Fingers and Toes Part 2

The forelimb “fingers” and hindlimb “toes” are visible in the flippers of this California sea lion.

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Five fingers. Five toes. These seem to be pretty standard numbers across the vertebrate animal kingdom. Sure, you have your three-toed and even two-toed sloths just hanging around, and horses walk on only a single toe, but even then, there is usually evidence that at one time there were five toes.

The fossil record points to the fact that five was not always a magical number. About 340 million years ago, six or even more digits seemed to be common. However, as the wrist structure became more complicated, the extra digits became obsolete and just impeded progress.

The changes didn’t stop there though. As mentioned last week, many mammals, birds and even reptiles, continued to modify fingers and toes. One adaptation is for flight—and birds and bats, our only true flying mammals, approached the evolution very differently.

Bat fingers (forelimb digits) are five times or more longer than those of similar-sized rodents. It is very much like a human arm and hand, except it has a thin membrane of skin (called the patagium) extending between the "hand" and the body, and between each finger bone. Because the wing is essentially a hand, bats have a lot of dexterity in wing movement, essentially "swimming" through the air. Besides four fingers, all bats also have a thumb on the leading edge of the wing. Although not opposable, it is not bound to the membrane and is useful for climbing, food handling and grasping.

Bird wings developed quite differently. They retained just three fingers, and while there is still a scientific debate as to which three fingers these are, most researchers believe them to be analogous to our middle three fingers—the thumb and little finger are missing. The difference between a bird wing and a bat wing is in the use of these fingers. The fingers of a bird’s wing are essentially grouped together and function more like the radius and ulna and less like fingers such as those of a bat. The diagram below highlights the differences.

 

© University of California Museum of Paleontology, Understanding Evolution, www.understandingevolution.org

Creative Commons License.

Marine mammals are another group that has incorporated the fingers in a unique way. If you see a diagram or x-ray of the bones of a cetacean (whales, porpoises and dolphins) flipper, you would immediately recognize it as hand-shaped. The same is true for pinnipeds (sea lions, seals and the walrus). When these animals began to return to the sea from life on land, the ratios of different bones in the fingers changed, with one finger, usually the first one, becoming much longer, but retained the general arrangement of a thumb and four fingers. Usually, the finger and toe bones are longer than the hand and arm bones, modifications that make for a larger flipper and make swimming more efficient.

With whales and other cetaceans and the sirenians (manatees and dugongs), there is a tail, usually called a fluke, but there are no hind legs. In a few of these species there is a vestigial hip bone, but in most species, there is none. Pinnipeds have retained fore and aft limbs with their respective fingers and toes.

For all marine mammals mentioned here, the fingers and toes (if they have them) are encased in tough materials that form a full web between the fingers/toes. Unlike fish, which have fins, these are referred to as flippers.

Fingers and toes. Whether it is hanging by two toes, adapting fingers for flight or using fingers and toes as flippers to dash through the seas, across the vertebrate world, these appendages or digits are critical for nearly every activity an animal does. I’m going to give mine a little more respect.

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Help Idaho Wildlife

When we traveled across the state in October 2017, most of the vehicles we saw using the wildlife management areas did not have wildlife plates. Buying wildlife plates is a great way for non-hunters and hunters alike to support wildlife-based recreation like birding.

C'mon folks, let's help Idaho's wildlife by proudly buying and displaying a wildlife license plate on each of our vehicles! 

See below for information on Idaho plates. Most states have wildlife plates so if you live outside Idaho, check with your state's wildlife department or vehicle licensing division for availability of state wildlife plates where you live. 

And tell them that you heard about it from Nature-track.com!

Wildlife License Plates

Idaho Wildlife license plates provide essential funding that benefits the great diversity of native plants and wildlife that are not hunted, fished or trapped—over 10,000 species or 98% of Idaho’s species diversity. Game species that share the same habitats (such as elk, deer, antelope, sage-grouse, salmon, trout) also benefit from these specialty plates.

No state tax dollars are provided for wildlife diversity, conservation education and recreation programs. Neither are any revenues from the sale of hunting or fishing licenses spent on nongame species. Instead, these species depend on direct donations, federal grants, fundraising initiatives—and the Idaho Wildlife license plates.

Both my vehicles have Bluebird Plates. I prefer the bluebird because the nongame program gets 70 percent of the money from bluebird plates, but only 60 percent of the money from elk and trout plates - 10 percent of the money from elk plates supports wildlife disease monitoring and testing programs (to benefit the livestock industry) and 10 percent from cutthroat plates supports non-motorized boat access.

Incidentally, in 2014, the Idaho Legislature denied the Department of Fish and Game the ability to add new plates or even to change the name of the elk and cutthroat plates (very specific) to wildlife and fish plates, a move that would have allowed for changing images occasionally and generating more revenue. It would seem that they believe that we Idahoans don't want a well funded wildlife program.

I think it is time we let the Legislature know that Idahoan support wildlife funding and that we would like to see these generic plates come to fruition.