Nambashag: an early cormorant from Australia’s inland lakes

Nambashag was a genus of early cormorants from late Oligocene to early Miocene deposits of South Australia. Its two named species are represented by dozens of bones from the Etadunna and Namba formations, including elements of the jaw, shoulder, wing and hind limb. A character-based analysis places the genus among the early branches of the cormorant family. Swimming, diving and fish-eating are reasonable comparisons with living cormorants, not behaviours directly preserved with the fossils. The extinct bird catalogue includes Nambashag among birds known from inland Australian wetlands.

Quick facts

Two species in the Etadunna and Namba formations

Trevor Worthy named Nambashag in a 2011 revision of Oligo-Miocene cormorants from Australia. The genus name combines the Namba Formation with “shag,” a common English name for cormorants. The fossils came from the Lake Eyre and Lake Frome basins in South Australia, in deposits dated broadly to about 26–24 million years ago.

The type species, N. billerooensis, is represented by 30 specimens in the original study. Its holotype, SAMA P29079, is a right tarsometatarsus from the White Sands Basin locality near Lake Palankarinna, collected by M. Fuller on 9 July 1987. The second species, N. microglaucus, is represented by 14 specimens. Its holotype, SAMA P32584, is a right femur from Billeroo Creek in the Namba Formation. These type bones anchor the names; other elements are referred through comparison.

The collection includes jaw and quadrate fragments, vertebrae, shoulder and wing bones, femora, lower-leg bones and additional tarsometatarsi. These parts make comparisons across the body possible, but they do not form a single articulated bird. The difference in size between the named forms is accompanied by anatomical distinctions in the leg and wing, so the original authors did not interpret them as merely young and adult versions of one species.

Why the genus is classified as a cormorant

Worthy coded 113 skeletal characters and two integumentary characters for fossil and living suliform birds. In his analysis, Nambashag grouped as the sister taxon to the early Miocene European cormorant Nectornis miocaenus and living Phalacrocoracidae. That group was, in turn, sister to the snakebirds, Anhingidae. This is the basis for placing the Australian fossils within the cormorant family.

A sister taxon is a close branch on an evolutionary tree, not necessarily a direct ancestor. The position depends on which characters can be scored for fragmentary fossils and which living taxa are included. It is therefore appropriate to call Nambashag an early member of the cormorant lineage, rather than claim that a modern species descended from it.

The fossils also do not settle where cormorants originated. Similar-age cormorant relatives are known from Europe and Australia, and the 2011 analysis noted that older fossils were not then available to resolve the biogeographic question. The presence of both regions records a broad early distribution; it does not identify a continent of origin.

Size and likely movement

The type tarsometatarsus of N. billerooensis is 48.7 millimetres long. The type femur of N. microglaucus measures 38.8 millimetres, roughly 30 per cent shorter than the corresponding element of the larger species. The smaller bird was below the size of the living pygmy cormorants used in the original comparison. Bone lengths support relative size; they do not provide a direct body-mass measurement.

Wing bones assigned to both species retain proportions consistent with powered flight. No fossil shows a reduced wing skeleton like that of a fully flightless bird. The most economical interpretation is that these birds could fly, although a maximum range or speed cannot be reconstructed from the scattered elements.

Modern cormorants commonly swim and dive for aquatic prey, and the limb anatomy and family placement make comparable behaviour plausible for Nambashag. No specimen preserves stomach contents or a fish trapped with a skeleton. The depth of dives, prey sizes, time spent on land and whether the two species used different feeding niches are unknown.

Lakes, vegetation and fossil context

The Etadunna and Namba formations accumulated in inland South Australian basins. Associated fishes, turtles, crocodilians and aquatic mammals indicate persistent bodies of water. Some dolomite layers have been interpreted as evidence for shallow margins that could dry seasonally. Pollen from the Namba Formation records a landscape mosaic that included wet and temperate forest, reeds and sedges around the lakes.

The region is now arid, but its modern climate is not a reliable picture of the late Oligocene landscape. Nambashag inhabited an inland water system, rather than necessarily the sea coast used by many living cormorants. Fossil material from Lake Palankarinna, Lake Pinpa, Lake Yanda and Billeroo Creek helps map its occurrence across several parts of the basin system.

Both species are reported from the same broad deposits, but mixed occurrences do not prove that they nested together. Bone fragments can be transported or accumulated over time. The record does not show a colony, the composition of a flock or a direct competition between the larger and smaller forms.

Evidence and reconstruction

The fossil evidence establishes two differently sized cormorant relatives in inland South Australia around the Oligocene–Miocene transition. Their classification comes from a broad character analysis, while flight and aquatic feeding are functional interpretations informed by living relatives. The fossil setting supports freshwater or lake-margin environments, not a single precise daily habitat.

A reconstruction may depict a cormorant-like bird beside a lake, but plumage, bill colour, exact diving technique and prey are not preserved. The best-supported image should respect the known scale difference between the species without combining every referred bone into a single oversized individual.

Comparison with the marine Kairuku illustrates that unrelated water birds could exploit aquatic food in different ways. A penguin’s wing-propelled underwater movement should not be assigned to Nambashag merely because both are associated with water.