Frogs are among the most primitive land vertebrates. Along with salamanders they have changed very little from that first fish like ancestor that crawled out of the water millions of years ago. Frogs, and all amphibians rely on water to reproduce. The must have some sort of water to lay their fish-like eggs. This water could be a pond, a lake or even a little water left in the cup of a tree. Frogs have adapted to all sorts of habitats and have exploited nearly every possible freshwater habitat.
When frogs make the metamorphosis from tadpole to frog they become froglets. They look like adult frog but still have a tiny little tadpole tail. Mammals like, humans, can think of this as the little bit of umbilical cord that is left over to make our belly button. These froglets soon lose that little tail and are then miniature versions of the adults. I found this Gray Tree Frog (sp? see previous post) in my front yard. It was only about the size of my thumb nail.
Here is a Leopard Frog. These frogs spend most of their time on the margins of marshes and wet prairies. The get their name from the spotted pattern on their back, even though not all leopard frogs will have these spots. Frogs eyes are not just for looking. When frogs swallow their food they use their eyes to push the food into their stomach. If you have ever watched a frog eat something they will always push their eyes into their head, this action mechanically forces the food into the stomach. Pretty sweet!!
As I discussed in a previous post frogs also have a very simple ear. If you look at this Green Frog you can see the large round structure right behind the eye, this is the tympanum. This simple ear works like a reverse drum. The tympanum will move very slightly as sound waves hit it. This slight mechanical movement is translated into and electric signal and is perceived as sound by the frog. Human ears work is a similar manner (think ear drums). This tympanum is tuned to the specific frequency of that species’ mating call. This is how the female frogs are able to pick out that one special male in a pond of thousands.
Frogs may be primitive as far as land vertebrates go but I think they are incredible survivors. Amphibians have changed very little in millions of years, humans have been around for just about one million years, I ‘m sure the ancient chorus of amphibians will resonate through the ponds and lakes of earth long after humans are gone.
Up Next: Adventures in Costa Rica (you can expect some more frogs!)