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The lungfish genome, tetrapods, and junk DNA

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  • #31
    Originally posted by lee_merrill View Post
    "Tiktaalik is clearly a transitional form..." Meaning an actual intermediate.

    Blessings,
    Lee
    What would a not actual intermediate look like Lee? Your incompetent blithering gets worse every passing day.

    Comment


    • #32
      Originally posted by HMS_Beagle View Post

      What would a not actual intermediate look like Lee? Your incompetent blithering gets worse every passing day.
      Something that's not actually an intermediate.

      Blessings,
      Lee
      "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

      Comment


      • #33
        Originally posted by shunyadragon View Post
        Yes, "Tiktaalik is clearly a transitional form, but this does not necessarily translate to an actual intermediate, which is a maybe.
        Well, not transitional in the sense that Nature meant it, but I agree that its placement is up in the air.

        Blessings,
        Lee
        "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

        Comment


        • #34
          Originally posted by lee_merrill View Post
          Well, not transitional in the sense that Nature meant it, but I agree that its placement is up in the air.

          Blessings,
          Lee
          How exactly do you think Nature meant it. Again, aside from copy pasting one sentence definitions, explain what constitutes a transitional fossil? There's a big clue in this thread. Let's see if you're capable of figuring it out.

          I'm always still in trouble again

          "You're by far the worst poster on TWeb" and "TWeb's biggest liar" --starlight (the guy who says Stalin was a right-winger)
          "Of course, human life begins at fertilization thatís not the argument." --Tassman

          Comment


          • #35
            Originally posted by lee_merrill View Post
            Something that's not actually an intermediate.

            Blessings,
            Lee
            Congratulations on winning the Jorge Fernandez "specified complex information is information which is complex and specified" Cowardly Non-Answer Award.

            Comment


            • #36
              Originally posted by lee_merrill View Post
              Source: Nature

              Now, however, Niedwiedzki et al. lob a grenade into that picture. They report the stunning discovery of tetrapod trackways with distinct digit imprints from Zachemie, Poland, that are unambiguously dated to the lowermost Eifelian (397 Myr ago). (source)

              © Copyright Original Source


              Source: Wikipedia

              Tiktaalik is a monospecific genus of extinct sarcopterygian (lobe-finned fish) from the Late Devonian Period, about 375 Mya (million years ago)... (source)

              © Copyright Original Source


              So the difference appears to be about 22 million years.
              Ok, my mistake. I apologize for being misinformed - must have been some other species that was closer in time to the traces.

              Originally posted by lee_merrill View Post
              No, the statement is simply that Tiktaalik is not a direct transitional form. That is why I quoted it, that is what they meant, Nature was incorrect in this assertion. That is not to say that there are major problems with evolutionary theory.
              I see others are handling this discussion quite well, so i'll leave it.

              Beyond all that, i fail to see the point of the blog post or its relevance to this discussion. It's clear that the author of the blog post doesn't understand terminology, and is accusing biologists of being deceptive because they're not following what he thinks the definition is. And then accusing the biologists who try to explain the real one of making excuses. Like everything else on the site, it's garbage. Do not use it in my threads again.

              In the larger picture, even if we deleted all knowledge of Tiktaalik somehow, we'd still have enough other fossils to clearly indicate tetrapods evolved from lobe-finned fishes. And now the DNA evidence lines up with that as well. That's the big picture, and anything else said here is just a distraction from that.

              Oh yes, and i hope whenever you bring up junk DNA in the future, you manage to keep this data in mind.
              "Any sufficiently advanced stupidity is indistinguishable from trolling."

              Comment


              • #37
                Originally posted by lee_merrill View Post
                Well, not transitional in the sense that Nature meant it, but I agree that its placement is up in the air.

                Blessings,
                Lee
                No, not up in thee air. Transitional form means a species is intermediate in form well dated in the geologic strata with other species that are transitional in form. and related in evolution. It does not mean a specific transitional species. Careful 'arguing from ignorance' and taking things out of context. It is a bad habit of yours.
                Glendower: I can call spirits from the vasty deep.
                Hotspur: Why, so can I, or so can any man;
                But will they come when you do call for them? Shakespeareís Henry IV, Part 1, Act III:

                go with the flow the river knows . . .

                Frank

                I do not know, therefore everything is in pencil.

                Comment


                • #38
                  This seems pertinent

                  Source: Harvard Scientists Reconstruct the Game-Changing Evolution From Fin-to-Limb in Early Tetrapods


                  It’s hard to overstate how much of a game-changer it was when vertebrates first rose up from the waters and moved onshore about 390 million years ago. That transition led to the rise of the dinosaurs and all the land animals that exist today.

                  “Being able to walk around on land essentially set the stage for all biodiversity and established modern terrestrial ecosystems,” said Stephanie Pierce, Thomas D. Cabot Associate Professor of Organismic and Evolutionary Biology and curator of vertebrate paleontology in the Museum of Comparative Zoology. “It represents an incredibly important period of time in evolutionary history.”

                  Scientists have been trying for more than a century to unravel exactly how this remarkable shift took place, and their understanding of the process is largely based on a few rare, intact fossils with anatomical gaps between them. A new study from Pierce and Blake Dickson, Ph.D. ’20, looks to provide a more thorough view by zeroing in on a single bone: the humerus.

                  The study, published in Nature, shows how and when the first groups of land explorers became better walkers than swimmers. The analysis spans the fin-to-limb transition and reconstructs the evolution of terrestrial movement in early tetrapods. These are the four-limbed land vertebrates whose descendants include extinct and living amphibians, reptiles, and mammals.

                  The researchers focused on the humerus, the long bone in the upper arm that runs down from the shoulder and connects with the lower arm at the elbow, to get around the dilemma of gaps between well-preserved fossils. Functionally, the humerus is invaluable for movement because it hosts key muscles that absorb much of the stress from quadrupedal locomotion. Most importantly, the bone is found in all tetrapods and the fishes they evolved from and is pretty common throughout the fossil record. The bone represents a time capsule of sorts, with which to reconstruct the evolution of locomotion since it can be examined across the fin-to-limb transition, the researchers said.

                  “We went in with the idea that the humerus should be able to tell us about the functional evolution of locomotion as you go from being a fish that’s just swimming around and as you come onto land and start walking,” Dickson said.

                  The researchers analyzed 40 3D fossil humeri for the study, including new fossils collected by collaborators at the University of Cambridge as part of the TW:eed Project. The team looked at how the bone changed over time and its effect on how these creatures likely moved.



                  Aquatic-Fish-Fossil-Humeri-768x1152.jpg
                  A fossil humeri from an aquatic fish (Eusthenopteron), a transitional tetrapod
                  (Acanthostega), and a terrestrial tetrapod (Ophiacodon). Credit: Stephanie Pierce



                  The analysis covered the transition from aquatic fishes to terrestrial tetrapods. It included an intermediate group of tetrapods with previously unknown locomotor capabilities. The researchers found that the emergence of limbs in this intermediate group coincided with a transition onto land, but that these early tetrapods weren’t very good at moving on it.

                  To understand this, the team measured the functional trade-offs associated with adapting to different environments. They found that as these creatures moved from water to land, the humerus changed shape, resulting in new combinations of functional traits that proved more advantageous for life on land than in the water.

                  That made sense to the researchers. “You can’t be good at everything,” Dickson said. “You have to give up something to go from being a fish to being a tetrapod on land.”

                  The researchers captured the changes on a topographical map showing where these early tetrapods stood in relation to water-based or land-based living. The scientists said these changes were likely driven by environmental pressures as these creatures adapted to terrestrial life.

                  The paper describes the transitional tetrapods as having an “L-shaped” humerus that provided some functional benefit for moving on land, but not much. These animals had a long way to go to develop the traits necessary to use their limbs on land to move with ease and skill.

                  As the humerus continued to change shape, tetrapods improved their movement. The “L” shaped humerus transformed into a more robust, elongated, twisted form, leading to new combinations of functional traits. This change allowed for more effective gaits on land and helped trigger biological diversity and expansion into terrestrial ecosystems. It also helped establish complex food chains based on predators, prey, herbivores, and carnivores still seen today.

                  Analysis took about four years to complete. Quantifying how the humerus changed shape and function took thousands of hours on a supercomputer. The researchers then analyzed how those changes impacted functional performance of the limb during locomotion and the trade-offs associated.

                  The innovative approach represents a new way of viewing and analyzing the fossil record — an effort Pierce said was well worth it.

                  “This study demonstrates how much information you can get from such a small part of an animal’s skeleton that’s been recorded in the fossil record and how it can help unravel one of the biggest evolutionary transformations that has ever occurred,” Pierce said. “This is really cutting-edge stuff.”



                  Source[/b]

                  © Copyright Original Source




                  Source: From Fins to Limbs and Water to Land: Evolution of Terrestrial Movement in Early Tetrapods


                  The water-to-land transition is one of the most important and inspiring major transitions in vertebrate evolution. And the question of how and when tetrapods transitioned from water to land has long been a source of wonder and scientific debate.

                  Early ideas posited that drying-up-pools of water stranded fish on land and that being out of water provided the selective pressure to evolve more limb-like appendages to walk back to water. In the 1990s newly discovered specimens suggested that the first tetrapods retained many aquatic features, like gills and a tail fin, and that limbs may have evolved in the water before tetrapods adapted to life on land. There is, however, still uncertainty about when the water-to-land transition took place and how terrestrial early tetrapods really were.

                  A paper published today (November 25, 2020) in Nature addresses these questions using high-resolution fossil data and shows that although these early tetrapods were still tied to water and had aquatic features, they also had adaptations that indicate some ability to move on land. Although, they may not have been very good at doing it, at least by today’s standards.

                  Lead author Blake Dickson, PhD ’20 in the Department of Organismic and Evolutionary Biology at Harvard University, and senior author Stephanie Pierce, Thomas D. Cabot Associate Professor in the Department of Organismic and Evolutionary Biology and curator of vertebrate paleontology in the Museum of Comparative Zoology at Harvard University, examined 40 three-dimensional models of fossil humeri (upper arm bone) from extinct animals that bridge the water-to-land transition.



                  Three major stages of humerus shape evolution: from the blocky humerus of aquatic fish, to the L-shape humerus of
                  transitional tetrapods, and the twisted humerus of terrestrial tetrapods. Columns (left to right) = aquatic fish,
                  transitional tetrapod, and terrestrial tetrapod. Rows = Top: extinct animal silhouettes; Middle: 3D humerus fossils;
                  Bottom: landmarks used to quantified shape. Credit: Courtesy of Blake Dickson


                  “Because the fossil record of the transition to land in tetrapods is so poor we went to a source of fossils that could better represent the entirety of the transition all the way from being a completely aquatic fish to a fully terrestrial tetrapod,” said Dickson.

                  Two thirds of the fossils came from the historical collections housed at Harvard’s Museum of Comparative Zoology, which are sourced from all over the world. To fill in the missing gaps, Pierce reached out to colleagues with key specimens from Canada, Scotland, and Australia. Of importance to the study were new fossils recently discovered by co-authors Dr. Tim Smithson and Professor Jennifer Clack, University of Cambridge, UK, as part of the TW:eed project, an initiative designed to understand the early evolution of land-going tetrapods.

                  The researchers chose the humerus bone because it is not only abundant and well preserved in the fossil record, but it is also present in all sarcopterygians — a group of animals which includes coelacanth fish, lungfish, and all tetrapods, including all of their fossil representatives. “We expected the humerus would carry a strong functional signal as the animals transitioned from being a fully functional fish to being fully terrestrial tetrapods, and that we could use that to predict when tetrapods started to move on land,” said Pierce. “We found that terrestrial ability appears to coincide with the origin of limbs, which is really exciting.”


                  Humerus-Shape-Change-Along-Evolutionary-Tree.gif
                  The evolutionary pathway and shape change from an aquatic fish humerus
                  to a terrestrial tetrapod humerus. Credit: Courtesy of Blake Dickson



                  The humerus anchors the front leg onto the body, hosts many muscles, and must resist a lot of stress during limb-based motion. Because of this, it holds a great deal of critical functional information related to an animal’s movement and ecology. Researchers have suggested that evolutionary changes in the shape of the humerus bone, from short and squat in fish to more elongate and featured in tetrapods, had important functional implications related to the transition to land locomotion. This idea has rarely been investigated from a quantitative perspective — that is, until now.

                  When Dickson was a second-year graduate student, he became fascinated with applying the theory of quantitative trait modeling to understanding functional evolution, a technique pioneered in a 2016 study led by a team of paleontologists and co-authored by Pierce. Central to quantitative trait modeling is paleontologist George Gaylord Simpson’s 1944 concept of the adaptive landscape, a rugged three-dimensional surface with peaks and valleys, like a mountain range. On this landscape, increasing height represents better functional performance and adaptive fitness, and over time it is expected that natural selection will drive populations uphill towards an adaptive peak.

                  Dickson and Pierce thought they could use this approach to model the tetrapod transition from water to land. They hypothesized that as the humerus changed shape, the adaptive landscape would change too. For instance, fish would have an adaptive peak where functional performance was maximized for swimming and terrestrial tetrapods would have an adaptive peak where functional performance was maximized for walking on land. “We could then use these landscapes to see if the humerus shape of earlier tetrapods was better adapted for performing in water or on land” said Pierce.

                  “We started to think about what functional traits would be important to glean from the humerus,” said Dickson. “Which wasn’t an easy task as fish fins are very different from tetrapod limbs.” In the end, they narrowed their focus on six traits that could be reliably measured on all of the fossils including simple measurements like the relative length of the bone as a proxy for stride length and more sophisticated analyses that simulated mechanical stress under different weight bearing scenarios to estimate humerus strength.

                  “If you have an equal representation of all the functional traits you can map out how the performance changes as you go from one adaptive peak to another,” Dickson explained. Using computational optimization the team was able to reveal the exact combination of functional traits that maximized performance for aquatic fish, terrestrial tetrapods, and the earliest tetrapods. Their results showed that the earliest tetrapods had a unique combination of functional traits, but did not conform to their own adaptive peak.

                  “What we found was that the humeri of the earliest tetrapods clustered at the base of the terrestrial landscape,” said Pierce. “indicating increasing performance for moving on land. But these animals had only evolved a limited set of functional traits for effective terrestrial walking.”

                  The researchers suggest that the ability to move on land may have been limited due to selection on other traits, like feeding in water, that tied early tetrapods to their ancestral aquatic habitat. Once tetrapods broke free of this constraint, the humerus was free to evolve morphologies and functions that enhanced limb-based locomotion and the eventual invasion of terrestrial ecosystems

                  “Our study provides the first quantitative, high-resolution insight into the evolution of terrestrial locomotion across the water-land transition,” said Dickson. “It also provides a prediction of when and how [the transition] happened and what functions were important in the transition, at least in the humerus.”

                  “Moving forward, we are interested in extending our research to other parts of the tetrapod skeleton,” Pierce said. “For instance, it has been suggested that the forelimbs became terrestrially capable before the hindlimbs and our novel methodology can be used to help test that hypothesis.”

                  Dickson recently started as a Postdoctoral Researcher in the Animal Locomotion lab at Duke University, but continues to collaborate with Pierce and her lab members on further studies involving the use of these methods on other parts of the skeleton and fossil record.


                  Source

                  © Copyright Original Source




                  The abstract for the paper Functional adaptive landscapes predict terrestrial capacity at the origin of limbs is below

                  Abstract

                  The acquisition of terrestrial, limb-based locomotion during tetrapod evolution has remained a subject of debate for more than a century1,2. Our current understanding of the locomotor transition from water to land is largely based on a few exemplar fossils such as Tiktaalik3, Acanthostega4, Ichthyostega5 and Pederpes6. However, isolated bony elements may reveal hidden functional diversity, providing a more comprehensive evolutionary perspective7. Here we analyse 40 three-dimensionally preserved humeri from extinct tetrapodomorphs that span the fin-to-limb transition and use functionally informed ecological adaptive landscapes8,9,10 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 gaits5,11 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 niches12,13.




                  I'm always still in trouble again

                  "You're by far the worst poster on TWeb" and "TWeb's biggest liar" --starlight (the guy who says Stalin was a right-winger)
                  "Of course, human life begins at fertilization thatís not the argument." --Tassman

                  Comment


                  • #39
                    Originally posted by rogue06 View Post
                    This seems pertinent

                    Source: Harvard Scientists Reconstruct the Game-Changing Evolution From Fin-to-Limb in Early Tetrapods


                    It’s hard to overstate how much of a game-changer it was when vertebrates first rose up from the waters and moved onshore about 390 million years ago. That transition led to the rise of the dinosaurs and all the land animals that exist today.

                    “Being able to walk around on land essentially set the stage for all biodiversity and established modern terrestrial ecosystems,” said Stephanie Pierce, Thomas D. Cabot Associate Professor of Organismic and Evolutionary Biology and curator of vertebrate paleontology in the Museum of Comparative Zoology. “It represents an incredibly important period of time in evolutionary history.”

                    Scientists have been trying for more than a century to unravel exactly how this remarkable shift took place, and their understanding of the process is largely based on a few rare, intact fossils with anatomical gaps between them. A new study from Pierce and Blake Dickson, Ph.D. ’20, looks to provide a more thorough view by zeroing in on a single bone: the humerus.

                    The study, published in Nature, shows how and when the first groups of land explorers became better walkers than swimmers. The analysis spans the fin-to-limb transition and reconstructs the evolution of terrestrial movement in early tetrapods. These are the four-limbed land vertebrates whose descendants include extinct and living amphibians, reptiles, and mammals.

                    The researchers focused on the humerus, the long bone in the upper arm that runs down from the shoulder and connects with the lower arm at the elbow, to get around the dilemma of gaps between well-preserved fossils. Functionally, the humerus is invaluable for movement because it hosts key muscles that absorb much of the stress from quadrupedal locomotion. Most importantly, the bone is found in all tetrapods and the fishes they evolved from and is pretty common throughout the fossil record. The bone represents a time capsule of sorts, with which to reconstruct the evolution of locomotion since it can be examined across the fin-to-limb transition, the researchers said.

                    “We went in with the idea that the humerus should be able to tell us about the functional evolution of locomotion as you go from being a fish that’s just swimming around and as you come onto land and start walking,” Dickson said.

                    The researchers analyzed 40 3D fossil humeri for the study, including new fossils collected by collaborators at the University of Cambridge as part of the TW:eed Project. The team looked at how the bone changed over time and its effect on how these creatures likely moved.



                    Aquatic-Fish-Fossil-Humeri-768x1152.jpg
                    A fossil humeri from an aquatic fish (Eusthenopteron), a transitional tetrapod
                    (Acanthostega), and a terrestrial tetrapod (Ophiacodon). Credit: Stephanie Pierce




                    The analysis covered the transition from aquatic fishes to terrestrial tetrapods. It included an intermediate group of tetrapods with previously unknown locomotor capabilities. The researchers found that the emergence of limbs in this intermediate group coincided with a transition onto land, but that these early tetrapods weren’t very good at moving on it.

                    To understand this, the team measured the functional trade-offs associated with adapting to different environments. They found that as these creatures moved from water to land, the humerus changed shape, resulting in new combinations of functional traits that proved more advantageous for life on land than in the water.

                    That made sense to the researchers. “You can’t be good at everything,” Dickson said. “You have to give up something to go from being a fish to being a tetrapod on land.”

                    The researchers captured the changes on a topographical map showing where these early tetrapods stood in relation to water-based or land-based living. The scientists said these changes were likely driven by environmental pressures as these creatures adapted to terrestrial life.

                    The paper describes the transitional tetrapods as having an “L-shaped” humerus that provided some functional benefit for moving on land, but not much. These animals had a long way to go to develop the traits necessary to use their limbs on land to move with ease and skill.

                    As the humerus continued to change shape, tetrapods improved their movement. The “L” shaped humerus transformed into a more robust, elongated, twisted form, leading to new combinations of functional traits. This change allowed for more effective gaits on land and helped trigger biological diversity and expansion into terrestrial ecosystems. It also helped establish complex food chains based on predators, prey, herbivores, and carnivores still seen today.

                    Analysis took about four years to complete. Quantifying how the humerus changed shape and function took thousands of hours on a supercomputer. The researchers then analyzed how those changes impacted functional performance of the limb during locomotion and the trade-offs associated.

                    The innovative approach represents a new way of viewing and analyzing the fossil record — an effort Pierce said was well worth it.

                    “This study demonstrates how much information you can get from such a small part of an animal’s skeleton that’s been recorded in the fossil record and how it can help unravel one of the biggest evolutionary transformations that has ever occurred,” Pierce said. “This is really cutting-edge stuff.”



                    Source[/b]

                    © Copyright Original Source




                    Source: From Fins to Limbs and Water to Land: Evolution of Terrestrial Movement in Early Tetrapods


                    The water-to-land transition is one of the most important and inspiring major transitions in vertebrate evolution. And the question of how and when tetrapods transitioned from water to land has long been a source of wonder and scientific debate.

                    Early ideas posited that drying-up-pools of water stranded fish on land and that being out of water provided the selective pressure to evolve more limb-like appendages to walk back to water. In the 1990s newly discovered specimens suggested that the first tetrapods retained many aquatic features, like gills and a tail fin, and that limbs may have evolved in the water before tetrapods adapted to life on land. There is, however, still uncertainty about when the water-to-land transition took place and how terrestrial early tetrapods really were.

                    A paper published today (November 25, 2020) in Nature addresses these questions using high-resolution fossil data and shows that although these early tetrapods were still tied to water and had aquatic features, they also had adaptations that indicate some ability to move on land. Although, they may not have been very good at doing it, at least by today’s standards.

                    Lead author Blake Dickson, PhD ’20 in the Department of Organismic and Evolutionary Biology at Harvard University, and senior author Stephanie Pierce, Thomas D. Cabot Associate Professor in the Department of Organismic and Evolutionary Biology and curator of vertebrate paleontology in the Museum of Comparative Zoology at Harvard University, examined 40 three-dimensional models of fossil humeri (upper arm bone) from extinct animals that bridge the water-to-land transition.


                    Three major stages of humerus shape evolution: from the blocky humerus of aquatic fish, to the L-shape humerus of
                    transitional tetrapods, and the twisted humerus of terrestrial tetrapods. Columns (left to right) = aquatic fish,
                    transitional tetrapod, and terrestrial tetrapod. Rows = Top: extinct animal silhouettes; Middle: 3D humerus fossils;
                    Bottom: landmarks used to quantified shape. Credit: Courtesy of Blake Dickson



                    “Because the fossil record of the transition to land in tetrapods is so poor we went to a source of fossils that could better represent the entirety of the transition all the way from being a completely aquatic fish to a fully terrestrial tetrapod,” said Dickson.

                    Two thirds of the fossils came from the historical collections housed at Harvard’s Museum of Comparative Zoology, which are sourced from all over the world. To fill in the missing gaps, Pierce reached out to colleagues with key specimens from Canada, Scotland, and Australia. Of importance to the study were new fossils recently discovered by co-authors Dr. Tim Smithson and Professor Jennifer Clack, University of Cambridge, UK, as part of the TW:eed project, an initiative designed to understand the early evolution of land-going tetrapods.

                    The researchers chose the humerus bone because it is not only abundant and well preserved in the fossil record, but it is also present in all sarcopterygians — a group of animals which includes coelacanth fish, lungfish, and all tetrapods, including all of their fossil representatives. “We expected the humerus would carry a strong functional signal as the animals transitioned from being a fully functional fish to being fully terrestrial tetrapods, and that we could use that to predict when tetrapods started to move on land,” said Pierce. “We found that terrestrial ability appears to coincide with the origin of limbs, which is really exciting.”


                    Humerus-Shape-Change-Along-Evolutionary-Tree.gif
                    The evolutionary pathway and shape change from an aquatic fish humerus
                    to a terrestrial tetrapod humerus. Credit: Courtesy of Blake Dickson




                    The humerus anchors the front leg onto the body, hosts many muscles, and must resist a lot of stress during limb-based motion. Because of this, it holds a great deal of critical functional information related to an animal’s movement and ecology. Researchers have suggested that evolutionary changes in the shape of the humerus bone, from short and squat in fish to more elongate and featured in tetrapods, had important functional implications related to the transition to land locomotion. This idea has rarely been investigated from a quantitative perspective — that is, until now.

                    When Dickson was a second-year graduate student, he became fascinated with applying the theory of quantitative trait modeling to understanding functional evolution, a technique pioneered in a 2016 study led by a team of paleontologists and co-authored by Pierce. Central to quantitative trait modeling is paleontologist George Gaylord Simpson’s 1944 concept of the adaptive landscape, a rugged three-dimensional surface with peaks and valleys, like a mountain range. On this landscape, increasing height represents better functional performance and adaptive fitness, and over time it is expected that natural selection will drive populations uphill towards an adaptive peak.

                    Dickson and Pierce thought they could use this approach to model the tetrapod transition from water to land. They hypothesized that as the humerus changed shape, the adaptive landscape would change too. For instance, fish would have an adaptive peak where functional performance was maximized for swimming and terrestrial tetrapods would have an adaptive peak where functional performance was maximized for walking on land. “We could then use these landscapes to see if the humerus shape of earlier tetrapods was better adapted for performing in water or on land” said Pierce.

                    “We started to think about what functional traits would be important to glean from the humerus,” said Dickson. “Which wasn’t an easy task as fish fins are very different from tetrapod limbs.” In the end, they narrowed their focus on six traits that could be reliably measured on all of the fossils including simple measurements like the relative length of the bone as a proxy for stride length and more sophisticated analyses that simulated mechanical stress under different weight bearing scenarios to estimate humerus strength.

                    “If you have an equal representation of all the functional traits you can map out how the performance changes as you go from one adaptive peak to another,” Dickson explained. Using computational optimization the team was able to reveal the exact combination of functional traits that maximized performance for aquatic fish, terrestrial tetrapods, and the earliest tetrapods. Their results showed that the earliest tetrapods had a unique combination of functional traits, but did not conform to their own adaptive peak.

                    “What we found was that the humeri of the earliest tetrapods clustered at the base of the terrestrial landscape,” said Pierce. “indicating increasing performance for moving on land. But these animals had only evolved a limited set of functional traits for effective terrestrial walking.”

                    The researchers suggest that the ability to move on land may have been limited due to selection on other traits, like feeding in water, that tied early tetrapods to their ancestral aquatic habitat. Once tetrapods broke free of this constraint, the humerus was free to evolve morphologies and functions that enhanced limb-based locomotion and the eventual invasion of terrestrial ecosystems

                    “Our study provides the first quantitative, high-resolution insight into the evolution of terrestrial locomotion across the water-land transition,” said Dickson. “It also provides a prediction of when and how [the transition] happened and what functions were important in the transition, at least in the humerus.”

                    “Moving forward, we are interested in extending our research to other parts of the tetrapod skeleton,” Pierce said. “For instance, it has been suggested that the forelimbs became terrestrially capable before the hindlimbs and our novel methodology can be used to help test that hypothesis.”

                    Dickson recently started as a Postdoctoral Researcher in the Animal Locomotion lab at Duke University, but continues to collaborate with Pierce and her lab members on further studies involving the use of these methods on other parts of the skeleton and fossil record.


                    Source

                    © Copyright Original Source




                    The abstract for the paper Functional adaptive landscapes predict terrestrial capacity at the origin of limbs is below

                    Abstract

                    The acquisition of terrestrial, limb-based locomotion during tetrapod evolution has remained a subject of debate for more than a century1,2. Our current understanding of the locomotor transition from water to land is largely based on a few exemplar fossils such as Tiktaalik3, Acanthostega4, Ichthyostega5 and Pederpes6. However, isolated bony elements may reveal hidden functional diversity, providing a more comprehensive evolutionary perspective7. Here we analyse 40 three-dimensionally preserved humeri from extinct tetrapodomorphs that span the fin-to-limb transition and use functionally informed ecological adaptive landscapes8,9,10 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 gaits5,11 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 niches12,13.





                    Left out the link and abstract for the more recent paper, Evolution of forelimb musculoskeletal function across the fish-to-tetrapod transition, which can be read in its entirety at the provided hyperlink. Here is the abstract

                    Abstract

                    One of the most intriguing questions in vertebrate evolution is how tetrapods gained the ability to walk on land. Although many hypotheses have been proposed, few have been rigorously tested using the fossil record. Here, we build three-dimensional musculoskeletal models of the pectoral appendage in Eusthenopteron, Acanthostega, and Pederpes and quantitatively examine changes in forelimb function across the fin-to-limb transition. Through comparison with extant fishes and tetrapods, we show that early tetrapods share a suite of characters including restricted mobility in humerus long-axis rotation, increased muscular leverage for humeral retraction, but not depression/adduction, and increased mobility in elbow flexion-extension. We infer that the earliest steps in tetrapod forelimb evolution were related to limb-substrate interactions, whereas specializations for weight support appeared later. Together, these results suggest that competing selective pressures for aquatic and terrestrial environments produced a unique, ancestral “early tetrapod” forelimb locomotor mode unlike that of any extant animal.


                    I'm always still in trouble again

                    "You're by far the worst poster on TWeb" and "TWeb's biggest liar" --starlight (the guy who says Stalin was a right-winger)
                    "Of course, human life begins at fertilization thatís not the argument." --Tassman

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                    • #40
                      Originally posted by TheLurch View Post
                      Beyond all that, i fail to see the point of the blog post or its relevance to this discussion. It's clear that the author of the blog post doesn't understand terminology, and is accusing biologists of being deceptive because they're not following what he thinks the definition is.
                      Actually, the author says biologists have two different definitions of a transitional form, a hard definition (an actual intermediate), and a soft definition (a morphological intermediate, which may not be an actual intermediate). He then takes biologists to task for switching definitions when it turns out that Tiktaalik may not be an actual intermediate, without acknowledging that the definition has been switched.

                      In the larger picture, even if we deleted all knowledge of Tiktaalik somehow, we'd still have enough other fossils to clearly indicate tetrapods evolved from lobe-finned fishes. And now the DNA evidence lines up with that as well.
                      Though I may still invoke common design instead of common descent!

                      Blessings,
                      Lee
                      "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

                      Comment


                      • #41
                        Originally posted by lee_merrill View Post
                        Actually, the author says biologists have two different definitions of a transitional form, a hard definition (an actual intermediate), and a soft definition (a morphological intermediate, which may not be an actual intermediate). He then takes biologists to task for switching definitions when it turns out that Tiktaalik may not be an actual intermediate, without acknowledging that the definition has been switched.
                        And this is what you get for depending on garbage sites like Evolution News.

                        If you had simply done as I asked and gone to any reputable site you'd find that there is no such thing as a "hard definition" and "soft definition" in biology. That is utter bilge.

                        While there is popular usage of the term it is not the same one scientists use (as is often the case - see "Theory" for instance). Your garbage site sleazily implies that this first way is one of the accepted ways that scientists use it in an attempt to deceive or bamboozle. But that is exactly what they are doing here.

                        It is not[1]

                        In biology it refers to any organism that displays characteristics that are commonly found in both an ancestral group and its derived descendant group. It does not have to be the progenitor of the descendant group itself, it just needs to display the traits found in both groups. As I said in post #27

                        It doesn't have to be a direct ancestor. It could even be an evolutionary dead end.


                        A transitional form serves to illustrate an evolutionary link, in that it can have features of two separate groups of species, but have no other species as descendants. Therefore, a transitional form merely needs to record aspects of evolutionary change that occurred as one lineage split from another. It does not need to be the direct descendant of one species and the direct ancestor of another, and is a mistake to assume otherwise.

                        As the noted paleontologist Donald Prothero (one of my favorite sources) noted in his Evolution: What the Fossils Say And Why It Matters, due to the incompleteness of the fossil record (and I'll add, because evolution is a branching process that creates a complex "bush" pattern of related species instead of being a straight line process producing a ladder-like progression), there is almost never any way for us to know for certain if a specific transitional is the direct ancestor of more recent groups. This is why transitional fossils are those that exhibit features that reveal the transitional anatomical characteristics of actual common ancestors of different taxa, instead of necessarily being actual ancestors.

                        For clarities sake, such closely-related taxa that do not share the same common ancestor are known as "sister" taxa.

                        IOW, Tiktaalik may well represent some late-surviving "relic" rather than be the direct ancestor but that does not detract from it being a transitional form in any way, shape or form. It still serves to exhibit traits found in both the ancestral and descendant taxa.







                        1. Some times individual scientists get sloppy and use terms that aren't scientific like "missing link" or slip and use a term in the popular meaning, but that does not mean that there are two accepted definitions for it in science. Just like everyone else scientists are human and to use such slips as some sort of aha! gotcha moment is unethical in the extreme. But then again, what else can you expect from such documented disreputable sources as Evolution News.
                        Last edited by rogue06; 01-25-2021, 05:05 PM.

                        I'm always still in trouble again

                        "You're by far the worst poster on TWeb" and "TWeb's biggest liar" --starlight (the guy who says Stalin was a right-winger)
                        "Of course, human life begins at fertilization thatís not the argument." --Tassman

                        Comment


                        • #42
                          Originally posted by lee_merrill View Post
                          Though I may still invoke common design instead of common descent!
                          Just like i can invoke Blue Meanies instead of a Higgs particle to explain recent events inside the Large Hadron Collider.*

                          We can invoke anything we want; the question is whether we can provide evidence that makes anyone else want to pay attention to us.



                          * I mean, doesn't this look like a great explanation for just about anything?
                          Blue_meanie_leader.png
                          "Any sufficiently advanced stupidity is indistinguishable from trolling."

                          Comment


                          • #43
                            Originally posted by lee_merrill View Post
                            Actually, the author says biologists have two different definitions of a transitional form, a hard definition (an actual intermediate), and a soft definition (a morphological intermediate, which may not be an actual intermediate). He then takes biologists to task for switching definitions when it turns out that Tiktaalik may not be an actual intermediate, without acknowledging that the definition has been switched.


                            Though I may still invoke common design instead of common descent!

                            Blessings,
                            Lee
                            Invoking is a matter of 'faith' without a scientific hypothesis nor evidence
                            Glendower: I can call spirits from the vasty deep.
                            Hotspur: Why, so can I, or so can any man;
                            But will they come when you do call for them? Shakespeareís Henry IV, Part 1, Act III:

                            go with the flow the river knows . . .

                            Frank

                            I do not know, therefore everything is in pencil.

                            Comment


                            • #44
                              Originally posted by rogue06 View Post
                              If you had simply done as I asked and gone to any reputable site you'd find that there is no such thing as a "hard definition" and "soft definition" in biology. That is utter bilge.
                              I did do what you asked, and found two instances that match the "hard definition."

                              Source: fossilmuseum.net

                              Transitional fossils are the fossilized remains of transitional forms of life that tangibly and demonstrably encode an evolutionary transition.

                              Source

                              © Copyright Original Source



                              In biology it refers to any organism that displays characteristics that are commonly found in both an ancestral group and its derived descendant group. It does not have to be the progenitor of the descendant group itself, it just needs to display the traits found in both groups. As I said in post #27

                              It doesn't have to be a direct ancestor. It could even be an evolutionary dead end.
                              And this is the soft definition.

                              Blessings,
                              Lee

                              "What I pray of you is, to keep your eye upon Him, for that is everything. Do you say, 'How am I to keep my eye on Him?' I reply, keep your eye off everything else, and you will soon see Him. All depends on the eye of faith being kept on Him. How simple it is!" (J.B. Stoney)

                              Comment


                              • #45
                                Originally posted by lee_merrill View Post
                                I did do what you asked, and found two instances that match the "hard definition."

                                And this is the soft definition.

                                Blessings,
                                Lee
                                There aren't any such things as a "hard" definition or "soft" definition of the scientific term transitional fossil. This is THE scientific definition:

                                A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group.
                                You ignorantly fell for yet one more lie from the ID-Creationist camp. Why are you continually so gullible?

                                Comment

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