One 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.
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.