Impalas (Aepyceros) and giraffes (Giraffa) share the same walking gait, namely an amble

@beartracker @magcl @ptexis

It is widely known that the walking gait of giraffes (Giraffa) is unusual (https://www.researchgate.net/figure/Categorisation-of-giraffes-walking-gait-Reproduction-of-Hildebrands-plot-for_fig3_329382181 and https://academic.oup.com/jmammal/article-abstract/41/2/282/933378?redirectedFrom=PDF&login=false).

However, like many 'factoids' about Nature, this is subject to context.

It is true that giraffes have a 'parallel', not a 'diagonal', stride while walking (https://www.youtube.com/watch?v=n9redgIffu4 and https://www.youtube.com/watch?v=FBz1rQ5z8uE and https://www.facebook.com/watch/?v=1723826704314545and https://www.youtube.com/watch?v=Vh2yveXTKaU and https://www.youtube.com/watch?v=o9TuZCG1f0k).

However, the same is true also for many Carnivora.

The lion (Panthera leo), walking behind its intended prey, a giraffe, uses the same 'parallel' stride (https://www.youtube.com/watch?v=o9TuZCG1f0k and https://www.youtube.com/watch?v=-QnyACx936I and https://stock.adobe.com/images/big-lion-walking-shot-in-profile/210044363 and https://www.africanreferencephotos.com/photo/2209/Profile-of-Male-Lion-Walking.html).

(Yes, it is true that the brown bear walks like a giraffe, in the sense that the hind foot lifts only once the opposite fore foot has landed, and the hind foot lands (i.e. 'oversteps') considerably anterior to the print of the fore foot on the same side.)

Why is it, then, that this 'parallel' stride is seen as remarkable in giraffes, but not in Carnivora - including the domestic dog (Canis familiaris, https://www.youtube.com/watch?v=eqBcBsmMQVA)?

The obvious answer is:
because a gait that is normal in a plantigrade (e.g. brown bear) and digitigrade (e.g. lion) mammal seems much odder in mammals (giraffes) that are not only unguligrade, but extremely long-legged even among ungulates.

The above framing may explain, at least partly, why giraffes have a reputation for walking in an odd way.

For it is indeed remarkable that, in going from a 'flat-footed' animal, such as a bear, to an animal with 'stilts' for legs, such as a giraffe, the same gait is retained.

However, if this was a complete explanation, then all other hoofed mammals, including those with relatively short legs, would also walk like giraffes and Carnivora.

And this far from being true.

In fact, most ruminants walk in a different way, using a 'diagonal' stride. This applies to all deer (Cervidae, https://www.inaturalist.org/journal/milewski/91548-walking-gaits-in-cervidae-deer-tend-to-cross-walk-as-opposed-to-the-ambling-typical-of-many-bovids-part-1#) and many bovids (Bovidae, https://www.inaturalist.org/posts/85349-gaits-and-other-aspects-of-locomotion-in-hippotragin-bovids#).

Consider the tiger (Panthera tigris) following the sambar deer (Rusa unicolor) (https://www.naturepl.com/stock-photo-bengal-tiger-nature-image01234681.html and https://www.facebook.com/watch/?v=282670022702595 and https://www.youtube.com/watch?v=qX7oEFWuV2I).

The predator uses a 'parallel' stride (https://www.youtube.com/watch?v=MIBAT6BGE6U and https://www.youtube.com/watch?v=6fhAzkK_s_Y), whereas the prey uses a 'diagonal' stride (https://videohive.net/item/beautiful-male-sambar-rusa-unicolor-deer-walking-in-the-forest-of-ranthambore-national-park/25553355 and https://www.shutterstock.com/da/video/clip-1086299906-medium-shot-alert-male-sambar-deer-rusa and https://www.shutterstock.com/da/video/clip-1104756293-sambar-deer-rusa-unicolor-walking-carefully-dense).

One explanation for this anomaly is as follows.

Unguligrady is an adaptation mainly for rapid and enduring fleeing from predators. In the 'arms-race' between prey and predator, hoofed mammals have compensated for the disadvantage of being surprised by predators, by having more efficient sprinting than that of Carnivora.

However, all benefits are accompanied by certain costs. And in the case of ruminants, a cost of 'living on stilts' (= unguligrady) is the risk of instability while walking.

Ruminants compensate for this risk by tending to use diagonal patterns in their walking strides.

This allows deer, for example,

to pick their way quietly through the undergrowth, then 'freeze' on two legs upon hearing an ominous rustling, and
to wade through water and snow, and to step over fallen logs, in the case of the species of deer with the longest legs, namely the moose (Alces alces, https://www.shutterstock.com/da/video/clip-1110160859-bull-moose-walks-off-road-into-wilderness and https://www.youtube.com/watch?v=zUE5FK3l_Lo and https://www.youtube.com/watch?v=MV3yLbKke-c).

It is only in two categories of ruminants that all 'diagonality' seems to have been abandoned while walking.

These are

giraffes, which achieve stability by means of the cantilever-effect of the long and massive neck, and
'plains game', adapted to open environments where hiding is impractical, and compensating for this in various ways in their anti-predator strategies.

'Plains game' artiodactyls emphasise efficiency of walking over stability of walking. This is, hypothetically, why they use a 'parallel' stride, rather than a 'diagonal stride (https://www.youtube.com/watch?v=0WcG532I4is and https://www.google.com.au/search?sca_esv=361d108b9e725553&sxsrf=ACQVn0_rxEkkCe56q3nf8k8XrPxMiTH8Hw:1712749994086&q=Wildebeest+walking+video&tbm=vid&source=lnms&prmd=visnmbtz&sa=X&ved=2ahUKEwi_vPH3yreFAxUrVmwGHb1bClcQ0pQJegQIDBAB&biw=1004&bih=549&dpr=2.7#fpstate=ive&vld=cid:2130b2ac,vid:-_if9UL39Lc,st:0). Their walking gaits are like that of giraffes, but for different reasons.

So, where do impalas fit into this conceptual framework?

Well, impalas walk like giraffes (https://www.inaturalist.org/posts/49366-locomotory-and-postural-peculiarities-of-impalas-aepyceros-part-1#activity_comment_b2dbc656-b062-4be7-9b31-eb6fdd6dc640).

This can perhaps best be explained by comparing impalas with alcelaphin bovids (Alcelaphini).

Alcelaphins (wildebeests, hartebeests, and damalisks) epitomise 'plains game'. They are odd among ruminants in their combination of

humped withers,
migration/nomadism, and
extreme speed and endurance when galloping and cantering.

It is as part of the above syndrome that the 'parallel' stride of alcelaphins, when walking, can be considered. Alcelaphins are locomotorily aberrant, as part of an extreme relationship to predation.

For their part, impalas are odd among ruminants in their combination of

dependence on woody plants,
sedentariness (excluding nomadism, let alone migration),
intimate gregariousness, and
extreme bounding while fleeing.

We can, in light of the above, think of impalas as 'plains game adapted to relatively dense vegetation' (https://www.inaturalist.org/journal/milewski/89704-can-precociality-in-the-colouration-of-impalas-aepyceros-be-explained-by-their-confusing-nature-as-sedentary-plains-game-part-1#).

This would place them - albeit with some 'sheohorning' - into the third category above, namely 'plains game'.

And this leads us to realise something shared by all the ruminants that use 'parallel' - as opposed to 'diagonal' - strides while walking, namely an inability/reluctance to use the ordinary running method known as trotting (https://www.inaturalist.org/posts/49366-locomotory-and-postural-peculiarities-of-the-impala-part-1#).

A trot is a 'diagonal' way of running. It is a standard gait in Carnivora and ungulates.

However, it is

absent in giraffes,
used by wildebeests and hartebeests only for display, and
peculiarly absent in impalas.

All of these ruminants have - in their own ways and for different reasons - abandoned trotting, as a gait for fleeing and commuting. It is in light of this common denominator that their adoption of a 'parallel' stride, when walking, can be appreciated.

What, then, should we call the 'parallel' gait used by giraffes, camels, 'plains game', and impalas alike?

I suggest that the best term is 'an amble'.

(This is not to be confused with a pace, which is also uses 'parallel' strides, but is a running gait, not a walking one.)

And this means that - to everyone's surprise - impalas and giraffes are evolutionarily convergent in ambling while walking (https://www.youtube.com/watch?v=K24qSp49HHg and https://www.youtube.com/watch?v=4jeoFaKDb70).

This is despite the obvious differences between impalas and giraffes in

Furthermore, any preoccupation that giraffes walk oddly - which remains true in its way but is easily misinterpreted - may now have been overtaken. The more current notion - given the ordinariness of their body-proportions - should be that impalas walk even more oddly.

And this invites the next step in my investigative stroll, as follows.

Warthogs (Phacochoerus) - equally surprisingly - seem to amble (https://www.inaturalist.org/posts/85161-variation-in-walking-gaits-in-ungulates-part-1-why-some-hoofed-mammals-cross-walk-whereas-others-amble#activity_comment_1c97f582-aac3-4d6d-b15f-c533aaba47b5).

This is in keeping with impalas inasmuch as these aberrant suids are 'plains game'. However, the new complication is that warthogs have certainly retained a trotting gait...

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Posted on April 10, 2024 01:22 AM by

milewski

Impalas (Aepyceros) and giraffes (Giraffa) share the same walking gait, namely an amble

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