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THIRD REVISED EDITION
Pages 19 - 20
In 1861, near the Bavarian town of Pappenheim, a worker in a lithographic limestone quarry found a fossil feather on a slab and its impression on the counter slab. Later in the same year the incomplete skeleton of a feathered animal was found in the quarry. This skeleton of the oldest known bird was the first of three to be unearthed, and it provided palaeontologists with tangible evidence of the reptilian origins of birds. This bird, Archaeopteryx lithographica, was about the size of a crow and lived in the cycad forests of the late Jurassic period, that is, about one hundred and forty million years ago. It seems to have survived unchanged for quite some time and may have been one of the earliest of birds, judging by the number of purely reptilian features absent in all later birds. Its feathers were identical in structure to those of modern birds.
Bird bones are fragile and many are hollow, and thus easily broken and fragmented. Few land birds die where their remains can be buried in waterlaid sediments, the richest source of fossils, and it may also be assumed that many ancient birds, like those of the present, were preyed upon by carnivorous animals. Therefore, birds are poorly represented in fossil deposits and our knowledge of their evolutionary history is not as good as for reptiles and mammals. Indeed, Brodkorb has estimated that, between the time of Archaeopteryx and the present, up to two million species of birds probably existed, yet we have specimen evidence for the existence of less than ten thousand species, that is about half of one per cent (in Austin, 1961). However, from what we do have we are able to reconstruct sketch pictures of the early histories of most present-day groups of birds.
The Eocene epoch commenced about sixty million years ago and spanned approximately twenty million years, and from this epoch onward bird fossils became increasingly plentiful. Forms closely resembling those living today had replaced the toothed birds of Mesozoic. So many fossil birds from the early Tertiary period are assignable to living groups that most, possibly all, living orders have arisen by, or evolved during Eocene. Of course, there were also characteristic forms which became extinct then or later (e.g. the terrestrial diatrymids).
Several authors have expressed clearly the doubts about conclusions reached by comparing fossil material with existing birds. It is widely accepted that forms related to birds living today existed as far back as the Eocene, but there have been unjustified identifications made from inadequate material. For example, Holyoak (I97Ib) points out that an upper mandible, fragment of a skull, and two palatines of a parrot collected in Pleistocene deposits near Buenos Aires, Argentina, were assigned by Lyddekker to the genus Conurus (= Aratinga), but from the few characters it shows the specimen could represent a member of any one of fourteen living South American genera.
The earliest fossil parrot is Archaeopsittacus verreauxi from the upper Oligocene or lower Miocene, that is, about thirty million years ago; it was described by Milne-Edwards from a complete tarsometatarsus found near Allier, France. Olson points out that there can be no doubt that Arachaeopsittacus is correctly referred to the Psittaciformes, and it seems to have been a rather small parrot (in litt., 1977). The oldest representative of a modern genus is Conuropsis fratercula from the upper Miocene, that is, approximately twenty million years ago; it was described from a left humerus found in Nebraska, United States of America. Cyanoliseus ensenadensis and Aratinga roosevelti, from Argentina and Ecuador respectively, date from the Pleistocene, that is, less than one million years ago, and are representatives of two extant South American genera.
PARROTS AND OTHER BIRDS
Dorst (1964) says, ‘Almost no other large group of birds is more sharply set apart from all others than the parrots, which form an exclusive order by themselves.’ Stresemann (1927 – 34) came to the conclusion that the parrots are a distinctive ancient group, well warranting their ordinal rank. In a A Classification for the Birds of the World (1960), Wetmore places Psittaciformes after Columbiformes (the pigeons) and before Cuculiformes (the cuckoos and touracos). Mayr and Amadon (1951) point out that that the parrots are a strongly differentiated group; resemblance to Falconiformes must be distant. After carrying out a comparative study of the egg-white proteins, Sibley and Ahlquist (1972) came to the conclusion that the parrots are a distinctive group of birds, but their nearest allies seem to be the pigeons; a single a single superorder comprising the Psittaciformes and Columbiformes was proposed. Burton (1974) also favours the view that Columbiformes are the order most closely related to the Psittaciformes, pointing out that several features seen in the Tooth-billed Pigeon Didunculus strigirostris show a significant trend towards conditions in parrots.
I agree that there seem to be no obvious close relationship between parrots
and other groups of birds, but pigeons may be nearest. While watching fruit
pigeons (Ptilinopus spp.) feeding with fig parrots and lorikeets in large
forest trees I have often noticed similarities in their actions and general
behaviour. Pigeons also have fleshy ceres at the base of their bills and
the plumage patterns of some species, particularly the fruit pigeons, are
like those of parrots. Of course, superficial similaritiescan be found in
other groups of birds. For example, hawks and owls have bills somewhat resembling
those of parrots. Zygodactylous feet are possessed by woodpecklers, jacamars,
barbets, and toucans, all members of Piciformes; by cuckoos and touracos,
both of which belong to Caculiformes, and by the Trogoniformes, which have
the inner or second instead of the outer or fourth toe turned backwards.
Powder downs, which are well developed in parrots, are also present in herons-members
of Ciconiformes, toucans-members of Piciformes, and in bowerbirds–members
Forshaw, Joseph M. (1989)
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