Science Editorial, Oct 25 (EFE).- Going from a reptilian posture to an upright one that allowed them to walk was anything but easy for mammals, as revealed this Friday by a study led by researchers at Harvard University published in the journal Science. Advances.
The authors have combined fossil data with advanced digital biomechanical models to reveal that the evolution of mammals towards an upright posture was much more complex and later than previously thought.
The transition from a stretched posture, such as that of lizards, to the upright posture of modern mammals, such as that of humans, dogs or horses, marked a crucial moment in evolution; but the explanation of how, why and when it occurred remained a mystery.
The Organismic and Evolutionary Biology team led by Stephanie Pierce at Harvard has managed to answer these questions thanks, in part, to the reconstruction of how extinct animals moved using simulation models with data from fossil remains.
To do this, the researchers began by studying current species that represent the entire spectrum of limb postures, with the aim of having a better understanding of animal anatomy and the ways of standing and moving.
Among the specimens of the present, they resorted to the tegu lizard (stretched), the alligator (semi-upright) or the greyhound (upright).
Reconstruct the movement of extinct animals
Next, they studied fossil samples of eight different extinct species, representative of four continents, covering a total of 300 million years of evolution.
Among them there were animals ranging from 35 grams to others that weighed 88 kilos, such as ‘Ophiacodon’, a pelycosaur synapsid.
Using principles from physics and engineering, the researchers created digital biomechanical models to recreate the way the muscles and bones of the animals the fossils belonged to joined together.
In this way, they were able to generate simulations that allowed them to determine how much force the mammals’ hind legs could exert on the ground.
Although these types of digital recreation models of animal movement have existed since the 1990s, this is the first time they have been used with data from fossil records of animals that no longer exist.
Findings
One of the results that has surprised researchers the most is that not all species went from being “lying down” to standing upright in a simple and linear way, but some had peaks in which they began to stand up but then returned to maintaining a stretched position. and it took millions of years to rise again.
Some extinct species also appeared to be more flexible, able to shift between more upright and less upright postures, as modern alligators and crocodiles do today.
The findings also help explain other unknowns about the fossil record, such as the existence of asymmetrical hands, feet and joints in many mammalian ancestors, traits typically associated with more “squashed” postures among modern animals.
The authors explain how sometimes this evolution was the result of fortuitous events, such as when the posture of pelycosaur synapsids towards more stretched out postures seems to coincide with the Permian-Triassic mass extinction, when 90% of life on planet Earth disappeared. .
This extinction caused other groups, such as dinosaurs, to become the dominant animal groups on land, relegating the synapsids to the background, and that kind of “ecological marginalization” may have prompted them to stand up more.
“Computer advances and digital modeling are allowing us to understand how mammals evolved and to verify that it was not such a simple and linear process in time, many things happened to reach the mammals we know today,” Pierce concludes in a statement. from Harvard.
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Interview with Dr. Stephanie Pierce, Lead Researcher on Mammalian Evolution Study at Harvard University
Interviewer: Thank you for joining us today, Dr. Pierce. Your team’s recent study provides fascinating insights into the evolution of mammals. Can you start by summarizing what your research discovered about the transition from a reptilian posture to an upright stance in mammals?
Dr. Pierce: Thank you for having me! Our research revealed that the evolution of mammals towards an upright posture was much more complex and occurred later than previously thought. We utilized advanced biomechanical models, combined with fossil data, to reconstruct the movement of various extinct species. By doing so, we could better understand how these early mammals transitioned from stretched postures—like that of modern lizards—to the upright positions seen in species like humans, dogs, and horses.
Interviewer: That sounds groundbreaking! What methodology did you use to study the movement of extinct animals, and which species were focused on in your research?
Dr. Pierce: We initiated our study by examining current species that represent a range of limb postures, such as the tegu lizard for stretched posture and the greyhound for upright posture. This helped us create a baseline for understanding animal anatomy. We then studied fossil samples from eight different extinct species across four continents—covering approximately 300 million years of evolution. Notable specimens included the synapsid ‘Ophiacodon’ and the mammal-like cynodont ‘Massetognathus.’
Interviewer: Your team utilized digital biomechanical models for recreating movements. How did this technology contribute to your findings?
Dr. Pierce: That’s correct! By applying principles from physics and engineering, we developed digital models that simulated how ancient muscles and bones interacted. This allowed us to determine the force exerted by the hind legs of these creatures. While digital recreation of animal movement isn’t new, we’ve uniquely applied it to actual fossil data from extinct species, lending significant insight into their locomotion.
Interviewer: What do you think are the broader implications of your findings for our understanding of mammalian evolution?
Dr. Pierce: Our study not only sheds light on the intricacies of our own evolutionary history but also emphasizes the gradual adaptation processes of mammals in response to changing environments. It suggests a more nuanced understanding of how anatomical features evolved over time, highlighting the influence of both biomechanical demands and ecological factors.
Interviewer: Fascinating! Lastly, what are the next steps for your research team following this study?
Dr. Pierce: We hope to expand our studies to include more fossil species and also explore the ecological contexts in which these transformations occurred. Understanding the pressures that influenced these adaptations can provide us with deeper insights into the evolutionary narratives of mammals as a whole.
Interviewer: Thank you for sharing your insights, Dr. Pierce. This study certainly adds a significant chapter to the story of mammalian evolution!
Dr. Pierce: Thank you for having me! It’s been a pleasure discussing our research.
Interviewer: What do you think was the most surprising finding from your research regarding the evolution of mammalian posture?
Dr. Pierce: One of the most surprising aspects was the realization that not all species transitioned from a “lying down” position to standing upright in a straightforward manner. In fact, some species exhibited peaks where they began to adopt more upright postures but then reverted back to stretched positions. This back-and-forth evolution took millions of years and illustrates that the path to an upright stance was anything but linear.
Interviewer: Fascinating! You mentioned that this research sheds light on other unknowns in the fossil record. Could you elaborate on that?
Dr. Pierce: Certainly! Our findings helped explain the presence of asymmetrical hands, feet, and joints in many ancestral mammal species. These traits are generally thought to be associated with more “squashed” postures seen in modern animals. Understanding these features provides better insight into how different postures and lifestyles evolved with environmental changes over time, such as major extinction events.
Interviewer: How does your research reinterpret the evolutionary challenges mammals faced, especially during significant events like the Permian-Triassic mass extinction?
Dr. Pierce: The Permian-Triassic mass extinction was a crucial turning point that led to a drastic loss of biodiversity. This ecological marginalization may have motivated certain synapsids to adopt more upright postures as they struggled to adapt to changing environments. Our study indicates that the evolution of mammalian posture was influenced not just by gradual developments but also by fortuitous events in Earth’s history.
Interviewer: What’s next for your research team in this area?
Dr. Pierce: Moving forward, we aim to expand our study to include a broader range of extinct species and further refine our biomechanical models. We hope to delve deeper into understanding how environmental pressures and anatomical adaptations influenced the evolution of locomotion across different lineages. Continued advancements in technology will also allow us to enhance our simulations and insights into the locomotion of both extinct and extant species.
Interviewer: Thank you so much for sharing your insights, Dr. Pierce. This research could indeed reshape our understanding of mammalian evolution.
Dr. Pierce: Thank you for having me. It’s an exciting time for evolutionary biology!
