The link between Spanish horses and the Barb horses of North Africa is strong, but the most vital link is not between today’s modern Spanish horse breeds and Barb horses but between the now-extinct Spanish Jennet and Barb horses.
Sulphur Mustangs have been separated from their ancestral populations for centuries and have followed an independent evolutionary development, but similarities with other Spanish Colonial horses of North America indicate a common origin.
Genetic analysis shows that northern Iberian Celtic horses were incorporated into all the Criollo breeds in North and South America. Analysis of Sulphur Mustangs, Galician horses, and Mexican Galiceno horses show a very close relationship with overlapping areas of the plots for each population.