English: In genomes there is an intricate association between SINE elements and the much longer long interspersed elements (LINEs), as the replication of SINEs ultimately depends on the enzymatic machinery of LINEs. Using the TinT method in marsupial genomes, we detected independent SINE-LINE associations that overlapped in time. The L1 system dominates SINE retropositions in Didelphimorphia (SINE1_Mdo, SINE1a_Mdo). The retroposon-like transposable element (RTE) system predominates in the lineage leading to the kangaroo (WALLSI1-4), and LINE2- (MIR, MdoRep1, THER1_MD) and LINE3- (MIR3) mobilized SINE systems are present in both lineages and were active over long periods of marsupial evolution. Experimental screening revealed the activities of two, sometimes three, SINE-LINE associations at some deep nodes. For instance, at least three SINE-LINE associations were active in the common ancestor of the four Australasian orders (RTE-WALLSI1a/L1-WSINE1/L2-MIR_Mars) (Figure S1). In most other mammalian genomes, only one SINE-LINE group was active at a time; thus, the discovery of multiple groups may indicate a long branch and/or overlapping activity. As several different SINE-LINE systems were also active at the Australidelphia node (RTE-Mar1a,b,c_Mdo/L1-WSINE1/RTE-WALLSI3), we favor overlapping, extended activity of retroposition systems in marsupials. The extended presence of diverse SINE transposition systems found in marsupial genomes is unique in mammals. Twenty-four SINE subfamilies were extracted from genomic data of M. domestica and M. eugenii to screen for nested insertions, revealing information about their relative activity periods. Elements shown in black denote L3-, those in blue L2-, those in green RTE-, and those in red L1-mobilized SINEs. Ovals represent the 50% probability of the activity distribution and horizontal lines indicate the 90% probability of the activity distribution. Relative time axes are given at the bottom.