It is the culmination of 2 years work. I am extremely proud of the finished product, and honoured to have taken part in this project. It started as an honours project in mid 2013. The aim of which was to assess the digging capabilities of the extinct giant Pacific Galliform bird Sylviornis neocaledoniae in order to address the veracity of its inclusion within the Megapodiidae family (mound-builder birds) and the claims that it was thus responsible for the enormous mounds that still exist on New Caledonia today.
This bird has been a mystery for the last 36 years. Extremely fragmentary specimens were originally described by Poplin in 1980, who originally concluded it was a ratite. Subsequent authors suggested that Sylviornis belonged among the megapodes. This was reassessed with the discovery of a skull, and the bird was placed in its own family Sylviornithidae (although still commonly, and erroneously referred to as ‘The New Caledonian Giant Megapode’). And there it remained for decades with little more than a horribly inaccurate skeletal reconstruction appearing in a single textbook – Vertebrate Palaeontology of Australasia by Pat Vickers Rich.
My honours supervisor Dr. Trevor Worthy collected hundreds of bones from the Pindai Caves on New Caledonia in 2003. I began work in mid 2013. For months it was my job to sort, prepare, and catalogue the fossils. I prepared the extremely fragile bones with acetone and Mowital B30 consolidant. Due to the porous nature of bone, the acetone penetrates to the core. At this point the Mowital is applied, and as the acetone evaporates it draws the fast drying plastic in. The hardened bone has a slight gloss and can now be handled safely.
I then measured the bones of Sylviornis and every single megapode and chicken specimen in the collection at the South Australian Museum. Trevor had several specimens mailed over from the Western Australian Museum. In search of more data points, I travelled interstate to Museum Victoria and spent several days measuring all of the megapode and chicken specimens in that collection as well (side note, it was a refrigerated room the size of three basketball courts, and I was woefully unprepared for that on the first day. I brought a coat with me the next day). We also managed to get someone from the bird group at Tring to access the holdings of the Natural History Museum (London) and measure the bones of two Macrocephalon maleo specimens which could not be mailed to South Australia. With this data I produced several size standardized PCA (principal component analysis) graphs comparing Sylviornis with extant megapodes and chickens. I also produced a Simpson Log Ratio Diagram which compared the megapodes and Sylviornis against Gallus as a reference taxon. I won’t go into details because these statistics eventually found their way into the published paper and you can read that if you are so inclined. Put simply; Sylviornis consistently aligned closest to Gallus and generally away from the ‘strongest’ mound-builders.The next clue came from studying the anatomy of Sylviornis. In fact, remember the exact moment it all started to fall into place. It was around 1:00 am and I was alone in the lab and just about to pack up for the night and go home. I decided to take one last look at the Sylviornis specimens before heading out. So I opened the compactus and picked up an ungual. I had previously spent the afternoon measuring the feet of several Leipoa specimens from the South Australian Museum, and turning the Sylviornis claw over in my hand a major morphological difference became suddenly apparent. There was virtually no tuberculum extensorium! The tuberculum extensorium is a very prominent knob of bone on the plantar surface of the unguals of most extant megapodes. This feature is reduced in ‘weak’ mound-builders such as Aepypodius and Talegalla, and non mound-builders such as Macrocephalon and Gallus. The unguals of Sylviornis were also slightly more curved, and more lateromedially compressed than those of any mound-building megapode, and more akin to Gallus which does not dig mounds at all.
Several weeks later I had assembled a composite adult foot of Sylviornis by selecting the largest examples of each bone. Another morphological difference jumped out at me while describing the pelvic limb. The toes of Sylviornis were robust and stout, quite unlike the long thin toes of the megapodes. The tarsometatarsus also exhibited several features indicative of a reduced digging ability. The wing-like flange on the external plantar surface of trochlea metatarsi II in Sylviornis, although present, is not as pronounced as in the extant mound-building megapodes, indicative of a limited dexterity in the second toe. The hypotarsus is reduced, and the fossa parahypotarsalis medialis is smaller and much shallower than that of any megapode. The foramen vasculare distale is closed in Sylviornis, resulting in a re-routing of the tendons and blood vessels that lead to the toes.
Combined these features indicate a reduction in the strength of the tendons that operate the toes.
The fossa metatarsi I of Sylviornis occurs low on the tarsus and is extremely shallow. This indicates a weak grip for perching. Due to its large size and reduced wings, Sylviornis was completely terrestrial. Therefore it stood to reason that it laid its eggs on the ground. The question then became, did it make a typical nest and incubate the clutch by sitting on the eggs like most birds do, or did it bury them in a trench or a mound as required of ectothermic incubation which typifies extant megapodes.
On the basis of the osteological observations outlined above, I concluded that Sylviornis was poorly adapted for the strenuous and prolonged digging effort required for digging a large mound.
Dr. Mike Lee conducted the phylogenetic study that was published in our paper, which removed Sylviornis from the megapodes and grouped it with Megavitiornis in the Sylviornithidae family as a stem Galliform, vindicating my conclusions from honours based solely on osteology.
The story hit the news about a week ago. It made the local paper, and a couple of online news sites picked it up.
It has since been making the rounds on several blogs and websites.
Stay tuned. I will upload the skeletal reconstruction, Life sketch, and the plates I made for the paper (along with some photos I took during honours) shorty...