The appearance of "Alamosaurus" may have represented an immigration event from South America. "Alamosaurus" appears and achieves dominance in its environment very abruptly, which might support the idea that it originated following an immigration event. Other scientists speculated that "Alamosaurus" was an immigrant from Asia. However, critics of the immigration hypothesis note that inhabitants of an upland environment like "Alamosaurus" are more likely to be endemic than coastal species, and tend to have less of an ability to cross bodies of water. Further, Early Cretaceous titanosaurs are already known, so North American potential ancestors for "Alamosaurus" already existed.