2002/09/27 by John Williams · 1 citation
Earth and Planetary Sciences · Environmental Science · #Paleontology and Evolutionary Biology #Marine animal studies overview #Avian ecology and behavior #Function (biology) #Biology #Evolutionary biology
paper · doi:10.1126/science.297.5590.2207b
openalex publication_date 2002/09/27 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/23
A. W. A. Kellner and D. A. Campos (“The function of the cranial crest and jaws of a unique pterosaur from the Early Cretaceous of Brazil,” Reports, 19 July, p. [389][1]) suggest that the huge cranial crest of a newly discovered pterosaur might have had multiple functions, including mating display and thermoregulation, but they say it might have interfered with flight. The authors compare the pterosaur with a modern bird less than one-fifth its size, speculating that the pterosaur might have caught fish by flying low over water with its lower jaw partially submerged. The relatively massive lower jaw of the analogous modern bird, drawn in the authors' Fig. 3, suggests that the pterosaur could not have maintained flight against water resistance with its entire lower jaw submerged, but must have skimmed with the distal third or so, where the greatest lateral compression is shown to occur. Not discussed by the authors is that the pterosaur probably needed its crest to balance its long jaws, the attitude of the head changing somewhat depending on locomotion on land, flying speed, or submergence of the lower jaw while flying over water. A crest inflatable with blood and possibly variable in air resistance (like a hand-held fan) would have helped the pterosaur adjust the long-term attitude of its head, reducing the need for heavy, powerful neck muscles, at the cost of requiring a little more forward thrust while skimming. The force of air against an extended crest would balance the force of water on the jaw, keeping the head from being rotated toward the water. Far from interfering with flight, an inflatable crest might have made longer flights possible. The spermaceti reservoir in the head of the sperm whale is supposed to have a similar function, allowing the whale to use blood flow to adjust the temperature and thus the buoyancy provided by the spermaceti. # Response #article-title-2 WORKING WITH EXTINCT ORGANISMS IS always a challenge, particularly when it comes to the interpretation of the function of previously unknown structures. In our report, we described a skull and lower jaw of a new pterosaur ( Thalassodromeus sethi ) from Early Cretaceous deposits of Brazil, which bears a gigantic bony crest never before recorded in any animal (fossil or recent). We listed several possible functions of this oversized structure, focusing primarily on its effect in signaling (e.g., species recognition) and on its possible use to control body temperature. Despite noting that it had to have an aerodynamic effect (due to its large size), we did not discuss this function in detail, as correctly pointed out by Williams. He further suggests that in Thalassodromeus , this crest might have been inflatable and acted to balance the force of water on the jaw in a similar function of the spermaceti reservoir in the head of the sperm whale that is supposed to adjust buoyancy. We reject the “inflatable crest hypothesis” on the basis of the reasons discussed below. The oversized cranial structure in Thalassodromeus is made up of two thin layers of bone connected on the sagittal plane by a well-developed system of trabeculae (see the [figure][2]). It is difficult to imagine that such a laterally compressed structure could be substantially “inflated” (even by soft tissue present on the lateral side) to have a strong aerodynamic effect that could not have been achieved otherwise (e.g., simple lateral movement of the head). The analogy with a supposed buoyancy adjustment of the spermaceti organ in sperm whales does not make much sense in a flying animal that had other perhaps more effective mechanisms to “float” in the air (e.g., wings). Furthermore, the spermaceti is mostly regarded as having other functions ranging from aggression (discarded for this pterosaur because of the fragility of the crest) to a sonar [e.g., ([1][3])]. On the basis of the large occipital region and muscle scars, Thalassodromeus did have strong neck muscles that (in conjunction with the flying apparatus) kept the head from being rotated toward the water during fishing. ![Figure][4] Perpendicular (coronal) section of the upper portion of the cranial crest of the pterosaur Thalassodromeus sethi. The gray area on the left-hand side is the matrix (m) that originally involves the bone (removed from the right side); the white substance is calcium carbonate (c) that occasionally forms geodes with the growth of calcite crystals (g). The actual bone (b) is very thin, forming the external part of the crest (two arrows) and the thin trabeculae inside the crest (double arrow). This configuration demonstrates the hollow nature of the crest. Scale bar, 5 mm. The main problem regarding the aerodynamic influence of the crest is empirically establishing the range of those effects considering all variables (e.g., angles and wind speed). The idea of this crest being used as a forward rudder, for example, is very tempting, and there seems to be little doubt that any lateral movement of the head would allow this animal to change direction during flight. Even during fishing, fast changes of the trajectory might have increased the capacity of Thalassodromeus to catch a prey—particularly when skimming the water surface. To properly study the aerodynamics of Thalassodromeus , however, there is a need for information from different sources starting with the fossils but including notions of biomechanics (e.g., muscle power and stress capacity of different biological tissues) and flight mechanics. Only a project with such an interdisciplinary approach, to which we would like to contribute, could empirically establish the limitations and effects of such an oversized cranial structure, including any effect that an extended crest might have had as a counterbalance to the forces of the water on the jaws, also suggested by Williams. 1. [↵][5]1. D. R. Carrier, 2. S. M. Deban, 3. J. Otterstrom , J. Exp. Biol. 205, 1755 (2002). [OpenUrl][6][Abstract/FREE Full Text][7] [1]: /lookup/doi/10.1126/science.1073186 [2]: #F1 [3]: #ref-1 [4]: pending:yes [5]: #xref-ref-1-1 View reference 1 in text [6]: openurl?query=rft.jtitle%253DJournal%2Bof%2BExperimental%2BBiology%26rft.stitle%253DJ.%2BExp.%2BBiol.%26rft.issn%253D0022-0949%26rft.aulast%253DCarrier%26rft.auinit1%253DD.%2BR.%26rft.volume%253D205%26rft.issue%253D12%26rft.spage%253D1755%26rft.epage%253D1763%26rft.atitle%253DThe%2Bface%2Bthat%2Bsank%2Bthe%2BEssex%253A%2Bpotential%2Bfunction%2Bof%2Bthe%2Bspermaceti%2Borgan%2Bin%2Baggression%26rftid%253Dinfo%253Apmid%252F12042334%26rft.genre%253Darticle%26rftvalfmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctxver%253DZ39.88-2004%26urlver%253DZ39.88-2004%26urlctxfmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [7]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NjoiamV4YmlvIjtzOjU6InJlc2lkIjtzOjExOiIyMDUvMTIvMTc1NSI7czo0OiJhdG9tIjtzOjI1OiIvc2NpLzI5Ny81NTkwLzIyMDcuMi5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30=