Ruffled feathers among fossil bird experts
The discovery of Protoavis texensis
Some fossil finds might be imagined that are particularly controversial for evolutionary theories. For example, suppose a human fossil were found in rocks that were belowAustralopithecus, the african ape thought to be ancestral to man? Such a find would generate intense controversy among anthropologists, as many of them have devoted their lives to the minute study of fossil bones in order to trace evolutionary relationships.
Transfering these thoughts to the world of fossil birds will assist understanding of developments in the past year. For over 100 years, Archaeopteryxhas been in the limelight: it occurs at a deeper horizon in the fossil record than any other known bird, and it has a remarkable variety of reptilian features which have been considered to be evidence of its transformation from a reptilian ancestor. The main discussion has been concerned with the question: which ancestor? The favoured route has been through the dinosaurs. Numerous experts support the idea that Archaeopteryx was a feathered dinosaur. The media have latched on to this theory: we are informed that the dinosaurs have not vanished leaving only fossils behind them; their descendants are alive and well - and have the habit of frequenting the bird-tables in our gardens!
The discovery of two fossil birds in Texan rocks by Chatterjee (of the Technical University in Lubbock, Texas) has really set the cat among the pigeons! The fossils come from rocks that are considered to be 75 million years older than Archaeopteryx - old enough to predate all potential dinosaurian ancestors. Scholars in this field have pronounced the discoveries `astounding'. Professor John Ostrom (of the Peabody Museum of Natural History, Yale University) declared: `It seemed unthinkable that birds 75 million years more ancient [than Archaeopteryx] could have existed'. (Nature, 19 September 1991, 212).
The story broke in 1986, when Chatterjee was able to examine closely some specimens first excavated in 1983. Then, a cloak of secrecy surrounded the fossils, and we have had to wait 5 years for the first of a series of formal reports by Chatterjee to appear. A complete issue of the Philosophical Transactions of the Royal Society ( B332, 1991, 277-364) was devoted to the description of a fossil bird called Protoavis texensis. This emergence into the limelight certainly caught the imagination of the headline writers, with: `Early bird catches Archaeopteryx on the hop' (The Independent, 24 June 1991) and `Early bird threatens Archaeopteryx's perch' (Science, 5 July 1991, 35). Larry Martin, a fossil bird expert at the University of Kansas, is quoted as saying: `There's going to be a lot of people with Archaeopteryxeggs on their face'.
What does Chatterjee claim for his fossils? They belong to two specimens of the same species. Like Archaeopteryx, Protoavis has a long bony tail and several other reptilian features, but the skull, forelimbs, shoulder and hip girdle are bird-like. It had a flexible neck, a large brain, binocular vision, portals linking the rear of the skull to the eye sockets, and a wishbone. Chatterjee argues that the find breaks all postulated links between birds and dinosaurs. If there was a common dinosaur ancestor of both birds and dinosaurs, it has yet to be discovered. Furthermore, all the hypotheses about the origin of flight in birds must be revised. Chatterjee considers that true flapping flight was well-developed in Protoavis.
Such a dramatic revision of the evolutionary consensus has provoked many firm responses. One authority on Archaeopteryx says of Chatterjee's conclusions: `Calling this the original bird is irresponsible'. The reconstructions presented were compared to `reading tea leaves in the bottom of a dark cup'. The strongest criticisms have come from Professor Ostrom (the originator of the hypothesis that birds are closely related to dinosaurs). He writes of Chatterjee's lengthy paper:
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`The reader is thus presented with an incomplete analysis and an inadequate
sense of the poor quality of preservation. Even Chatterjee's promise of
a sequel, in which he says he will deal with the post-cranial remains and
discuss the origin of avian flight, cannot remove the strong feelings that
emerge after reading the report in detail - ones of disbelief about the
claim and disappointment about the way it has been presented'.
Creationists are able to make several observations on this controversy. Since the Bible speaks of God creating the winged birds as `kinds'separate from the livestock, creatures that move along the ground, and wild animals (Genesis 1:21-25), we do not feel under any obligation to explain the origin of birds, nor even the origin of flight, by evolutionary processes. Furthermore, we do not find anything astounding about discovering a fossil bird at a geological horizon below others containing dinosaurs. Consequently, Chatterjee's work can be evaluated on its merits, without the emotionally-charged atmosphere which is apparent from the reported reactions.
Although science is presented popularly as the work of fair-minded and objective seekers-after-truth, we are able sometimes to go backstage, to get beyond the formality and to see scientists behaving in very human ways. Such is the case here: some of the criticisms of Chatterjee are valid, but the reactions of scholars to his published report come far short of objective assessment. We might note that this situation is not new to creationists: we have often found that our arguments provoke emotional, rather than rational responses. We look forward with great interest to Chatterjee's further contributions.
David J. Tyler (1992)
