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Here's a question from my son I've found interesting enough to ask here. There are plenty examples of species returning back to the water environment, like dolphins, sea lions, walruses, some snakes, crocodiles etc.

The question is - are there any evidences that in evolution of certain species there was return to the land twice, that is, they've came from sea, then evolve as land species, then, again, evolved to somewhat marine or fresh-water and, finally, turn into land species again?

UPD Chordate are the most interesting but any example, even plants, would be nice.

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  • $\begingroup$ What you describe in the last sentence is "returning to the water", not "returning to the land twice". What you mean is "water -> land -> water -> land", right? $\endgroup$
    – Remi.b
    Jan 3, 2018 at 14:44
  • $\begingroup$ Related: Has any flying creature evolved into a sea creature? $\endgroup$
    – Remi.b
    Jan 3, 2018 at 14:55
  • $\begingroup$ Are you interested exclusively in animals? Note that the absence of a clear definition of what is a "water species" and a "land species" might make it hard to answer. $\endgroup$
    – Remi.b
    Jan 3, 2018 at 14:57
  • $\begingroup$ I am sure that there are no animals that have gone from land to water, and then back to land. I am not sure about plants though. The transition to land is a very difficult one. By the way, I would not say "returning to land twice", because they would only be "returning" once. $\endgroup$
    – Karl Kjer
    Jan 3, 2018 at 17:22
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    $\begingroup$ Yes, I am sure. Crustacians and Chelicerates evolved in water. I know that woodlice are both terrestrial and aquatic, but that does not necessarily mean the the aquatic species did not move onto land. $\endgroup$
    – Karl Kjer
    Jan 4, 2018 at 1:43

2 Answers 2

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Woodlouse

Life emerged in the water. Ancestors of insects, spiders, myriapods and crustaceans were probably terrestrial (please correct me if that is wrong) but then, crustaceans evolved to living in the water again. Finally, woodlice went back onto land!

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  • $\begingroup$ Following your link in Wikipedia (and other) I wouldn't say that crustaceans appeared on land. $\endgroup$
    – Pere
    Jan 29, 2019 at 13:13
  • $\begingroup$ I did not say "crustaceans appeared on land" but "Ancestors of insects, spiders, myriapods and crustaceans [in other words, ancestor of all arthropods] were probably terrestrial". Again, I might be wrong. Can you please give me a reference stating that this ancestor was not terrestrial? From wikipedia > arthropoda, I could not find anything definitive but only that among the oldest fossils of arthropoda are marine and others terrestrial. $\endgroup$
    – Remi.b
    Jan 29, 2019 at 17:46
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    $\begingroup$ To hopefully resolve the question, I opened the post Were there any terrestrial species in the ancestry of all crustaceans? $\endgroup$
    – Remi.b
    Jan 29, 2019 at 17:46
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Echidna come from platypus like ancestors about 14-20 mil years ago. so they count if platypus count as returning to water although not 100% of there like cycle.

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