South America has four camelids: two wild, the guanaco and the vicuna, and two domestic, the llama and the alpaca. Which wild ancestor produced which domestic form was argued for two centuries, and the alpaca was usually written as Lama pacos, implying descent from guanaco stock.
A study led by Miranda Kadwell and colleagues, published in 2001, combined mitochondrial and microsatellite markers across all four. It concluded that the llama derives from the guanaco and the alpaca from the vicuna, and that centuries of hybridisation after the Spanish conquest had blurred the picture badly enough to mislead earlier morphological work. The alpaca was reassigned to Vicugna pacos.
The fleece supports the reading, since alpaca and vicuna fibre are both fine while guanaco and llama are coarser. What complicates it is that a large share of modern alpacas carry llama ancestry from that post-conquest mixing, so the clean ancestral line survives more in the genome than in any individual herd.