REVIEWS J. Paleont., 79(3), 2005, pp. 625–627 Copyright q 2005, The Paleontological Society 0022-3360/05/0079-625$03.00
Posture, Locomotion, and Paleoecology of Pterosaurs. Sankar Chatterjee and R. J. Templin. 2004. The Geological Society of America, Special Paper 376, Boulder, Colorado, 64 1 iv p. ISBN 0-8137-2376-0; Evolution and Palaeobiology of Pterosaurs. 2003. Eric Buffetaut and Jean-Michel Mazin, eds. Geological Society, London, Special Publications 217, London, 347 p. ISBN 18623-9143-2. In the past year, two books about pterosaurs have been published: Posture, Locomotion, and Paleoecology of Pterosaurs by Chatterjee and Templin and Evolution and Palaeobiology of Pterosaurs edited by Buffetaut and Mazin. Although both books include broad coverage of the present knowledge of pterosaurs, they are very different in approach and not equally successful. Chatterjee and Templin’s work suffers from a split personality. It was clearly written by two people with different styles, who seem not to have been able to decide whether it was intended as a general review of pterosaurs and their literature or as a new contribution to our understanding of pterosaur flight. The majority of the book is a general review of pterosaurs that is rather muddled and often omits recent contributions. The authors suggest that there is little agreement among pterosaur workers on even the smallest details; however, a general consensus on almost all topics has been forged by pterosaur workers in a recent series of workshops and symposia, and while there are dissenters on most subjects, the extent of agreement is remarkable. The book includes various inaccuracies and inconsistencies. For example, the term pterodactyl is used in a number of places to refer to all pterodactyloids when it properly refers only to members of the genus Pterodactylus; pterosaurs are described as quadrupedal knuckle walkers whereas knuckle walking properly refers to walking on flexed proximal interphalangeal joints of the manus and pterosaurs walked with their metacarpophalangeal joints hyperextended and the palmar surfaces of digits I-III in contact with the ground; Martill and Unwin’s (1989) interpretation of soft tissue preserved in association with a radius and ulna as wing membrane is accepted, while Kellner’s (1996) strident arguments that the soft tissue was body wall are not mentioned; and large pterodactyloids such as Pteranodon are described as feeding by dipping fish while swimming (p. 56) and as probably unable to take off from water (p. 53)—perhaps this explains the large numbers of Pteranodon specimens in the Niobrara Formation. The book also perpetuates some misinterpretations of pterosaurs. The interpretation of pterosaur wing structure is presented in terms of a birdlike versus batlike dichotomy, whereas it is now clear that the pterosaur wing was as different from bird and bat wings as bird and bat wings are from each other. Actinofibrils are described as flattening the wing membrane to prevent billowing, whereas they were too slender to have resisted bending and instead redistributed tension and prevented chordwise narrowing of the membrane under load. The cranial crests of large pterodactyloids are described as primarily functioning as rudders for steering, whereas although the large, laterally projected area of the crest could have produced yaw forces, the significant intraspecific variation in crest size—including their complete absence in immature individuals—the much greater yaw forces that could be produced by controlled wing asymmetry, and the great variation in size, shape, and position of crests indicate that the primary function was display. The discussion of pterosaur flight goes beyond mere review
and presents a new analysis of the flight of 10 genera using momentum streamtube theory based in large part on earlier work by Templin (2000). Previous analyses have compared pterosaurs to fixed wing aircraft to estimate gliding performance or used vortex field theory to model flapping wing performance, whereas momentum streamtube theory compares the flapping wings of pterosaurs to the actuator disk of helicopters. The authors suggest that it is a reliable method because of the agreement of predicted and measured performance for some extant birds. The work is interesting but suffers from two main problems: the data upon which the analysis was based (i.e., estimates of mass, wingspan, and wing area) were not produced using a uniform methodology, which makes the results of uncertain validity; and although the results of the analysis differ significantly from previous analyses, there is insufficient discussion of why that is. Mass estimates of six taxa were taken from works by Brower and Hazlehurst; however, other estimates of mass for Rhamphorhynchus and Pterodactylus by them were ignored without explanation. In addition, the estimates of mass and span for Pteranodon ultimately came from an earlier study that used a specimen with only its humerus and femur complete enough to measure as its exemplar and yet arrived at an estimate of span 11% larger than the largest known specimen from the Niobrara Formation. Mass estimates for the four other taxa were based on measurement data and a regression analysis of mass and measurements of the first six taxa. Estimates of wing area of two taxa were taken from work by Hazlehurst, whereas his similar estimates for five other taxa were ignored without explanation, and wing areas for the other eight taxa were measured from reconstructed wing planforms that are not reproduced (except perhaps as tiny silhouettes) and so cannot be evaluated. As for the comparison of the results of this analysis and previous ones, Chatterjee and Templin’s analysis suggests that pterosaurs had significantly better flight performance than previously thought, and it is suggested that the differences result from lower estimates of drag due to flatter camber and cleaner flow. However, there is no discussion of whether some of the improved performance results from differences in the data upon which the analyses were based or from using momentum streamtube theory, and there is no discussion of why the results of this analysis are preferable to those of previous analyses. Based on the improved flight performance and estimates of continuously available power, the latter estimated on the assumptions that muscle mass was directly proportional to body mass and that muscle power output was equivalent to that of extant birds, the authors suggest that there were three modes of pterosaur flight: hovering, continuous flapping, and soaring. While the first assumption is probably not unreasonable, the second may not be because it is not clear that early pterosaurs were endothermic or that their muscle physiology and aerobic capacity was equivalent to that of extant birds. Despite that, it is suggested that small pterosaurs with wingspans of less than 1 m (e.g., Eudimorphodon, Dorygnathus, Rhamphorhynchus, and Pterodactylus) were capable of continuous hovering flight, and fed by hovering just above water and dipping prey at its surface. However, the fact that small pterosaurs might have been capable of continuous hovering flight should not be taken as evidence that it was a major component of their behavioral repertoire. The analysis suggests that all but the very largest pterosaurs (e.g., 70 kg, 10.4 m Quetzalcoatlus) were capable of continuous flapping flight, quite different from previous works that suggested that large pterosaurs over perhaps 5 m wingspan were incapable of continuous flapping. Chatterjee and Templin acknowledge that large pterosaurs probably utilized
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thermal and slope soaring to a considerable extent, and also suggest that Pteranodon and Quetzalcoatlus might also have utilized dynamic soaring. Previous authors have concluded that Pteranodon could not fly fast enough to soar dynamically, but the improved performance predicted by this analysis would have permitted high speeds making dynamic soaring possible; however, given what we know of the ecology of Quetzalcoatlus, it is unlikely that it had access to the sustained winds that are necessary for dynamic soaring. Buffetaut and Mazin’s Evolution and Palaeobiology of Pterosaurs is an excellent symposium volume resulting from the very successful 200 Years of Pterosaurs Symposium held in 2001 in Toulouse to commemorate the bicentennial of Cuvier’s interpretation of Pterodactylus antiquus as a flying reptile. The volume includes 20 papers from 34 authors covering almost the entire breadth of pterosaur research. Discovery of new specimens and new taxa is continuing worldwide, and eight papers describe new finds. Wellnhofer describes a new specimen from the Triassic of Austria identified as Eudimorphodon cf. ranzii that differs from other Eudimorphodon specimens in that the ventral end of the coracoid is expanded anteroposteriorly and the corresponding articular facets on the sternum are borne on elongate processes. As a result the sternocoracoid articulations would have prevented fore and aft rocking of the coracoid on the sternum, which seems to be an early solution to the problem of stabilizing the pectoral girdle that was solved by the evolution of the rotated scapulae and scapulonotarial articulations in the advanced pectoral girdle of large pterodactyloids. Carpenter et al. describe an incomplete rostrum of a new scaphognathine, Harpactognathus, that is the first record from the Americas and is two-and-one-half times larger than the known Scaphognathus. The specimen has a bony sagittal crest on its rostrum, and so adds to the rapidly growing record of crested rhamphorhynchoids. Buffetaut, Grigorescu, and Csiki describe a new giant azhdarchid, Hatzegopterus, from Romania based on humeral and skull fragments with an estimated wingspan rivaling that of Quetzalcoatlus and an estimated skull length of 2.7–2.9 m, an almost inconceivable size in a flying animal. Pereda-Superbiola et al. describe Phosphatodraco, a new azhdarchid from Morocco with an estimated wingspan of 5 m, based on an incomplete cervical series, and Kellner and Moody describe an anhanguerid scapulocoracoid from Venezuela. Frey, Martill, and Buchy describe two new specimens from Brazil: Ludodactylus, an ornithocheirid with a backward-directed crest like Pteranodon and abundantly toothed jaws that looks as though it could easily be ancestral to Pteranodon; and a new Tapejara species with a tall soft tissue crest that may have been four to five times as tall as the bony skull proper. The same authors plus Tischlinger also describe spectacular soft tissue preservation in new specimens from Solnhofen and the Santana Formation, including the now famous ‘dark wing’ specimen of Rhamphorhynchus that shows the fine structure of the patagium with a network of blood vessels and muscle or collagenous fibers lying perpendicular to actinofibrils. Other specimens reveal traces of a rhamphotheca, claw sheathes, heel pads, and webbing between toes. Six papers present reviews, new studies, and reinterpretations of materials. Dalla Vecchia provides a thoughtful review of Triassic pterosaurs that includes new observations. He notes that Peteinosaurus has trimorphodont dentition and Preondactylus has serrate teeth that suggest it also had trimorphodont dentition, thus all Triassic pterosaurs seem to share it; all also seem to share the compressed metatarsus that is also seen in Dimorphodon and Anurognathus; and Eudimorphodon and Preondactylus lack the elongate pre- and postzygapophyses and hemal arches that stiffen the tail in many rhamphorhynchoids, and so may be primitive. However, Dalla Vecchia points out that our window into the world
of Triassic pterosaurs is very narrow, and we need more material and better geographic and temporal coverage to clarify the early evolution of pterosaurs. Bonde and Christiansen describe an acidtransfer-prepared specimen of Rhamphorhynchus and document fine details of vertebral and sternal pneumaticity. They note that there is no clear evidence of similar pneumatization in Triassic pterosaurs, so the pneumatization of the axial skeleton in pterosaurs, sauropodomorphs, and theropods may be convergent. Steel reviews the surviving examples of the first thin sections of pterosaur bones that were prepared in 1855, and Sayao looks at bone histology of multiple different bones in two specimens from Brazil, documenting variation, and noting that the cessation of growth as the animal reached adult size was not simultaneous in all skeletal elements. Bennett, in what must be most sincere flattery of Dilkes for his dissertation on Maiasaura, reconstructed the pectoral myology of basal and derived pterosaurs to examine the evolution of the pectoral girdle of pterosaurs, and argues that the complexity of the advanced pectoral girdle of large pterodactyloids is so great as to make convergent evolution in multiple lineages unlikely. The pectoral girdle is approached from another angle by Frey, Buchy, and Martill, who divide large pterodactyloids into low wing (i.e., azhdarchoids) and high wing (i.e., ornithocheiroids) groups on the basis of their girdle morphology. Based on comparisons to low and high wing airplanes, they suggest that the low wing configuration would have been more unstable and resulted in a more maneuverable flight; however, in flapping cylindrically cambered pterosaur wings the position of the center of lift is not fixed relative to the center of gravity, and the two pectoral girdle configurations may reflect musculoskeletal rather than aerodynamic selection. An important focus of the symposium was the tracksite at Crayssac, and four papers examine pterosaur trackways. Mazin, Billon-Bruyat, Hantzpergue, and Lafaurie reviewed the Crayssac trackways, which provide a wonderful record of pterosaur locomotion, though one produced on a quite incompetent substrate and as a result recording much kinematic information and often lacking anatomical detail. In a surprising and intriguing result, they show that the width between manus prints is directly correlated with speed (i.e., the faster the wider), and the opposite of what Bennett predicted. They also describe clear crocodilian trackways from Crayssac that finally put to rest the notion that any Pteraichnus trackways could have been made by crocodilians. Rodriguez-de la Rosa describes a new trackway locality from the Campanian of Mexico that is interpreted as a freshwater, lacustrine environment, whereas heretofore trackways have been associated with marine tidal environments. Lockley and Wright review swim tracks and feeding traces made by pterosaurs that presumably would have produced typical Pteraichnus trackways under other conditions. The swim marks typically consist of four closely spaced scratches produced by the toes of an extended pes barely contacting the substrate, and no manus scratch marks seem to be present, which suggests that the forelimb may not have been used when swimming. Billon-Bruyat and Mazin throw caution to the wind and stride boldly into the field of ichnotaxonomy, concluding that all presently known pterosaur footprints pertain to a single ichnospecies, Pteraichnus saltwashensis, with a stratigraphic range from the Kimmeridgian through the Maastrichtian. They doubt that Purbeckopus is pterosaurian and note that Agadirichnus from the Moroccan Cretaceous may be a senior synonym of Pteraichnus; if so, it is to be hoped that Pteraichnus can be conserved so as to avoid unnecessary confusion. In separate papers, Kellner and Unwin present cladistic analyses of the Pterosauria, which differ significantly in a number of areas. There is uncertainty about the relationships of Triassic and Early Jurassic pterosaurs and one major difference between the
REVIEWS two cladograms is in the placement of the anurognathids. Kellner’s analysis suggests that they are the sister group of all other pterosaurs despite no fossil record before the Middle Jurassic, whereas Unwin’s places them further up the tree close to the campylognathoidids. Another major difference between the two cladograms is in the relationships of the large pterodactyloids. Kellner’s analysis suggests that large pterodactyloids with advanced pectoral girdles form a monophyletic Dsungaripteroidea, whereas Unwin’s analysis suggests parallel evolution of the advanced pectoral girdle in two or three lineages as they increased in size. Both analyses use more proportional characters (e.g., wing phalanx 1 longer than 2) than I am comfortable with, and both authors coined new names for many nodes, which seems unwise given the present state of flux of our understanding of pterosaur relationships; however, their contrasting views show where more work is needed. Both books include broad general coverage of the state of knowledge of pterosaurs, but neither replaces Wellnhofer’s (1991) Illustrated Encyclopedia of Pterosaurs with its excellent coverage of pterosaurs and their fossil record and a thorough bibliography, now unfortunately out of print. Anyone wanting an excellent general review of pterosaurs should get Wellnhofer’s book first, and supplement it with newer technical publications as needed. Buffetaut and Mazin’s volume is an essential addition to the library
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of anyone interested in pterosaurs; it is a finger on the pulse of pterosaur research that provides up-to-date, broad coverage of pterosaur research since Wellnhofer’s book and an entre´e into the newest technical literature. I cannot recommend Chatterjee and Templin’s book as a general review of pterosaurs, but the flight analysis is very intriguing and should be of interest to anyone fascinated by the flight of pterosaurs or other extinct animals. REFERENCES
KELLNER, A. W. A. 1996. Reinterpretation of a remarkably well preserved pterosaur soft tissue from the Early Cretaceous of Brazil. Journal of Vertebrate Paleontology, 16:718–722. MARTILL, D. M., AND D. M. UNWIN. 1989. Exceptionally well preserved pterosaur wing membrane from the Cretaceous of Brazil. Nature, 340: 138–140. TEMPLIN, R. J. 2000. The spectrum of animal flight: Insects to pterosaurs. Progress in Aerospace Sciences, 36:393–436. WELLNHOFER, P. 1991. The Illustrated Encyclopedia of Pterosaurs. Salamander Books, Ltd., London, 192 p. S. CHRISTOPHER BENNETT Department of Biological Sciences & Sternberg Museum of Natural History Fort Hays State University Hays, Kansas 67601-4099