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Analogous organs: Different origin, same functions, Homologous organs: Same origin, different functions but same main structure// right? So, what is the case for the pectoral fins of a shark and a whale?

Are they analogous organs, because the two animals have different ancestors(shark-Some Chondrichthyes fish, Whale-some mammal) but have organs that do the same thing?

Or are they homologous organs, because the two animals have the same ancestor(A vertebrate animal) and have organs that have a similar structure?(I learned that it is alright for homologous organs to do the same function, for example the wings of a bat and a bird are homologous organs, although they do the same thing)

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They are analogous at to function. Whales derive from terresterial animals that "returned" to the sea. Evolution adapted the forearms to fins. Here's a great diagram: http://evolution.berkeley.edu/evolibrary/article/evograms_03

The bat wing and the bird wing are also analogous as to function. Their functional aspects evolved independently. But as forelimbs they are homologous sharing a common ancestor with forelimbs.http://evolution.berkeley.edu/evolibrary/article/evo_09

We haven't yet answered the question of whether the whale fin and shark fin are homologous in origin: http://evolution.berkeley.edu/evolibrary/article/similarity_hs_09

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  • $\begingroup$ There is more recent evidence they are homologous as limbs, shark pectoral fins and bony fish fins (and thus tetrapod limbs) share the same hox genes. ncbi.nlm.nih.gov/pmc/articles/PMC1937022 $\endgroup$ – John Apr 18 at 4:06
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The ancestors of all jawed animals probably had pectoral fins [Ref]. This primitive feature is homologous to shark pectoral fins (fig. 1). The forelimbs of quadrupeds are evolved from the pectoral fins of lobe-finned fish (fig. 2), and the pectoral fins of whales evolved from the forelimbs of their mammal ancestors. Thus, these organs are homologous as one can follow the gradual changes in morphology and find continuity between the fin to leg to fin transitions.

However, the internal structure of the fins themselves are quite different between whales and sharks as they evolved from a leg structure with fingers (fig. 3 & fig. 1). The external similarity of the fins is an example of convergent evolution, not directly the result of their shared origin. Some of the internal features of the fins may be homologous (I haven't checked), but you should not assume that a shared origin for the fins means they are the same.

sharkfins
Fig 1. Shark anatomy



lobeamph
Fig 2. Lobefinned fish and amphibian homologous limbs.

whalefin
(source: ftexploring.com)

Fig 3. Whale fin

Reference: 1. New study showing pelvic girdles arose before the origin of movable jaws, : Institute of Vertebrae Paleontology and Paleoanthropology, 2012

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