Nanantius eos
Molnar 1986

Click image to enlarge

    Tiny Enantiornithine bird
    Enantiornithes, Aves, Aviale, Maniraptora,
    Coelurosauria, Tetanurae, Theropoda
    Early Cretaceous (Albian)
    Toolebuc Formation
    The size of a blackbird

    Near Boulia,
    western Queensland

Nanantius eos remains were found in bone-rich limestone deposits of the Toolebuc Formation, on Warra Station near Boulia, in Queensland. Dr Ralph Molnar dissolved samples of this limestone in an acidic solution to expose the delicate fossils. The holotype is an almost complete 3 centimetre (1.2 inch) tibiotarsus (lower leg bone). It has been recognised as Enantiorithine by the round proximal articular surface, the smooth craniolateral cnemial crest, and a wide and bulbous medial condyl (all that from one 3 cm bone!). Other remains from the same region have also been designated as Nanantius sp. These include another (less complete) tibiotarsis found in 1990, which has some areas preserved that were missing from the type material. A vertebra (back bone) was also discovered in 1979, although it had been identified as that of a lepidosauromorph (lizard), then correctly as a bird, then as that of a small theropod dinosaur, until finally being recognised as being Enantiornithine. Few complete and uncrushed Enantiornithine vertebrae are known, and this well preserved specimen suggests that Enantiornithines had a distinctive process of vertebral development unlike that of "true" birds.

Other Enantiornithine species are known from the Maastrichtian of Argentina (Enantiornis leali, Neuquenornis volans, Yungavolueris brevipedalis, Soroavisaurus australis), the Campanian of Mexico (Alexornis antecedens) and Mongolia (Gobipteryx minuta, Nanantius valifanovi), and from the Early Cretaceous of Spain (Concornis lacustris) and China (Sinornis and Cathayornis). Sizes ranged from a 1 metre (3.5 foot) wing span for Enantiornis, down to the sparrow-sized Concornis. Avisaurus archibaldi From Late Cretaceous Montana in the U.S.A., and Hulsanpes perlei from the Late Cretaceous of Mongolia, may also belong to this clad.

Enantiornithines were primitive flying birds that belonged to a separate branch than that which led to modern "true" birds. They had some things in common with "true" birds, such as advanced flight capability and perching feet. However there seem to be more differences than similarities. The structure of the pelvis, and the articulating surfaces of the hind limbs, are quite different. Some Early Cretaceous forms had toothed beaks, like those of many Mesozoic bird species, although most later Enantiornithines developed toothless beaks like those of "true" birds (although this condition was probably achieved independantly from that of the "true" bird line).

Enantiornithines became extinct at the end of the Cretaceous, along with their dinosaur relatives, and are thought to have no living decendants.

Chiappe, L.M. 1996 Early avian evolution in the southern hemisphere: the fossil record of birds in the Mesozoic of Gondwana. Memoirs of the Queensland Museum 39(3):533-554

Kurochkan, E.N. and R.E.Molnar 1997 New material of enantiornithine birds from the Early Cretaceous of Australia. Alcheringa 21:291-297.

Molnar, R.E. 1986 An enantiornithine bird from the Lower Cretaceous of Queensland, Australia. Nature 322:736-738.