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If you ask Wikidata "Does the species lion (Q140) have a parent taxon line up to the Osteichthyes (Q27207, bony fishes)?", it answers yes:

SELECT ?item1
 WHERE {
  wd:Q140 wdt:P171* ?item1.
  ?item1 wdt:P171 wd:Q27207.
 }

Here's a direct link.

Now, I assume that this must be wrong at some level (I'm no biologist, so please correct me if I'm wrong), so I tried to find the error.

This query displays that path more explicitly, starting with mammals:

  1. Mammals (Q7377) have Tetrapoda (Q19159) as a parent taxon.
  2. Tetrapoda (Q19159) have Tetrapodomorph (Q1209254) as a parent taxon.
  3. Tetrapodomorph (Q1209254) have Rhipidistia (Q150598) as a parent taxon.
  4. Rhipidistia (Q150598) have Sarcopterygii (Q160830) as a parent taxon.
  5. Sarcopterygii (Q160830) have Osteichthyes (Q27207) as a parent taxon.

The third point seems strange, because Rhipidistia are described as a taxon of fish, which would mean that all mammals are fish.

Maybe this comes from the fact that tetrapods (and therefore mammals) evolved from Sarcopterygii 390 million years ago, as described here.

Is "having evolved from" considered a parent taxon in biology? If not, which of the five statements above is wrong?

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    $\begingroup$ Hi Cheeesus and welcome to Bio.SE! As you guessed, lions are unsurprisingly categorically not bony fish. I think you should be clear about what exactly the parent taxons are. To me it looks like they are ancestors. So we may have evolved from species that were bony fish, but that does not make us bony fish. $\endgroup$ – James Oct 28 at 10:44
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    $\begingroup$ @James, thank you. Yes, to me too it appears like the data in Wikidata confuses "parent taxon" in the evolutionary sense ("mammals evolved from bony fish") with "parent taxon" in a classification sense ("lions are a subtaxon of mammals"). $\endgroup$ – cheesus SO stop harming Monica Oct 28 at 13:31
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    $\begingroup$ If you take cladistics literally (instead of as a useful tool), then yes, lions - and humans - are just bony fishes, by the same logic that says birds are dinosaurs. (But both are just bony fishes, so there :-)) $\endgroup$ – jamesqf Oct 28 at 16:34
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    $\begingroup$ Possible duplicate of Am I a lobe-finned fish? $\endgroup$ – John Oct 30 at 11:08
  • $\begingroup$ related questions biology.stackexchange.com/questions/87725/… and biology.stackexchange.com/questions/70874/… you should really be searching for similar questions before oyu ask. $\endgroup$ – John Oct 30 at 11:25
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The path is correct. The safest reading is to say that the lion shares a set of characteristics with the lungfish. You can also say that lion and carps are bony vertebrates (Euteleostomes).

In evolutionary taxonomy, each taxon does not need to consist of a single ancestral node and all its descendants: it allows for groups to be excluded from their parent taxa (in other words, not "being part of" but, as you said, "having evolved from"). Thus, lungfishes are closer to the lions than they are from, e.g., sharks or trout. In other words (even if this is too simplistic to say so), their "common ancestor" is more "recent".

In the Linnaean taxonomic system, all fishes were in the same class. This corresponds to our "everyday life" classification of fishes but not to the most recents findings about the "common ancestors".

To make things clearer, you need to understand the concept of paraphyly. The bony fishes group is paraphyletic with respect to the tetrapoda. In other words, it consists of the group's last common ancestor and all descendants of that ancestor excluding the tetrapoda. "Bony fish" is therefore not a clade, but "Osteichthyes/Euteleostomes" is a clade (= a monophyletic group of the bony vertebrate with a common ancestor that looked like our "modern" fishes).

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  • $\begingroup$ Thanks, but this should somehow be indicated when using the property "parent taxon". Lions and extant bony fish like clown fish both have Osteichthyes as an ancestral taxon, but you cannot really say "A lion is a bony fish", can you? $\endgroup$ – cheesus SO stop harming Monica Oct 27 at 21:09
  • $\begingroup$ Oh, maybe I'm confusing Osteichthyes with Teleostei? $\endgroup$ – cheesus SO stop harming Monica Oct 27 at 21:17
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    $\begingroup$ Yes, I think that this is where the confusion takes place. Teleostei is distinct from mammals, but they share a common parent taxon (Osteichthyes) from which they evolved. $\endgroup$ – radouxju Oct 28 at 10:16
  • $\begingroup$ Are there any extant Osteichthyes which are not Teleostei? I don't mean "extant species which have evolved from Osteichthyes", I mean species which are now considered a subtaxon of Osteichthyes. $\endgroup$ – cheesus SO stop harming Monica Oct 28 at 13:29
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    $\begingroup$ you mean "modern" bony fishes that are not teleostei ? Yes, the lungfish, this is why I took it as an example. $\endgroup$ – radouxju Oct 30 at 10:52

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