Extremes of locomotion

amis-athousedoorOne of the things I like to highlight on here is the problems of trying to extrapolate the present into the past, or to put it another way, reconstructing fossil animals based on living examples. Of course this is the way we have to do things and far more often than not those inferences are reasonable and accurate. However it is also worth highlighting the bizarre and unusual exceptions in biology both to reinforce the idea that we are not always right, and to show off the remarkable diversity and adaptability that is life. Last time out on this theme I dealt with arboreality and ther remarkable abilites of some non-arboreal animals to climb trees. This time it’s the far less predicatable world of bipeds.

You might think that an animal is either bipedal or it isn’t. That it, it is dedicated to walking on two legs alone (like humans or jerboas say) or is not. A few of you might be thinking of things like facultative bipeds – those that can strand, walk or run bipedally at times, but generally do not (like gorillas, or many small lizards, or the alligator at the top of this page which is admittedly using the wall and tail for support and would hardly count under a normal definition), but that is not really what I am getting at (interesting though those animals and their locomotion are). None of them, here I want to specifically talk about animal that, for want of a better word, *shouldn’t* be bipeds.

Yes there are various records out there of animals with missing limbs (through accident or deformity) that are able to get around despite the obvious handicap of being a fourlegged animal with only two legs. While you have probably seen things like deer balance and even totter around on two legs while feeding high in trees or pet dogs trained to walk upright, this is something rather different. Those animals usually struggle (understandably) to maintain control since they are not really build as bipeds and don’t get to practice much, but that does not mean that under the right (or perhaps rather wrong) circumstances they can become really quite adept at getting around on just two legs.

Below are some video links to youtube showing off various animals that are restricted in odd ways (and there are plenty more if you go hunting on the net) and it’s interesting (if slightly creepy) to see them. In most cases is is the forelimbs that are lost so the animal walks upright on its hindlegs or forelegs alone, but some are missing a fore and hind limb on the same side that make for a very odd biped.

There are:
an upright dog
an upright goat
an upright cat
and a ‘lateral’ dog

What this hopefully demonstrates is my earlier remark about adapatation. I think it’s fair to assume that dogs and goats don’t have ‘bipedal’ genes. It is obviously evolutionary useful for them to be able to rear up and prop themselves against things or whatever and thus the joints allow that kind of stretching, but the neuromusculature control for active walking (or an instict to even attempt the behaviour) and the extra stresses it will place on the joints, ligaments and muscles is adaptive, not inherited. For those upright bipeds the leg is basically operating anyhting up to 90 degrees out of it’s normal (and by extension probably ‘best’) orientation, yet the animals display reasonable speed and control all things considered. Animals are phenomenally adaptive to strange and unusual situations, and also us palaeontolgoists when reconstructing beahviours or activities need to be aware of that. That doesn’t mean we should assume fossil canids were bipeds, but it does mean that we need to be more cautious with absolutes as to what animals could and could not do, they can clearly do things no-one might suspect, if only very rarely and in very odd ways.

The alligator image at the top comes courtesy of John Hutchinson, but he’s not sure where he got it from, so if it is yours and you want it taken down, just let me know.

7 Responses to “Extremes of locomotion”

  1. 1 Alan Kellogg 08/07/2009 at 9:39 am

    “Bipedal” Gator

    Don’t recall where I first saw the picture, I do recall it was in a story about Florida gators invading suburbia and pestering people. I believe that particular animal was removed by local animal control and later destroyed as a persistent pest.

  2. 2 Jura 08/07/2009 at 10:46 am

    Hmm, I wonder what that alligator wanted.

  3. 3 Diego 08/07/2009 at 7:59 pm

    “Hmm, I wonder what that alligator wanted.”

    To borrow a cup of sugar?

  4. 4 John Hutchinson 08/07/2009 at 8:41 pm

    I’ve never, ever seen a crocodylian stand (let alone locomote) on two legs (using the tail and/or head, belly as a prop does not count; that’s 3+ “legs”), and have worked with ~23 species over 8 years.

    We’ve found that the center of mass is generally too far in front of the hips [paper coming out soon] for the short, stubby legs to get the feet underneath it. That poses a problem for bipedalism…

    True bipedalism in extant crocs has never been reliably documented either (just 1-2 speculative anecdotes), so I would not agree that “some can stand on two legs.” Of course, who knows, but extraordinary claims require more than anecdotes; “who knows” does not equal “can”. I’d love to see a bipedal croc though; show me the money!

  5. 5 David Hone 08/07/2009 at 8:54 pm

    Sorry John, I even asked you about that in advance and then manged to make it not very clear. I meant to use the picture as an example of a posture not normally associated with an animal, the use of bipedal (even referring to the stance and with the tail) was a mistake I should have picked up. Not overly clear! My bad. Now changed. Thanks for pointing that out.

  6. 6 Zach Miller 09/07/2009 at 12:54 am

    My leopard geckos do that ALL THE TIME. They’ll just start trying to crawl up the side of their tank, as if responding to some ancient call to use the toe-pads their ancestors lost. If I let them stand on my hand, they excitedly try to further move up the glass. I lift my hand somewhat, and they continuously flail.

    Eventually they reach the top of the tank, and they don’t really know what to do next. I always figure they just want to get out of their tank, so I let Mr. Fat and Liquid wander around, but when Solid gets out, he has a little freak-out!

  1. 1 Croc terrestrial locomotion « Dave Hone's Archosaur Musings Trackback on 01/12/2010 at 6:22 pm
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