The Evolutionary study of some Archaeologically Significant Avian Taxa in the Quaternary of the Western Palaearctic.
Authors: Stewart, J.R.
Place of Publication: Oxford, England
The book sets out to examine four taxa of birds in the Quaternary that exhibited interesting morphological anomalies in order to address whether these were the result of inter- or intraspecific processes. Modern skeletal material of these taxa from a wide geographical area was examined so as to make a more realistic assessment of the fossils than had previously been achieved. Similarly, fossils were studied from a wider geographical and temporal range than before.
The study of the four chosen taxa was carried out with an acknowledgement of a variety of theoretical issues in biology, which affect the interpretation of such fossils.
Both members of the genus Lagopus (Red/willow grouse Lagopus lagopus and ptarmigan L. mutus) were found to change in the robusticity of certain osteological elements through time. This change may have occurred at the Pleistocene / Holocene boundary, and has been interpreted as indicating a reduction in mean size, possibly due to the environmental transition taking placeat this time. The study of cranes (Grus) revealed that the extinct species G.
primigenia, which was named in the last century, should be synonymised with the common crane G. grus. This study found that there were few birds prior to the Roman period which corresponded in size to modern females of G. grus. As cranes are distinctly sexually dimorphic, it would seem that the large fossil bones which were described as a larger extinct species represent the males, and the fossils which were the size of modern males were probably the females.
Ravens were also studied here and were found to be highly variable in size and shape across their range in Europe. They appear to follow both Bergmann’s and Allen’s rules. A more thorough study of Corvus antecorax, the extinct middle Pleistocene raven, confirmed its size and metric-shape differences from all modern populations and subspecies available. However, the validity of the species’ status is questionable because of the variability within the species today.
Finally, the work on Quaternary fossil starlings (Sturnus), showed that a population of large starlings, probably with different wing bone length ratios, had existed in south-west Britain about 100,000 years ago. Furthermore, based on ecomorphological criteria, the fossil population of starlings may have been more sedentary than modern British starlings. Today, there are similarly large sedentary starlings in the south-west and west of Europe, some of which are distinct subspecies and one of which is a separate species. This led to the suggestion that the genus Sturnus has more than once given rise to large sedentary populations of starlings along its western and south-western limits. This is likely to be a climatically driven system, which may be a novel speciation mechanism for birds - the degree of migratory versus sedentary lifestyles of the various populations being the mechanism for isolation that enabled genetic differentiation.
The study has shown that it is necessary to examine as much modern and fossil material as is available before fossils can be interpreted realistically. This generally leads to a more conservative assessment of morphologically anomalous fossils because variation occurs both above and below the level of species. This in turn has lead to a greater emphasis on ecomorphology than on taxonomy.
Preferred by: John Stewart