Demise of the "Birds are Dinosaurs" Theory (Part 2)

by Richard L. Deem M.Sc.

This Paper is Part 2. To see Part 1 Click here,


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 See Part 1. 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 Second Study4


Figure 5. The septate reptile lung.

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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 (See figure 5). 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 (see figure 6).

birdlung.gif (5296 bytes)gator.gif (6405 bytes)
Figure 6. The lung arrangement of A) mammals; B) reptiles, and C) birds. Symbols: lu - lung; li - liver. D) Alligator, showing major organs/systems involved in breathing.

Both mammals (fig. 6A) and reptiles (fig 6B) 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 (fig. 6D). 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.

Evidence 1: The structure of the pelvis and ribs of the theropod dinosaurs is incompatible with the breathing apparatus of Archaeopteryx or modern birds

perching.gif (6358 bytes)

Figure 7. The pelvic bones of A) modern modern perching birds and  B) Archaeopteryx. Abbreviations: is, ischium; p, pubis; hc, hypopubic cup; sp, suprapubic muscles; sp*, probable suprapubic muscles;

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Figure 8. The pelvic bones of A) modern crocodiles and the theropod dinosaurs B) Herrerasaurus, C) Allosaurus, and D), Unenlagia.

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 (fig. 7A) and Archaeopteryx (fig. 7B) are profoundly different, they most likely served the same purpose - to assist breathing during perching.

In contrast, the pelvic bones of the theropod dinosaurs (fig. 8B-D) look nothing like that of either modern birds or Archaeopteryx, but look very similar to that of modern reptiles, such as the crocodile (fig. 8A). 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.

Evidence 2: The structure of the lungs of the theropod dinosaurs is indistinguishable from that of modern reptiles

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Figure 9 (Click to enlarge)
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Figure 10

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."5 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." Figure 9 above show the specimen from which Dr. Ruben drew those conclusions. The small inset of the figure (upper right) shows the area covered in the main part of the photo. The fossil clearly shows the demarcation of the thoracic and abdominal cavities. A cross-section of an alligator (fig. 10) shows 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.

The big problem for evolution

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"4

Birds are not dinosaurs

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 theropod 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."

There are other problems with the "birds are dinosaurs" theory.1 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 theropod 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. There is also the minor problem that the vast majority of the theropods appeared after the appearance of Archaeopteryx.

The bottom line

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.

Visit Richard Deem's web site: Saved By Grace

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.

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  1. Richard Hinchliffe. 1997. EVOLUTION: The Forward March of the Bird-Dinosaurs Halted? Science 278: 596.
  2. A. C. Burke and A. Feduccia. 1997. Developmental Patterns and the Identification of Homologies in the Avian Hand. Science 278: 666.
  3. Anne Gibbons. 1997. Lung Fossils Suggest Dinos Breathed in Cold Blood. Science 278: 1229.
  4. Ruben, J.A., T.D. Jones, N.R. Geist, and W.J Hillenius. Lung structure and ventilation in theropod dinosaurs and early birds. Science 278: 1267.
  5. Anne Gibbons. 1997. Plucking the feathered dinosaur. Science 278: 1229.