Suction Cups, Fangs, and a Grab-Bag of Digestive Parts in an Inefficient Package.

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Okay. Welcome to ‘why this weird thing is my favorite animal’ masterpost.

This is a Rock Hyrax.

Looks like a cute rodent, right? NOPE. They’re in their own Order with three other species of hyrax, and the closest non-extinct relatives they have after that are… *drumroll* … elephants and manatees. I’ll just leave you with that for a second. Back in the Eocene, there were proto-hyrax of all sizes. Bovids out-competed most of the them, but apparently some stayed tiny and others turned into sirenians and elephants. You can tell they’re related through a few similarly weird similar characteristics – they all have tusky incisors (yes, even that cute bub has them), no scrotum, and toenails instead of claws.

Rock Hyrax are one of the only terrestrial species to basically have suction cups on their bodies. Because they run around on top of rocks all the time, having things to help you grip better is kind of an important adaptation. So they’ve got this weird musculature in the bottoms of their paw pads that retracts the tissue after the paw has been placed, effectively creating a tiny little vacuum chamber. Their one of the only animals that actually sweats on their paws, because it helps keep them moist and make a better seal against the rocks.

Now we get to the fun part. Digestion! In case you don’t know how basic herbivore digestion works, here’s the breakdown. Ruminants have multi-chambered stomachs, where they pass food back and forth to digest it. Hindgut fermenters have pouches in their large intestine where they let bacteria chew on the food for them. Hyrax… do something that can only have made the first dude to dissect them very confused.

That is the digestive system of the hyrax, pulled from a studbook for them. I’ll break it down for you.

The stomach of a hyrax does very little actual digestion. It has two sections, one (1) that is unlined and is for storage – it’s basically anaglogus to the crop of a bird, which, wtf, does not belong in a mammal – and a lined bit that sorta kinda digests something, sorta (2). (3) is the small intestine, which is the only part of this that functions how you’d expect. The hindgut is where things get wonky. (4) is the caecum, which is normally where most hindgut fermenters have the digestion happen. It’s a big sac where digesta sits and buggies nom on it. For hyrax, it does some but not all of it – it circulates the digest around a bunch while it’s in there, for the most surface area of food getting chewed up by buggies. Next, you have two isolated segments of the large intestine (labeled as the connecting colon here) – one with a narrow diameter and thick, bulky walls (5) and one with a wide diameter and super thin walls (6) that is highly specialized in absorbing fatty acids, which are hopefully what some of the food has been broken down into by now. Then you hit the colon, which normally just absorbs a lot of water to produce compact stool, but in hyrax it actually allows for more fermentation. So of course you’ve got to have (7) which is a sac with more weird blind ends to let digesta sit in – unlike in the ceacum, the digesta moves very slowly around in here and doesn’t circulate. Then (8), the distal end of the colon, absorbs most of the newly processed nutrients and it passes through  (9) and (10) on the way to the anus.

That was a lot of boring digestion, so have a cute photo of a hyrax. Yes, they do really have tusks, and that’s going to be important shortly.

Okay, so what does that actually all mean. It sounds like it takes forever!

Whelp, it does. About six days for food that goes in one end to come out as poop on the other. It’s incredibly inefficient, partially because of how they digest things, and partially because the forage they survive on is really tough and low in nutrients and has to be very thoroughly broken down for every last bit. That means they have a very low metabolic rate… which means they don’t produce a ton of heat.. which means they’re absolutely useless at thermoregulation and have to sun themselves or hide in the shade to control their internal temperature. What’s a hallmark of most mammals? warm-blood. Efficient thermoregulation. Not needing to behave like a bloody snake to get it right, yeesh. It does mean they often sleep in piles, though, which is cute.

Okay, look back up at those tusks. Do they look efficient for eating grass? Nope! Because nothing about these guys make sense, they never evolved front teeth for clipping grass like most grazing animals so they bite food off with their molars. They’re also born without the bacteria in their stomach they need to do all the boring, complicated digestion above, so the babies have to immediately eat poop in order to acquire it.

I just felt like showing you that photo. Um, what else about these guys is weird? They’re not kosher in the Old Testment, for one. They also have incredibly complex communication: they use trills, yips, grunts, wails, snorts, twitters, shrieks, growls, and whistles and the males sing very complex songs during mating with very distinctive syntax, combining the 21 different sounds they can make into syllables of wails, chucks, snorts, squeaks, and tweets.

So yeah. Weird, tusky, song-singing inefficient hindgut fermenters who also happen to have a crop who can’t stay warm, grow up to 2ft in length and run around in giant colonies on sheer rock faces. Rock Hyraxes!