A distal enhancer and an ultraconserved exon are derived from a novel retroposon : Nature
In essence: DNA sequencing of all modern vertebrates shows that there are many regions that are always the same, whatever the organism. Enter the modern "coelacanth", an organism (recently thought to be extinct) that has changed very little (in multiple measures) in hundreds of millions of years. When comparing the DNA of the coelacanth with vertebrates (especially mammals), it is found that some of the highly conserved regions in vertebrate DNA act as transposons (sequences of DNA that frequently switch position within the genome) in the coelacanth. Researchers looked at the vertebrate function of one of these transposon sequences and found that it had positioned itself within an RNA processing gene, making it possible for the cell to have another alternative splicing pattern for that protein product (thereby altering the function of the protein).