An enantiornithine bird from the Lower Cretaceous of Queensland, Australia
Current classification of birds recognizes four subclasses: the Archaeornithes, the Enantiornithes, the Odontornithes and the Neornithes. Three of these subclasses were proposed during the nineteenth century, but the Enantiornithes was proposed only five years ago, based on material from the Lecho Formation (Maas-trichtian) of Salt a Province in Argentina1. Further material from Asia (Mongolia) and North America (Mexico) has been referred to the Enantiornithes2, all of it from the Campanian. Now, in addition, a small tibiotarsus found in the Lower Cretaceous (Albian) of Queensland not only represents the first bony material of Mesozoic birds from Australia, but is also the first reported occurrence of an enantiornithine bird in the Lower Cretaceous.
Why Australasian vertebrate animals are so unique - A palaeontological perspective.
Australasia has a unique fauna of living vertebrates, which include the oldest known species on the planet (the lungfish Neoceratodus) as well as many diverse, highly endemic families of fish, amphibians, reptiles, birds and mammals. The origin of most of the Australian vertebrate fauna has developed from two phases. Firstly, when Australia was subsumed within the greater Gondwana landmass, migration of animals from one region to another was possible by a land connection. Many of our most primitive forms of reptiles and mammals probably entered the country at this time, such as varanids, madtsooid snakes, monotremes and basal marsupials. Secondly, following the breakup of Gondwana, the isolation of Australia for its last 40 million years and subsequent changing climatic conditions drove the radiation of marsupial, reptile and amphibian families within the continent. The gradual aridification of central Australia further divided the landmass into discrete regional areas characterised by rainfall, vegetation, and climatic zones.
An Additional Character Linking Ratites and Tinamous, and an Interpretation of Their Monophyly
For more than a century there has been a debate as to whether the so-called ratites-the ostriches, rheas, emus, cassowaries, and kiwis, plus the extinct moas and elephant birds-were of common ancestry, or had evolved convergently from unrelated stocks. Superimposed on this argument was a debate as to whether these flightless birds had ever had flying ancestors, or had evolved directly from preflying ancestral forms. The latter school of thought has been largely discredited, but has had a few persistent advocates (see Verheyen, 1961, and papers cited therein). The debate as to monophyletic versus polyphyletic origin of the ratites, however, has continued, with outspoken adherents to either position. The volant tinamous were thought long ago by various authors to have some kind of affiliation with the flightless ratites, but their relationships could not be clarified until the “preflying ancestor” theory of ratite origins was disposed of. Much of the history of these debates, together with useful bibliographies, can be found in recent publications by Bock (1963), Meise (1963), and de Beer (1956, 1964), and details need not be recapitulated here. It is oversimplifying to state that the monophyletic and polyphyletic schools of thought have alternated in popularity, as at any one time adherents to both could probably be found. We suspect that some of the early classifiers might have admitted that the ratites could have arisen independently from unrelated flying ancestors, but that these birds were placed together in avian classifications merely for lack of any evidence as to what such ancestors may have been. McDowell (1948) concluded that the palaeognathous arrangement of the bones of the palate, long considered one of the major characters held in common by the ratites, was a heterogeneous composite. His work gave strong impetus to the polyphyletic school, which gave rise to some widely quoted papers (see Mayr and Amadon, 1951:3, and Stresemann, 1959:275), and reached its zenith in the dogmatic statement of the late Rene Verheyen (1960:293), part of which reads “. . . it is already firmly established that close relationship between the orders of Ratitae is pure fiction . . . .” Some of the recent synthetic and secondary literature has reflected this viewpoint. For example, Lagler et al. (1962:412) state, in a section entitled “Parallel evolution or convergence” in an ichthyology text: “The distribution of the large, flightless birds, the Ratites . . . is a classic example. Once thought to be intimately related and hence all placed in a single group, these birds are now knozm [italics ours] to have sprung from divergent ancestors . . . .” See also, in this connection, Mayr et al. (1953:42-43). As various kinds of evidence are reexamined and new data forthcoming, however, students of the ratites are returning to the theory that the similarities among these birds are, indeed, to be attributed to common ancestry (Sibley, 1960; Bock, 1963; Meise, 1963). There are obvious difficulties inherent in making comparisons between external features of adult birds as large as most ratites. During a study of natal downs, we handled and compared downy young of several ratites and tinamous, and we were struck by the constancy of a character of the bill, visible on adults but seen to much better advantage on small young. We believe this to be an additional piece of evidence favoring the theory of monophyletic origin of ratites and tinamous, and one