An artist reconstruction of Ailurarctos from Shuitangba. The grasping function of its false thumb (shown in the right individual) has reached to the level of modern pandas, whereas the radial sesamoid may have protruded slightly more than its modern counterpart during walking (seen in the left individual).
Illustration by Mauricio Anton
Technically, of course, all fossils are transitional since they represent a species at a given point in time and come precisely between its parent's generation and it's descendants, but creationists continue to demand examples of 'transitions' that illustrate their childish parody of evolution - one species, or order, changing into another with individuals midway between the two - a half fish - half monkey, or something equally ludicrous that no-one in their right mind would expect to see.
In other words, as often with creationists, they have been conditioned to demand proof of something that no scientists has ever claimed happened and something that is so different to what the TOE actually predicts, it would actually falsify the TOE if it were found.
But of course, real 'transitional' fossils abound because, like the example in this article, there are abundant examples of gradual changes in morphology over time. In this instance, the example is of the evolution of the pseudo-digit or 'thumb' in the panda, which is one of the anatomical differences between pandas and the other bears. Clearly, if, pandas, which are no known to be closely related to bears, share a common ancestor with them, we should expect an ancestor of the pandas to have a pseudo thumb, which is a development of the radial sesamoid bone of the wrist, somewhere between that of bears, which don't have one, and that of modern pandas.
And this is exactly what has been found in a fossil from the Shuitangba site in the City of Zhaotong, Yunnan Province, China dated to about 6-7 million years old. The only thing is that it is actually longer that that of modern pandas, although this doesn't necessarily mean it isn't intermediate, since a long pseudo thumb might not have been especially well adapted for both walking and gripping which involves a compromise.
The Natural History Museums of Los Angeles County news release explains:
When is a thumb not a thumb? When it’s an elongated wrist bone of the giant panda used to grasp bamboo. Through its long evolutionary history, the panda’s hand has never developed a truly opposable thumb and instead evolved a thumb-like digit from a wrist bone, the radial sesamoid. This unique adaptation helps these bears survive entirely on bamboo despite being bears (members of the order Carnivora, or meat-eaters). In a new paper published in Scientific Reports, the Natural History Museum of Los Angeles County’s Curator of Vertebrate Paleontology Xiaoming Wang and colleagues report on the discovery of the earliest bamboo-eating ancestral panda to have this “thumb.” Surprisingly, it’s longer than its modern descendants.
While the celebrated false thumb in living giant pandas (Ailuropoda melanoleuca) has been known for more than 100 years, how this wrist bone evolved was not understood due to a near-total absence of fossil records. Uncovered at the Shuitangba site in the City of Zhaotong, Yunnan Province in south China and dating back 6–7 million years ago, a fossil false thumb from an ancestral giant panda, Ailurarctos, gives scientists a first look at the early use of this extra (sixth) digit–and the earliest evidence of a bamboo diet in ancestral pandas–helping us better understanding the evolution of this unique structure.
How to Walk and Chew Bamboo at the Same TimeDeep in the bamboo forest, giant pandas traded an omnivorous diet of meat and berries to quietly consuming bamboos, a plant plentiful in the subtropical forest but of low nutrient value. Tightly holding bamboo stems in order to crush them into bite sizes is perhaps the most crucial adaptation to consuming a prodigious quantity of bamboo.
Panda’s false thumb must walk and ‘chew’. Such a dual function serves as the limit on how big this ‘thumb’ can become.
Evolving from a carnivorous ancestor and becoming a pure bamboo-feeder, pandas must overcome many obstacles. An opposable ‘thumb’ from a wrist bone may be the most amazing development against these hurdles.
Dr. Xiaoming Wang, lead author
Department of Vertebrate Paleontology
Natural History Museum of Los Angeles County, Los Angeles, CA, USA
This discovery could also help solve an enduring panda mystery: why are their false thumbs so seemingly underdeveloped? As an ancestor to modern pandas, Ailurarctos might be expected to have even less well-developed false “thumbs,” but the fossil Wang and his colleagues discovered revealed a longer false thumb with a straighter end than its modern descendants' shorter, hooked digit. So why did pandas’ false thumbs stop growing to achieve a longer digit?
Wang and his colleagues think that modern panda’s shorter false thumbs are an evolutionary compromise between the need to manipulate bamboo and the need to walk. The hooked tip of a modern panda’s second thumb lets them manipulate bamboo while letting them carry their impressive weight to the next bamboo meal. After all, the “thumb” is doing double duty as the radial sesamoid–a bone in the animal’s wrist.Five to six million years should be enough time for the panda to develop longer false thumbs, but it seems that the evolutionary pressure of needing to travel and bear its weight kept the ‘thumb’ short–strong enough to be useful without being big enough to get in the way.
Denise Su, co-project leader
Associate professor
School of Human Evolution and Social Change
Institute of Human Origins
Arizona State University, Tempe, AZ, USA
Photo: Sharon Fisher
Hand bones of a living giant panda.
Photo: Natural History Museum of L.A. County.Panda gripping vs walking
(white bone is the false thumb).
Natural History Museum of L.A. County.
The authors of this article are affiliated with the Natural History Museum of Los Angeles County, Los Angeles, CA, USA; Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China; Arizona State University, Tempe, Arizona, USA; Pennsylvania State University, University Park, Pennsylvania, USA; Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan, China; Yunnan Institute of Cultural Relics and Archaeology, Kunming, Yunnan, China; Harvard University, Cambridge, Massachusetts, USA.
In the abstract to their open access paper in Scientific Reports, the authors say:
AbstractThis example neatly illustrates how evolution can work, firstly to produce a modified structure to produce a new function, then, because that structure is sub-optimal it becomes subject to more subtle environmental selectors working in opposition to the original selectors that produced the new structure in the first place.
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.
Wang, Xiaoming; Su, Denise F.; Jablonski, Nina G.; Ji, Xueping; Kelley, Jay; Flynn, Lawrence J.; Deng, Tao (2022)
Earliest giant panda false thumb suggests conflicting demands for locomotion and feeding
Scientific Reports 12(1); DOI: 10.1038/s41598-022-13402-y
Copyright: © 22 The authors.
Published by Springer Nature Ltd. Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
In this instance, there were competing selectors for gripping and for walking, so the result today is a compromise. Of course, if this was an intelligent design process there would be no need to refine and improve on an original design, since the design would be perfect in the first place. But the process that actually produced the panda’s ‘thumb’ is not sentient and could not have predicted the need to modify a crude, initial utilitarian design.
In fact, of course, there is no reason why an intelligent designer could not have given the panda a fully opposable 6th digit, or even an opposable thumb like humans have, to begin with, so would not have needed to modify a bone designed for another function.
Contrary to creationist claims, this is a perfect example of the sort of transitional fossil that Darwin was referring to and which the Theory of Evolution predicts. Admittedly, it's not an example of the sort of 'transitional' fossil that the childish parody of evolution with which creationist frauds fool their scientifically illiterate dupes in the creationist cults leads creationist to claim have never been found.
No comments:
Post a Comment
Obscene, threatening or obnoxious messages, preaching, abuse and spam will be removed, as will anything by known Internet trolls and stalkers, by known sock-puppet accounts and anything not connected with the post,
A claim made without evidence can be dismissed without evidence. Remember: your opinion is not an established fact unless corroborated.