The Bone Reader
I’ve often wondered just how people know how a certain animal would walk when all they have is bones. Well low and behold my Dinosaur course (I for the life of me will never remember its technical name) has explained it quite well. I’m not sure if this will be a long update but it should be informative.
For those curious most of these images are snagged from the PowerPoint presentation which probably were initially snagged from Google images. Unfortunately I can’t cite them specifically better than that.
Dinosaurs were erect walkers, that is to say while reptiles such as the Comodo Dragon below actually have legs that first go to the left or right (away from the body) and then at the elbow or knee bend to go earth ward, Dinosaurs instead stood straight up and down on their four legs (think Elephant). Anyone who has seen this bone configuration will note that it requires large exaggerated body movements for the animal to move forward. There are various videos online of these animals moving and I highly suggest checking one out.
(Imaged from: elalmanaque)
But as I was saying earlier how do we know this? Well interestingly enough (and somewhat intuitive once you think about it) bones do not very greatly between organisms. There are a series of bone formations depending on a few strict walking options. You have the 45% comodo like stance, the literal 90% exactly comodo stance, the straight stance of an elephant or Gazelle like animal (or bipeds even) or perhaps 1 or 2 other variations that I’m not thinking about .
When you look at the leg bones of an animal that are in good condition you can discern which of these stances they would have used and it just becomes a matter of thinking like an architect.
On the left you have an alligator femur. It may be hard to tell from the image but essentially the top part of the femur that goes into the Alligators hip is essentially just one big ball. This is because nearly all alligators (and crocodiles) walk in the exaggerated arcing motion (again think Comodo if necessary). The reason for this is that no other shape would effectively work in these large circular motions but a sphere, at least no other shape that is easy to make ;)…evolution is a lazy lazy mistress (more on that tomorrow maybe). However on the right you have the bone of an erect walker, in fact doubly so because it is also a bipedal walker, that is-you guessed it-a human femur. Alright…I don’t know if you DID guess it but I have always wanted to put that in a post.
The human femur join basically plugs in like a socket, because it is only moving in one plane (if you are lucky haha). Likewise the knee joint is very specialized with a channel down its center because all dragging happens forward and back and the channel probably provides a region for adequate cushioning. For a better visual let me grab the image that actually inspired this post.
This is an amazing shot that seems to perfectly portray my point. The knee joint on a human or any upright walker is made quite specialized. It REALLY does not want to go to the left or right and anyone who has ever had their leg do that can tell you it is a terribly painful experience.
This is why we know how dinosaurs walk, and indeed we most likely even know how they swam. All animals in any particular walking style swim almost (if not exactly) the same! It’s really fascinating, you can take a snake that has is not native to lakes or ponds and chuck it in. You’ll find it swimming along like absolutely any other snake. You take any reptile or lizard with the same arm and leg setup of crocs or Comodo’s and they will swim exactly the same. These little bits of info are courtesy of the professor of course, I just felt they were important enough to get out to you folks.
In a closing note since this should pretty much inform people is something else extremely fascinating to me and frankly something that should be brought up in every evolutionary discussion. Has anyone ever wondered why all sea mammals swim in a different manner than any other type of sea creature? A dolphin swims in the same manner as a Gazelle runs! It’s really fascinating to watch a dolphin swim straight along a path and then watch a gazelle run down a straight path. You will see the exact same body motions between the two organisms. At some point long ago a land mammal, for whatever reason, returned to the sea and structurally it changed enough to streamline to the water however, and this is what I find so intriguing, it didn’t change the way that it moves. Essentially if a dolphin had legs instead of a tail fin I’m sure it would swim even more hauntingly like its land based siblings.
Indeed who needs to imagine?: http://www.ebaumsworld.com/video/watch/481248/ . The kid in this video actually exists, this is his record breaking performance. You’ll notice how he is armless and motions through the water almost exactly like a dolphin. Fascinating stuff.