This link shows the basic relationships between the main vertebrate groups. Note that this is a cladistic arrangement: all groups above a particular node in the tree are more closely related to each other than they are to any group that branches off at a lower level. Therefore the ray-fin, or bony, fishes are more closely related to all the groups above them than to the group below them, the cartilaginous fishes.
One error in the diagram: as **Darwin’s Finch ** has mentioned, a bony skeleton evolved before the cartilaginous fishes branched off (rather than after, as the diagram indicates), and they secondarily converted their bony skeleton to cartilage.
Is that what Dunkleosteus is? There’s a few Dunky models hanging in musea around the Cleveland area (representing the long-gone time when what is now Cleveland was underwater), and I was always very impressed by them growing up.
And I was not aware that bugs all sucked. I had thought that the defining characterisic for the bugs was the wing shape (two pairs of wings, with the forewings hardened as covers for the hindwings, but not meeting in a line down the back as with beetles). Certainly, there are sucking insects which are not bugs, such as the dipterans (housefly, mosquito, and others).
The bugs are defined by a number of characteristics including the wings, sucking mouthparts and incomplete metamorphosis. But if I recall distant entomology lectures correctly bugs are the only insects that have sucking moutparts for their entire lifecycle, which separates them from the diptera, lepidopera etc. which may have sucking mouthparts as adults but not as larvae.
IOW bugs are the only insects whose entire life sucks.
:smack: The first website I checked had the other form, hence the slip.
It may be worth pointing out that, according to cladistic classification, the Osteoichthyes or bony fishes itself is not a valid group if the the terrestrial vertebrates are left out. Since the lobe-fins are more closely related to tetrapods - Amphibia, Reptilia (including Aves), and Mammalia - than they are to the ray-finned fishes, it’s not proper to include them in the same group as the ray-fins unless all the tetrapods are also included.
Re “bug,” it’s always bugged me that entomologists presume to limit the term to the Homoptera/Hemiptera, and claim any other use is “incorrect.” The word as applied to any small terrestrial arthropod surely long predates its use in taxonomy, and it is presumptuous for entomologists to co-opt it after the fact. IMO it is perfectly legitimate to call any insect, spider, sowbug, centipede, etc. a “bug.” Trying to limit the term to a couple of orders is like ichthylogists insisting that only ray-finned fishes should properly be called “fish,” and that it is incorrect to call sharks, rays, lobe-fins, or lampreys by that term.
I didn’t realize that there was such a distinct diachotomy between binomial and cladistic taxonomy; I’d always assumed that Linnaeun nomenclature was more of a convenient shorthand, where as fully cladistic description better described the line of descent (though the traditional taxonomies are, at the more general classifications, thoroughly confused on the matter). Binomial nomenclature is too constrained to be descriptive of an organism’s true relationships.
I’d just never understood them to be properly considered (placoid) scales, but rather a proto-scale feature (denticle). At any rate, sharks aren’t “scaley”, i.e. covered with large flattened plates that provide protection for the relatively thin epidermis, but rather have a thick, tough skin with the denticle sticking out which, AFAIK, is distinct from all other fish.
I wasn’t aware of this–clearly, my knowledge of phylogeny is out of date–but that’s very interesting. I’m surprised the IDer’s haven’t latched onto the feather as a better example of uncertain phylogenesis of a “perfect” feature.
This brings up the interesting (at least to me) fact that Whales are closer to Cod than Cod are to Sharks. So maybe the old idea that Whales are Fish is not nearly so daft as it might now seem.
Me and a couple friends used to drive one of the TAs crazy in an evo-devo class in college. We would always write “fish” (with quotes) instead of just fish (without quotes), for precisely that reason (we were brainwashed as cladists, while the teacher and TAs of this class were devout Linnaean taxonomists). “Fish” ain’t a proper group unless we get to be included
Darn paraphyletic groups…
I get the feeling that the whole “feathers as derived scales” hypothesis came from the assumption that feathers evolved for flight (and by noting the similarity in shape between a typical scale and a pinnate flight feather). Now that evidence is rather clear that feathers didn’t evolve for flight, and that feathers predate birds, the evolutionary and developmental origins of feathers have been re-examined.
The exact same thing bugs me about ornithologists trying to limit the usage of common names and insisting that what has been called a magpie for centuries can not a be called a magpie, and insisting that the term magpie can only be used for a very limited number of corvids.
I probably agree with that. Fine with me to call antipodean magpies “magpies” - they’re from the general corvid clade after all. Common names are just common names. I have a friend who wants to standardize “robin.” Since there are probably half a dozen unrelated kinds of robins, it ain’t gonna happen. “Warblers” of course are even worse.
AFAIK the Cractidae, while not corvids in the restricted sense (Corvidae), are regarded as pretty close to them, being within the Corvoidea in the “Corvida” clade of passerines. Old World flycatchers (Muscicapida) are in the Muscicapoidea in the “Passerida” clade.
Let me take the negative here. As pointed out above, grouping sharks with ray-finned fish results in a paraphyletic clade, that is to say, an invalid grouping.
I appreciate the argument that “fish” has no real scientific meaning, but when we call sharks ‘cartilingious fish" and tuna “ray-finned fish”, we ought not to be surprised why so many people don’t understand evolution. Furthermore, if we are going to be that loose with the term, there isn’t much reason to not go to back calling whales and dolphins "spouting fish.’ Given that whales and dolphins are more closely related to tuna than tuna are to sharks, it makes a certain amount of sense. Sure, whales and tuna form an invaild clade (this time polyphyletic) but in terms of actual relationships, cetaceans and ray-finned fish are more closely related to each other than either is to sharks.
I will also point out that “lobe-finned fish”, such as coelcanths and lungfish are more closely related to whales (and elephants and humans) than to ray-finned fish such as trout and tuna. Most people when looking at a coelcanth or a lungfish would say, “well that’s a fish.” Well then, so are we.
The point is that if you want to understand evolutionary relationships then you need to make classifications by evolutionary relationships. If you want to call sharks fish, then you need to call whales and dolphins and humans fish as well. You can limit the term “fish” to just ray-finned fish, a monophyletic clade, but keep in mind that means that lungfish are not fish (just as whale sharks are not whales).
That wonderful old grouping that you may have learned as a child (“the groups of vertebrates are fish, amphibians, reptiles, birds and mammals”) was a remarkable bit of work for its time but it’s wrong, in part because it predates evolution and has no evolutionary understanding. We now have the understanding (cladistics) and the tools (genetic analysis). We ought to use them.
Calling sharks “fish” implies that sharks and rays are more related to tuna (and trout and eels) than tuna are to people or whales or elephants. It’s time to stop.
