by Richard L. Deem M.Sc.
The striking resemblance between the bones of the theropod dinosaurs (the so-called "bird-like" dinosaurs) and Archaeopteryx (one of the most ancient birds - which lived roughly 150 millions years ago) has led scientists to hypothesize that birds are descendants of these dinosaurs. The figure at the right illustrates this point, since the bones of the wing of Archaeopteryx look very much like the bones of the theropod dinosaur, Deinonychus. Indeed, the resemblance is so striking that it convinced a very large percentage of the scientific community that birds are descended from the theropod dinosaurs.
This "Birds are Dinosaurs" theory has become one of the dominant theories of evolution, since its introduction 20 years ago by John Ostrom. The theory is in real trouble now, since a recent study has demonstrated that the bones that make up the wings and feet of birds and the theropod dinosaurs are not derived from the same digits.
The feet and hands of theropod dinosaurs develop from digits I, II, and III
The determination of what digits the feet and hands of theropod dinosaurs are derived from comes from the fossil record. All dinosaurs before the theropods had 5 digits on their feet and hands. The earliest known theropod dinosaur, Herrerasaurus, clearly demonstrates the presence of 5 digits in the hand, although the fourth and fifth digits are reduced in size (see "A" and "B" from figure 2, to the left). Other theropod dinosaurs show a similar loss of digits IV and V. The figure at left shows the left hand of Syntarsus/Coelophysis (C), Plateosaurus englehardti (D), and Lespthosaurus diagnosticus (E), all of which show loss or reduction of digits IV and V, with Syntarsus/Coelophysis showing loss of digit V. Therefore, it seems clear that the theropod dinosaurs derive their hands from digits I, II, and III.
The wings of birds develop from digits II, and III, and IV
The paleontological evidence for the derivation of the wings and feet of birds is completely lacking, since there is no known predecessor of Archaeopteryx. Therefore, the fossil record cannot answer this question. However an ingenious idea by Alan Feduccia (an expert in the study of bird evolution) led to the study of the embryology of reptiles and birds to determine from which digits the wings and feet of birds are derived. Figure 3 (to the right) shows the development of the right hand (or wing) of the alligator (top row), the bird (middle row) and the turtle (bottom row). The results demonstrate the transient appearance of digit V for stages 3 and 4 (see black arrow to the right and compare to the same stage in the alligator and turtle, which develop all five digits). These results clearly indicate that the bird's wing is derived from digits II, III, and IV.
Both the feet and wings of birds develop from digits II, and III, and IV
A comparison of the feet (Figure 4, bottom row) and wings (Figure 4, top row) of developing bird embryos shows that both demonstrate a transient appearance of digit V. In the feet, both digits I and V appear transiently before disappearing. These pictures clearly indicate that the bird's wing and feet are derived from digits II, III, and IV.
The results of the recent study show that the hands of the theropod dinosaurs are derived from digits I, II, and III, whereas the wings of birds, although they look alike in terms of structure, are derived from digits II, III, and IV. If birds were descended from the theropod dinosaurs, we would expect homologous structures to be derived from comparable regions. One could propose that bird wings were originally derived from digits I, II, and III, but later developed another fourth digit, while the first digit regressed. However, there is no fossil evidence that this ever happened (and would be extremely unlikely, since the bird wing was fully developed, even in Archaeopteryx).
There are other problems with the "birds are dinosaurs" theory. The theropod forelimb is much smaller (relative to body size) than that of Archaeopteryx. The small "proto-wing" of the theropods is not very convincing, especially considering the rather hefty weight of these dinosaurs. The vast majority of the theropods lack the semilunate wrist bone, and have a large number of other wrist elements which have no homology to the bones of Archaeopteryx. There is also the minor problem that the theropods appeared after the appearance of Archaeopteryx.
The really difficult problem for the evolutionists is that the supposed link between the dinosaurs and birds is now all but gone. There are no bird-like thecodonts from which Archaeopteryx could have descended (another missing link!). Therefore, the much-touted link between dinosaurs and birds has just evaporated.
This Paper is Part 1. To see Part 2 Click here
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Richard Deem has a B.S. in Biology and an M.S. in Microbiology, and currently works in basic sciences research in Inflammatory Bowel Disease at Cedars-Sinai Medical Center in Los Angeles. He has been on Dr. Hugh Ross' Reasons To Believe apologetics team for 3 years, doing correspondence, speaking, and recently, web site development for RTB.