@Ionus,
common descendancy can be ruled out when the specimen cannot be included in the phylo tree. This one is such an example. MDNA will allow the "lookback" through the female linneage and the Y chromosome can similarly be traced to define the migrations that the specimen hs endured by matching its genome to possible descendents.
Since the Smilodon specimens were lumped together, they presumably are able to demo the trends that the entire genus had gone through in both Nand S America. But since the specimens could NOT be made unique, their own descendents (both m and Y chromosomal DNA) cannot be accurately pinpointed , mostly because the very segments they need to use, just arent there and theyve been substituted.
This is done all the damn time an popular presses get it wrong all the time when we get stuff in "Science weeklies " in some of the National news.