This re-estimation of the age of the therian XY system is based on the finding that sequences that are on the X chromosomes of marsupials and eutherian mammals are present on the autosomes of platypus and birds.
Esta reestimación da idade do sistema XY dos terios está baseado no descubrimento de que secuencias que están nos cromosomas X dos mamíferos marsupiais e euterios (placentarios) están presentes nos autosomas do ornitorrinco e aves.