Which of the following is more apt, about elephants?
Elephants are so massive that they need their extreme body shapes in order to function at such sizes
OR
Elephants are specialists in bodily shape-shifting, which happen also to be massive.
We can call the first the graviportal hypothesis, and the second the morphodynamic hypothesis.
In the graviportal hypothesis, bodily shape-shifting is necessitated by extreme body size. In the morphodynamic hypothesis, there is merely correlation, not cause, because the shape-shifting of elephants - as their main specialisation - would remain even if body mass was only a few hundred kg.
Elephants have columnar legs which locomote forwards in only one gait, the amble. They can catch up to a fleeing human at a speeded-up walk, but are technically unable to run because there is always at least one foot touching the ground (see https://news.stanford.edu/pr/03/elephants49.html).
At the same time elephants are more posturally versatile than most ungulates (see https://www.facebook.com/watch/?v=1309487399231553), particularly in being able to free-stand bipedally (see https://www.alamy.com/african-elephant-loxodonta-africana-standing-on-hind-legs-to-feed-on-tree-mana-pools-national-park-zimbabwe-october-image213516661.html and https://www.catersnews.com/stories/animals/standing-up-for-himself-elephant-stands-up-on-its-back-legs-to-reach-tree-top-leaves/ and https://www.sciencephoto.com/media/989928/view/african-elephant-standing-on-hind-legs-to-feed-on-tree and http://www.peoplesweather.com/news/the-elephant-that-thinks-its-a-giraffe-animal-stands-on-its-hind-legs-as-it-reaches-to-pluck-leaves-from-the-tree-908/ and https://www.natureplprints.com/2019-january-highlights/elephant-loxodonta-africana-male-standing-hind-18331096.html and http://www.storytrender.com/104922/incredible-photos-show-elephant-standing-up-for-a-bite-to-eat/ and https://www.alamy.com/desert-dwelling-african-elephant-loxodonta-fricana-bull-standing-up-to-browse-high-branches-in-the-dry-river-bed-of-the-hoanib-river-damaraland-n-image357576271.html and https://www.alamy.com/stock-photo-elephant-standing-on-hind-legs-mana-pools-national-park-zimbabwe-africa-58091600.html).
Elephants have a short neck, compensated for by a long, remarkably elastic proboscis (is this fake? https://www.agefotostock.com/age/en/details-photo/elephant-stretching-trunk-up-towards-tree-branch/FLI-FL5634) in which the nose and upper lip, seamlessly fused, have been jointly modified into the equivalent of a combination of hose and versatile limb.
Elephants have a voluminous, spongy cranium which functions as a buoy when the animal is immersed. They are exceptionally capable swimmers among land mammals (see https://www.stevebloom.com/index.php?page=single&id=003603-SB1 and https://www.youtube.com/watch?v=vCejxaub9Ao).
Elephants have the vulva shifted farther forward, relative to the anus, than in any other land animal (see https://elephantist.wordpress.com/2014/05/15/the-basics/ and https://www.slideshare.net/DrShehzadNiazi/facts-of-elephant-reproduction), and the penis reaches the vagina by being extremely long and flexible (see https://www.youtube.com/watch?v=IBDq-mOcRZA and https://www.shutterstock.com/nb/video/clip-10885283-close-up-elephant-penis).
Elephants have a tail which is even longer than it looks (see https://kidsanimalsfacts.com/borneo-pygmy-elephant-facts/) because it is partly buried in the buttocks (see https://www.subpng.com/png-jbbwft/ and https://www.dreamstime.com/silhouette-skeleton-elephant-vector-animal-illustration-image182072865 and https://www.alamy.com/stock-photo-elephant-skeleton-49290607.html).
Note that not just the proboscis, but also the vagina, penis and tail of elephants are extremely elongated.
There are at least three immediate reasons to question the graviportal hypothesis.
Firstly, an extinct perissodactyl (see https://en.wikipedia.org/wiki/Paraceratherium) was more massive than elephants but not correspondingly modified.
Secondly, the largest specimens of living rhinos (e.g. Ceratotherium simum) and hippopotamus (Hippopotamus amphibius) overlap elephants in body mass but lack any of the specialisations listed above. In particular, they remain able to use similar running gaits to medium-size ungulates (e.g. see https://www.shutterstock.com/nb/video/clip-9435902-white-rhino-running-past-camera and https://www.youtube.com/watch?v=yUBNs9HrsX4 and https://www.youtube.com/watch?v=Rv6BbD74gI4).
Thirdly, elephants inhabiting marine islands retained their bodily proportions despite becoming diminutive (see https://twitter.com/diffendale/status/1090003177305530369/photo/1 and https://prehistoric-fauna.com/Cretan-dwarf-mammoth and https://www.deviantart.com/artbyjrc/art/Pocket-pachyderms-Island-dwarf-proboscideans-1-870223240 and https://www.deviantart.com/sanciusart/art/Size-Chart-Sicily-and-Malta-854254198).
to be continued...
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