Could an herbivore species become sentient? I noticed that most of your alien species eat primarily meat like Talita having hypercarnitivity and the avians eating mostly meat. Could it be biologically possible for a creature that doesn't primarily eat meat to evolve to be the most intelligent thing on their planet? Or do carnivorous animals have a greater likelihood to sort of 'gain sentience' because they would have higher intelligence to hunt and outsmart the prey and then evolve tools and therefore evolve to be the most intelligent creature of their world? Sorry I'm not the best with words or explaining things, I hope this make any sense at all.

I wouldn't say carnivory is highly correlated with intelligence as much as opportunistic omnivory. An extremely varied diet needs more brain power to stay on top of, since it requires adaptability and problem solving depending on what food is available where. Urban animals tend to be pretty good examples of that. However, in the diet of an opportunistic omnivore, meat and fat tend to rank pretty highly as they're a great source of calories. Foods dense in carbohydrates/sugar are high ranking too, for the same reasons. There's a reason humans love chicken nuggets so much, it's a meat pellet surrounded by carbs that you dip into fat sauce.

As for making a sapient herbivore, why not? Some of our closest primate relatives are primarily herbivorous. Browsing herbivores, frugivores, and nectarivores have to stay on top of seasonal availability of local flora, and that takes some brain management. Grazing herbivores have it easier when it comes to food acquisition but there's other reasons and animal could evolve sapience besides food being complicated. It's fiction, we get to play around.

What sort of cultural foods do the Runaway to the Stars aliens eat? Any particularly popular traditional foods or fast foods or industrial/packaged foods?

Centaurs, as I’ve mentioned, eat a lot of raw meat and live meats. A common snack food is a bag full of live invertebrates, maybe sprinkled with spices and salt. A lot of these delicacies are not available off their home planet, as most food in space and on non-terriformed planets is made with synthesizer machines, which can make pretty alright fake meat out of organic molecules, but cannot create life Frankenstein style. Another weird food stuff of centaurs… is meat soda….. they can’t taste sugar very well so a lot of their fun beverages are either basically weak vinegar, or meat broth. They also serve hot beverages with animal fats in them (so like a hot buttered rum, but with lard. They have no dairy equivalent).

Ferrets eat a lot of invertebrates (not so much bigger meats), chemosynthetic “plant” products, and they have a huge sweet tooth. It’s a fairly similar diet to ours, although they are more equipped to eat tons of sugar; the ferrets’ immediate ancestors were pollinator/predators. Typical snacks are sweets and bugs. Ferrets usually eat their bugs roasted, not live, because their guts are adapted to eat cooked and processed foods like us. Other methods of processing they use are smoking, canning, pickling, candying, and dehydrating. Most of the hard foods they create are intended to be rehydrated before consumption…. although they can chew, they have no lips to form a seal with and not a ton of saliva, so grinding down on jerky or sucking on hard candies is slobbery and inconvenient. They also have a ton of sugary alcoholic beverages, but can’t get drunk. Alcohol is just a fun spicy flavor to them.

Avians swallow chunks of food whole. Centaurs also tend to do this, but they at least have a few grinding teeth to savor a meal, avians just have a beak and an esophagus. Food is more of a tactile and visual presentation to them than anything else. Texture, temperature, and size of food pieces are very important to a meal, spices…. not so much. Almost never. Their diet consists of a lot of high calorie, fatty foods like meat, invertebrates, and seeds. They cook a fair amount of their meats, but eat a lot of them raw or just warmed as well. The meat is almost always dead on arrival to the table, as it needs to be cut into swallowable sizes. Some cultures will eat live bugs, but many find it distasteful to eat anything before it’s been killed.

…So sounds boring, right? Well… even though avians rarely add spices to their food, they commonly add psychoactive drugs! Avians have a huge blood filtering organ (sort of kidney, sort of liver) that refreshes the coboglobin in their blood cells about every 24 hours when the compound stops bonding to oxygen. This means that almost any drug they absorb to their blood stream will be cycled out into their urine in an hour or two. Compounds that are poisonous to other species in small doses are slathered onto avian foods for the entertainment of dinner guests. Snack foods also often contain fun “side effects,” even ones marketed to kids. Addiction is a huge problem in avian culture.

I'm having trouble envisioning the environment of Irune, considering that it's supposed to be an ammonia-based ecosystem on a super high-pressure, high-gravity greenhouse world. Would there be liquid water? Would the massive pressure difference mean that liquid ammonia could exist at those lower temperatures? Would liquid bodies be all ammonia, all water, or mixed? The only ammonia-based aliens I'm familiar with are the Avali, and their creators went with an iceball planet instead.

From what I've gathered, the whole sci-fi speculative biology appeal of ammonia is that its molecular structure makes it a pretty decent substitute for water as a liquid solvent in the body of an organism. Ammonia boils at -28ºF, which is pretty cold! So the Avali* living on an iceball planet makes sense if their planet has an atmospheric pressure like Earth's. On a more temperate planet like Irune, with an average surface temp of 48ºF (going from the wiki), the high atmospheric pressure raises the boiling point of ammonia to where it can still remain liquid at those comparatively much warmer temperatures.

So going from that, I feel like the ecology of Irune might mostly be based on liquid ammonia (mixed with other compounds and elements to varying degrees) existing and functioning in the same ways that water does for most organisms on Earth. Little volus kids color in pictures of “the ammonia cycle” in school and learn songs about it and stuff. There's likely liquid water on the planet's surface too, and maybe even water ice caps at the poles or something, but maybe it's considered a hazardous substance? At least, if you're a volus. There are all kinds of wacky organisms on Earth who thrive on what humans consider toxic chemicals, so the same is probably true on Irune.

But I'm not a molecular biologist or any other kind of -ologist, I just like drawing weird aliens! So this is all just my speculation.

*I've never heard of these guys, so I had to google them! They seem like a neat collaborative worldbuilding project.

Fantasy-biology-ish: how do you feel about the Xenomorphs of the Alien/s franchise? How would you tweak them, hypothetically?

Pre-pandemic, some friends were very patiently introducing me to pop culture movies that everybody should have seen, because I simply hadn’t. So I’d only seen the first Alien movie 3 or 4 years ago. It was quite well crafted and enjoyable, though there’s a lot of biology missing. There is probably also a lot of their biology that I haven’t seen so it’s hard to have a detailed comment.

But the most apparent thing to me is that this is a species which is not in the ecosystem to which is belongs. It has an egg stage, a transport stage, a parasitic larval stage, an ambulatory predatory stage. Other than that last part, they remind me a lot of tapeworms, actually.

And the thing about parasites is their form and function is developed in response to the species which they parasitise. Now there is a lot of leeway because the xenomorphs (a name which just means ‘alien shape’, I mean, how’s that for creativity) change a bit depending on what they’re parasitising or predating, but that basic lifecycle pattern is there.

So the first thing I would do is look at giving them the rest of their ecology. Needing a host for your larvae that paralyses, suffocates and kills them is great for a horror movie, but really inefficient in a biological system. A nest had, let’s say, 200 eggs in it. You need to find 200 seperate hosts for those face huggers? That’s difficult.

So instead imagine a different species, a very large herbivore or opportunistic omnivore. And I mean something the size of a small house which is coated in segments, and each of those segments has part of a respiratory system (think about how insects have multiple breathing holes along their body). The host comes across a nest of xenomorph eggs, or possibly seeks it out because hey, free protein, the vibrations from the presence of the massive organism cause the eggs to hatch, and the eggs/facehuggers that don’t get quickly eaten attach themselves to some of the various respiratory pores that the host creature had, anaesthetising the local tissue so that host doesn’t know, in that sneaky way a lot of parasites do. So you start with 200 eggs but maybe only 20 attach, and that’s plenty.

Now eventually the larvae, aka chest burster, is going to aggravate that host’s tissues enough to be a problem. But if the host is segmented, and it just walls it off, allowing access only to that segment and not the whole host, then the xenomorph can still develop without killing that host, and once it has developed and popped out it needs to leave very quickly to get out of the way of the massive creature. Then it sheds, has a predatory adult lifestyle, etc.

I would have other species in their ecology too, but adults predate different species to what their young and larvae need to grow, I. Order to spread their demands through the ecological web.

So mostly I feel like the xenomorphs are just kind of displaced. They’re doing their best, but they don’t belong where they are, and who’s fault is that?

Oh my goodness, they’re feral cats.

Can scuds go into freshwater? Since they live in saltwater I was wondering if the lack of salt in freshwater would hurt their gills or other parts of their body.

Freshwater skinnydips in the range of 10 minutes or so will not hurt a scud, but repeated or prolonged submersion will result in painful bloating of the gills and eventually death. Scuds, like most saltwater animals, simply cannot pee out freshwater as fast as it enters them.

Freshwater explorers usually wear salinity filters over their gills, which trap a layer of salt water against the gills while allowing regular respiration. Bigger and more expensive equipment will do this better and longer. A mouthpiece is sometimes worn for extra safety on long dives as freshwater can also enter the throat and cause similar bloating problems.

Tango and Swing are wearing simple salinity filters in this pic!

After reading the Orc biology post, I was wondering how significantly different in size or shape do noses or ears need to be, in a humanoid creature, to have noticeably better sense of smell or hearing?

It’s not just the shape of the ears or nose that will improve those senses, but also their position on the head, size, and the size of the relevant area of the brain dedicated to interpreting those senses. So you’re going to be really renovating the skull and brain cavity if you’re enhancing any senses.

Consider this basic model of the human brain and the relative areas where we process each input. We have vision at the very back, in the occipital lobe. Hearing, taste and touch (and movement) are in the middle on either side, and smell is at the very front, so little in a human we can barely see it.

Now, I wont show pictures of the real animal brains, just link them, but consider the following comparative anatomy.

The polar bear, which has a much better sense of smell, has additional prominences at the front (rostral) part of the brain to accommodate the extra nerves.

The rabbit has these same sort of prominences, and packed on a little extra lateral tissue, probably for hearing.

The bat requires excellent smell, hearing and fine movement in order to function.

And the elephant has just got so much going on, notice all that extra space for movement and touch, and think about what that trunk can do.

There’s a bunch of other species here if you want to look around. Remember that the depth of sulci and gyri on the surface of the brain is widely believed to be associated with intelligence because it increases the surface area of the brain. Comparative anatomy is fascinating.

So you need both the hardware and the software to enhance a sense in any given fantasy or sci-fi species. Sticking cat ears or a pig snout on someone wont grant them an enhanced sense alone, you need the brain tissue to go along with it.