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Mystery of giraffe's long necks solved?

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  • Mystery of giraffe's long necks solved?

    For many years scientists have pondered the mystery of why the giraffe evolved such a long neck. To be sure, they aren't the only long-necked creature to have evolved, look at flamingos for instance, but why the giraffe has one has long perplexed scientists with most siding with Darwin who posited it could be the result of allowing those with longer necks to reach food that those with shorter necks couldn't.

    But now a recent discovery is challenging that hypothesis. The fossilized remains of an early giraffoid is pointing to another possibility.

    Researchers in northwestern China unearthed the cranium along with some cervical vertebrae from a creature that lived during the Early Miocene between 17 and 16.9 mya that they named Discokeryx xiezhi, and discovered that they exhibited tell-tale signs of adaptations for head-butting behavior like we see in modern rams and musk-oxen.

    The cranium itself was thick-boned and possessed a disc-shaped large ossicone in the middle of its head, whereas the vertebrae were very stout, with a thickened centra, and have the most complex joints between head and neck and between cervical vertebrae of any mammal known to date.

    All of this drew attention to the mating behavior of modern giraffes where the males compete against one another by "necking," or swinging their necks and heads against one another delivering powerful blows. With the giraffe's head bristling with ossicones, they could do substantial damage if they were swung into flesh. The point being, the giraffes with the longest neck is at an advantage in such fights for mates and the new discovery indicates that they evolved out of the original head-butting behavior of their ancestors.

    This isn't the first time that researchers have theorized that sexual selection was the driving force behind the lengthening of necks (see Winning by a Neck: Sexual Selection in the Evolution of Giraffe from 1996 for one instance), but the discovery is probably the first concrete physical evidence in support of it.

    Source: Strange fossil solves giraffe evolutionary mystery





    Fossils of a strange early giraffoid have revealed the key driving forces in giraffe evolution, according to a study led by researchers from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences.

    The study was published in Science on June 2.

    How the giraffe's long neck evolved has long been an evolutionary mystery. Although there have been different opinions about the process of giraffe neck elongation, scientists never doubted that the impetus for neck elongation was high foliage.

    However, as observation of giraffe behavior increased, scientists began to realize that the elegant, long neck of giraffes actually serves as a weapon in male courtship competition and this may be the key to the giraffe evolutionary mystery.

    Specifically, giraffes use their two-to-three-meter-long swinging necks to hurl their heavy skulls—equipped with small ossicones and osteomas—against the weak parts of competitors. As a result, the longer the neck, the greater the damage to the opponent.

    IVPP researchers and their collaborators conducted their study on Discokeryx xiezhi, a strange early giraffoid. This research contributes to understanding how the giraffe's long neck evolved as well as to understanding the extensive integration of courtship struggles and feeding pressure. In fact, the neck size of male giraffes is directly related to social hierarchy, and courtship competition is the driving force behind the evolution of long necks.




    Modeling of high-speed head-butting in Discokeryx xiezhi using finite element analyses, with (A) and without
    (B) the complicated joints between cranium and vertebrae, showing the stable (A) or over-bending (B) head-neck articulation



    The fossils in this study were found in early Miocene strata from about 17 million years ago on the northern margin of the Junggar Basin, Xinjiang. A full skull and four cervical vertebrae were part of the find.

    "Discokeryx xiezhi featured many unique characteristics among mammals, including the development of a disc-like large ossicone in the middle of its head," said Prof. Deng Tao from IVPP, a corresponding author of the study. Deng said the single ossicone resembles that of the xiezhi, a one-horned creature from ancient Chinese mythology—thus giving the fossil its name.

    According to the researchers, the cervical vertebrae of Discokeryx xiezhi are very stout and have the most complex joints between head and neck and between cervical vertebrae of any mammal. The team demonstrated that the complex articulations between the skull and cervical vertebrae of Discokeryx xiezhi was particularly adapted to high-speed head-to-head impact. They found this structure was far more effective than that of extant animals, such as musk oxen, that are adapted to head impact. In fact, Discokeryx xiezhi may have been the vertebrate best adapted to head impact.

    "Both living giraffes and Discokeryx xiezhi belong to the Giraffoidea, a superfamily. Although their skull and neck morphologies differ greatly, both are associated with male courtship struggles and both have evolved in an extreme direction," said Wang Shiqi, first author of the study.

    The research team compared the horn morphology of several groups of ruminants, including giraffoids, cattle, sheep, deer and pronghorns. They found that horn diversity in giraffes is much greater than in other groups, with a tendency toward extreme differences in morphology, thus indicating that courtship struggles are more intense and diverse in giraffes than in other ruminants.

    The research team further analyzed the ecological environment of Discokeryx xiezhi and the niche it occupied. The Earth was in a warm period and generally densely forested, but the Xinjiang region, where Discokeryx xiezhi lived, was somewhat drier than other areas because the Tibetan Plateau to the south had been rising dramatically, thus blocking the transfer of water vapor.

    "Stable isotopes of tooth enamel have indicated that Discokeryx xiezhi was living in open grasslands and may have migrated seasonally," said MENG Jin, another corresponding author of the study. For animals of the time, the grassland environment was more barren and less comfortable than the forest environment. The violent fighting behavior of Discokeryx xiezhi may have been related to survival-related stress caused by the environment.

    At the beginning of the emergence of the genus Giraffa, a similar environment existed. Around 7 million years ago, the East African Plateau also changed from a forested environment to open grassland, and the direct ancestors of giraffes had to adapt to new changes. It is possible that, among giraffe ancestors during this period, mating males developed a way of attacking their competitors by swinging their necks and heads. This extreme struggle, supported by sexual selection, thus led to the rapid elongation of the giraffe's neck over a period of 2 million years to become the extant genus, Giraffa.

    Based on this elongation, Giraffa were well-suited for the niche of feeding on high foliage. However, their ecological status was necessarily less secure than that of bovids and cervids. As a result, Giraffa's marginal ecological niche may have promoted extreme intraspecific courtship competition, which in turn may have promoted extreme morphological evolution.


    Source

    © Copyright Original Source




    The abstract from the paper, Sexual selection promotes giraffoid head-neck evolution and ecological adaptation can be read below:

    Abstract

    The long neck of the giraffe has been held as a classic example of adaptive evolution since Darwin’s time. Here we report on an unusual fossil giraffoid, Discokeryx xiezhi, from the early Miocene, which has an unusual disk-shaped headgear and the most complicated head-neck joints in known mammals. The distinctive morphology and our finite element analyses indicate an adaptation for fierce head-butting behavior. Tooth enamel isotope data suggest that D. xiezhi occupied a niche different from that of other herbivores, comparable to the characteristic high-level browsing niche of modern giraffes. The study shows that giraffoids exhibit a higher headgear diversity than other ruminants and that living in specific ecological niches may have fostered various intraspecific combat behaviors that resulted in extreme head-neck morphologies in different giraffoid lineages.



    One observation... Am I the only one that thinks that Discokeryx looks like they're wearing bowlers?
    ​​​​​​​

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  • #2

    I'm always still in trouble again

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    "Overall I would rate the withdrawal from Afghanistan as by far the best thing Biden's done" --Starlight
    "Of course, human life begins at fertilization that’s not the argument." --Tassman

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    • #3
      Um, that doesn't make a lot of sense. Head butting strengthens the skull and neck along the line of the spine - and necks in modern head butting animals are fairly short and stout. Long necked animals have different musculature. The transition from head butting to neck fighting would be dangerous for the animals - necks good for one aren't usually safe for the other. But this transition occurs after the skull adapted to head butting?

      Unless the head butting were dorsal - which modern giraffes kinda pantomime - but that is singular. Doesn't seem to be the posit anyway because that would more likely develop in conjunction.

      And it makes no sense for camels - although they are hard headed in temperament.
      "He is no fool who gives what he cannot keep to gain that which he cannot lose." - Jim Elliot

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      • #4
        Originally posted by Teallaura View Post
        Um, that doesn't make a lot of sense. Head butting strengthens the skull and neck along the line of the spine - and necks in modern head butting animals are fairly short and stout. Long necked animals have different musculature. The transition from head butting to neck fighting would be dangerous for the animals - necks good for one aren't usually safe for the other. But this transition occurs after the skull adapted to head butting?

        Unless the head butting were dorsal - which modern giraffes kinda pantomime - but that is singular. Doesn't seem to be the posit anyway because that would more likely develop in conjunction.

        And it makes no sense for camels - although they are hard headed in temperament.

        Possible solution: Perhaps the head was used like a flail to attack unarmoured body parts rather than for face on butting? Seems to me; that would promote the development of both longer necks and armoured heads.
        Last edited by tabibito; 06-13-2022, 01:49 AM.
        1Cor 15:34 εκνηψατε δικαιως και μη αμαρτανετε αγνωσιαν γαρ θεου τινες εχουσιν προς εντροπην υμιν λεγω
        Come to your senses as you ought and stop sinning; for I say to your shame, there are some who know not God.
        .
        "when the church no longer teaches its people why they believe what they believe, the world will often step in and fill in the gaps." Ryan Danker

        "The synoptic gospels claim that Jesus was crucified on the 15th day of Nisan and buried on the 14th day of Nisan:" Majority Consensus

        Comment


        • #5
          Originally posted by Teallaura View Post
          Um, that doesn't make a lot of sense. Head butting strengthens the skull and neck along the line of the spine - and necks in modern head butting animals are fairly short and stout. Long necked animals have different musculature. The transition from head butting to neck fighting would be dangerous for the animals - necks good for one aren't usually safe for the other. But this transition occurs after the skull adapted to head butting?

          Unless the head butting were dorsal - which modern giraffes kinda pantomime - but that is singular. Doesn't seem to be the posit anyway because that would more likely develop in conjunction.

          And it makes no sense for camels - although they are hard headed in temperament.
          It would depend on how the heads were used in combat. Straight on ramming like we see with rams, or was there also slamming with it from the sides. I think that the unique configuration of the cervical vertebrae holds the answer.

          Personally, I think it was likely several factors that drove the evolution of giraffes since this doesn’t exactly explain why female giraffes also have long necks, nor why giraffes also have such long limbs



          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)
          "Overall I would rate the withdrawal from Afghanistan as by far the best thing Biden's done" --Starlight
          "Of course, human life begins at fertilization that’s not the argument." --Tassman

          Comment


          • #6
            Originally posted by rogue06 View Post
            It would depend on how the heads were used in combat. Straight on ramming like we see with rams, or was there also slamming with it from the sides. I think that the unique configuration of the cervical vertebrae holds the answer.

            Personally, I think it was likely several factors that drove the evolution of giraffes since this doesn’t exactly explain why female giraffes also have long necks, nor why giraffes also have such long limbs

            The basic premise still has issues with camels and now horses (horses do use the neck fighting to an extent - although they put teeth in it..).

            Multiple factors makes much more sense. Of course, Lamarck might simply have been right.
            "He is no fool who gives what he cannot keep to gain that which he cannot lose." - Jim Elliot

            "Forgiveness is the way of love." Gary Chapman

            My Personal Blog

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            • #7
              Originally posted by Teallaura View Post

              The basic premise still has issues with camels and now horses (horses do use the neck fighting to an extent - although they put teeth in it..).

              Multiple factors makes much more sense. Of course, Lamarck might simply have been right.
              Lamarkian thought is making a resurgence in a few areas but isn't likely applicable here.

              And again, the unique cervical vertebrae are likely the key here.

              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)
              "Overall I would rate the withdrawal from Afghanistan as by far the best thing Biden's done" --Starlight
              "Of course, human life begins at fertilization that’s not the argument." --Tassman

              Comment


              • #8
                Originally posted by Teallaura View Post

                The basic premise still has issues with camels and now horses (horses do use the neck fighting to an extent - although they put teeth in it..).

                Multiple factors makes much more sense. Of course, Lamarck might simply have been right.
                Maybe they just preferred the view from up there. 
                1Cor 15:34 εκνηψατε δικαιως και μη αμαρτανετε αγνωσιαν γαρ θεου τινες εχουσιν προς εντροπην υμιν λεγω
                Come to your senses as you ought and stop sinning; for I say to your shame, there are some who know not God.
                .
                "when the church no longer teaches its people why they believe what they believe, the world will often step in and fill in the gaps." Ryan Danker

                "The synoptic gospels claim that Jesus was crucified on the 15th day of Nisan and buried on the 14th day of Nisan:" Majority Consensus

                Comment


                • #9
                  Originally posted by tabibito View Post

                  Maybe they just preferred the view from up there. 
                  What did you say down there?

                  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)
                  "Overall I would rate the withdrawal from Afghanistan as by far the best thing Biden's done" --Starlight
                  "Of course, human life begins at fertilization that’s not the argument." --Tassman

                  Comment


                  • #10
                    IMO, there is no mystery. If giraffes grazed meadowland grasses then their neck length would be a mystery. But the fact their diet is in the trees explains their long necks quite well. There may be other contributing factors, but diet is likely the main one.
                    "You should just assume going forward that if I am ever wrong it is a typo" - Backup
                    "
                    Reality simply does not change based upon consensus or desire." - rogue

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                    • #11
                      Originally posted by Ronson View Post
                      IMO, there is no mystery. If giraffes grazed meadowland grasses then their neck length would be a mystery. But the fact their diet is in the trees explains their long necks quite well. There may be other contributing factors, but diet is likely the main one.
                      That's just it. As the older study I linked to in the OP explains

                      However, in searching for present-day evidence for the maintenance of the long neck, we find that during the dry season (when feeding competition should be most intense) giraffe generally feed from low shrubs, not tall trees; females spend over 50% of their time feeding with their necks horizontal; both sexes feed faster and most often with their necks bent; and other sympatric browsers show little foraging height partitioning.


                      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)
                      "Overall I would rate the withdrawal from Afghanistan as by far the best thing Biden's done" --Starlight
                      "Of course, human life begins at fertilization that’s not the argument." --Tassman

                      Comment


                      • #12
                        Originally posted by rogue06 View Post
                        That's just it. As the older study I linked to in the OP explains

                        However, in searching for present-day evidence for the maintenance of the long neck, we find that during the dry season (when feeding competition should be most intense) giraffe generally feed from low shrubs, not tall trees; females spend over 50% of their time feeding with their necks horizontal; both sexes feed faster and most often with their necks bent; and other sympatric browsers show little foraging height partitioning.
                        I don't know. It seems like they're over-thinking the obvious, to me.

                        During critical periods of giraffe evolution they were able to maintain a diet in the trees when competitors couldn't. So that neck-length attribute grew. Their ability to graze on grass efficiently only points to where they originally started, and they've just retained that ability. Their diet is still mainly in the trees (based on my reading).
                        "You should just assume going forward that if I am ever wrong it is a typo" - Backup
                        "
                        Reality simply does not change based upon consensus or desire." - rogue

                        Comment


                        • #13
                          Originally posted by Ronson View Post

                          I don't know. It seems like they're over-thinking the obvious, to me.

                          During critical periods of giraffe evolution they were able to maintain a diet in the trees when competitors couldn't. So that neck-length attribute grew. Their ability to graze on grass efficiently only points to where they originally started, and they've just retained that ability. Their diet is still mainly in the trees (based on my reading).
                          When the evidence does not support what is thought to be obvious then maybe it isn't as obvious as was thought.

                          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)
                          "Overall I would rate the withdrawal from Afghanistan as by far the best thing Biden's done" --Starlight
                          "Of course, human life begins at fertilization that’s not the argument." --Tassman

                          Comment


                          • #14
                            Originally posted by rogue06 View Post
                            Lamarkian thought is making a resurgence in a few areas but isn't likely applicable here.

                            And again, the unique cervical vertebrae are likely the key here.
                            I'd noticed that - I was wondering if I was just imagining it.

                            Also, giraffe - of course Lamarck applies! :
                            "He is no fool who gives what he cannot keep to gain that which he cannot lose." - Jim Elliot

                            "Forgiveness is the way of love." Gary Chapman

                            My Personal Blog

                            My Novella blog (Current Novella Begins on 7/25/14)

                            Quill Sword

                            Comment


                            • #15
                              Originally posted by rogue06 View Post
                              That's just it. As the older study I linked to in the OP explains

                              However, in searching for present-day evidence for the maintenance of the long neck, we find that during the dry season (when feeding competition should be most intense) giraffe generally feed from low shrubs, not tall trees; females spend over 50% of their time feeding with their necks horizontal; both sexes feed faster and most often with their necks bent; and other sympatric browsers show little foraging height partitioning.
                              Um, that doesn't actually prove the point. Browsers rarely eat the topmost leaves if they are eating from the bottom up - even bending over, the longer neck should be an advantage.

                              Might mean shorter shrubs are less competitive - or just tastier...
                              "He is no fool who gives what he cannot keep to gain that which he cannot lose." - Jim Elliot

                              "Forgiveness is the way of love." Gary Chapman

                              My Personal Blog

                              My Novella blog (Current Novella Begins on 7/25/14)

                              Quill Sword

                              Comment

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