Moa-nalo are a group of extinct aberrant, goose-like ducks that formerly lived on the Hawaiian Islands in the Pacific. They were the major herbivores on most of these islands for the last 3 million years or so, until they became extinct after human settlement.
Chelychelynechen, meaning turtle-jawed goose, had a large heavy bill like that of a tortoise, while the other two genera, Thambetochen and Ptaiochen all had serrations in their bills known as pseudoteeth. All the species were large, weighing between 4 to 7.5 kg, and were flightless.
From the DNA sequences it has been estimated that the ancestors of the moa-nalo reached the Hawaiian Islands about 3.6 million years ago, by which time the genus Anas was already distributed worldwide. There they increased in size, but must have retained the ability to fly until they had spread to the newer islands. They seem to have lost the power of flight by the time the main island of Hawaii had emerged from the sea; there, their niche was filled by a giant Branta goose related to the Nēnē.
The unusual shape and size of the moa-nalo can be attributed to their role in the ecology of prehistoric Hawaii. A study of coprolites (fossil dung) of Thambetochen chauliodous found in Puu Naio Cave on lowland Maui has shown they were folivorous, at least in dry shrub or mesic forest habitats eating particularly fronds from ferns (possibly Asplenium nidus or Dryopteris wallichiana). This conclusion is backed up by the shapes of their beaks (James & Burney 1997). This indicates they were the principal browsers on the island.
The presence of prominent spines on the leaves and soft young stems of several Hawaiian lobelioids in the genus Cyanea - unusual in an island flora where such defenses are frequently lost, as in the ākala (Hawaiian raspberry) - suggests that the Cyanea evolved these thorn-like prickles on new growth as protection against browsing by the moa-nalo. The moa-nalo themselves filled the niche of herbivore usually filled by mammals such as goats and deer, or the giant tortoises of Galápagos and other archipelagoes. This has implications for the ecology of Hawaiian Islands today, as a major group of species have been lost.
The moa-nalo went extinct after the arrival of Polynesian settlers in the islands, along with many other species; because the flightless birds must have been considered a prime source of meat, probably around 1000 AD or even earlier. Like island taxa from Mauritius, New Zealand and Polynesia, they were unused to mammals and were easily taken by hunters or the animals that were introduced and became feral, such as domestic pigs.