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[Infinity Blade]

I'm not 100% sure I understand the question, but the thing about fish is that some animals we deem "fish" are more closely related to amniotes than they are to other so-called "fish" (a coelacanth is more closely related to you than it is to a marlin, for example). So not all fish are equally close to mammals & reptiles. Amphibians as traditionally defined ("cold-blooded, slimy/smooth-skinned thingy") aren't really a natural group either (especially if you include those extinct amphibian thingies that we amniotes are descended from), so it's kind of hard to answer for them too.

[theropod]

So here’s where the crown-group concept comes in usefully again; there is a crown-group of "amphibians", called Lissamphibia, which is a natural (monophyletic) group that includes all extant amphibians, and nothing that’s not an amphibian. So amphibians in the strict sense are closer to reptiles and mammals than to anything commonly called "fish", but they aren’t as closely related to reptiles as reptiles are to us, meaning Amphibians are equally close to reptiles as to mammals (in fact that goes for everything that’s called an amphibian, not just Lissamphibians).

However there’s a bunch of extinct groups usually called Amphibians, which aren’t all more closely related to crown-group amphibians than they are to other living groups. For example Reptiliomorpha (that is, Amniotes and their stem-lineage) includes a bunch of groups that had a more or less amphibious lifestyle, and are usually called "amphibians", but they are obviously more closely related to us than to Lissamphibia. There are also some taxa that are on the stem-lineage of Tetrapods, i.e. branched off before our most recent common ancestor with Lissamphibians.

So "Amphibians" in the traditional sense are a paraphyletic grouping, because they share a common ancestor that is included in this categorization, but they do not include all of its descendants (Amniotes are arbitrarily excluded; nobody would call you or me an "Amphibian", even though in order for that definition of Amphibians to be an objectively defineable group, we would have to be). This is similar to issues that exist with Reptilia; there are many traditionalists (who I tend to ignore) who insist that "reptile" should be used in a sense that specifically excludes birds (but none of them can produce a coherent argument as to why), but it really works perfectly well to simply repurpose the old term reptile in a monophyletic sense.

There is, however, also a relatively large monophyletic group called Batrachomorpha that includes Lissamphibia and their entire stem-lineage, and that could be referred to as Amphibians in a monophyletic sense.

As for fish, essentially the same situation. There are no monophyletic "fish", as any monophyletic group that includes everything commonly called "fish" would also have to include us. There are however several major crown-groups that all extant "fish" belong in. In order of relatedness to us: Cyclostomata (hagfish and lampreys), Chondrichthyes (sharks, rays and chimaeras), Actinopterygii (ray-finned fish, i.e. the vast majority of your run of the mill bony fish), Actinista (only one extant member, the coelacanth) and Dipnoi (lungfish, only three extant genera).
so each one of these is successively more closely related to you and me than to the groups of fish mentioned preceding it in the list.

I feel dumb for asking that now.

No, that’s not a dumb thing to ask at all, in fact I’ve had long arguments with people over that exact question.
But in the end I think "closer to extant reptiles than to mammals" is the definition we should all follow, and it’s easy to grasp, so I simply gave you that one rather than overcomplicating stuff the way I usually do.

[Exalt]

This is going to be another one that I'm going to have to come back to, as this gets complicated. That said:

1. I have no idea how to define reptiles in a way that excludes birds without causing other problems: reptiles are more likely to have teeth but I doubt that this is universally true (the first birds may have had them?), and thanks to non-avian dinosaurs, we can't say that reptiles have feathers or are exclusively cold-blooded.

2. Which fish lineage are amphibians believed to be descended from? I would think that it'd be the "run of the mill bony fish", but if it's not the most closely related...

[theropod]

Sept 14, 2023 4:14:11 GMT 5 Exalt said:

This is going to be another one that I'm going to have to come back to, as this gets complicated. That said:

1. I have no idea how to define reptiles in a way that excludes birds without causing other problems: reptiles are more likely to have teeth but I doubt that this is universally true (the first birds may have had them?), and thanks to non-avian dinosaurs, we can't say that reptiles have feathers or are exclusively cold-blooded.

2. Which fish lineage are amphibians believed to be descended from? I would think that it'd be the "run of the mill bony fish", but if it's not the most closely related...

Amphibians (and other land living vertebrates, together called Tetrapods) don't descend from ray-finned fish, no.
They are part of a group called sarcopterygians, the "lobe-finned fish" (yes, we are lobe-finned fish too), that includes coelacanths, lungfish, various extinct groups, and Tetrapods. The closest living relatives to tetrapods are lungfish, and the closest thing to early amphibians that is not itself commonly considered an amphibian (though that is purely subjective,and I might be wrong about it anyway) is Tiktaalik. Not a direct ancestor, probably, but very close to what the direct ancestors likely looked like.

[Exalt]

I actually thought that such an organism was being portrayed for a moment in the LOOP trailer.

But then it got eaten.

[Exalt]

Two more things:

Does this mean that Sarcopterygii is one of the most successful groups of all time? Since it has both significant length, and if you count it's descendants, profound diversity?

Also, where do the Placoderms fit in? I tried looking this one up on my own, but I'm not seeing it.

EDIT: I remembered some things while I was in the shower.

1. Yesterday, I was at the store, and there were very loud small children there. How did our ancestors avoid alerting other animals to their position every five minutes when they had them?

2. Have there been any updates on the Perucetus situation? I want to know if we think that there is a skull present, or not.

[Infinity Blade]

Sept 14, 2023 5:08:03 GMT 5 Exalt said:

Two more things:

Does this mean that Sarcopterygii is one of the most successful groups of all time? Since it has both significant length, and if you count it's descendants, profound diversity?

Also, where do the Placoderms fit in? I tried looking this one up on my own, but I'm not seeing it.

EDIT: I remembered some things while I was in the shower.

1. Yesterday, I was at the store, and there were very loud small children there. How did our ancestors avoid alerting other animals to their position every five minutes when they had them?

2. Have there been any updates on the Perucetus situation? I want to know if we think that there is a skull present, or not.

Well, there's no question that Sarcopterygii is massively successful. Not sure if we could say they're necessarily more successful than other groups of animals, though. Ray-finned fishes have been around for just as long, and while they don't have any terrestrial forms, they certainly are extremely successful underwater. Arthropods have been around for longer than either, and they're unquestionably extremely diverse too. Placoderms are just another group of jawed vertebrates.

As for your shower questions:

1. It could just be that there was a lot more pressure on our ancestors (especially Homo) to hush their kids up, and for said kids to be quiet, when they know there's a whole slew of predators out to get them (or angry herbivores that might want to squash them). Even in a relatively safe public place like a store parents are likely to tell their kids to be quiet, let alone when they're in the wild. Although, it's also possible that other animals don't want to mess with a band of Homo armed with spears and stones, so maybe it wasn't quite that big of a deal?

2. Nope, we still don't have a confirmed skull. I somehow doubt they're going to find one anytime soon either, unless maybe they still have people over where the original fossils were found, extensively searching for more.

[Exalt]

The placoderm thing was more about where they fit in the family tree, sorry.

And yeah, I had a hunch that you'd say that in regards to Perucetus, although it is odd that a skull would be the missing piece. Then again, this is an animal with monster vertebra that we've only recently found...

[theropod]

In terms of where placoderms fit in the family tree:


They aren’t a natural group, but a paraphyletic grade consisting of several different groups of stem-lineage gnathostomes, which branched off after the evolution of jaws, but before the last common ancestor of all extant jawed vertebrates (i.e. crown-group gnathostomes, Eugnathostomata).
Placoderms really aren’t any more of a natural group than "Ostracoderms" or "Agnathans" are.

Regarding Perucetus, no new material so far, and I wouldn’t expect any for a while yet, even if it had been found (had they already known about anything, I should hope they would have included or at least mentioned it in the paper, and if anything has been found since then, it might take years to excavate, prepare and study.
However, someone on Twitter ran an interesting phylogenetic analysis. The results need to be taken with a big grain of salt, but they do suggest that Perucetus being a stem-cetacean isn’t a certainty, and it might be a stem-Mysticete instead (closely allied to such forms as Llanocetus, which, curiously, is very large, would be the third-earliest known Mysticete in this scenario, and is only known from skull remains).

[Exalt]

Which phorusrhacids would Barinasuchus have lived at the same time as? I know the geography would be disputable, but what prompted this was a paleoart piece that I just saw.

Edit: this is why I hate phones

[Exalt]

Is there a good resource for finding the meanings of some binomial names? They are by no means all readily available, even for extant mammals.

[creature386]

I'm not sure there is an encyclopedia specifically for this (Wikipedia sometimes provides them, though not always), but what sometimes helps is to dig up the taxon's original description (if available). It will frequently contain a section on its entymology.

[Exalt]

Thanks.

I almost just made this a thread, but I'd like to ask a bit about snake biology. As weird as this sounds, I mean the weak points: the animals in question appear to be 90% spine and ribs, so I was wondering what the actual vulnerable points are. Additionally, what do the methods of snake-hunting animals entail?

[creature386]

Sept 15, 2023 5:54:19 GMT 5 Exalt said:

As weird as this sounds, I mean the weak points: the animals in question appear to be 90% spine and ribs, so I was wondering what the actual vulnerable points are. Additionally, what do the methods of snake-hunting animals entail?

I don't know much about what animals do, but some humans who deal with snakes recommend grabbing them closely behind the head. It's especially useful in venomous species, who can't bite back under such circumstances.

[Exalt]

Thanks, but let me stress that I don't plan to demonstrate what I learn here.

Also, I was thinking about a time I heard about when a certain paleontologist argued that Triceratops horns were not weapons because why would you have weapons on your head? Needless to say, people made fun of this line of reasoning.

That said...why might some weapons be found on the head?