Why the vast majority of modern birds remain an evolutionary puzzle for scientists

Nature · Published 30 September 2026 Swipe more like this →

In short: Almost every bird you see today belongs to a single, massive group called Neoaves. Despite making up 95% of all known avian species, their family tree is notoriously difficult to map. Rapid evolution during a mass extinction event left behind a tangled web of relationships that researchers are still struggling to untangle.

Neoaves encompasses nearly all modern birds, excluding only the ratites and the group containing ducks and chickens. Defined in 2022 by George Sangster and his team, this clade accounts for roughly 9,500 of the 10,000 known bird species. Their early history is marked by an explosive radiation that occurred around the time of the Cretaceous–Paleogene extinction, a period of such rapid diversification that it obscured the ancestral links between different lineages.

Because this expansion happened so quickly, scientists have faced significant hurdles in determining how these groups relate to one another. Early attempts to reconstruct their history were highly contentious, and even modern genomic studies struggle to reach a consensus. For instance, a 2014 study by Jarvis and colleagues split the group into two primary branches, while a 2015 analysis by Prum and colleagues proposed an entirely different structure. Later research by Reddy in 2017 suggested these discrepancies stem from the specific types of genetic data used, with coding sequences favoring the Prum model.

The ongoing debate is so intense that some researchers, such as Alexander Suh in 2016, have argued that the base of the Neoaves tree should be viewed as a simultaneous split into nine distinct lineages rather than a traditional branching pattern. While a 2019 study by Houde and colleagues refined this to a smaller set of six, the overall high-level structure remains unresolved. Despite these disagreements, there is some stability; most experts now recognize a set of supraordinal groups, including the large waterbird clade Aequornithes and the landbird clade Telluraves. Currently, the most widely accepted arrangement involves grouping Aequornithes with Eurypygimorphae into a single unit known as Phaethoquornithes, though even this remains a subject of active scientific investigation.

Ultimately, the true phylogeny of Neoaves is best described as a polytomy—a point where the relationships between branches remain uncertain. While the magnificent seven clades and three orphaned orders provide a framework, the exact sequence of their emergence is still a work in progress, highlighting how much remains to be discovered about the history of the avian world.

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