Surprisingly, the tiger (Panthera tigris) exceeds the lion (Panthera leo) in expressing bipedality

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The lion (Panthera leo) and the tiger (Panthera tigris)

are closely related (https://en.wikipedia.org/wiki/Panthera),
have a similarly limited ability to climb the vertical boles of trees, and
have hindlegs of similar length relative to the length of the torso (https://www.123rf.com/photo_43556506_lion-walking-in-profile.html and https://stock.adobe.com/au/images/lioness-walking-at-sun-rise/144599399 and https://www.picxy.com/photo/991738 and https://www.researchgate.net/figure/One-of-the-female-tigers-walking-on-a-track-plot-TP-during-the-sampling-period-in_fig2_263702911).

Therefore, one would not expect these species to differ in their ability to adopt bipedal postures.

Yet there does seem to be a difference. The lion has not been observed to adopt bipedal postures to the extent and degree observed in the tiger.

The photographic evidence falls into three categories, namely

circus acts,
intraspecific antagonism, and
territorial marking.

CIRCUS ACTS

Please see http://www.chinadaily.com.cn/china/2007-11/12/content_6247657.htm.

I have yet to see a similar photo for the lion.

INTRASPECIFIC ANTAGONISM

Both in play and in combat, the lion and the tiger rear up on their hindlegs to some degree.

However, the lion differs considerably from the tiger, as evident from the many photos (and a few video clips) shown at the end of this Post.

In combat/sparring, the tiger adopts a ritualised transitory posture, in which the animal stands/locomotes briefly on its hindlegs. At the same time, it spreads its forelegs - mirrored by its antagonist - in a way yet to be photographed/filmed in the lion.

TERRITORIAL MARKING

The tiger often stands bipedally at the base of trees, in order to

rub its jowls on the bole, and/or
make conspicuous scratch-marks on the bark:

This is shown in the following:

https://www.reddit.com/media?url=https%3A%2F%2Fi.redd.it%2Fuoahj1bjnqo71.jpg

https://www.alamy.com/stock-photo-siberian-tiger-panthera-tigris-altaica-scent-marking-tree-20328118.html?imageid=BE2CBD26-4D9F-412D-9760-8A936B782357&p=3663&pn=1&searchId=ae1ddc7afd7c91c5b34e5ea40340ae72&searchtype=0)

https://www.alamy.com/bengal-tiger-standing-on-rear-legs-and-stretching-up-to-scratch-a-tree-trunk-a-way-of-marking-territory-ranthambore-national-park-sawai-madhopur-rajasthan-india-asia-image415610844.html?imageid=434A55DB-E1B5-454A-9AFB-0ABBE0E03AEC&p=148099&pn=1&searchId=ac5e77b5654481dc9dd3cfd10b494232&searchtype=0

https://www.alamy.com/stock-photo-a-bengal-tiger-making-scratch-marks-on-a-tree-ranthambore-tiger-reserve-19805813.html?imageid=A6A19F20-867F-4798-9C5E-288C81120E73&p=57430&pn=1&searchId=ac5e77b5654481dc9dd3cfd10b494232&searchtype=0

https://www.alamy.com/stock-image-17-months-old-bengal-tiger-cub-scratch-marking-tree-early-morning-168781557.html?imageid=B611EA12-E9FC-4024-9BB7-5842A5928E0E&p=571810&pn=1&searchId=ac5e77b5654481dc9dd3cfd10b494232&searchtype=0

https://www.alamy.com/siberian-tiger-panthera-tigris-altaica-male-tree-marking-captive-e-russia-fl011327-s-image552952737.html?imageid=AC955E3E-81F4-4076-B908-6C1AC79EC785&p=2130853&pn=1&searchId=ac5e77b5654481dc9dd3cfd10b494232&searchtype=0

https://www.alamy.com/stock-photo-siberian-tiger-panthera-tigris-altaica-immature-male-scratching-tree-47790412.html?imageid=52BBCBD9-A25D-4D79-AAFB-5A24EA412833&p=11592&pn=1&searchId=ac5e77b5654481dc9dd3cfd10b494232&searchtype=0

https://www.alamy.com/stock-photo-siberian-tiger-panthera-tigris-altaica-adult-male-scratching-tree-47790443.html?imageid=2ED629B6-5141-43A0-81BF-F4CBFC7A666D&p=11592&pn=1&searchId=ac5e77b5654481dc9dd3cfd10b494232&searchtype=0

https://www.gettyimages.com.au/detail/photo/tiger-sharpening-claws-on-tree-standing-on-hind-royalty-free-image/200329297-001

https://www.quora.com/What-sort-of-tree-does-a-tiger-choose-to-scratch-in-the-wild-and-why

https://www.gettyimages.co.uk/detail/news-photo/siberian-tiger-adult-standing-up-to-scratch-claws-on-tree-news-photo/1143011570?adppopup=true

https://www.gettyimages.co.uk/detail/news-photo/asie-inde-rajasthan-parc-national-de-rathambore-tigre-du-news-photo/953401420?adppopup=true

https://dailywildlifephoto.nathab.com/contests/1-2016-wildlife-photo-contest/photos/1966-tiger-marking-the-tree

https://www.stevebloom.com/index.php?page=single&id=503140-BS1

https://www.dreamstime.com/stock-photo-tiger-climbing-tree-image38107520

I have yet to find any photo of the lion adopting a similar posture, in this context.

The closest are https://www.123rf.com/photo_100367973_lion-standing-on-his-hind-legs-at-a-tree-in-morning-light.html and https://www.stevebloom.com/index.php?page=single&id=506649-BS1 and https://www.istockphoto.com/photo/female-white-lion-scratching-tree-bark-gm1195489631-340768364 and https://www.shutterstock.com/image-photo/african-lion-felis-leo-marking-territory-528839812.

DISCUSSION

It would be particularly surprising for the tiger to exceed the lion in bipedal ability, given that it is the more massive of the two species (https://www.diffen.com/difference/Lion_vs_Tiger and https://www.quora.com/Are-tigers-and-lions-the-same-size).

Perhaps the difference can be explained partly by the fact that the lion typically inhabits open vegetation, whereas the tiger typically inhabits wooded vegetation.

These findings should raise a search-image, among naturalists, for bipedal modes in

the various other species of Panthera (https://www.pinterest.co.uk/pin/118430665190308481/ and https://i.imgur.com/cj8aznU.jpg), as well as
Puma concolor (https://www.alamy.com/puma-felis-concolor-standing-on-its-back-paws-image6401372.html and https://www.agefotostock.com/age/en/Stock-Images/cougar-scratching-tree.html), and Acinonyx jubatus (https://www.artflakes.com/en/products/gepard-in-namibia-african-cheetah-standing and https://www.stevebloom.com/index.php?page=single&id=500915-BS1).

The leopard (Panthera pardus) has repeatedly been photographed sitting bolt-upright in vigilance (https://www.dailymail.co.uk/news/article-2143766/Simples-Leopard-surprises-safari-goers-stands-legs-like-meerkat-stalk-dinner.html and https://m.facebook.com/IntenseWalls/photos/a.527980250611783/3363912873685159/?type=3&_rdr). However, this is different from standing.

Bipedal standing during marking on trees is the least important of the three lines of evidence considered here. This is because the animal does not free-stand, but instead uses the bole to support itself with its forepaws.

I offer the hypothesis that it is the lion, rather than the tiger, that is aberrant, among 'big cats', in its (lack of) expression of bipedality.

However, part of the explanation may lie in the fact that the tiger is significantly more brainy than the lion (https://www.researchgate.net/publication/229958542_Brain_size_of_the_lion_Panthera_leo_and_the_tiger_P_tigris_Implications_for_intrageneric_phylogeny_intraspecific_differences_and_the_effects_of_captivity).

INTRASPECIFIC ANTAGONISM: PANTHERA LEO:

https://depositphotos.com/photo/lions-fighting-4018529.html

https://www.gettyimages.com.au/detail/photo/young-male-lions-playing-with-each-other-jumping-royalty-free-image/171116536?adppopup=true

https://www.gettyimages.com.au/detail/news-photo/two-lioness-panthera-leo-sparring-masai-mara-national-news-photo/1371855370?adppopup=true

https://www.gettyimages.com.au/detail/photo/lion-and-lioness-fighting-fighting-masai-mara-royalty-free-image/1027619214?adppopup=true

https://www.flickr.com/photos/jaffles/24851778939

https://www.dreamstime.com/two-lions-fiercely-fighting-their-pride-creating-using-generative-ai-tools-pair-engage-territorial-fight-image280293785

https://www.mediastorehouse.com.au/nature-picture-library/2020-april-highlights/lion-panthera-leo-males-mock-fighting-play-19960056.html

https://www.flickr.com/photos/sheldrickfalls/32953986190

https://www.facebook.com/thewildestafrica/photos/a.2245536979094388/2405427793105305/?type=3&locale=zh_CN