Origin and Range
Enantiornithines have been found in North America, South America, Europe, Asia, and Australia. Known fossils attributable to this group are exclusively Cretaceous and it is believed that enantiornithines became extinct at the same time as their non-avian dinosaur relatives. One biogeographic study in the 1990s suggested that the distribution of enantiornithines implies a Middle Jurassic origin for the clade, but this theory has not been widely accepted by paleoornithologists; a Late Jurassic/Early Cretaceous origin is more in line with the fossil record. The earliest known enantiornithines are from the Early Cretaceous) of Spain (e.g. Noguerornis, a basal genus) and China (e.g. Protopteryx) and the latest from the Late Cretaceous of North and South America (e.g. Avisaurus). The widespread occurrence suggests that the Enantiornithes were able to cross oceans on their own power; they are the first bird lineage with a global distribution. Some might thus even have been migratory, but given the markedly warmer climate of the Mesozoic and the fact that the known Enantiornithes are from regions that were subtropical if not tropical at that time, it seems unlikely that the known diversity of these birds contains long-distance migrants.
Read more about this topic: Euenantiornithes
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