A recent paper by Mazin and Poeuch in the journal Geobios describes the first known trackways of non-pterodactyloid (formerly called “Rhamphorynchoid”) pterosaurs (1). I began my master’s degree with the intention of studying pterosaur locomotion and trackways by using bats as living comparisons. “Rhamphorynchoid” pterosaurs – a hodgepodge group that contains all pterosaurs that don’t belong to the superfamily Pterodactyloidea – were particularly interesting to me due to the lack of known trackways and the amount of debate existing about how they walked. In the end, my interest in filling the gaps in our collective knowledge about how bats walk trumped my interest in non-pterodactyloid locomotion and I ended up abandoning that portion of my thesis. I remain interested in the terrestrial capabilities of pterosaurs, however, so I was very excited to read this new paper. Recognized trackways of pterodactyloid pterosaurs have become increasingly common since the 1990s (2), demonstrating that those late Jurassic to late Cretaceous animals were terrestrially adept quadrupeds with erect gaits. The absence of trackways belonging to the Triassic through Jurassic non-pterodactyloids, however, has sparked debate as to how terrestrially competent these animals were and whether they walked on two or four legs. This new paper describes trackways belonging to three new ichnospecies of non-pterodactyloid pterosaurs from an intertidal region in the late Jurassic Period of France. It suggests that non-pterodactyloids were not only quadrupedal on the ground, but that they held their hands with fingers aligned with the body, unlike pterodactyloids which held their fingers perpendicular. In 2015, Mark Witton presented a number of reasons that he felt suggested the terrestrial abilities of non-pterodactyloids were underestimated (3). Two of the points he focused on were whether the uropatagium (the part of the flight membrane that extends between the two hind legs) restricted movement of the legs, and whether the limbs were sprawled and how that would influence terrestrial locomotion. Witton observed that many living animals with extensive uropatagia are nonetheless adept walkers. My master’s research on living bats underscored this point as we documented walking and bounding gaits in the common vampire bat (Desmodus rotundus) and Seba’s short-tailed bat (Carollia perspicillata), while noting that other bats with relatively small patagia, like the greater sac-winged bat (Saccopteryx bilineata), appeared incapable of anything but a sprawling crawl (4). Other studies have shown bats with even larger uropatagia, such as the pallid bat (Antrozous pallidus), are capable of rapid and coordinated gaits (5). Walking postures of two non-pterodactyloid pterosaurs: sprawling gait of Dorygnathus (A); erect gait of Dimorphodon (B). Credit Mark Witton/PeerJ. Bats can inform Witton’s point about sprawling, too. Due to hindlimbs that are rotated 90⁰ from those of a typical mammal, bats cannot stand erect and must sprawl when on the ground. Their forelimbs--like those of pterosaurs--dwarf their hindlimbs, resulting in trackways in which the tracks produced by their hands are located outside those produced by the feet (4, 6). Nonetheless, Desmodus, Antrozous, and many other bat species are quite capable on the ground. Witton points out that not all non-pterodactlyoids appear to have had a sprawling posture, and those like Dimorphodon and Darwinopterus may have had terrestrial abilities similar to pterodactyloid pterosaurs. The trackways illustrated in the paper by Mazin and Poeuch seem to confirm this, as there is little evidence that the trackmaker possessed notably sprawled forelimbs.
Ultimately, it seems that the rarity of non-pterodactyloid pterosaur tracks is not a result of a lack of terrestrial ability, but may instead stem from differences in habitat and behavior. Not all environments are uniformly suited to preserve fossil trackways, and if non-pteryodactyloid pterosaurs were not occupying those favorable environments their trackways will not frequently be preserved. It is also unlikely that even the most terrestrially inept pterosaurs were completely helpless on the ground, and sprawling pterosaurs may have been able to employ a breaststrokelike crawl (similar to what we have documented in many phyllostomid bats and Saccopteryx). Ever since pterodactyoid tracks were first recognized in the fossil record they have been identified with increasing regularity all over the world. While non-pterodactyoid tracks may not prove to be as common as those of pterodactyoids, it is extremely likely that there are more out there, waiting to tell us more about how these animals moved and lived. References 1) Mazin, J.-M., & Pouech, J. (2020). The first non-pterodactyloid pterosaurian trackways and the terrestrial ability of non-pterodactyloid pterosaurs. Geobios https://doi.org/10.1016/j.geobios.2019.12.002 2) Lockley, M., Harris, J. D., & Mitchell, L. (2008). A global overview of pterosaur ichnology: tracksite distribution in space and time. Zitteliana, B28: 185-198. 3) Witton, M. P. (2015). Were early pterosaurs inept terrestrial locomotors? PeerJ, 3:e1018; DOI 10.7717/peerj.1018 4) Jones, M. F., & Hasiotis, S. T. (2018). Terrestrial behavior and trackway morphology of Neotropical bats. Acta Chiropterologica, 20: 229-250. 5) Dietz, C. L. (1973). Bat walking behavior. Journal of Mammalogy, 54: 790-792. 6) Lawrence, M. J. (1969). Some observations on non-volant locomotion in vespertilionid bats. Journal of Zoology, 157: 309-317.
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Matthew JonesMusings on evolution and paleontology-related research and news. Archives
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