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)
Yes, a shark is a fish.
Your goldfish is much more related to you than either of you are to a shark.
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
“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.
:dubious: :eek: 
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 :).
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.
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.
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.
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.
Jellyfish, crayfish, shellfish, starfish. It really did just mean “animal that lives in the water”.
Good answer (the answer I was looking for)
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.
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.
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.
Yeah, well just where do fish fingers come from then, eh smart guy? :dubious:
Crayfish is an interesting case in point - the name originates from an old Germanic word that might have been krebiz or krebitz - 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.
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?
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.
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.
Of course it’s a fish just not exactly the same size as a goldfish haha!