The Lakshmi case (the little indian girl who was born with a parasitic brother attached to her body) wasn’t the first one out there, it was the most recent one we know, but it isn’t definitely the first one, which is shocking! Parasitic twins occur when a twin embryo begins developing in utero, but the pair does not fully separate, and one embryo maintains dominant development at the expense of the other. Unlike conjoined twins, one ceases development during gestation and is vestigial to a mostly fully-formed, otherwise healthy individual twin. The undeveloped twin is defined as parasitic, rather than conjoined, because it is incompletely formed or wholly dependent on the body functions of the complete fetus, as shown on this video:
I thought it was a rare, but it seems I was wrong! it happened a lot!