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Latest on the Panda's Thumb

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  • shunyadragon
    replied
    Interesting research!!!!!

    Leave a comment:


  • rogue06
    started a topic Latest on the Panda's Thumb

    Latest on the Panda's Thumb

    Not the website but the feature found on Giant Panda's


    The Giant Panda is a type of bear that evolved to live on a diet of bamboo. Due to not having an efficient digestive system for this change, and bamboo not being exactly packed with nutrients, pandas have to spend 14 to 15 hours every day eating between 15 to 45kg (33-99lbs.) of it. Of the many transforming adjustments that allow the modern giant panda to adapt to life as a bamboo eater, the evolutionary adaptation which augmented the existing five actual digits of the panda's hand through a greatly enlarged wrist bone (radial sesamoid) that acts as a sixth digit, a kind of an opposable "thumb," that is probably the best known (largely in part to Stephen Jay Gould) as well as most remarkable.

    Panda fossils are rather scare as is not uncommon for creatures that inhabit jungles. This meant scientists had little to go on in trying to solve how they evolved this particular feature. What evidence they had indicated that the feature was around somewhere about 100,000 years ago in the same species of panda around today, and that led to the assumption that the feature is a relatively new development.

    But a discovery from Shuitangba, a site near the city of Zhaotong in the northern part of the Yunnan Province in southwest China, has challenged this view. The fossils from an extinct panda ancestor dating back to between 6 and 7 mya, consisting of an arm, wrist (including the "false thumb") and teeth were unearthed between 2010 and 2015 confirming that pandas had already evolved their "thumb" by this time.

    That would be cool if that was all there was to it, but what came as a surprise is that this extinct Late Miocene ancestor, called Ailurarctos (which means "cat bear"), which was smaller than modern Great Pandas, actually possessed a significantly longer, straighter "thumb" than seen on their modern descendants.

    Xiaoming Wang, curator of vertebrate paleontology at the Natural History Museum of Los Angeles County as well as the Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, figures that the shorter protrusion which hooks at the end, shows several distinct advantages over the earlier longer and straighter model possessed by Ailurarctos.

    "The hooked false thumb offers a tighter grasp of the bamboo and, at the same time, its less-protruded tip -- because of the bended hook -- makes it easier for the panda to walk. Think of the false thumb as being stepped on every time the panda walks. And therefore, we think that is the reason that the false thumb in modern pandas has become shorter, not longer,"


    The researchers noted that the wrists of an earlier ancient bear, Indarctos arctoides, thought to be closely related and likely to share the same common ancestor as giant pandas, does not show evidence of it's radial sesamoid having enlarged, indicating that the feature may not be that old. Of course, it could be present in an undiscovered lineage, but that's supposition.


    Source: ‘Amazing development’: fossil finds show how panda’s false thumb evolved


    Fossils of Ailurarctos, an extinct panda relative, are oldest known evidence for the radial sesamoid

    Ancient fossils discovered in China have helped researchers get a grip on the enduring mystery of the panda’s false thumb.

    Modern giant pandas sport a thumb-like sixth digit on their wrists, which scientists believe was pivotal in their transition from omnivores to bamboo-munching vegetarians.

    While the stubby extra digit, known as a radial sesamoid, is not as versatile as the human thumb, it enables pandas to hold and crush bamboo stems into bite-size pieces and fuel their formidable appetite.

    The panda’s false thumb has been known for more than 100 years, but a near-total lack of fossil evidence has left researchers puzzled as to when the digit evolved.

    Writing in Scientific Reports, Xiaoming Wang, curator of vertebrate palaeontology at the Natural History Museum of Los Angeles County, sheds light on the mystery. New fossils of an ancient panda discovered near the city of Zhaotong in the north of China’s Yunnan province not only sport the false thumb, but suggest it was once larger than those seen in pandas today.

    The fossils, which are 6 to 7 million years old, belong to an extinct panda relative called Ailurarctos and are believed to be the oldest known evidence for the unusual digit.

    Denise Su, an associate professor at Arizona State University and co-leader on the project that recovered the panda specimens, said modern pandas have had enough time to evolve longer false thumbs, but the evolutionary pressure of needing to walk on their hands as well as handle bamboo had apparently kept them short and strong.

    In evolving from a carnivorous ancestor to a bamboo-feeder, the panda had to overcome plenty of obstacles, Wang added. “An opposable ‘thumb’ from a wrist bone may be the most amazing development against these hurdles,” he said.

    The researchers found an Ailurarctos arm bone in 2010 and discovered teeth and the false thumb in 2015. Until now, the oldest-known evidence of the thumb-like structure came from fossils of modern panda species dated to about 100,000 years ago. As well as being shorter than its ancestor’s, the modern panda’s false thumb has a hook on the end, which the authors believe might help it to grasp bamboo.

    While the panda’s diet is 99% vegetarian, they occasionally eat small animals. To meet their nutritional needs, pandas eat for up to 14 hours a day, consuming nearly 40kg of bamboo a day as adults.



    Source

    © Copyright Original Source



    The full paper, Earliest giant panda false thumb suggests conflicting demands for locomotion and feeding is available by clicking the hyperlink, although the abstract can be read below:

    Abstract

    Of the many peculiarities that enable the giant panda (Ailuropoda melanoleuca), a member of the order Carnivora, to adapt to life as a dedicated bamboo feeder, its extra “thumb” is arguably the most celebrated yet enigmatic. In addition to the normal five digits in the hands of most mammals, the giant panda has a greatly enlarged wrist bone, the radial sesamoid, that acts as a sixth digit, an opposable “thumb” for manipulating bamboo. We report the earliest enlarged radial sesamoid, already a functional opposable “thumb,” in the ancestral panda Ailurarctos from the late Miocene site of Shuitangba in Yunnan Province, China. However, since the late Miocene, the “thumb” has not enlarged further because it must be balanced with the constraints of weight bearing while walking in a plantigrade posture. This morphological adaptation in panda evolution thus reflects a dual function of the radial sesamoid for both bamboo manipulation and weight distribution. The latter constraint could be the main reason why the panda’s false thumb never evolved into a full digit. This crude “thumb” suggests that the origin of the panda’s dedicated bamboo diet goes back to as early as 6–7 Ma.




    8c7ae4eb-5abc-47e9-9af6-b878244ecc0e.jpg
    Comparison of the radial sesamoid in the basal ursoid, Ailuropoda, and Homo and the positioning of the radial sesamoid; illustrations are of
    left hands: (A) a basal ursoid from the early Oligocene of North Dakota showing the primitive condition of an unenlarged radial sesamoid;
    (B) grasping hand in extant Ailuropoda; (C) grasping hand of modern human; (D) walking hand of extant Ailuropoda in a plantigrade posture;
    (E) external ventral surface of the hand of Ailuropoda showing a fleshy, plantar pad that corresponds to the radial sesamoid (red dash lines).

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