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Please also see the following
INTRODUCTION
A cross-walk is a diagonal walking gait, in which left fore tends to move together with right hind, and right fore tends to move together with left hind.
Among ungulates, a 'perfect' example is Hippopotamus amphibius (https://www.pond5.com/stock-footage/item/56467947-hippo-walking-isolated-hippopotamus-video-includes-alpha-cha).
Cross-walking occurs in certain small (body mass less than 35 kilograms) ruminants. More particularly, I refer to cover-dependent, nocturnal, solitary species with inconspicuous colouration (https://www.inaturalist.org/journal/milewski/91630-walking-gaits-in-cervidae-deer-tend-to-cross-walk-as-opposed-to-the-ambling-typical-of-many-bovids-part-2-odocoileinae#).
However, a naturalist can observe these ruminants attentively without noticing that the gait is a cross-walk.
Furthermore, baboons (Papio spp.), macaques (Macaca spp.), and the proboscis monkey (Nasalis larvatus) - all of which habitually cross-walk on the ground - seem to have yet another different action (https://www.gettyimages.com.au/detail/photo/proboscis-monkey-walking-through-mangrove-royalty-free-image/527127928?phrase=proboscis+monkey&adppopup=true and https://www.gettyimages.com.au/detail/photo/proboscis-monkey-walking-through-mangrove-swamp-royalty-free-image/114995835?phrase=proboscis+monkey&adppopup=true).
However, here again, the gait is a cross-walk.
So, how can these disparate impressions be reconciled?
A NOTE ON TECHNICAL TERMS
A problem in studying gaits is confusion of terms.
What I call a cross-walk is alternatively called a 'walking trot' or 'diagonal-sequence walk' (https://onlinelibrary.wiley.com/doi/abs/10.1002/ajpa.1330260203#:~:text=Diagonal%2Dsequence%20gaits%20have%20the,opposite%20side%20of%20the%20body).
'Diagonal-couplets gaits' (see the reference above) include both a running gait (trot) and a walking gait (which I call a cross-walk).
What I call an amble is alternatively called a 'walking pace' or 'lateral-sequence walk'. In my terminology, just as a trot is the running version of a cross-walk, so a pace is the running version of an amble.
I have invented the term 'semi cross-walk' because
AIMS
The aim of this Post is to explain why the walking gaits seem so different in ruminants and monkeys that it took me decades to realise that both kinds of mammals cross-walk.
RESULTS AND DISCUSSION
Please compare
Which reader would have known that all of these photos illustrate cross-walking?
There are six main reasons why cross-walking in ruminants and monkeys seems to consist of categorically different gaits.
These are as follows.
In the ruminants,
Part of the reason why ruminants and monkeys deviate, in opposite directions, from the synchronous placement of the diagonally-opposite feet may be
In the ruminants in question, the rump is higher than the withers (https://www.inaturalist.org/observations/83544190). This is part of a 'hunched' conformation in which - presumably to boost acceleration when predators pounce - the hind legs are longer and springier than the fore legs.
In the monkeys in question, the rump tends to be lower than the withers (https://es.123rf.com/photo_126109982_a-monkey-walking-in-the-street-on-the-sunny-day.html).
This is because
Both the ruminants and the monkeys deviate from Hippopotamus amphibius, in which fore and hind legs are similar in length (https://www.shutterstock.com/image-photo/rare-sighting-hippo-walking-out-water-60570064).
Therefore,
Finally, two relevant differences between the ruminants and the monkeys are that
Comments
Nasalis larvatus:
https://hakaimagazine.com/features/the-wonderful-transcendent-life-of-an-odd-nosed-monkey/
Nasalis larvatus:
https://www.agefotostock.com/age/en/details-photo/proboscis-monkey-male-walking-on-the-mudflats-of-a-mangrove-swamp-revealed-at-low-tide-nasalis-larvatus-bako-national-park-sarawak-borneo-malaysia/AAM-AAES113158
CROSS-WALKING IN PAPIO
https://www.inaturalist.org/observations/199537269
https://www.inaturalist.org/observations/199067257
https://www.inaturalist.org/observations/195944062
https://www.inaturalist.org/observations/195924413
https://www.inaturalist.org/observations/194604835
https://www.inaturalist.org/observations/194356932
https://www.inaturalist.org/observations/194307747
https://www.inaturalist.org/observations/192803418
https://www.inaturalist.org/observations/192022177
https://www.inaturalist.org/observations/190818844
https://www.inaturalist.org/observations/188285929
https://www.inaturalist.org/observations/187353169
https://www.inaturalist.org/observations/186956613
https://www.inaturalist.org/observations/184243555
https://www.inaturalist.org/observations/184088782
https://www.inaturalist.org/observations/183964646
https://www.inaturalist.org/observations/183900731
https://www.inaturalist.org/observations/178870318
Gaits in Equus caballus:
https://www.youtube.com/watch?v=3rSf5OLe2v4
The following shows that, in the cross-walk of monkeys, the fore and opposite hind foot lift at the same time (this does not occur in any ruminant):
https://www.inaturalist.org/observations/195575696
In the following of Papio, the hind foot has been placed behind, not next to, the fore foot on the same side.
This is probably because the animal is walking slowly in https://www.inaturalist.org/observations/189107260.
In https://www.inaturalist.org/observations/188946435, it is possibly in accommodation of the infant.
https://www.researchgate.net/profile/Borja-Figueirido-2/publication/254315156_On_Their_Knees_Distal_Femur_Asymmetry_in_Ungulates_and_Its_Relationship_to_Body_Size_and_Locomotion/links/54f8347e0cf28d6deca08cee/On-Their-Knees-Distal-Femur-Asymmetry-in-Ungulates-and-Its-Relationship-to-Body-Size-and-Locomotion.pdf
Equus caballus:
https://www.visualdictionaryonline.com/animal-kingdom/ungulate-mammals/horse/gaits_1.php
https://vanat.ahc.umn.edu/run/plate1.html
https://d1wqtxts1xzle7.cloudfront.net/38898576/Franklin_Vicuna_1974.pdf?1443280555=&response-content-disposition=inline%3B+filename%3DThe_Social_Behavior_of_the_Vicuna_p_477.pdf&Expires=1712170909&Signature=ZselF5OyWQYh87erYezyN-xU4Uix7jqbg7d6vx1lBp5eZtIfGwqItinmpPPfREqxQOUg1MffIHShCxd1IsEoZofvSTw~a-02bfNT1fn242BPifMhTiyED7Ie3~McH5TE1gRnJpBHyL1DjKsHGAT0MO8vRJbp3t~fGY41soS7KwDNRTHzEcS8lScG9U6Cx-DTQjD~pokIdMa8gbXx1Mn4V6NV5h4GWH5Nhox7iK39H~2xWDgk0PB0r3JBVF5WzXpO~LUoSZ7lOGHjDKSzzPVPqHGO~H8Lq~zBZFZZT3js1V9LMuS-bFzQZ4g11xXN4S5aIN56U7T-4SBCpq1OWxIgMg__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA#page=272
https://royalsocietypublishing.org/doi/full/10.1098/rspb.2016.1908
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