Is a shark a fish?

[Mikeisskeptical]

Settling a bet here. Am I or am I not more closely related to my pet goldfish than he is to a shark? (My guess is shark is the outgroup, but I'm not a biologist)

[DCnDC]

Yes.

From here,

A fish is any member of a paraphyletic group of organisms that consist of all gill-bearing aquatic craniate animals that lack limbs with digits.

From here,

Sharks are a group of fishes characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head.

[Blake]

Originally Posted by Mikeisskeptical

Is a shark a fish?

Yes, a shark is a fish.

Am I or am I not more closely related to my pet goldfish than he is to a shark?

Your goldfish is much more related to you than either of you are to a shark.

[VOW]

A shark is definitely lower on the evolutionary scale than either you or your goldfish.

It's been a LONG, LONG time since I had my comparative anatomy class, but the IIRC, the shark jawbone is comparable, anatomically, to the tiny bones in the mammalian ear.

Or something like that.


~VOW

[Colibri]

"Fish" is really a meaningless term with respect to taxonomic classification. It's really just a popular term for any gill-breathing aquatic vertebrate (not including larval amphibians). Originally it included most aquatic animals, including whales, sea turtles, etc.

"Fish" as used today includes members of four traditional classes, the Agnatha (jawless fish), Placoderms (extinct armored fish), Chondrichthyes (cartilaginous fish), and Osteoichthyes (bony fish). However, some of these groups themselves turn out to be polyphyletic (made up of organisms that are not one another's closest relatives), so the actual taxonomy is more complex.

[Lukeinva]

Originally Posted by Blake

Yes, a shark is a fish.



Your goldfish is much more related to you than either of you are to a shark.

Say whaaaaaat?

[Tamerlane]

Originally Posted by Blake

Your goldfish is much more related to you than either of you are to a shark.

Originally Posted by Colibri

"Fish" as used today includes members of four traditional classes, the Agnatha (jawless fish), Placoderms (extinct armored fish), Chondrichthyes (cartilaginous fish), and Osteoichthyes (bony fish).

Originally Posted by Lukeinva

Say whaaaaaat?

Just to tie the first two posts together, sharks are members of the Chondrichthyes, while humans and goldfish are both in the Osteichthyes. Might be odd to think of humans as "bony fish", but if you accept traditional Linnaean hiearchy that's how it works out .

[robert_columbia]

Originally Posted by Tamerlane

Just to tie the first two posts together, sharks are members of the Chondrichthyes, while humans and goldfish are both in the Osteichthyes. Might be odd to think of humans as "bony fish", but if you accept traditional Linnaean hiearchy that's how it works out .

I was always taught as a child that while sharks were really and truly-o fish (as opposed to whales which are mammals), they do not have bones, unlike other fish. They do have a skeleton, which is all cartilage.

Dolphins and porpoises are also mammals.

[Mikeisskeptical]

Originally Posted by VOW

A shark is definitely lower on the evolutionary scale than either you or your goldfish

~VOW

No such thing as an evolutionary scale I'm afraid. All modern animals are exactly the same amount of 'evolved'. 'Primative' can refer to animals who have deviated less from an ancestral 'archetype'in any way you care to define, but it does not mean 'less evolved'. All extant lifeforms have an unbroken 100% survival rate going back to the original replicator who gave rise to all life on Earth.

[Colibri]

Originally Posted by Lukeinva

Say whaaaaaat?

To put it another way, we share a much more recent common ancestor with goldfish than we do with sharks. We are also share basic anatomical similarities with goldfish that we don't share with sharks.

Originally Posted by Tamerlane

Just to tie the first two posts together, sharks are members of the Chondrichthyes, while humans and goldfish are both in the Osteichthyes. Might be odd to think of humans as "bony fish", but if you accept traditional Linnaean hiearchy that's how it works out .

It doesn't work very well to use Linnaean hierarchies with cladistic classifications, so in this sense we are talking about the clade Osteichthyes rather than the Class Osteichthyes.

[Blake]

Originally Posted by Colibri

Originally it included most aquatic animals, including whales, sea turtles, etc.

Jellyfish, crayfish, shellfish, starfish. It really did just mean "animal that lives in the water".

[Mikeisskeptical]

Originally Posted by Colibri

"Fish" is really a meaningless term with respect to taxonomic classification. It's really just a popular term for any gill-breathing aquatic vertebrate (not including larval amphibians). Originally it included most aquatic animals, including whales, sea turtles, etc.

"Fish" as used today includes members of four traditional classes, the Agnatha (jawless fish), Placoderms (extinct armored fish), Chondrichthyes (cartilaginous fish), and Osteoichthyes (bony fish). However, some of these groups themselves turn out to be polyphyletic (made up of organisms that are not one another's closest relatives), so the actual taxonomy is more complex.

Good answer (the answer I was looking for)

[Colibri]

Originally Posted by VOW

A shark is definitely lower on the evolutionary scale than either you or your goldfish.

Sharks branched off the line that we belong to earlier than goldfish did, but that doesn't mean that they are "lower" in the sense of primitive. Sharks share some characteristics with early vertebrates, but have some very advanced ones of their own. For example, the ancestors of sharks probably had bony skeletons, and the cartilaginous skeleton is a derived condition.

It's been a LONG, LONG time since I had my comparative anatomy class, but the IIRC, the shark jawbone is comparable, anatomically, to the tiny bones in the mammalian ear.

Or something like that.


~VOW

Sharks don't actually have jawbones, or any bones, for that matter. But some bones in the jaws of bony fish eventually developed into the inner ear bones of mammals.

[Chronos]

No such thing as an evolutionary scale I'm afraid. All modern animals are exactly the same amount of 'evolved'.

Depends on how you define how evolved something is. If you're counting by years back to common ancestor, then all contemporary species are trivially equally evolved. If, however, you count by number of generations back to common ancestor, then you'd find that longer-lived and slow-maturing species (such as us) are actually less evolved than faster-breeding species.

[Rhythmdvl]

Originally Posted by DCnDC

Yes.



From here

Yeah, well just where do fish fingers come from then, eh smart guy?

[Mangetout]

Originally Posted by Blake

Jellyfish, crayfish, shellfish, starfish. It really did just mean "animal that lives in the water".

Crayfish is an interesting case in point - the name originates from an old Germanic word that might have been krebiz or [/i]krebitz[/i] - so did not originally refer to 'fish', but people were so accustomed to assigning the term 'fish' to things that live in water that this influenced the change (in English) of the tail-end of the word, resulting in crayfish.

In French, this process didn't happen - and the modern word is écrevisse.

[njtt]

Originally Posted by Colibri

To put it another way, we share a much more recent common ancestor with goldfish than we do with sharks. We are also share basic anatomical similarities with goldfish that we don't share with sharks.

Yes, but this does not really address the source of Lukeinva's (and my) surprise and confusion. While I can certainly see (and would have expected) that we are more closely related to goldfish than we are to sharks, it does not follow from that that we are more closely related to goldfish than goldfish are to sharks. The latter is what Blake seemed to be saying. Is that correct, or was it a slip? If it is correct, some sort of explanation would be appreciated. What is this huge (but, intuitively, not all that obviously huge) evolutionary distance between sharks and goldfish that exceeds the (intuitively quite large) distance between goldfish and humans?

[DrFidelius]

Humans and goldfish share many derived characters which sharks do not, which indicates that humans and goldfish have a more recent common ancestor. We did not seperate from the lineage which led to goldfish until after the linage which leads to sharks ahd split off.

Intuitively, we see cold-blooded critters breathing through gills and we think those are significant characters. However, when we look at bony skeletons and a lung/swim baldder we see that despite superficial similarities we share more derived traits with the goldfish than either of us do with sharks.

[Hari Seldon]

If you want to pursue this more deeply, read "Your Inner Fish" be Neil Shubin. Very interesting.

And yes, the fact that the clade that includes us and bony fish split into our respective branches after we all split from the sharks does imply we are more closely related to each other than to sharks.

[NUFCToon]

Of course it's a fish just not exactly the same size as a goldfish haha!

[Colibri]

Originally Posted by njtt

Yes, but this does not really address the source of Lukeinva's (and my) surprise and confusion. While I can certainly see (and would have expected) that we are more closely related to goldfish than we are to sharks, it does not follow from that that we are more closely related to goldfish than goldfish are to sharks. The latter is what Blake seemed to be saying. Is that correct, or was it a slip? If it is correct, some sort of explanation would be appreciated. What is this huge (but, intuitively, not all that obviously huge) evolutionary distance between sharks and goldfish that exceeds the (intuitively quite large) distance between goldfish and humans?

In terms of years since divergence, there is exactly the same evolutionary distance between goldfish and sharks as between humans and sharks. We belong to the same branch as goldfish and split with the lineage that led to sharks at the same time, maybe 420 million years ago. (In terms of generations, since mammals and particularly the ape lineage have longer generation times than most bony fish, there are actually fewer generations between humans and the divergence with sharks than the number of generations for goldfish).

The lobe finned fishes, the lineage we belong to, split from other bony fish very soon after the divergence of bony fish themselves, the oldest fossils being about 418 million years old.

[Sir T-Cups]

Originally Posted by Rhythmdvl

Yeah, well just where do fish fingers come from then, eh smart guy?

No where. They're actually called fish STICKS

[Mikeisskeptical]

Originally Posted by Hari Seldon

And yes, the fact that the clade that includes us and bony fish split into our respective branches after we all split from the sharks does imply we are more closely related to each other than to sharks.

Erm... Doesn't it? I'd have thought that this was exactly the implication.

[Lemur866]

Think of it this way. Waaay back hundreds of millions of years ago there was a little fishy creature. It swam around in the water and had little finny things and gills and so on. Then half these creatures split off and developed into sharks and rays. And half these creatures split off and developed into bony fish. Except, some of those bony fish learned to flop around on land, and then evolved legs, and became mammals.

You can see that even though some bony fish stayed in the water and some moved on land, they should belong to the same group. All members of the bony fish group are related by the same amount to the shark group, even though some bony fish have changed a lot by growing hair and legs.

This is the same concept that people use when they say that humans are apes. We're more closely related to a chimpanzee than we are to a gorilla. But a chimpanzee is also more closely related to a human than it is to a gorilla. Even though a chimp looks a lot more like a gorilla than it does to a human, in fact a chimp's closest relative is a human, not a gorilla.

This is a hard concept to understand. Most people can easily grasp that a human is more like a chimp than a human is like a gorilla, but they think that there's a continuum from gorilla to chimp to human which would make a chimp more closely related to a gorilla than a human is related to a gorilla. But that's not the case. It's not a continuum or a ladder, it's a branching family tree. There's a branch that splits into two twigs, the gorilla twig and the human/chimp twig. The human/chimp twig then splits into the human twig and the chimp twig. But neither twig on the human/chimp twig is closer to the gorilla twig, they are equally distant from the gorilla twig.

[Earl Snake-Hips Tucker]

And along the same primate line, we're more closely related to Old World monkeys than Old World monkeys are to New World monkeys.

[Mikeisskeptical]

Originally Posted by Chronos

Depends on how you define how evolved something is. If you're counting by years back to common ancestor, then all contemporary species are trivially equally evolved. If, however, you count by number of generations back to common ancestor, then you'd find that longer-lived and slow-maturing species (such as us) are actually less evolved than faster-breeding species.

OK, the main point I was refuting was the idea that there is a ladder of evolution starting with bacteria, leading up through worms, insects, vertibrates and of course, with humans sitting smugly on the top. I don't think this is what was being implied, but I think terms like 'further up the evolutionary scale' should be avoided as they are misleading and uninformative. The other thing I'd say is that surely more generations does not neccessarily mean more evolution. Small rodents have hugely quicker generations than us, but many of them have deviated very little from there anscestoral archetypes in tens of millions of years, at least morphologically. I have no idea about genetically, I'd guess that the unread DNA of, say a shrew has evolved much more rapidly than that in slower-maturing species, whereas the sections expressed phenotypically may have changed less. Is this true? Even if it's not though, if a shrew has completely different genes to ancestral forms, coding for pretty much the same bodies, would you really want to call them 'more evolved'? I'm sure I'm betraying my ignorance here, but since I've already admitted to it, I don't mind.

[ZenBeam]

Originally Posted by Mikeisskeptical

Erm... Doesn't it? I'd have thought that this was exactly the implication.

Can you double-check whether you're misreading what Hari Seldon wrote? Otherwise, what you wrote doesn't make sense to me.

[Mikeisskeptical]

Originally Posted by ZenBeam

Can you double-check whether you're misreading what Hari Seldon wrote? Otherwise, what you wrote doesn't make sense to me.

Yes, I did misread it. Oops.

[njtt]

Originally Posted by ZenBeam

Can you double-check whether you're misreading what Hari Seldon wrote? Otherwise, what you wrote doesn't make sense to me.

If Hari Seldon was replying to me (it is not altogether clear, but it looks like it) he misread what I wrote too. I quite explicitly acknowledged that we are closer to goldfish than we are to sharks.

Originally Posted by Colibri

In terms of years since divergence, there is exactly the same evolutionary distance between goldfish and sharks as between humans and sharks. We belong to the same branch as goldfish and split with the lineage that led to sharks at the same time, maybe 420 million years ago. (In terms of generations, since mammals and particularly the ape lineage have longer generation times than most bony fish, there are actually fewer generations between humans and the divergence with sharks than the number of generations for goldfish).

Are you saying that there is no other metric of evolutionary distance other than time (or number of generations) since there was a common ancestor? That seems implausible to me.

Quite apart from the sort of morphological similarities and differences that biologists used to rely upon in the dark ages of a few decades ago (do they really count for nothing at all, now?), what about differences in DNA sequences? That, surely, is thoroughly quantifiable. Is it not the case that, as measured by rate of DNA change, evolution sometimes goes quickly in a particular line, and sometimes much slower? Does it not even make sense to say (regardless of whether it is true or not) that sharks might not have evolved all that much since the time they split from bony fishes, but that the line leading to humans has evolved much faster over the somewhat shorter time since it split from the bony fishes?

[Leo Bloom]

But can you relate to a sea slug?

[BowlOfDucks]

You're forgetting how evolution happened

The common ancestor of all fish is also the common ancestor of all amphibians, reptiles, birds and mammals.

Are you more closely related to a fish than a shark?

Depends on the fish.

[Polycarp]

Okay, start with the common ancestor of all vertebrates.

The first group to split off gave rise to the modern hagfish, or "slime eel", a noxious ectoparasite which had a cranium but no vertebrae. Everything else, from lampreys to llamas, is more closely related to each other than any of them are to the hagfish.

The next few groups to split off were the "jawless fish," including 2. the modern lamprey; 3. the conodont animals (eel-haped filter feeders whose only hard part was the bony framework for the filter apparatus, the so-called conodonts; 4. the Osteostracans, 5. the Heterostracans, and 6. the Anaspids, all three of which were bony-armored groups of jawelss fish on three distinct body plans, each of which radiated into three or four major subgroups. There were also a couple of 7-8. minor groups of jawless fish. Paleontologists will argue at inordinate length about which of these diverged before which others; the sequence I listed them gives one of several common orders of divergence.

This now leaves us with the Gnathostomes, the jawed vertebrates. First group to split off here is 9. the Acanthodians, the so-called "spiny sharks" of the Paleozoic. (Though definitely spiny, they were not sharks.) Next probably was 10. the Placoderms, a large array of armored Paleozoic fish including the Arthrodires and the Antiarchs. Some exxperts don't believe the Placoderms are a natural group, but rather a lumping together of several lineages of jawed fish that didn't survive.

11. Next group to split off were the Chondrichthyes, the cartiliginous fish. This includes two main groups (which may be closely related separate groups), the Holocephalians which are made up of the chimeras or ratfish and two extinct related groups, and the Selachians, which include primitive extinct sharks, modern sharks, skates, rays, the dogfish, the sawfish, etc.

What we're left with at that point is the Osteichthyes, including on the one hand the Actinopterygians, the ray-finned fish that constitute most modern bony fish, and on the other the Sarcopterygians, including a wide range of extinct forms, the three lungfish, the coelacanth, and all tetrapods (land vertebrates).

We can break this stuff down into more detail, but the fact of the matter is that the goldfish, the sturtgeon, the marlin, the lungfish, the snake, frog, the dinosaur, the sparrow, and you and me, are all more closely related to each other than any of them is to the shark -- and more closly related to the shark than to the lamprey or any of the extinct forms noted above.

[Chronos]

You're forgetting how evolution happened

The common ancestor of all fish is also the common ancestor of all amphibians, reptiles, birds and mammals.

The common ancestor of all fish is certainly a common ancestor of tetrapodes, but it's not the most recent common ancestor of tetrapodes. The most recent common ancestor of the tetrapodes would have been an amphibian-like thing that was not the ancestor of anything that we would call a fish.

It's like saying that my great-grandfather is the common ancestor of my sister and I. It's true, but it's misleading about our degree of relatedness.

[Mikeisskeptical]

Originally Posted by Polycarp

"slime eel", a noxious ectoparasite

I read this and thought it sounded pretty disgusting. Then I googled it wished I hadn't. I'm never going swimming again.

[Mister Rik]

Originally Posted by Rhythmdvl

Yeah, well just where do fish fingers come from then, eh smart guy?

Same place buffalo wings come from

[Alessan]

Originally Posted by Mikeisskeptical

I read this and thought it sounded pretty disgusting. Then I googled it wished I hadn't. I'm never going swimming again.

I don't know - it sounds like a great superpower.

[John Mace]

Originally Posted by Leo Bloom

But can you relate to a sea slug?

Last Saturday, about 2AM, yes. The sea slug had an intellectual advantage on my, though, so it was hardly fair!

[The dread simoom]

Originally Posted by Rhythmdvl

Yeah, well just where do fish fingers come from then, eh smart guy?

He said they lack limbs, not digits.

[BMalion]

This was no boating accident!

[Mikeisskeptical]

Originally Posted by BMalion

This was no boating accident!

Furthermore, It was no propeller, it wasn't any coral reef and it wasn't Jack the Ripper.