The Hawaiian Superducks

The turtle-jawed moa-nalo, Chelychelynechen quassus, largest of this group of birds. Image by Stanton Fink.

The always impressive Darren Naish put up a post a couple of days ago on recent publications about phorusrhacoids, the giant carnivorous birds that once stalked South America (and only a gigantic carnivorous bird can truly be said to "stalk"), including (among other things) the recent claim that one supposed phorusrhacoid, Brontornis, was not a phorusrhacoid at all but a relative of the Anseriformes. In the course of the comment thread on that post, mention has been made of the moa-nalo, and I thought I'd put up an explanatory post for anyone not familiar with the latter.

Moa-nalo were large (up to 7.6 kg - Ziegler, 2002), flightless goose-like birds that were once found in the Hawaiian Islands, but seem to have not long survived the arrival of hungry humans. To date, four species have been described from various islands (Olson & James, 1991) - Chelychelynechen quassus from Kauai*, Thambetochen xanion from Oahu, T. chauliodous from lowland Maui and Molokai, and Ptaiochen pau from highland Maui. Moa-nalo are not yet known from the main island of Hawaii, which was home to two species of Branta goose (Paxinos et al., 2002), including the (just) surviving nene (B. sandvicensis). Branta geese were also found on the other Hawaiian islands. Wetmore (1943) described a fossil anserid species from Hawaii, Geochen rhuax, that he regarded as distinct from Branta (and very like the Australian Cereopsis), but the fragmentary remains this species was described from are not really sufficient to tell whether it is a goose or moa-nalo (or something else again)**. The unnamed 'giant Hawaiian goose' of Olson & James (1991) is quite definitely a Branta (Paxinos et al., 2002).

*Wryly amusing quote of the day comes from the etymology of the species name for this taxon (Olson & James, 1991): "Latin, quassus , broken, shattered, in reference to the regrettably fragmented condition of the type material, which was probably deposited as a complete skeleton but was unfortunately exposed in a jeep trail."

**Olson & James (1991) again, referring to the discovery of the Geochen material underneath an old lava flow: "From their very friable and warped appearance, the bones were almost certainly heated until glowing, with all organic material in the bone having been combusted."

Perhaps most interesting about the moa-nalo is their phylogenetic relationships (isn't it always?). Despite their goose-like appearance, Olson & James (1991) suggested on the basis of their ossified syringeal bullae that moa-nalo were actually more closely related to the dabbling ducks of the genus Anas (two species of which are also found on Hawaii), and possibly even derived from the common mallard (A. platyrhynchos). This view was corroborated to some extent by ancient DNA analysis (Sorenson et al., 1999) which, while it found the moa-nalo as the sister group to Anas rather than within it, definitely indicated a duck rather than goose ancestry for them. The moa-nalo therefore seem to have undergone a rapid and significant change in morphology as they adapted to flightless herbivory. The Molokai population of Thambetochen chauliodous seems to have actually gone so far as to lose the furcula!

REFERENCES

Olson, S. L., & H. F. James. 1991. Descriptions of thirty-two new species of birds from the Hawaiian Islands: part I. Non-Passeriformes. Ornithological Monographs 45: 1-88.

Paxinos, E. E., H. F. James, S. L. Olson, M. D. Sorenson, J. Jackson & R. C. Fleischer. 2002. mtDNA from fossils reveals a radiation of Hawaiian geese recently derived from the Canada goose (Branta canadensis). Proceedings of the National Academy of Sciences of the USA 99: 1399-1404.

Sorenson, M. D., A. Cooper, E. E. Paxinos, T. W. Quinn, H. F. James, S. L. Olson & R. C. Fleischer. 1999. Relationships of the extinct moa-nalos, flightless Hawaiian waterfowl, based on ancient DNA. Proceedings of the Royal Society of London Series B – Biological Sciences 266: 2187-2193.

Wetmore, A. 1943. An extinct goose from the island of Hawaii. Condor 45 (4): 146-148.

Ziegler, A. C. 2002. Hawaiian Natural History, Ecology, and Evolution. University of Hawaii Press.