The Wonderful World of Frogs

     It was hard deciding on my second post topic… I have too many topics I want to share with you, and definitely not enough time to do them! All in good time though. As a warning, you may be getting an inordinate amount of information on reptiles and amphibians because I’m (finally!) taking Herpetology this semester! And no, non-science friends, herpetology has nothing to do with herpes. So let me give you a crash course on what it is and what it means.

     Modern herpetology includes the study of reptiles and amphibians. The Greek word herpeton literally translates to “crawling thing”. So herpetology translates to the study of crawling things…. anti-climactic, I know. But in the young, golden age of discovery and biology there was a very simplistic grouping of vertebrates: birds fly, fish swim, mammals are fuzzy, and everything else is a nasty, slimy, despicable creepy-crawly (seriously, read some of the things Linnaeus had to say about amphibians. Boy was he rude. And wrong.) This means amphibians and reptiles were incorrectly grouped together.

Yup. Incorrectly. The closest relatives that reptiles and amphibians share are tetrapods – which are simply the first group of animals to develop 4 legs to walk on land. It just so happens that tetrapods also gave rise to mammals and birds…. both of which are more closely related to reptiles than any of them are to amphibians. And that’s as far into the fossil record I’ll go. Let’s get into the exciting stuff!

     Most of you who have known me for any great amount of time will recall that my first love – of any wild, living thing – was frogs. I don’t recall any precise moment of realization, or specific capture that instilled this fascination. It was just always there, waiting to be fed information so it could grow. And grow it has. I have always known this group of creatures was awesome. I read everything I could about them growing up, watched every nature show, and captured countless frogs of different species and varieties. But formal education has taught me things that I never came across in independent studies.

Guys, frogs can HEAR THROUGH THEIR LEGS. And make COCOONS. And brood eggs INSIDE THEIR THROATS. I’ll be damned if those aren’t the three coolest things you’ve heard all day.

     Haven’t you always wondered why frogs know exactly when to stop croaking when you walk by so you don’t find them? I’ve always wondered that. Because I’ve always been frustrated by it. Part of the reason is because they can feel-hear you (just invented a term. yay!). Next time you see or catch a frog, notice that their front legs are strikingly close to their tympanum – that round disc behind the eye, which acts sort of like an external eardrum. A frog’s (and salamanders!) front legs and inner ear are actually sort of connected through muscle and middle ear structures, and they have a special inner ear sensory area called the papilla amphibiorum which receives low-frequency sounds that travel up from the ground through the forelimbs. They feel-hear you!! I can feel-hear your amazement.

     So the cocoon thing. This was stunning. Like, I made an audible gasp of amazement in class, stunning. Frogs have thin, permeable skin, which means water and salts and things can easily pass in and out of their bodies. This makes it easy for them to breathe through their skin and make the most of moist environments. But if you’ve been paying any attention to the world, you’ve probably noticed that not all amphibians live in moist environments. There are frogs living in deserts around the world, so how do they not dry up into little froggy crisps?? Well first off, they don’t come out during the heat of the day. Most desert animals don’t come out during the heat of the day basically because it sucks. But especially amphibians, because their skin needs to stay moist for them to survive. During dry periods in these areas (which is most of the time…) frogs will burrow underground, where soil stays fairly moist. This was not new information for me and probably not for you either. What I didn’t know was that before burrowing, some frogs are already hard at work creating a cocoon.
     To understand how a frog makes a cocoon, you need to know that amphibians shed their very top layer of skin, sort of how reptiles do too. I think most people don’t know this because it isn’t quite as dramatic an effect, as it is with reptiles. Frogs and other amphibians eat their skin as it’s peeling off their bodies, or immediately after, and the skin is so thin that this event is hardly noticeable – and the frog just looks like it’s gulping a lot. Anyways, this is a regular occurrence to keep their skin nice and permeable. But frogs that are getting ready to retreat underground will halt this shedding process, and let their skin build up many layers, to be nice and thick. When the frog goes underground, he will sometimes have up to 40 layers of skin built up. These layers keep water from evaporating out of his body because of heat! Extra skin secretions keep these layers sticking together and sort of seal him in his cocoon for the dry season. Water retention is of the utmost importance in desert environments, and frogs have taken these extreme measures to retain every drop. When rains come, frogs will wiggle and bust out of their cocoons, and continue with their lives til they next have to retreat underground again.

     Ok for this last one I’ll admit that I did know about frogs that brood their eggs in their throats. I just wanted a nice group of weird facts to throw at you in the beginning! Brooding is taking care of developing eggs, and frogs do this in so many different ways! But throat brooding is funny, because of its end result. Darwin’s frogs (Rhinoderma darwinii) in South America will initially breed like normal frogs. But after the eggs are laid, the male will engulf the eggs! He isn’t eating them, but rather gently storing them in his vocal sac. Think of a frog croaking, and that large bubble on his throat that extends when he takes in air; that stretchy sac is where he is putting the eggs to develop. What safer place than in the mouth of your parent? Unless the frog is eaten, very little can happen to the eggs. The eggs develop, hatch, and metamorphose in his throat, AND THEN DAD BURPS THEM UP INTO THE WORLD:

I really hope you learned something.

Til next time, friends!


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