Klallamornis: the changing identity of a fossil diving bird

Klallamornis was a plotopterid, an extinct North Pacific seabird whose wings powered underwater swimming. The genus is known from fragmentary bones in Washington State and belongs to a group that evolved a penguin-like body plan independently of penguins. Its species history has recently changed: a 2025 revision transferred the older name Tonsala buchanani to Klallamornis and treated K. abyssa as a junior synonym because its limited type material could not be distinguished reliably. This makes the specimen record and its uncertainty central to the story. The extinct bird catalogue places Klallamornis among marine birds known from bones and separates evidence for diving anatomy from estimates of its full ecology.

Quick facts

A plotopterid from Washington

Klallamornis belongs to Plotopteridae, a family of large flightless seabirds known chiefly from the North Pacific. Plotopterids had powerful forelimbs adapted for underwater propulsion, giving them a penguin-like appearance in life. Their resemblance to penguins is an example of convergence: similar demands in water shaped similar functional solutions in birds that were not members of the same group.

The genus was established from fossils found in Washington State. Its type species, K. abyssa, was described from a partial skeleton collected in the Pysht Formation. Additional material from the region includes isolated bones assigned to Klallamornis or related plotopterids. Because the skeletons are incomplete, comparisons often depend on individual elements rather than a complete set of proportions.

The classification changed again in 2025. Mayr and Goedert reassessed the plotopterid fossils and transferred Tonsala buchanani to Klallamornis. They concluded that the holotype of K. abyssa is not clearly distinguishable from K. buchanani and synonymised the former name. The currently preferred combination is therefore Klallamornis buchanani, while earlier publications using K. abyssa remain part of the taxonomic history.

Why species names have shifted

Fossil species are diagnosed by features that distinguish their specimens from close relatives. The problem for Klallamornis is that several key fossils are incomplete and some species are represented by very few bones. The 2025 revision emphasized that the femur is the only major limb element preserved in the holotype of Tonsala buchanani. Without overlapping diagnostic bones, comparisons with K. abyssa are limited.

The two names had been separated in part because the known K. abyssa specimen was larger. Size differences alone can reflect individual growth, sex, geographic variation or a distinct species. A small sample makes it difficult to choose among those explanations. The recent authors judged the available diagnostic evidence insufficient to maintain both names, so they treated K. abyssa as a junior synonym of K. buchanani.

This taxonomic decision is not a claim that every plotopterid fossil belongs to one species. The genus has other material and the family includes several lineages. Rather, it revises a particular pair of names based on the specimens that can be compared. Future discoveries with overlapping bones could support or challenge this arrangement.

Wings built for underwater flight

Plotopterids are reconstructed as wing-propelled divers. Their shoulder and wing bones show features associated with forceful strokes through water, while their bodies were flightless. The fossil anatomy supports this broad locomotor interpretation, but muscles, feathers and exact motion are not preserved in the bones. Comparisons with living penguins and other diving birds help model function without making the groups close relatives.

Some plotopterid skeletons preserve strong attachment areas and robust elements suited to repeated loading. Those structures can indicate the direction and relative demands of movement. They do not yield an observed swimming speed or maximum depth. Such estimates require biomechanical assumptions and depend on body mass, feathering and physiology that may not be fully known for the fossil.

The group’s penguin-like outline can dominate reconstructions, but details such as plumage colour, bill covering and soft-tissue shape are not preserved for Klallamornis. Artistic scenes may depict a marine bird in motion, yet the precise appearance should be understood as an informed reconstruction. Direct evidence remains concentrated in the bones and their geological setting.

A North Pacific marine record

Plotopterid fossils are known from North Pacific coastal and marine deposits in Japan and western North America. Washington specimens place Klallamornis within this broader regional history. Formations such as the Pysht preserve marine vertebrates from changing Paleogene coastlines, but the fossil site marks where remains were buried, not the full route used by a living bird.

Fragmentary seabird bones may be separated before burial or lost through scavenging and erosion. As a result, local collections can contain a mixture of isolated elements and incomplete individuals. That uneven preservation affects both ecological reconstruction and taxonomy. A bone assigned to a genus may be informative about anatomy while still lacking enough characters to separate closely related species.

Plotopterids eventually disappeared, but the causes and local timing are not established by the Klallamornis specimens alone. Climate, ocean conditions and ecological competition are possible parts of a wider account, yet this fossil material does not test a single extinction mechanism. Its strongest contribution is evidence that a distinct family of large, wing-propelled divers occupied North Pacific seas during the Paleogene.