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Two startling studies, relying on completely different methods, published just three weeks apart, have dealt a "one-two punch to the dinosaurs origins of birds hypothesis" according to paleontologist James Farlow of Indiana University-Purdue University at Fort Wayne. The first study examined the origins of the three bones of the fingers/wings and feet of the theropod dinosaurs and modern birds. The results clearly indicated 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. The second study looked at the lungs of the theropod dinosaurs (from fossil evidence) and compared them to the lungs of modern reptiles and birds. The results indicated that the theropod dinosaurs likely possessed a diaphragm and bellows-like septate lungs (similar to modern reptiles), which are not found in modern birds. In addition, the theropod dinosaurs lacked the proper pelvic structure to assist breathing by means of tail movements. Such structures are incapable of supporting warm-blooded respiration and the aerobic requirements of flight. |
The striking superficial 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 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.1
What does it matter if birds are descended from theropod dinosaurs? If birds are not descended from theropods, they are not descended from any other known species. Here is a quote from the University of California, Berkeley website:
"The opponents of the theropod hypothesis refuse to propose an alternative hypothesis that is falsifiable. This is probably because there are no other suitable candidates for avian ancestors".2
This is quite an admission, and demonstrates the dogmatism of Darwinism. The paradigm takes precedence over the data, since falsification of descent of birds from theropods would falsify all of evolutionary theory.
The determination of what digits the feet and hands of theropod dinosaurs are derived from comes from the fossil record. All dinosaurs before the theropod 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. Other theropod dinosaurs show a similar loss of digits IV and V. The hands of Syntarsus/Coelophysis, Plateosaurus englehardti, and Lespthosaurus diagnosticus, all 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 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. The authors of the study showed that during the development of the hand (or wing) of the bird, there was a transient appearance of digit V, which did not occur 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.
A comparison of the feet and wings of developing bird embryos showed that both demonstrate a transient appearance of digit V. In the feet, both digits I and V appear transiently before disappearing. These results clearly indicate that the bird's wing and feet are derived from digits II, III, and IV. The evidence is quite clear that the bird feet and wings could not have developed from digits I, II, and III of the theropod dinosaurs. Alan Feduccia is frustrated that palentologists have ignored the evidence:
In spite of developmental evidence that overwhelmingly supports a II-III-IV bird hand, in contrast to the I-II-III theropod hand [8,9], paleontologists will do whatever is necessary to accommodate the cladogram.3
The lungs of birds, mammals, and reptiles are vastly different in terms of morphology and function. The lungs of mammals and birds are far more efficient than those of reptiles, which allows for prolonged periods of intensive physical activity. The lungs of mammals consists of millions of alveoli, which are highly vascularized air sacs. The degree of vascularization (the capillary blood supply surrounding the alveoli) and the large surface area allow for efficient exchange of oxygen and carbon dioxide, which allow for mammals' high metabolic rate. The lungs of reptiles are termed "septate," consisting of the equivalent of a large single alveolus divided by vascularized ingrowths, or septae. The bellows-like septate lung of the reptile is poorly vascularized, which prohibits endothermic ("warm-blooded") metabolism. The avian (bird) lung is also a septate lung, but consists of a series of extensive, highly vascularized air sacs, which extend into both the thoracic (chest) and abdominal cavities.
Both mammals and reptiles posses a diaphragm, the muscle separating the thoracic and abdominal cavities. The reptile breathes through contraction of the diaphragmatic muscles, which are attached to the pubis and the liver. This contraction pulls the liver further down into the abdominal cavity, therefore enlarging the thoracic cavity, which expands the lungs. The diaphragm of the reptile must completely separate the thoracic and abdominal cavities for this mechanism to work. Any gap in its integrity would result in the inability to induce a partial vacuum in the thoracic cavity, which would prevent the filling of the lungs (keep this in mind, since it is important for later discussion). In contrast, the bird has no diaphragm and there is no separation of the thoracic and abdominal cavities. Breathing is accomplished through contraction of the muscles of the rib cage and pelvis.
The pelvic bones of modern perching birds and Archaeopteryx reveal that both probably assisted their breathing while perching by means of muscles attached between their pubis and tail. Through pelvic and tail movements, birds are able to assist their breathing by expanding or contracting their septate lungs. Although the design of the pelvic bones of modern birds and Archaeopteryx are profoundly different, they most likely served the same purpose - to assist breathing during perching.
In contrast, the pelvic bones of the theropod dinosaurs look nothing like that of either modern birds or Archaeopteryx, but look very similar to that of modern reptiles, such as the crocodile. There is no way for the pubis of modern reptiles or the theropod dinosaurs to serve as an attachment point for suprapubic muscles to serve in assisting breathing during perching. Since there are no "intermediate" theropod which possesses a pelvic structure similar to Archaeopteryx, it seems unlikely that they could have given rise to Archaeopteryx. In addition, the fossil evidence clearly demonstrates that the theropod dinosaurs lack the avian jointed or hinged ribs and expansive sternum - all of which are necessary to maintain air flow in the avian lung. Therefore, it seems unlikely that the theropod dinosaurs could have given rise to modern birds either.
A remarkable fossil find from the Yixian formation in China revealed the theropod dinosaur called Sinosauropteryx, which was nicknamed the "feathered dinosaur." Subsequent studies have indicated that the feathers were probably "frayed collagenous fibers beneath the skin."6 However, the remarkable preservation of the specimen reveals not only skin, but some of the internal organs as well. When Dr. John Ruben, a respiratory physiology expert from Oregon State University, the primary author of the second study, first saw the specimen, he recalled, "My eyes popped out." He also concluded, "I realized that here was the first evidence in the soft tissue that theropod had the same kind of compartmentalization of lungs, liver, and intestines that you would find in a crocodile." The fossil clearly shows the demarcation of the thoracic and abdominal cavities. A cross-section of a neonatal alligator showed a nearly identical pattern. The results indicate that the theropod dinosaurs almost certainly possessed a diaphragm, which separated the thoracic and abdominal cavities. This would make the theropod dinosaurs unlikely candidates as ancestors of modern birds, which posses no diaphragm.
It is virtually impossible for an animal that breathes by means of a diaphragm to evolve into an animal which breathes the way modern birds do, because the hypothetical intermediate creature would be severely hampered in its ability to breathe. Here is what Dr. Ruben says about the problem:
"Recently, conventional wisdom has held that birds are direct descendants of theropod dinosaurs. However, the apparently steadfast maintenance of hepatic-piston diaphragmatic lung ventilation in theropod throughout the Mesozoic poses a fundamental problem for such a relationship. The earliest stages in the derivation of the avian abdominal air sac system from a diaphragmatic-ventilating ancestor would have necessitated selection for a diaphragmatic hernia [or hole] in taxa transitional between theropod and birds. Such a debilitating condition would have immediately compromised the entire pulmonary ventilatory apparatus and seems unlikely to have been of any selective advantage"5
The results of the recent studies 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).
The second study shows that the theropod dinosaurs did not possess the correct skeletal structure or lung structure to have evolved into birds. The evolution of theropods into birds would have required the introduction of a serious handicap (a hole in their diaphragm), which would have severely limited their ability to breathe. As Dr. Ruben said, such a debilitating mutation "seems unlikely to have been of any selective advantage," which is quite an understatement.
There are other problems with the "birds are dinosaurs" theory.7 The theropod forelimb is much smaller (relative to body size) than that of Archaeopteryx. The small "proto-wing" of the theropod 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. In addition, in almost all theropods, nerve V1 exits the braincase out the side, along with several other nerves, whereas in birds, it exits out the front of the braincase, though its own hole. Then there is the problem that birds are warm blooded. The evidence for warm-blooded dinosaurs has been thoroughly dismantled lately8 and Archaeopteryx has been shown to be a bird in the modern sense,9 with fully developed elliptical wings similar to modern woodland birds, and asymmetric flight feathers that form individual airfoils, a flight scapula/coracoid arrangement, and a reserved hallux, found only in perching birds, and known in no dinosaur. There is also the minor problem that the vast majority of the theropods appeared after the appearance of Archaeopteryx.
According to Dr. Alan Feduccia, the problems with the evolution of birds from theropods is virtually incompatible with the evidence:
"Although the digital mismatch between birds and dinosaurs is anatomically the most serious problem, other versions of frame-shift hypotheses will be needed to explain such problems as the transformation of teeth and tooth replacement, the transformation of a dinosaurian septate, hepatic-piston breathing system to a bird flow-through lung, the complete abandonment of a balanced seesaw body plan to the avian model, and the reelongation of already foreshortened forelimbs, to mention a few. Perhaps the greatest form of special pleading will be necessary to explain how flight could have originated from the ground up; our present knowledge indicates that there are two requisites for flight origin: small size and high places. Also, it must be explained why these superficially birdlike theropods only occur in the fossil record 30 to 80 million years after the appearance of the earliest known bird, which is already well developed, and why Triassic theropods are devoid of birdlike features."10
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.
Evolutionists are not happy with the study by Burke and Feduccia because they realize that this study refutes any evolutionary descent from dinosaurs and birds. As the authors maintain in a recent defense of their data, "The relationship of birds and dinosaurs is an hypothesis, and our report points out an inconsistency in this popular idea" that is "inconsistent with the observation and current evidence of comparative embryology." The debates can be found in the April 17, 1998 issue of Science (download the PDF file).
Archaeopteryx has been described as a link between birds and dinosaurs, although it is remarkably similar to modern birds. Attempts to find more primitive intermediates have been unsuccessful - until now - so say a group of paleontologists (see the July, 1998 issue of National Geographic). The group has found two turkey-sized dinosaurs that have both downy and modern flight feathers on their arms and tail. Their skeletal structure is similar to theropod dinosaurs (short arms - too short to be useful in flight, serrated teeth, theropod-like pelvis, etc.). The conclusions are obvious - Right? However, other researchers dispute these claims.11 They point to shortened tail and fused sternum, arguing that they are more advanced than Archaeopteryx. These researchers believe that the intermediates are actually flightless birds. Oh, did I mention that the new fossils are dated to have appeared at least 20 million years after the appearance of the first Archaeopteryx? Those little details do get in the way of evolutionary theory, don't they!
According to an article by Alan Feduccia:
"Despite the popularity of the dinosaurian origin of birds, many ornithologists and physiologists, in particular, have had tremendous difficulty with the theory (8, 10, 11) because of a huge and growing body of contrary evidence and the fact that a ground-up origin of avian flight is considered a near biophysical impossibility (12). Aside from criticism concerning the cursorial origin of avian flight, there are problems related to the geologic, temporal occurrence of putative dinosaurian ancestors, which occur some 30 to 80 million years after the appearance of the earliest known bird Archaeopteryx, and these forms become more and more superficially birdlike as one approaches the latest Cretaceous. There is also the fact that virtually all of the anatomical features used to ally birds and dinosaurs have been disputed."9
Last updated 05/31/01