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Which bird groups lived during the Cretaceous Period?

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A zebra finch (Taeniopygia guttata) with a bright orange beak, gray head, orange cheek patch, and black-and-white striped tail perches on a branch. — Bird A brightly colored zebra finch (*Taeniopygia guttata*) perched on a branch.

During the Cretaceous Period, several distinct groups of birds existed, reflecting a period of significant avian diversification rather than a narrow evolutionary bottleneck. Key groups from this era include:1

Enantiornithes: A major, widely distributed subclass of extinct birds that flourished throughout most of the Cretaceous Period.12
Odontornithes: A primitive group of toothed birds that included specialized foot-propelled divers such as Hesperornis and its relative Baptornis, as well as flying birds like Ichthyornis and Apatornis.31
Confuciusornithidae: An Early Cretaceous group that exhibited relatively primitive features compared to other lineages.1
Neornithes (Modern Birds): The infraclass that includes all living birds. Evidence suggests that ancestors related to modern groups—such as loons, grebes, flamingos, cranes, parrots, and shorebirds—were already present by the latest Cretaceous.31

While Archaeopteryx is often discussed in the context of avian evolution, it dates to the Jurassic Period, not the Cretaceous.3