Did This Dino Have Bird Breath?
Birds are the only vertebrates with a unique one-way, flow-through breathing system that includes hollow bones. Their unique respiratory system is part of the set of features that allows flying with its need for rapid metabolism. Science news outlets are clucking wildly about another putative missing link between dinosaurs and birds: “Meat-eating dinosaur from Argentina had bird-like breathing system,” announced PhysOrg, for instance. Does the evidence fly?
The original paper in PLoS ONE is much more subdued.1 Paul Sereno and team found an allosaur-like dinosaur with more hollow bones than usual, which they interpreted to be associated with air sacs. Air sacs are a feature of the avian lung system, but not the only feature; nor is this the first dinosaur fossil with “pneumatized” (hollow, air-filled) bone. The big sauropods like Diplodocus had them. Opinions differ on what function they served in the dinosaurs: thermal regulation, weight reduction, balance and other functions are possibilities unrelated to respiration.
Sereno’s team has been examining this fossil for 12 years. In short, they found more of hollow bones than usual in this dinosaur, some in the thoracic region. Using this evidence as a launching pad for speculation, they devised a four-stage hypothesis on how the avian lung might have evolved. They did not claim that this dinosaur had a bird-like breathing system, despite the headlines.
The following excerpts from the paper give a feel for the conservative tone of the authors about their find:
- Evidence from the fossil record for the origin and evolution of this system is extremely limited, because lungs do not fossilize and because the bellow-like air sacs in living birds only rarely penetrate (pneumatize) skeletal bone and thus leave a record of their presence.
- Principal findings: We describe a new predatory dinosaur from Upper Cretaceous rocks in Argentina, Aerosteon riocoloradensis gen. et sp. nov., that exhibits extreme pneumatization of skeletal bone, including pneumatic hollowing of the furcula and ilium. In living birds, these two bones are pneumatized by diverticulae of air sacs (clavicular, abdominal) that are involved in pulmonary ventilation. We also describe several pneumatized gastralia (“stomach ribs”), which suggest that diverticulae of the air sac system were present in surface tissues of the thorax.
- The advent of avian unidirectional lung ventilation is not possible to pinpoint, as osteological correlates have yet to be identified for uni- or bidirectional lung ventilation.
- The origin and evolution of avian air sacs may have been driven by one or more of the following three factors: flow-through lung ventilation, locomotory balance, and/or thermal regulation.
- As a result of an extraordinary level of pneumatization, as well as the excellent state of preservation of much of the axial column and girdles, Aerosteon helps to constrain hypotheses for the evolution of avian-style respiration.
- The capacity of the cervical air sacs to invade centra to form invaginated pleurocoels may have evolved independently in sauropodomorphs (sauropods) and basal theropods and appears to have been lost several times within theropods.
- The osteological or logical correlates needed to support some of these inferences have been poorly articulated, which may explain the wide range of opinions on when intrathoracic air sacs like those in birds first evolved and how these relate to ventilatory patterns.
- Based on the osteological correlates we have assembled (Table 4), we would argue, first, that until we can show evidence of the presence of at least one avian ventilatory air sac (besides the non-ventilatory cervical air sac), it is problematic to infer the presence of flow-through ventilation or a rigid, dorsally-attached lung. Second, we know of no osteological correlates in the gastral cuirass that would justify the inference of abdominal air sacs. Potential kinesis of the gastral cuirass and an accessory role in aspiration breathing potentially characterizes many amniotes besides nonavian dinosaurs. The absence of gastralia in crown birds or in any extant bipeds also hinders functional inferences. And third, it is not well established that abdominal air sacs were either first to evolve or are functionally critical to unidirectional ventilation.
- Avian lung ventilation is driven by muscles that expand and contract thoracic volume by deforming the ribcage and rocking a large bony sternum. Basal maniraptorans have many of the features associated with this ventilatory mechanism including a large ossified sternum, ossified sternal ribs, uncinate processes a deepened coracoid that contacts the sternum along a synovial hinge joint. By contrast Aerosteon and the abelisaurid Majungasaurus lack these features. Does that mean that maniraptorans had evolved unidirectional lung ventilation? Or does it indicate only that the maniraptoran ribcage functioned in aspiration breathing more like that in avians? We do not know of any osteological correlates that are specifically tied to uni- or bidirectional lung ventilation (Table 4), which may explain the range of opinion as to how and when avian unidirectional lung ventilation first evolved.
- The factors driving the origin and evolution of the functional capacity of avian air sacs and lung ventilation remain poorly known and tested.
After the fossil was described with its typical taxonomic details, the paper primarily contained a good deal of speculation on the origin of the avian lung system, with no firm conclusions. The authors discussed problems with all existing theories. The most optimistic claim they could make was stated as follows: “In sum, although we may never be able to sort out the most important factors behind the origin and evolution of the unique avian pulmonary system, discoveries such as Aerosteon provide clues that help to constrain the timing and circumstances when many of the fundamental features of avian respiration arose.” Such a statement merely assumes that avian respiration “arose” by evolution somehow. The “wide range of opinions” within the evolutionist community undermines the confident claims in the popular press. It also shows that non-evolutionary explanations for the unique system that enables birds to soar gracefully in the air were completely ignored.
For problems with bird lung evolution theories, see an article on CMI that reviewed Michael Denton’s use of the topic to argue against Darwinism in his classic book, Evolution: A Theory in Crisis. A diagram of the bird respiratory system is shown in the article. Carl Wieland on CMI (PDF file) also critiqued an earlier claim (2005) that hollow bones in some dinosaurs revealed an evolutionary link to the avian lung.
1. Sereno et al, “Evidence for Avian Intrathoracic Air Sacs in a New Predatory Dinosaur from Argentina,” Public Library of Science ONE, 09/30/2008, 3(9): e3303 doi:10.1371/journal.pone.0003303.
The bluffing about evolution in many science news reports is shameful. Search on Aerosteon and you will find examples, like this one on InTheNews.co.uk: “Dinosaurs: Breathed like birds. A carnivorous dinosaur with a bird-like breathing system has provided more evidence of the connection between the two groups of animals separated by millions of years.” The whole article is fluff. “Palaeontologists are now satisfied Aerosteon provides the evidence needed to seal the connection with birds,” it ends. One cannot bluff about fluff.
National Geographic must have panicked at our expose, so they cranked out a propaganda piece immediately announcing, “New Birdlike Dinosaur Found in Argentina.” They even put imaginary feathers on it: “The new dinosaur probably had feathers, but did not actually fly,” they said (cf. 06/13/2007). OK, so we went hunting for feathers in the original paper. “The fossil evidence for intrathoracic air sacs now closely overlaps that for feathers, which had evolved in coelurosaurian theropods most likely for heat retention.” That was the only mention of feathers. This appeal to imaginary feathers was followed by more storytelling in lieu of empirical evidence:
Air sacs may have initially been employed as an antagonist to feathers in theropod thermoregulation. Although this hypothesis has been criticized for lack of empirical evidence in living birds, air sacs have been implicated in avian heat transfer and/or evaporative heat loss, and Aerosteon and many other theropods had a body weight more than an order of magnitude greater than that for any living bird. A thermoregulatory role for the early evolution of air sacs in nonavian dinosaurs should not be ruled out without further evidence from nonvolant ratites.
Can you believe that? They invented imaginary feathers out of thin air for this big heavy meat-eater to compensate for imaginary air sacs that they presume existed near its hollow bones. So now their evolutionary magic produced two imaginary thermoregulatory systems competing with each other – what, for survival of the coolest?
For the fun of it, let’s grant them air sacs and even imagine with them a respiratory system that had some birdlike features; after all, any two vertebrates, like mice and camels, or frogs and penguins, are bound to have similarities as well as differences, depending on what you decide to focus on for the moment. Paul Sereno told National Geographic that the beast didn’t fly (obviously, unless you can imagine wings on a T. rex), so NG concluded, “even though this species was birdlike [sic], feathers and air sacs didn’t necessarily evolve for flight.” So their point is… ? All the hype about feathers was supposed to reinforce the idea that birds evolved from dinosaurs. They were practically ready to name this thing Tweety Rex, and now they seem to be telling us this beast evolved air sacs for a completely different function, about which no one is sure, and it was an evolutionary dead end anyway. Even NG’s accompanying slide show didn’t show feathers. The only suggestion of a birdlike respiratory system was in slide 2, where colored regions represent the imaginary air sacs in the thorax.
But excuse me, Mr. Scientist sir, did any of that soft air-sac material fossilize? “Evidence from the fossil record for the origin and evolution of this system is extremely limited, because lungs do not fossilize and because the bellow-like air sacs in living birds only rarely penetrate (pneumatize) skeletal bone and thus leave a record of their presence.” Are you telling me there was no direct evidence for the air sacs in this dinosaur? “Some of its postcranial bones show pneumatic hollowing that can be linked to intrathoracic air sacs that are directly involved in lung ventilation.” They can be, you say, but how strong is the inference? “We do not know of any osteological correlates [fossil evidence] that are specifically tied to uni- or bidirectional lung ventilation (Table 4), which may explain the range of opinion as to how and when avian unidirectional lung ventilation first evolved.” But isn’t a unidirectional lung ventilation system the primary distinguishing feature in birds? Are you telling the court that this is all inference, not evidence?
The tale gets more speculative and implausible with each lawyer’s question. Darwin’s defense attorneys are sweating in their seats. NG quoted a colleague admitting, “It shows that evolution is not a chalk line—there are many dead ends.” Being interpreted, this means evolutionists can always concoct a story for any possible combination of data. (Chalk is erasable, you know.) We think a scientist who wants to feather his monster should produce the feathers in the fossil, not draw feathery dragons on the chalkboard and tell the press that it “probably had feathers.” Chalk lines are supposed to be snapped to a level that has been carefully measured. So he’s right; evolution is not a chalk line; it’s a crooked crack in the wall of a theory that is about to collapse. Don’t build to it.
We brought you extended quotes to illustrate the difference between original sources and the news media hype. The lesson: always check out the original data. The authors with the bones in their hand usually know better than to make any outlandish claims to their colleagues. In front of reporters, though, they lose restraint. Reporters go ape to praise Darwin. For example, Live Science, that perennial Darwin billboard, shouted Extra! Extra! “Bus-sized Dinosaur Breathed Like Birds. A huge carnivorous dinosaur that lived about 85 million years ago had a breathing system much like that of today’s birds, a new analysis of fossils reveals, reinforcing the evolutionary link between dinos and modern birds.” That, in turn, got passed around to all the major news outlets as gospel truth. This is bad breath, not bird breath. The sound of flapping dino-feathers is only the pompons made of synthetic material manufactured for the Darwin Party cheerleaders.