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Platy-1 retroposons are short interspersed elements (SINEs) unique to platyrrhine primates. Discovered in the common marmoset (Callithrix jacchus) genome in 2016, these 100 bp mobile element insertions (MEIs) appeared to be novel drivers of platyrrhine evolution, with over 2200 full-length members across 62 different subfamilies, and strong evidence of ongoing proliferation in C. jacchus. Subsequent characterization of Platy-1 elements in Aotus, Saimiri and Cebus genera, suggested that the widespread mobilization detected in marmoset (family Callithrichidae) was perhaps an anomaly. Two additional Callithrichidae genomes are now available, a scaffold level genome assembly for Saguinus imperator (tamarin; SagImp_v1) and a chromosome-level assembly for Saguinus midas (Midas tamarin; ASM2_v1). Here, we report that each tamarin genome contains over 11,000 full-length Platy-1 insertions, about 1150 are shared by both Saguinus tamarins, 7511 are unique to S. imperator, and another 8187 are unique to S. midas. Roughly 325 are shared among the three callithrichids. We identified six new Platy-1 subfamilies derived from Platy-1-8, with the youngest new subfamily, Platy-1-8c_Saguinus, being the primary source of the Saguinus amplification burst. This constitutes the largest expansion of Platy-1 MEIs reported to date and the most extensive independent SINE amplification between two closely related species. [ABSTRACT FROM AUTHOR]