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Many small mammals have scaly skin on their tails and sometimes limbs. The examples can be found among rodents (rats, degu, scaly-tailed squirrels), insectivores (shrews, desmans), oppossums, musky rat kangaroo. There are much more prominent examples like pangolin scales but I would like to concentrate on as simple things as possible.

I would like to know the answers or at least what is known on the following quiestions.

  1. Are scales of these different mammals actually something similar or is it just an illusion?
  2. Does the scaly pattern at least in some cases represent some primitive characteristic of a common mammalian ancestor?
  3. In case of positive answer on the previous question is there any connection to the scales of the diapsid reptiles? As I understand the latter are built from $\beta$-keratin absent in mammals but perhaps there are still similarities or even a common origin.

For now my search on this topic resulted in some contradictory claims without any solid references. I would update in case I find anything that seems relevant.

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  • $\begingroup$ biology.stackexchange.com/questions/1138/… ......... thomas-hopp.com/blog/2013/01/26/even-more-dinosaur-skin $\endgroup$ – com.prehensible Dec 8 '17 at 21:44
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    $\begingroup$ @com.prehensible Well, there's a reference on pangoline scale evolution (which I sadly can't read right now) but from reading the abstract I'm not sure that would answer my question. And surely the answers on that question don't answer mine. I probably shouldn't have mention the pangoline at all... $\endgroup$ – OON Dec 8 '17 at 21:50
  • $\begingroup$ The most primitive mammals from the list are probably Opossums and Beavers, which have the most reptile like tails of all. dolly.jorgensenweb.net/nordicnature/wp-content/uploads/2014/04/… ...... media.gettyimages.com/photos/… $\endgroup$ – com.prehensible Dec 9 '17 at 7:44
  • $\begingroup$ @com.prehensible ...or their ancestors had furry tails and this is actually a derived trait. Contrary to cartoons platypus has furry tail! $\endgroup$ – OON Dec 9 '17 at 8:14
  • $\begingroup$ @com.prehensible For me (not possessing any considerable knowledge on this topic) this is main weakness of the idea that protomammals had scaly tails and limbs - as far as I know monotremes don't have any scales. Though that may prove nothing as they are not very diverse and experienced considerable evolution themselves $\endgroup$ – OON Dec 9 '17 at 8:57

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