Why Are Rain Frogs So Round? What's /inside/ Of Them Around Such An Itty Bitty Skeleton?

Why are rain frogs so round? What's /inside/ of them around such an itty bitty skeleton?

So it turns out this is a really interesting question.

The first thing we must be aware of is that rainfrogs as we see them in videos of them squeaking are not quite the same shape as they are when at rest:

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But you are quite right, they are very round. This is exemplified by the skeletal photo you refer to:

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So what are we seeing?

Well, firstly, note that the body cavity in these frogs actually envelops the femurs, such that only the tibiofibula (fused in frogs) and the tarsals and metatarsals are outside the body. The arms are quite similarly enveloped, but a bit of the humerus does extend outside the body cavity too. This predisposes them to a rounder body shape.

Next, note the ilia - the U-shaped bone in the pelvic region. These in some breviceptid frogs are synostotically fused with the sacrum - that is to say, they are bound by bone-based connections to the bow-shaped vertebra at their tips. This whole joint seems to be quite smooth, and as a consequence, the back of the frog is quite smooth. The other thing we can see here is that the urostyle (i.e. the frog version of a coccyx) juts quite far beyond the ischium and pubis. This extends the body cavity beyond the hips. Note also that the pelvic girdle seems to be largely below the spine, rather than the typical position for frogs behind it and continuous with it. This makes the legs sit below the spine, rather than at its end, enhnacing the vertical roundness of the animal.

Next, let’s talk some soft tissue. Now, I’m not as familiar with soft-tissue in frogs as I am their skeletons, so you’ll have to bear with me a bit (rawr). Beddard (1908!!) studied the soft tissue of Breviceps verrucosus Rapp 1842. It seems that the majority of the body of these frogs is actually muscle. Beddard noted that muscles join the leg at the knee that extend into the body cavity, such that the inclusion of the thigh in the body cavity is further accentuated by musculature. The rectus abdominalis muscle is unusually large, extending from the lower abdomen up and around the sides of the body. Indeed, this large size appears to be the pattern with all of the major muscles, though in the throat the typical arrangement of large and small muscles is somewhat reversed. On the lateral side of the head, there is a substance that is not muscle, but appears to be loose tissue in which sits what is apparently the thymus gland.

There is a very large gap between the end of the urostyle and the anus (one fifth of the total length of the frog), in which there are almost no muscles, save for the one surrounding the lower cloaca. On either side of this area, between the posterior-most muscles of the thigh, lie two large ‘lymph-hearts’, as described by Beddard. These are between one quarter and one third of the total length of the frog. A further lypmh-sac sits between these lymph-hearts and the skin of the femoral region, and they are thus probably analogous to the femoral lymph-sacs of other frogs.

I find it interesting that Beddard (1908) did not mention any glandular formations in the dorsal region. As is evidence from many images (see below), these frogs are able to secrete a white, sticky, noxious substance from their skin (which they actually have to use during amplexus, as the male is too small relative to the female to mount her properly, and so he sticks himself to her with his glandular glue… kinky).

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These glands do not apparently take up a great deal of the cutaneous tissue, and so I suppose are of no consequence to the size of the frog, especially relative to its enormous muscles.

The diet of these frogs consists almost exclusively of hymenopterans and isopterans (ants and termites). Neither of these insect groups are particularly fatty, so it is little surprise that their bodies appear to contain no large fat deposits - fatty bodies extend from the gonads up to the lungs and heart, but these comprise only a tiny fraction of the frog’s mass, and don’t contribute to the round shape. Instead, their bodies are extremely muscular, allowing them to be adept burrowers, ideal for their fossorial lifestyle.

So TL;DR: rain frogs are little balls of muscle (maybe the largest muscle mass relative to body mass of any vertebrate? science just doesn’t know).

Why Are Rain Frogs So Round? What's /inside/ Of Them Around Such An Itty Bitty Skeleton?

Ref:

Beddard, F.E. 1908. On the Musculature and other Points in the Anatomy of the Engystomatid Frog, Breviceps verrucosus. Proceedings of the Zoological Society of London, 1908:11-41 [x]

Alligator Body Language and You, or: How To Know When An Alligator On Social Media is Being Stressed for Views

Alligators are wild animals. Despite the idiotic claims of animal abusers like Jay Brewer, they cannot be domesticated, which means they are always going to react on the same natural instincts they've had for millions of years. Habituated, yes. Tamed, yes. Trained, definitely. Crocodilians can form bonds with people- they're social and quite intelligent. They can solve problems, use tools, and they're actually quite playful. Alligators are also really good at communicating how they're feeling, but to somebody who doesn't spend much time around them, their body language can be a bit mystifying. And it doesn't help when social media influencers are saying shit like this:

That is not what a happy gator looks like.

That's a terrified, furious gator who isn't attacking because the ogre handling her has her in a chokehold. She's doing everything she can to express her displeasure, and he's lying about it because he knows his audience doesn't even know how to think critically about what he's doing. He knows that because his audience doesn't know anything about these animals, he can get away with it. This I think is why I hate him so much- he deliberately miseducates his audience. He knows what he's doing is factually inaccurate, he just doesn't care because attention means more to him than anything else in the world.

Let's change that! Here are two really important lessons for understanding alligator body language on social media.

Lesson 1: Alligators Don't Smile (in fact, most animals don't)

So what's going on in this video? Jay Brewer is aggressively choking his white alligator Coconut while scrubbing algae off of her with a toothbrush. And make no mistake, he is digging into the creature's throat while she is visibly distressed. He claims she's happy- but she's not. He is willfully misrepresenting what this animal is feeling. That's a problem, because people... well, we actually kind of suck at reading other species' body language. The reason for this is that we tend to overlay our own responses on their physical cues, and that's a problem. For example, let's look at an animal with a really similar face to ours, the chimpanzee. Check out Ama's toothy grin!

Wait, no. That's not a happy smile. That's a threat display. When a chimpanzee "smiles," it's either terrified and doing a fear grimace, or it's showing you its teeth because it intends on using them in your face.

How about a dog? Look at my smiling, happy puppy!

Oh wait no, this is a picture of Ryder when he was super overwhelmed by noise and people during a holiday party. He'd hopped up in my sister's lap to get away from stuff that was happening on the floor and was panting quite heavily. See the tension in the corners of his mouth and his eyes? A lot of the time when a dog "smiles," the smile isn't happy. It's stress! Why Animals Do The Thing has a nice writeup about that, but the point is, our body language is not the same as other species. And for reptiles, body language is wildly different.

For instance, look at these two alligators. Pretty cute, right? Look at 'em, they're posing for a Christmas card or something! How do you think they're feeling?

Well, I'll tell you how the normal one is feeling. He's annoyed! Why is he annoyed? Because the albino just rolled up, pushed another gator off the platform, and is trying to push this guy, too. I know this because I actually saw it happen. It was pretty funny, not gonna lie. He's not gaping all the way, but he was hissing- you can actually see him getting annoyed in the sequence I took right before this shot. Look at him in this first shot here- he's just relaxing, and you can see he isn't gaping even a little bit.

By the end, he's expressing displeasure, but not enough to actually do anything about it. He's annoyed, but he's comfy and that's where one of the best basking areas is, so he'll put up with it.

Reptiles open their mouths wide for a lot of reasons, but never because they are actively enjoying a sensation. Unless they're eating. No reptile smiles- they can't. They don't even have moveable lips. If a reptile is gaping, it's doing so because:

It is doing a threat display.

It is making certain vocalizations, all of which are threats. Alligators are one of the rare reptiles that do regularly vocalize, but most of their calls aren't made with a wide open mouth.

It is about to bite something delicious or somebody stupid. Check out this video- virtually all of the gaping here is anticipatory because these trained gators know darn well that the bowl is full of delicious snacks. (I have some issues with Florida's Wildest, but the man knows how to train a gator AND he is honest about explaining what they're doing and why, and all of his animals are healthy and well-cared for, and he doesn't put the public or his staff at risk- just himself.)

It's too hot and it has opened its mouth to vent some of that heat and thermoregulate. This is the main reason why alligators will often have their mouths part of the way open, but sometimes they'll open all the way for thermoregulation. This is what a thermoregulatory gape looks like- usually it's not all the way open, kinda more like < rather than V, but you can't say that 100% of the time. Additionally, a thermoregulatory gape... typically happens when it's hot out. If they're inside, maybe they've been under their basking light for too long. Heat's the dominant factor, is what I'm getting at.

There is another reason that a captive crocodilian might be gaping, and that's because it's doing so on command. Some places have their gators trained to gape on cue, like St. Augustine Alligator Farm and other good zoos. They have the animals do this in presentations that are genuinely educational. They ask the animals to open their mouths so that they can show off their teeth and demonstrate how their tongues seal off the back of their mouth. They'll also do it as part of routine healthcare, because looking at their teeth is important.

In this case, the animals aren't gaping because they're stressed, they're gaping because they know they're gonna get a piece of chicken or fish if they do it. And what's more, they're doing it on cue. They have a specific command or signal that tells them to open wide. It's not an instinctive response to a situation. It's trained. If the animal provides the behavior after a cue, the situation is much less likely to be negatively impactful.

It's also important to remember that there's a difference between a partially open mouth and a gape! As discussed above, alligators will often have their mouths a little bit open just to maintain temperature homeostasis. It helps them stay comfy, temperature-wise. These guys are all doing thermoregulatory open-mouthed behavior- that slight open and relaxed body posture is a dead giveaway. (That and it's the hottest spot in the enclosure.)

Lesson 2: A Happy Gator Is A Chill Gator

So if alligators don't smile or have facial expressions other than the :V that typically signifies distress, how else can you tell how they're feeling? One way is stillness. See, alligators subscribe to the philosophy of if it sucks... hit da bricks.

Basically, if they hate it, they'll leave. Unless, y'know, somebody has their meaty claws digging into their throat or is otherwise restraining them. (Restraint isn't always bad, btw. Sometimes the animal is going through a medical thing or needs to be restrained for their safety- which a responsible educator will explain.)

Let's look at a very similar scenario, in which a captive alligator is getting his back scrubbed.

YouTube

Natures would you scrub an alligators back?

As you can see, it's quite different. First, he's not being restrained at all. Second, look at how relaxed he is! He's just chilling there vibing! He could simply get up and leave if he wanted to, because he's not being held. Towards the end of the video, as he lifts his head, you can see that his respiratory rate is very even as his throat flutters a bit. I'm not sure what this facility is, so I can't comment on care/general ethics, but like. In this specific case, this is an alligator enjoying being scrubbed! And you can tell because he's not doing anything. A happy gator is content to be doing what they're doing.

Why Should I Listen To You?

Now, you should ask yourself, why should you listen to me? Why should you trust me, who does not own an alligator, versus Jay Brewer, who owns several?

Well, first off, there's no profit for me in telling you that what you're seeing on social media is in fact not what you're being told you're seeing. I'm not getting paid to do this. That's the thing with people who make social media content. The big names aren't doing it just for fun. They're doing it for money. Whether that's profit through partnerships or sponsorships, or getting more people to visit their facilities, or ad revenue, you can't ignore the factor of money. And this is NOT a bad thing, because it allows educators to do what they're passionate about! People deserve to be paid for the work that they do!

But the problem starts when you chase the algorithm instead of actually educating. A "smiling" alligator gets the views, and if people don't know enough to know better, it keeps getting the views. People love unconventional animal stories and they want those animals to be happy- but the inability to even know where to start with critically evaluating these posts really hinders the ability to spread real information. Like, this post will probably get a couple hundred notes, but that video of Coconut being scrubbed had almost 400,000 likes when I took that screenshot. Think about how many eyeballs that's reached by now. What I'm saying here is that it's just... really important to think critically about who you're getting your information from. What do dissenters say in the comments? What do other professionals say? You won't find a single herpetologist that has anything good to say about Prehistoric Pets, I can tell you that right now.

Another reason you can trust me is that my sources are not "just trust me bro," or "years of experience pretending my pet shop where animals come to die is a real zoo." Instead, here are my primary sources for my information on alligator behavior:

Dragon Songs: Love and Adventure among Crocodiles, Alligators, and Other Dinosaur Relations- Vladimir Dinets

The Secret Social Lives of Reptiles- J. Sean Doody, Vladimir Dinets, Gordon M. Burghardt

Social Behavior Deficiencies in Captive American Alligators (Alligator mississippiensis)- Z Walsh, H Olson, M Clendening, A Rycyk

Social Displays of the American Alligator (Alligator mississippiensis)- Kent Vliet

Social Signals and Behaviors of Adult Alligators and Crocodiles- Leslie Garrick, Jeffery Lang

Never smile at a crocodile: Gaping behaviour in the Nile crocodile at Ndumo Game Reserve, South Africa- Cormac Price, Mohamed Ezat, Céline Hanzen, Colleen Downs (this one's Nile crocs, not American alligators, but it's really useful for modeling an understanding of gape behaviors and proximity)

Thermoregulatory Behavior of Captive American Alligators (Alligator mississippiensis)- Cheryl S. Asa, Gary D. London, Ronald R. Goellner, Norman Haskell, Glenn Roberts, Crispen Wilson

Unprovoked Mouth Gaping Behavior in Extant Crocodylia- Noah J. Carl, Heather A. Stewart, Jenny S. Paul

Thank you for reading! Here's a very happy wild alligator from Sanibel for your trouble.