned fish. They analyzed how different strategies for capturing prey had evolved alongside tooth size across the evolutionary tree.
They found that small-toothed fishes used a wider variety of methods to capture prey, including extending their jaw to create suction. In contrast, fishes with larger teeth were more likely to use rapid bursts of swimming to close-in on their prey, and fish with the largest teeth exclusively used this strategy. The researchers calculated that the optimum tooth size for fish that use jaw extension to capture prey was 4 times smaller than for fish that use rapid swimming.
The results indicate that large teeth and a highly extendible upper jaw are incompatible adaptations, creating a trade-off in the evolution of fish feeding behavior... (MORE - details, no ads)