Updated November 13 with a new skull from an 1896 academic journal,
evidently the best data available at present… better than a commercially available restored skull cast.
today’s topic fits in nicely with our current ‘giant birds‘ series.
While looking for data
on the palate of Aepyornis (the last data was published in Andrews 1896 and the palate, still unknown, was not recovered with the other skull pieces), I found a paper (Balanoff and Rowe 2007) and a Digimorph.org link that reconstructed the skull of an embryo (Fig. 4) found within a huge Aepyornis-sized egg (Figs. 1, 2) found in Madagascar and currently on display at the National Geographic Society.
Balanoff and Rowe report:
“The referral of this specimen to Aepyornithidae, including both Aepyornis and Mullerornis, is based largely on a geographical argument. No other ratites are known from the island of Madagascar, the source area for the National Geographic egg. The large size of the egg, provides a character with which this specimen may be diagnosed to Aepyornis. The length of the egg is 315 mm, and it is 224 mm at its widest point. The difference in the sizes of the eggs is large enough to distinguish between other ratite eggs and this particular Aepyornis egg.”
Alright… so what’s true here?
So far, only elephant birds (genus: Aepyornis, Fig. 1) are known to have eggs as large as the NatGeo egg (Fig. 1) and elephant birds are indeed from Madagascar. The large reptile tree (LRT, 1120 taxa) nests Aepyornis with the ostrich, Struthio, not the kiwi, Apteryx, which DNA suggests is the closest relative.
But more importantly,
what is inside the egg trumps size and location. With the earlier restored skull, analysis, nested the NatGeo embryo with the ostrich (genus: Struthio, Fig. 4) and the adult with the corn crake, Crex. The new skull nests Aepyornis with Struthio. Elephant birds have long been considered ratites, and this new data returns the elephant bird to the ratites, but not with the kiwi.
As in Struthio
and unlike other tested birds, the skull sutures of the NatGeo embryo are not fused.
As in Struthio and Aepyornis (with the new Andrews 1896 data)
and unlike other tested birds, the scapula and coracoid are fused.
The premaxilla + maxilla
are fused in the NatGeo embryo. These elements were misidentified originally as the premaxilla alone. As a result, Balanoff and Rowe also misidentified the palatines as the maxillae (Fig. 4) and, of course, did not identify any palatines despite the fact they could not be lost within the intact egg shell.
Furthermore, the skull of the NatGeo embryo
has the large, puffy squamosals found in Struthio and lacking in Aepyornis and other birds. The NatGeo embryo looks like Struthio (Fig. 4) and Aepyornis (Fig. 1). Note the flaring prefrontals (orange), the shape of the mesethmoid (light green) and the matching domed crania. All are strongly distinct from the restored commercial cast of Aepyornis, but are similar to the Andrews 1896 data.
The post-crania has not been considered here because
- embryo birds have different proportions than adults
- the NatGeo embryo long bones do not have ossified articular surfaces
This is not the first time a giant reptile
(birds are still reptiles!) became known first from its embryo. The IVPP embryo anurognathid pterosaur is the size of contemporary adult anurognathids and this taxon is also known, so far, only from its embryo. More info here.
Andrews CW 1896. On the skull, sternum, and shoulder-girdle of Aepyornis. Ibis, Seventh Series, 2:376-389.
Balanoff AM 2003. Osteological description of an embryonic elephant bird (Ratitae: Aepyornis) using high-resolution X-ray computed tomography, with a discussion of growth in Aepyornis. M.S. thesis, The University of Texas, Austin, Texas, 175 pp.
Balanoff AM and Rowe T 2007. Osteological description of an embryonic skeleton of the extinct elephant bird, Aepyornis (Palaeognathae: Ratitae). Journal of Vertebrate Paleontology 27(sp9):1–53.
Gefen E and Ar A 2001. Morphological description of the developing ostrich embryo: a tool for embryonic age estimation. Israel Journal of Zoology 47:87-97.