Do Frogs Have Teeth?

Once again, I’m without a context for a question I’m working on. I know my son asked me this question: “Do frogs have teeth?” I know it because it’s on my list of questions to answer, right between “How small is a leprechaun? Are mice their friends?” and “Who trained Yoda?”

As you may have noticed, my son has a wide range of eclectic questions.

So, do frogs have teeth? My gut feeling was… maybe? I’m pretty sure I’ve seen pictures of a frog or two with a couple of small teeth that are used to keep insects from escaping. But I haven’t really got a solid idea about that.

Interestingly enough, the answer turns out to be an unqualified “yes”. In Frogs: The Animal Answer Guide, we read:

“Most frogs have small teeth, primarily maxillary (upper jaw) and vomerine (in the roof of the mouth) teeth. Only one species of frog, Guenther’s marsupial frog (Gastrotheca guentheri) of Ecuador and Colombia, has teeth in the lower jaw. Species in the large family of toads, the Bufonidae, lack teeth. Frog teeth are small, mostly cone shpaed, and are used to grasp theirprey. Frogs do not chew their food but instead swallow prey whole. They use their tongue, forelimbs, and even their eyes (by pushing them backward) to force captured prey backward into the mouth and down the throat. Toothless toads are evidence that teeth play a minor role in eating and are unnecessary. In general, frogs with teeth do not bite for defense but only for handling prey.

The African bullfrog (Pyxicephalus adspersus; family Ranidae) has what appear to be large fang-like teeth: two large, bony spines on each side of the lower jaw separated by a smaller spine. These project upward from the lower jaw; and although they are odontoids, not true teeth but formed from bone, they function i the same manner. Although their teeth are not as large as those found in the African bullfrog, lower jaw odontoids can be found in the Sumaco horned treefrog (Hemiphractus proboscideus; family Hemiphractidae) of South America, in the Solomon Island leaf frog (Ceratobatrachus guentheri; family Ranidae), and in the tusked frog (Adelotus brevis; family Myobatrachidae) of Australia.

Most aquatic tadpoles have teeth-like horny plates in rows across the mouth in both the upper and lower jaws. The teeth are made of keratin and are often shaped for effectively scraping algae from rocks or other surfaces.

marsupial frog
Guenther’s Marsupial Frog

So, it seems clear that frogs do have teeth. But they didn’t always have them – or, at least, not the lower jaw teeth. Writing in Re-Evolution of Lost Mandibular Teeth in Frogs After More Than 200 Million Years, and Re-Evaluating Dollo’s Law (published in Evolution – Dr. John Wiens writes that “mandibular teeth were lost in the ancestor of modern frogs at least 230 million years ago (Mya) and have been regained in the last ∼5–17 My”. The rest of the article is an explanation of the molecular data, how it was obtained, and how it was interpreted.

So, cool.  Right?  But what’s this “Dollo’s Law” thing?  Well, Dollo’s Law (aka Dollo’s Law of Irreversibility) states that “An organism is unable to return, even partially, to a previous stage already realized in the ranks of its ancestors.” This is a “law” in the scientific sense, simply meaning that it is the description of an observed phenomenon with no attempt to explain the phenomena.

That’s something important to keep in mind, by the way: scientific laws can be violated, without invalidating the science. Because all that violation does is demonstrate that there are exceptions to the observed phenomena. Dollo’s Law states that an organism won’t re-evolve something, once that something has been lost. Frogs lost mandibular teeth. Gastrotheca guentheri re-evolved them. And the scientific response was not “Oh noes, evolutionary theory is overturned!” It was “We did not see that coming! Neat!”