...or WAS it? Aepyornis maximus could reach a height of 9' or 10' when need be, although it probably didn't maintain that posture for long; more likely, it carried its head before it, rather than up like a periscope. The Giant Moa Dinornis giganteus edged it out in the height department, but Vorompatra is believed to have weighed in the neighborhood of ½-ton, heavier than any other bird...
...that is, until palaeontologists started unearthing the remains of rather large birds in Australia, which they now call "Dromornithids" ("Running Birds"). These flightless avians are also known as "Mihirungs": one particular species, Dromornis stirtoni, must have at least rivaled the Vorompatra in weight, but the evidence is not conclusive...yet.
There are a few sites out there that mention Mihirungs: I recently had to euthanize some dead links here, so you're better off using Google to find current information.
Finally, here's a selection from Alan Feduccia's The Origin and Evolution of Birds:
(p.286) Mihirungs. In 1979 and 1980, Patricia Rich (now Vickers-Rich) of Monash University unveiled a new group of large flightless Australian birds that she considered to be highly derived ratites. These mihirungs (Dromornithidae), as they are now known (from their aboriginal name meaning giant emus), are well represented in the Australian fossil record from the medial Miocene to the Pleistocene and are known from trackways in the late Oligocene of Tasmania, as well as from New Guinea. The dromornithids are also found in the late Paleogene and appear to have survived until at least 26,000 years ago. They were large (slightly larger than the living emu) to truly gigantic, ground-dwelling birds and have been variously allied with the ratites and galliforms, though their relations remain unclear. Storrs Olson (1985a, 104-105 1 ) argued that dromornithids were definitely not ratites based on cranial material in the Smithsonian that showed a trough-like mandible, and Vickers-Rich (1991, 742 2 ) stated that the cranial material is robust in the same manner as the Psittaciformes and the Alcedinedae, but in their detailed morphology were unique. Recently recovered cranial material shows a highly derived skull that is not clearly ratite or galliform (Vickers-Rich 1991 2 ).
At present, five genera and eight species, some quite gigantic, are known, with the greatest diversity occurring during the Miocene. Study of hindlimb morphology suggests that the graviportal (Dromornis) and cursorial (Ilbandornis lawsoni) forms existed, often sympatrically. Rich has argues that the mihirungs were herbivores, lacking both the hooked beak of such forms as the phorusrhacids and hooked ungual phalanges, and has suggested (Vickers-Rich 1991, 743 2 ) that they may have not been particularly successful at invading open grasslands, losing out to the emus and kangaroos, which were undergoing a rapid adaptive radiation as aridity, hence grassland, was overtaking Australia during the later Tertiary.
Dromornithids had a flat, unkeeled ratite-like sternum but lacked an open ilioischiatic fenestra of the pelvis. The Pleistocene genus Genyornis was about 2 meters (6.6 ft.) tall and was typical of the group in having a reduced medial digit of the foot and hooflike ungual phalanges. Other dromornithids, known from isolated bones, indicate a bird which may have rivaled or exceeded in weight any known fossil bird, including the elephantbird Aepyornis maximus (Rich 1979 3 ).
(p.401) In 1979 Pat Vickers-Rich described the then-newly discovered Australian mihirungs as a new group of large flightless birds considered to be highly derived ratites (see above, 286 3 ). Now, however, palaeontologist Peter F. Murray has discovered several skulls of Bullockornis planei 400 kilometers (250 mi.) north of Alice Springs. Murray concludes that these birds are not ratites, as cladistic analysis has indicated, but instead find their closest kin among the geese and ducks. This would certainly not be surprising, given the discovery of bizarre flightless gooselike birds, the moa-nalos, in Hawaii.
1 Olson, S.L. 1985. The fossil record of birds. In Avian biology, vol. 8, ed. D.S. Farner, J.R. King, and K.C. Parkes, 79-252. New York: Academic Press.
2 Vickers-Rich, P. 1991. The Mesozoic and Tertiary history of birds on the Australian Plate. In Vertebrate Palaeontology of Australasia, ed. P. Vickers-Rich, T.M. Monaghan, R.R. Baird, and T.H. Rich, 721-808. Melbourne: Pioneer Design Studio and Monash University Publications Committee.
3 Rich, P. V. 1979. The Dromornithidae. Bureau of Mineral Resources (Geology and Geophysics) Bulletin 184. Canberra: Australian Government Publishing.
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