Dinos breathed like birds?
A preliminary response to a new study that has excited some evolutionists, probably more than the facts allow
Published: 10 February 2006 (GMT+10)
The internet in mid-July 2005 was abuzz with headlines which implied to the layperson that it has now been proven beyond doubt that dinosaurs ‘breathed like birds’.
Comparisons between a bird (a, b) and theropod dinosaur (c, d) in caudal (a, c) and right lateral (b, d) views, illustrating the topological similarity of pneumatic features. a, b, Cranial thoracic vertebra of a sarus crane (Grus antigone, SBU AV104063). c, d, Mid-cervical (c) and cervicothoracic (d) vertebra of an abelisauroid theropod (Majungatholus atopus, UA 8678). Scale bar, 1 cm (a, b) and 3 cm in (c, d). CeP, central pneumatic foramen; NaP, neural arch pneumatic foramen; Nc, neural canal; Ns, neural spine; Pp, parapophysis.
All this has come from a new study dealing with the fossil remains of a very beautifully preserved theropod dinosaur, Majungatholus atopusi, just published in the prestigious British science journal Nature.1 The fact that theropod dinosaurs (that group believed by many evolutionists to have given rise to birds) have pneumatization (special hollow air spaces) in some of their bones is not new, nor that birds do, too. In particular, the lungs of birds interact with a system of air sacs which ‘invade’ sections of the skeleton, particularly the vertebral bodies.
Those vertebral bodies which are present in this dinosaur show in remarkable detail (see diagram, from the Nature article, reproduced under the ‘fair use’ provisions of copyright) air cavities within the bone (pneumatizations). These are so strongly analogous with ones in a modern bird that I think one can reasonably infer that the dinosaur possessed the following:
- A cervical air sac similar to modern birds;
- A lung which itself invaded some of the thoracic vertebrae, pneumatizing them in the same way as modern bird lungs do;
- An abdominal air sac similar to modern birds. This is the aspect of the study that appears to be most encouraging to evolutionists, as being ‘caudal’2 to the lung, it allows for the possibility of a ‘flow-through’ lung as in birds (see later).
Note that the sacs themselves are not preserved, nor available to study, so the above cannot be known for certain, just that, as stated, it is very reasonable to infer it.
Stretching the point
In another diagram associated with the article, the dinosaur skeleton is drawn with not just the above three features but, in addition, (4) a clavicular air sac and (5) a thoracic air sac as modern birds have. However, there appears to be no fossil evidence of (4) and (5). The caption states that these are ‘tertiary-level inferences emphasizing the uncertainty surrounding the reconstruction of soft tissues not constrained by osteological evidence.’ In other words, there is no evidence from fossil bones from which one can even infer the existence of these soft tissue air sacs. Rather, they are believed to be present by way of ‘tertiary inference’—presumably as follows: if (1) – (3), all known to be features of bird respiration, are (secondarily) inferred to be present, then it’s an educated guess that probably (4) – (5) are present as well. However, this guess is heavily influenced by the presumption that theropods are the evolutionary ancestors of birds. But this is hotly disputed by some evolutionist experts themselves, and it is just as reasonable to presume that theropods did not have those last two sacs.
Further, even if it were to turn out that theropods did have all five ‘pneumatic features’, it is again very much a ‘tertiary inference’ (an indirect assumption, more than one step from the evidence) that this theropod therefore had the same flow-through ventilation system as birds. It is this flow-through aspect, where the air keeps moving in the same direction, that makes the avian lung so special (and as far as is known for certain, unique), compared to the ‘bellows’ (in and out) lung of mammals or reptiles.
At present, all one can say is that the presence of a flow-through lung in this theropod may have been the case (mildly supported by certain aspects of spine and ribcage anatomy), but for all anyone knows, theropods may in fact have had a unique combination of a bellows lung (unlike birds) and a system of (some) air sacs and pneumatized vertebrae (like birds). The air sacs may have served to enhance oxygen efficiency during running.
Lightening the load
In fact, pneumatizations of bone are already known to have existed in non-theropod dinosaurs, such as the large sauropods, and in the flying reptiles (pterosaurs). Neither of these are believed to be the ancestors of birds, so evolutionary speculations about these pneumatizations have been much more circumspect, and related more straightforwardly to their obvious design function of lightening the bones.
Such lightening is important, not just for flight, but obviously also to make locomotion easier for the big lumbering sauropod earth-shakers. Theropods (at least the smaller ones) are believed to have been speedy runners, so lighter bones would seem to be an important design feature for them, too. There is no reason, though, why they may not also have shared with birds all or some of the same design features for efficient use of oxygen, as already stated.
What if they really did breathe like birds?
Finally, let’s assume for the sake of argument that theropod dinosaurs indeed had the same flow-through lung type as birds. It would bring evolutionists not a single step closer to being able to conceive of the inconceivable—how such a lung could have evolved step by step from the bellows lung of its assumed evolutionary forebears. It would only shift the name of the problem from the origin of the avian lung to the origin of the theropod-avian lung.
How could any creature breathe while the in-between stages were evolving, while air was not yet flowing through but no longer going in and out? What conceivable selection pressure could act on an already efficient system of breathing, especially one that would have had to get worse before it got better in efficiency terms? (The Nature article, generally conservatively written, speculates cautiously but lamely about how somehow the development of an air sac behind the lung might facilitate the evolution of flow-through ventilation, without touching upon the logistic ‘in principle’ barriers. For this and still more problems, see Bird evolution?)
Actually, the above has really been excessively kind to evolutionists. We need to remember the discovery of the theropod Scipionyx samniticus, with traces of internal organs suggesting to several researchers that it did not breathe like birds, but rather more like the ‘liver-pump’ system in crocodiles. Then there is the evidence from ostrich embryos that the thumb development in theropods is all wrong for them to have been the ancestors of birds. (See also Which came first, the dino or the bird?)
- Several lines of evidence are already known to suggest a number of aspects in which theropod dinosaurs are more similar to birds than to reptiles.
- This is not in any way inconsistent with the Genesis creation of separate kinds. All creatures share similarities to greater and lesser degrees; in the evolution model these are either derived from a common ancestor, or by chance ‘parallel evolution’. In the creation model, they are either derived from a common ancestral kind (not applicable in the case of birds and theropods, definitely not the same kind) or from shared design features applied by a common Designer.
- The bony pneumatizations in a theropod dinosaur described in the recent Nature article are remarkably similar to those in birds.
- It cannot be known for certain that theropod dinosaurs had any air sacs at all as modern birds do, although it is not an unreasonable inference that they had at least some, including an abdominal air sac.
- If they did not have air sacs, then the pneumatizations discovered in the vertebrae presumably only served the function of lightening the bones for running. (The bones of large, heavy dinos, and of the flying reptiles, also had pneumatizations which are believed to be for lightening.)
- If they did have air sacs as birds do, there is no way of knowing whether they also had a flow-through lung like birds. An abdominal (caudal) air sac is necessary for a flow-through lung, but it does not therefore follow that having such a sac means one has a flow-through lung. (That would be like saying ‘a circulatory system is necessary to support the human brain. Therefore any creature with a circulatory system has a human brain.’) The Nature authors believe theropods likely did have a flow-through lung, and cite certain features of the skeleton in support. But there have been other detailed studies suggesting theropods had a crocodile-like liver-pumping mechanism for ventilation.3
- Those evolutionists in the faction that believes dinosaurs (specifically theropods) gave rise to birds would be understandably encouraged by this paper, but it has not even begun to address the huge difficulties (including embryonic development paradoxes) pointed out by the opposing evolutionary faction.
- If it turned out (say from some remarkable soft-tissue preservation as in the recent T. rex ‘squishosaur’) that theropods did indeed have the same type of flow-through lung as birds, that would be an even bigger encouragement for the dino-bird faction, but it also fits perfectly comfortably within a creation framework; it would be a very reasonable design feature for fast-running small dinosaurs. However:
- Evolutionists would still be stuck with exactly the same massive problem of explaining the seemingly impossible transition from bellows to flow-through ventilation.
References and notes
- O’Connor, P. and Claessens, L., Basic avian pulmonary design and flow-through ventilation in non-avian theropod dinosaurs, Nature 436:253–256, 14 July 2005. Return to Text.
- This means closer to the tail of the skeleton, i.e. on the ‘other side’ of the lung from where the air enters. Return to Text.
- Forster, C.A., Sampson, S.D., Chiappe, L.M. & Krause, D.W., The theropod ancestry of birds: new evidence from the Late Cretaceous of Madagascar, Science 279, pp. 1915–1919, 1998. Also Sereno, P.C., The evolution of dinosaurs, Science 284, pp. 2137–2147, 1999. Return to Text.