Sylviornis

Sylviornis Temporal range: Holocene
Sylviornis neocaledoniae skull fragment and tibia, Muséum national d'histoire naturelle, Paris
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Pangalliformes
Family:	†Sylviornithidae Mourer-Chauviré & Balouet, 2005
Genus:	†Sylviornis Poplin, 1980
Species:	†S. neocaledoniae
Binomial name
†Sylviornis neocaledoniae Poplin, 1980

Sylviornis is an extinct genus of stem-galliform bird containing a single species, S. neocaledoniae, or erroneously, "New Caledonian Giant Megapode". Technically, the latter is incorrect because it has recently been found not to be a megapode, but the sole known member of its own family, the Sylviornithidae; at the time of its description, it was believed to be a ratite. Sylviornis was never encountered alive by scientists, but it is known from many thousands of subfossil bones found in deposits, some of them from the Holocene, on New Caledonia and the adjacent Île des Pins. Recent morphology studies indicate that it was sister taxa with Megavitiornis, in a clade outside of the Galliformes crown group.

Sylviornis was a huge, flightless bird, 1.7 m (5.6 ft) long altogether, and weighing around 30 kg (66 lb) on average. It is the most massive galliform known to have ever existed. It had a large skull with a high and laterally compressed beak surmounted by a bony knob. Its legs were rather short, but had strong toes with long nails. The skeleton has a number of peculiarities and differences that make Sylviornis stand apart from all other known birds: the clavicles were not fused to a furcula, the number of caudal vertebrae was very high, and the ribcage and pelvis were almost dinosaurian in appearance. The wings were reduced to small stubs.

A large proportion—up to 50% in some deposits—of the remains found were from juvenile animals. Thus, it has been theorized that Sylviornis had a clutch of at least two, more probably closer to 10 eggs, and that the average lifespan was not much more than 5–7 years, which would be extremely low for such a large bird. It was thought that the bird did not incubate its eggs but built a mound similar to the megapodes. Tumuli on the Île des Pins which were initially believed to be graves were found to contain no human remains or grave goods, and it has been hypothesized that they were in reality the incubation mounds of Sylviornis. As these mounds are up to 5 m high and 50 m wide even after nearly four millennia, they seem too large to have been made by the giant scrubfowl, an extinct New Caledonian species of megapode.

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