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Mammals have external qualifying characteristics like body hair, ear pinna, etc. But a whale has none of that. So, can it be identified as a mammal just by external observations?

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    $\begingroup$ Whales and dolphins have a few hairs on their snout that they usually shed just after birth, in addition to the warm-blooded thing and the live birth and the milk. $\endgroup$ – Resonating Nov 16 '14 at 17:14
  • $\begingroup$ @JeremyKemball Only milk and hairs make them mammals. Warm-blooded and live birth are present outside of mammals. $\endgroup$ – kmm Nov 16 '14 at 21:00
  • $\begingroup$ Whales dont have gills. $\endgroup$ – biogirl Nov 18 '14 at 17:02
  • $\begingroup$ @biogirl , I said 'external characteristics"... $\endgroup$ – souvik bhattacharya Nov 19 '14 at 3:51
  • $\begingroup$ Gills can easily be seen in a fish $\endgroup$ – biogirl Nov 19 '14 at 4:04
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A whale has a horizontal tail fin which is a typical feature of mammalian marine animals see link. Mammalian sea animals typically have a vertical movement of the tail fin for swimming. Fishes like sharks have a vertically oriented tail fin and move it side-ways for locomotion.

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  • $\begingroup$ This is the answer. +1 $\endgroup$ – anongoodnurse Nov 17 '14 at 1:23
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Identification of an organism to a taxonomic rank (Class Mammalia) is not based only on morphological characteristics. It is a function of all characteristics that members of that rank share to the exclusion of others. Mammals have multiple features that have been mentioned before (the obvious ones are milk and hair) that they all share that are not present in other taxa. If you only based identification on external morphology you would risk grouping organisms based on convergent evolution (e.g., bats and birds would be in the same taxa).

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