ever since rising from the ocean 400 million years ago, and since the fish turned into a frog, there have been "unused DNA" carried in vertebrate species

they are turned on and turned of by random mutation but the DNA is never "loss"

meanwile, insects lost ALL OF THEIR extra DNA 400 million years ago, probably due to some population bottleneck which favored smaller DNA molecules

if you compare human DNA + mice with that of several insects species you will note how insects are missing pieces of DNA in many places while human + mouse align perfectly with each other having of course some 20% of DNA different between a human and a mouse but nevertheless all the DNA is still there

in insects, nothing, huge gaps, less DNA than either human or mouse

HOWEVER the exceptions like moths, which have larger DNA than humans, are just twisted and horribly mutated ancient wasps. they have copied their COX3 gene about 1000 times and its one megabyte long, but this is not the norm in insect world, beetles dont have it like that

having one big COX3 gene doesnt mean you are having all the DNA that is missing between a human and a insect

ok but the final verdict is: a frog still has the potential of turning into a mammal if a whole lot of its unused extra DNA is turned on

a human embryo still has gill slits evolved from fish, these disappear within a few weeks and turn into ears and whatnot (this is not an example of extra DNAthough)