Andalusian horse
Mitochondrial DNA studies of the closely related modern Andalusian horse, compared to the Barb horse of North Africa, present convincing evidence that Barbs and Iberian horses crossed the Strait of Gibraltar in each direction, were crossbred with each other, and thus each influenced the other's maternal bloodlines. While Portuguese historian Ruy d'Andrade hypothesized that the ancient Sorraia breed was an ancestor of the Southern Iberian breeds, including the Lusitano, genetic studies using mitochondrial DNA show that the Sorraia is part of a genetic cluster that is largely separated from most Iberian breeds. One maternal lineage is shared with the Lusitano, however, Sorraia lineages in Iberian breeds are relatively recent, dating to the Middle Ages, making the Sorraia an unlikely prehistoric ancestor of the Lusitano.