Mancalla: a flightless diving auk of the Pacific coast

Mancalla was a genus of flightless auks from the eastern Pacific coast of North America. Its short, robust wings were adapted for underwater propulsion rather than aerial flight, a solution that evolved independently from the wing-propelled diving seen in penguins. Fossils, especially the characteristic humerus, come from Miocene and Pliocene marine deposits in California and nearby regions. A 2011 revision re-examined old names, recognised new species and separated the very large genus Miomancalla. The extinct bird catalogue treats Mancalla as a member of the auk lineage, not as a penguin or an ancestor of the much later great auk.

Quick facts

A distinctive auk from Pacific deposits

Frederic Lucas established the genus Mancalla in 1901 for flightless auks from the Pacific coast. During the following century, additional bones from California and other coastal localities accumulated in museum collections. Humeri are especially common and robust, so they became central to identifying the group. Their shape records a powerful wing built for movement underwater, even though the same wing no longer supported flight through the air.

The growing collection also made taxonomy difficult. Fossils differed in size and proportion, and authors had to decide whether those differences represented distinct species, variation within one species, or specimens belonging to another genus. Labels created under an older arrangement can therefore conflict with a modern catalogue. The fossil itself remains the same; the scientific name changes when comparison and diagnosis are revised.

In 2011, N. Adam Smith published a major systematic revision of flightless mancallines. It reviewed previously described and newly studied fossils, diagnosed three new species and presented a species-level phylogenetic hypothesis. The revision also erected Miomancalla for the exceptionally large form formerly grouped with Mancalla. This left Mancalla more narrowly defined and made it easier to compare species without treating every large mancalline bone as interchangeable.

Wings built for diving, not flight

Mancallines were members of Pan-Alcidae, the broader auk lineage. Within that northern seabird group, the wings of Mancalla became short and robust. The proportions and muscle-attachment areas of the humerus support strong strokes in water. Once specialised for underwater flight, the wing was no longer effective for taking off and travelling through the air. This functional transition is evident from the skeleton, although the precise swimming performance of each species cannot be measured from isolated bones alone.

The resemblance to penguins is a case of convergent evolution. Penguins use their wings to fly underwater in southern oceans, while mancallines were a separate branch of northern auks. Similar demands of pursuing prey below the surface can lead to compact, forceful wings in unrelated lineages. The body shape of a reconstruction should not be read as evidence that a mancalline was a penguin or shared a recent ancestor with one.

The great auk, Pinguinus impennis, is another flightless alcid, but it lived much later and was not simply the direct continuation of Mancalla. Flightlessness arose more than once within the auk lineage. The evolutionary relationships recovered in the 2011 analysis help separate those events from superficial similarities in body form.

Species, size and the Miomancalla distinction

The genus includes several named species recognised through differences in the preserved bones. The 2011 revision reassessed long-used names such as M. californiensis and M. cedrosensis, described new species including M. lucasi, and reassigned some fossils that had previously been placed in M. diegensis. The exact contents of the genus therefore depend on the updated diagnoses, not on every historical label that used the name.

Body size varied among species. The especially large bird named Miomancalla is no longer counted as an unusually huge Mancalla. This distinction matters for estimates of mass and comparisons with living auks: combining the genera would exaggerate the size range attributed to Mancalla and blur the evolutionary pattern. It is not possible to assign one precise length or mass to the entire genus from a mixed collection of isolated elements.

Most fossils are disarticulated, so a complete skeleton for each species is not available. Some elements overlap enough to compare, while others are known only from particular deposits. New finds can test the diagnoses, especially where a specimen preserves bones not represented in the type material. Until then, the safest approach is to state which species and bones support a particular anatomical or size claim.

Pacific seas and the limits of diet evidence

Mancalla fossils occur in marine deposits along the eastern Pacific margin, including Miocene and Pliocene formations of western North America. The coastal record places the birds in a productive marine setting, but a bone's burial locality is not a complete map of an animal's foraging range. Sea level, currents and the preservation of coastal sediments changed through time, so species from different formations lived in distinct ecological contexts.

Fish and squid are reasonable candidate prey for a wing-propelled diving auk. Other marine invertebrates may also have contributed. Yet the known skeletons do not preserve stomach contents tied to a particular species, so the exact menu and feeding technique remain uncertain. Wing anatomy shows how the bird moved underwater more clearly than what it ate there.

The disappearance of mancallines is also not explained by one proven event. Late Neogene changes in marine conditions and food webs may have altered habitats, while other diving seabirds occupied the same broad environment. Competition is a possible ecological hypothesis, not a conclusion established simply because different taxa occur in the same fossil record. The secure result is a diverse auk lineage that included independent, flightless underwater specialists.