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Foot posture in a primitive pterosaur

Nature volume 391, pages 886–889 (1998)Cite this article

Abstract

The nature of the hindlimb posture and gait of pterosaurs has been controversial1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16, partly because most of the pterosaur skeletons that have been found were flattened in thin-bedded rocks, therefore obscuring three-dimensional anatomy. A major controversy concerns the extent to which pterosaurs move on the ground; they have been variously interpreted as ranging from sprawling, quadrupedal walkers to erect, bird-like bipedal cursors1. Study of pelvis and femur material from the derived group Pterodactyloidea11,12,13 has resolved which movements are possible at the hip, but the lack of three-dimensional, articulated pterosaur feet has prevented examination of all of the movements that are possible within the foot. We have found a large, uncrushed, partial skeleton of a new species of the basal pterosaur Dimorphodon in thick-bedded deposits of Tamaulipas, Mexico; this material includes such a three-dimensional foot. The nature of this skeleton contradicts an important part of the cursorial interpretation, that is, that only the toes contacted the ground during terrestrial locomotion2,3,4,5,6,7. The flattened metatarsal–phalangeal joint at the base of the first four toes of this specimen would not allow such a digitigrade posture without separating most of the joints. A flat-footed stance is consistent with presumed footprints of pterosaurs8,9,10 that show impressions of the entire sole of the foot.

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Figure 1: Alternative reconstructions of locomotor posture and trackways of D. macronyx.
Figure 2: Stereophotographs of the right foot of D. weintraubi in ventral view.
Figure 3: Metatarsal–phalangeal (MP) joints of D. weintraubi and a bird.
Figure 4: Length of the articulation surface on the distal end of the metatarsus in avian and non-avian reptiles, illustrating the greater extent of this surface in birds.
Figure 5: Ternary diagram showing relative lengths of the three non-ungual phalanges of pedal digit III in living birds and fossil archosaurs expressed as a percentage of the summed lengths of the three phalanges.

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Acknowledgements

This work was supported by the National Geographical Society and National Science Foundation. We thank the Huizachal Ejido and the Consejo Estatal para la Cultura y las Artes de Estado de Tamaulipas for permission to collect fossils in Huizachal Canyon; the Instituto de Geologia of U.N.A.M. for support; the Instituto Nacional de Antropologia e Historia for permission to borrow the specimen; C.Vanderslice, D. Chaney, and A. Davidson for fossil preparation; M. Ellison, M. Parrish and C.Vanderslice for illustrations; L. Grande and those who helped collect the fossil; M. Lockley, K.Padian, S. Gatesy, R. Blob, M. Carrano, F. A. Jenkins Jr., J. Gauthier, and S. Swartz for comments and the Field Museum of National History, the National Museum of Natural History, and the Natural History Museum, London for access to specimens.

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Authors and Affiliations

  1. the Department of Biological Sciences, George Washington University, 20052, Washington DC, USA

    J. M. Clark

  2. the Department of Organismal Biology and Anatomy, University of Chicago, Chicago, 60637, Illinois, USA

    J. A. Hopson

  3. Instituto de Geología, Universidad Nacional Autónoma de México, Del. Coyoacan, DF 04510, México

    R. Hernández R. & M. Montellano

  4. the Department of Geology, University of Rhode Island, Kingston, 02881, Rhode Island, USA

    D. E. Fastovsky

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  1. J. M. Clark
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  5. M. Montellano
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Correspondence to J. M. Clark.

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Clark, J., Hopson, J., Hernández R., R. et al. Foot posture in a primitive pterosaur. Nature 391, 886–889 (1998). https://doi.org/10.1038/36092

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