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December 11, 2004
Comparative Anatomy
Once you become sensitive to the basics of how the human body is constructed, you start to see the same patterns in use in animal anatomy. Since all living creatures on Earth trace their origins to a common ancestor, the same basic patterns arise again and again and again and again. Here's an example:
A human has two bones in his forearm, the radius, and the ulna. When a human rotates (supinates and pronates) his wrist, his radius rolls over his ulna. The relationship between the two bones at the elbow remains unchanged.
A cat (in this case a Sabre Tooth Tiger) needs the ability to manipulate its prey, so it may not surprise you to notice that it, too, has a radius and ulna in its forearms.
Let's take a stroll through the Page Museum at the La Brea Tar Pits and see if any other animals use this mechanism.
There it is again in the forearm of a Ground Sloth. Perhaps they needed dexterity to handle their food as well.
It's in a Wolf's forelimbs, too.
Birds also have a radius and ulna. Maybe it helps them fold their wings.
But look: There it is as a vestigial leftover in the skeleton of the Extinct Western Horse.
An unusable radius forever crosses an ulna in the pronated forelimb of the Antique Bison.
The massive legs that transport Mammoths, Mastadons and modern day Elephants have this arrangement of bones.
You can find a radius and ulna in ancient Dinosaurs and Fish fins.
Posted by digital artform at December 11, 2004 11:37 AM
Comments
I think you'll find the radius and ulna are an elongated hinge that enables creatures to adjust the rotation of the end of their limbs. The raptor would want to adjust its wings and angle of attack. Cool stuff.
Posted by: Chris at December 11, 2004 08:55 PM
Neat pictures and article! Only one mistake: the white arrow on the picture of the extinct western horse is actually pointing to its cannon bone, which is the fused bones that are the equivalent of our metacarpals (bones of the palm). The bison below it is correct.
Posted by: Squirrel Jam at September 7, 2006 05:06 PM