There is an adaptive trend among the ruminants of the world, as follows.
Species adapted to dense cover tend to have
A typical example is bushbucks (Tragelaphus, https://www.inaturalist.org/taxa/1431867-Tragelaphus-sylvaticus and https://www.inaturalist.org/taxa/42341-Tragelaphus-scriptus).
By contrast, species adapted to short, sparse vegetation tend to have
A typical example is the springbok (https://www.inaturalist.org/taxa/42283-Antidorcas-marsupialis).
Intermediate species show intermediate traits.
In the context of this adaptive axis, certain anomalies emerge. The following are prime examples.
Deer of genus Odocoileus in North and central America, and impalas (Aepyceros) in southern and East Africa, are comparable. Both fall into the intermediate part of the axis described above.
Both are associated with some woody cover, as opposed to treeless grassland. Accordingly, both are somewhat gregarious.
Both have
However, two incongruities emerge, as follows.
Firstly, Odocoileus deer combine
By contrast, impalas combine
Secondly, both genera have stotting displays. However, the gaits used are surprisingly different.
Odocoileus deer display by
By contrast, impalas display by
Stating the puzzle concisely:
The deer referred to are incongruently demonstrative, whereas impalas are incongruently non-demonstrative.
Before attempting to explain this puzzle, let us examine the evidence by means of photos/video clips.
The following show the semi crosswalk, which is
What is remarkable is that a halting gait, allowing the animal to 'freeze' with two legs in the air in order to blend into the background when hearing or seeing something suspicious, has been converted from an adaptation for concealment to an adaptation for advertisement. This has been done not by changing the footfall-sequence, but by exaggerating the lifting/lowering of the feet into conspicuous movements, probably together with release of odour from the pedal glands.
https://www.pond5.com/stock-footage/item/246892228-white-tail-deer-walking-ridge-whitetail-deer-rut
https://www.pond5.com/stock-footage/item/150433074-whitetail-deer-casually-walking-sand-dunes
https://www.pond5.com/stock-footage/item/168721004-young-whitetail-deer-walking-snow
https://en.wikipedia.org/wiki/White-tailed_deer
https://www.youtube.com/watch?v=zADVhWj51Vg
https://www.youtube.com/watch?v=0FcWHBhqKkU
https://www.youtube.com/watch?v=KHxu7QxHmL4
https://www.youtube.com/watch?v=sxq09JUPh5s
https://www.youtube.com/watch?v=rmmpBklsfUY
https://www.youtube.com/watch?v=8XRhlvmAMpk
https://www.youtube.com/watch?v=F9DLRNhuXI4
https://www.youtube.com/watch?app=desktop&v=VX1_gswmoew
https://www.pond5.com/stock-footage/item/65151043-whitetail-buck-deer-velvet-walking-down-river
Comments
https://www.youtube.com/watch?v=E7X_u565A3w
https://www.youtube.com/watch?v=tXYxGf0CKWs
Vertically-piloerected caudal flag:
https://www.gettyimages.ie/detail/photo/male-impala-leader-showing-off-his-supremacy-royalty-free-image/464393061?phrase=impala+the+animal&adppopup=true
https://www.shutterstock.com/image-photo/impala-aepyceros-melampus-mediumsized-antelope-found-1560109967
https://www.shutterstock.com/image-photo/jumping-impala-kruger-360519452
https://www.shutterstock.com/image-photo/impala-aepyceros-melampus-mediumsized-antelope-found-1644189367
Aepyceros petersi kick-stotting
https://www.shutterstock.com/image-photo/antelope-off-jump-589030901
Aepyceros melampus
The following are unusual in resembling 'conventional' stotting. However, I suspect that they are simply part of the sequence in kick-stotting.
The first photo also shows an unusual view of the tail.
https://www.shutterstock.com/image-photo/young-impala-jumping-pronking-midair-2138114997
https://www.shutterstock.com/image-photo/impala-male-running-jumping-masai-mara-1145667239
https://www.shutterstock.com/image-photo/female-impala-showing-off-her-running-2253548605
https://www.gettyimages.ie/detail/photo/african-impala-in-motion-royalty-free-image/520856762?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impala-female-jumping-on-the-run-moremi-wildlife-royalty-free-image/1183098027?phrase=impala+the+animal&adppopup=true
KOBUS LECHE
https://www.shutterstock.com/image-photo/wild-impala-antelope-african-botswana-savannah-750719554
https://www.gettyimages.com.au/detail/photo/male-impala-near-water-hole-royalty-free-image/77283390?phrase=african+impala&adppopup=true
TRAGELAPHUS SYLVATICUS
https://www.shutterstock.com/image-photo/bushbuck-ram-golden-light-soft-focus-246247477
https://www.shutterstock.com/image-photo/bushbuck-ram-golden-light-soft-focus-271634987
https://www.shutterstock.com/image-photo/bushbuck-ram-golden-light-244048546
Shift to precociality of coronal flag
https://www.shutterstock.com/image-photo/young-male-impala-play-fighting-2138115423
https://www.gettyimages.com.au/detail/news-photo/impala-bovidae-news-photo/492754709?adppopup=true
Penicillate caudal flag
Aepyceros melampus:
https://www.shutterstock.com/image-photo/after-leaving-brees-herd-harem-young-2337216589
Aepyceros petersi:
https://www.shutterstock.com/image-photo/impala-defecating-214377745
https://www.shutterstock.com/image-photo/common-impala-kruger-national-park-south-1216568287
BLACK-TAILED DEER
https://www.gettyimages.com.au/detail/photo/animals-image-royalty-free-image/1141949014?phrase=southern+giraffe&adppopup=true
https://www.wilddeer.net.au/2021/05/06/black-tailed-deer-odocoileus-hemionus-by-josh-rafin/
https://myodfw.com/big-game-hunting/species/black-tailed-deer
https://wildernessawareness.org/articles/black-tailed-deer-tracks-and-sign/
https://www.youtube.com/watch?v=dXd87nAxHSo
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1685856/
The following illustrate the semi cross-walk in Odocoileus hemionus:
https://www.dreamstime.com/black-tailed-deer-walking-green-lawn-glances-viewer-as-walk-grass-image113274654
https://www.alamy.com/stock-photo-male-black-tailed-deer-walking-in-the-meadows-92471685.html
Caudal flag in Strepsiceros strepsiceros
https://www.dreamstime.com/stock-image-kudu-trot-african-antelope-image26164551
Elaphurus davidianus
https://www.youtube.com/watch?v=s6KT9HyEqwc
https://www.youtube.com/watch?v=qvuQK9M5O5w
https://www.youtube.com/watch?v=Z0-28AzUyxw
https://www.youtube.com/watch?v=pUmHClrRPxc
Aepyceros melampus walking
https://www.istockphoto.com/video/beautiful-and-graceful-impala-antelope-walking-in-savannah-gm932522106-255537892
Dama dama walking
https://www.youtube.com/watch?v=5DuKpftCyYQ
https://www.youtube.com/watch?v=plyXHT_AFys
https://www.youtube.com/watch?v=dBaW7gt4Z4M
https://www.sciencephoto.com/media/625669/view/male-fallow-deer-walking
Cervus elaphus walking and trotting
https://www.facebook.com/watch/?v=627414221905924
Aepyceros petersi
https://www.gettyimages.com.au/detail/photo/black-faced-impala-aepyceros-melampus-petersi-royalty-free-image/90052756?phrase=impala+4&adppopup=true
https://www.gettyimages.ie/detail/news-photo/black-faced-impala-male-black-faced-impala-picture-taken-in-news-photo/157890498?adppopup=true
https://www.gettyimages.ie/detail/news-photo/grants-gazelles-and-impala-in-samburu-national-reserve-in-news-photo/621196304?adppopup=true
OUREBIA
https://www.gettyimages.ie/detail/photo/portrait-of-deer-standing-on-grassy-field-romania-royalty-free-image/1485160906?phrase=impala+the+animal&adppopup=true
SEXUAL DIMORPHISM IN COLOURATION IN AEPYCEROS MELAMPUS
The following illustrates the fact that the ground-colour on the neck is somewhat darker in mature males than in adult females, in Aepyceros melampus:
https://www.gettyimages.ie/detail/photo/two-impala-mating-in-the-morning-royalty-free-image/1490254228?phrase=impala+the+animal&adppopup=true
The following shows that the gular semet is a masculine feature:
https://www.gettyimages.ie/detail/news-photo/schwarzfersenantilopenbock-mit-weibchen-im-abendlicht-imm-news-photo/645833321?adppopup=true
https://www.gettyimages.ie/detail/photo/impala-male-standing-in-the-savannah-masai-mara-royalty-free-image/1456615533?phrase=impala+the+animal&adppopup=true and https://www.gettyimages.ie/detail/photo/impala-male-standing-in-the-savannah-masai-mara-royalty-free-image/1456615532?phrase=impala+the+animal&adppopup=true
Back-of-ear pattern in Aepyceros melampus:
https://www.gettyimages.ie/detail/news-photo/impala-aepyceros-melampus-herd-of-females-in-grass-alert-to-news-photo/578257132?adppopup=true
https://www.gettyimages.ie/detail/photo/impalas-in-serengeti-national-park-royalty-free-image/585992190?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impala-male-watching-intently-rear-view-royalty-free-image/103092298?phrase=impala+the+animal&adppopup=true
Kick-stotting, with only partial/intermittent caudal flagging:
https://www.gettyimages.ie/detail/photo/leaping-impala-moremi-game-reserve-botswana-royalty-free-image/534976134?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impala-royalty-free-image/520764534?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impala-royalty-free-image/520764550?phrase=impala+the+animal&adppopup=true and https://www.gettyimages.ie/detail/photo/impala-royalty-free-image/520764540?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impala-female-jumping-on-the-run-moremi-wildlife-royalty-free-image/1183098043?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impala-female-with-fawn-royalty-free-image/591071468?phrase=impala+the+animal&adppopup=true
Comparison of Aepyceros melampus rendilis with Damaliscus jimela:
https://www.gettyimages.ie/detail/photo/male-impalas-and-topi-royalty-free-image/519948262?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/young-impala-bucks-play-fighting-royalty-free-image/520575618?phrase=impala+the+animal&adppopup=true
GEOPHAGY IN AEPYCEROS
https://www.gettyimages.ie/detail/photo/bachelor-herd-of-impala-licking-minerals-from-a-royalty-free-image/617783349?phrase=impala+the+animal&adppopup=true
Excellent
https://www.gettyimages.ie/detail/photo/female-impala-running-royalty-free-image/822523658?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/male-impala-running-royalty-free-image/822524232?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impala-baby-grooming-royalty-free-image/462866809?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impala-herd-royalty-free-image/543976826?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/ma-hes-making-eyes-at-me-royalty-free-image/167170335?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/male-impala-running-royalty-free-image/822524252?phrase=impala+the+animal&adppopup=true
Gregarious camouflage
https://www.gettyimages.ie/detail/photo/impala-female-herd-royalty-free-image/121775236?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/watchful-herd-of-impala-mana-pools-national-park-royalty-free-image/702543057?phrase=impala+the+animal&adppopup=true
Gazella subgutturosa
https://www.gettyimages.ie/detail/photo/impala-calf-in-the-wilderness-of-africa-royalty-free-image/1207632324?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impala-calf-in-the-wilderness-of-africa-royalty-free-image/1207633119?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impala-calf-in-the-wilderness-of-africa-royalty-free-image/1206934322?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/wild-tibetan-antelope-royalty-free-image/1298937436?phrase=impala+the+animal&adppopup=true
Kobus vardoni
https://www.gettyimages.ie/detail/photo/portrait-of-deer-standing-amidst-plants-south-royalty-free-image/1280599681?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/baby-impala-nursing-with-mom-on-savannah-in-kafue-royalty-free-image/1180482636?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impalas-drinking-next-to-giraffe-legs-royalty-free-image/90258413?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impala-calf-in-the-wilderness-of-africa-royalty-free-image/1207634985?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/leopard-panthera-pardus-walks-across-a-clearing-royalty-free-image/1126918447?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/brave-impala-face-off-against-lions-in-kruger-royalty-free-image/1401757330?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/lion-cubs-royalty-free-image/1284185605?phrase=impala+the+animal&adppopup=true
Tail of Aepyceros melampus
https://www.gettyimages.ie/detail/photo/backside-of-an-impala-male-serengeti-royalty-free-image/1256290141?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impalas-in-the-wild-royalty-free-image/1376567978?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/wilderbeast-and-impalas-in-african-bush-south-royalty-free-image/535657465?phrase=impala+the+animal&adppopup=true
Acinonyx jubatus
https://www.gettyimages.ie/detail/photo/a-gepard-is-going-in-the-grassland-in-kenya-royalty-free-image/1203198295?phrase=impala+the+animal&adppopup=true
Caudal flagging during suckling
https://www.gettyimages.ie/detail/photo/impala-and-calf-masai-mara-national-park-kenya-royalty-free-image/1196621564?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impalas-female-with-young-suckling-maasai-mara-royalty-free-image/993497958?phrase=impala+the+animal&adppopup=true
Infant colouration in Gazella arabica
https://www.gettyimages.ie/detail/photo/side-view-of-deer-walking-on-road-royalty-free-image/1292463044?phrase=impala+the+animal&adppopup=true
Kobus ellipsiprymnus
https://www.gettyimages.ie/detail/photo/baby-waterbuck-and-its-mother-at-pinalesberg-game-royalty-free-image/1169147437?phrase=impala+the+animal&adppopup=true
Nanger granti
https://www.gettyimages.ie/detail/photo/impala-grazing-the-filed-royalty-free-image/578850320?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/two-young-impala-antelopes-in-tanzania-africa-royalty-free-image/1215529477?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/impalas-herd-females-with-cubs-maasai-mara-national-royalty-free-image/993497992?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/stalking-lioness-moving-closer-towards-a-herd-of-royalty-free-image/130866121?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/young-male-impala-royalty-free-image/1344357666?phrase=impala+the+animal&adppopup=true
Odocoileus virginianus
https://www.gettyimages.ie/detail/photo/young-bucks-royalty-free-image/989094752?phrase=impala+the+animal&adppopup=true
Horizontally-piloerected caudal flag:
https://www.gettyimages.ie/detail/photo/impala-ram-looking-out-royalty-free-image/1163624310?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/tranquil-african-landscape-with-impala-royalty-free-image/1199494086?phrase=impala+the+animal&adppopup=true
One of the few photos showing kneeling in Aepyceros:
https://www.gettyimages.ie/detail/photo/wildlife-royalty-free-image/886755618?phrase=impala+the+animal&adppopup=true
The normal posture is splaying:
https://www.gettyimages.ie/detail/photo/imapala-drinking-mana-pools-zimbabwe-royalty-free-image/141467801?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.com.au/detail/photo/impala-at-the-waterhole-royalty-free-image/992420420?phrase=african+impala&adppopup=true
Caudal flagging during masculine display in Aepyceros petersi:
https://www.gettyimages.ie/detail/photo/black-faced-impala-etosha-pan-namibia-royalty-free-image/970408544?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/black-faced-impala-etosha-pan-namibia-royalty-free-image/970408714?phrase=impala+the+animal&adppopup=true
https://www.gettyimages.ie/detail/photo/black-faced-impala-etosha-pan-namibia-royalty-free-image/970408744?phrase=impala+the+animal&adppopup=true
Picture worth a thousand words:
https://www.gettyimages.ie/detail/photo/giraffe-impalas-springbok-and-ostriches-near-a-royalty-free-image/130866595?phrase=impala+the+animal&adppopup=true
Tongue of Giraffa:
https://www.gettyimages.ie/detail/photo/impala-tounge-kruger-national-park-mpumalanga-royalty-free-image/106676864?phrase=impala+the+animal&adppopup=true
Tail of Aepyceros melampus, with particular reference to the jointed feather-tassel:
https://www.gettyimages.com.au/detail/photo/male-impala-in-kruger-national-park-royalty-free-image/840935044?phrase=african+impala&adppopup=true
https://www.gettyimages.com.au/detail/photo/male-impala-in-kruger-national-park-royalty-free-image/840935034?phrase=african+impala&adppopup=true
The ventral surface of the tongue is flesh-coloured in Aepyceros melampus, despite the upper surface being dark:
https://www.gettyimages.com.au/detail/photo/alert-impala-antelope-standing-in-grass-royalty-free-image/77283344?phrase=african+impala&adppopup=true
ODOCOILEUS VIRGINIANUS
https://www.istockphoto.com/photo/white-tailed-deer-doe-and-fawns-running-on-the-oronoco-prairie-gm1761757335-544909640?phrase=tan+colored+doe&searchscope=image%2Cfilm
EXCELLENT ILLUSTRATION OF 'DISPLAY-WALKING' IN ODOCOILEUS VIRGINIANUS
https://www.istockphoto.com/photo/white-tailed-deer-fawn-gm1285356227-382220524?phrase=tan+colored+doe&searchscope=image%2Cfilm
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