Anatomy and locomotion of Pterodactylus (Archosauria: Pterosauria) from the Late Jurassic Solnhofen Formation of Germany

Abstract

The first vertebrates to evolve powered flight were the pterosaurs, which dominated the Mesozoic skies for 160 million years before going extinct at the end of the Cretaceous. Pterodactylus was the first pterosaur ever identified, based on a fossil specimen from the Late Jurassic Solnhofen Formation of Germany. Since then numerous species were assigned to Pterodactylus, until 1996 when year classes were discovered. Consequently, only one species remains, Pterodactylus antiquus. Due to this reclassification a redescription of the skeleton is needed. Pterodactylus is represented by numerous specimens, which are unfortunately badly crushed and sometimes disarticulated, making the interpretation of the skeleton difficult. Based on the numerous specimens, a three-dimensional cast model skeleton has been reconstructed that provides clear anatomical detail of Pterodactylus for the first time. Thus, the 3D cast model skeleton formed the basis of the redescription, which was also supplemented by actual specimens located at the Carnegie Museum of Natural History and the Museum of Texas Tech University. Using the redescription of Pterodactylus the locomotion, both terrestrial and flight, of Pterodactylus are discussed. 3D surface laser scans were created and animated to help illustrate and visualize the morphology and locomotion of Pterodactylus. The aerodynamic function as the tail is lost in pterodactyloids is also discussed. Pterodactylus is a small pterodactyloid pterosaur that shares several features with other pterodactyloids such as a proportionately large skull, long neck, short body, reduced bony tail, greatly enlarged forelimbs, and short hindlimbs. The redescription allowed for an examination of the palate and brain case regions of Pterodactylus for the first time. Based on the morphology of the skeleton and fossil trackways Pterodactylus was a quadrupedal walker with the fore and hindlimbs in a semi-erect to erect stance. Pterodactylus also had the ability to rear up on its hindlimbs in order to become bipedal. This allowed Pterodactylus to make bipedal takeoffs and landings, as confirmed by the animations. Pterodactylus modified its forelimbs into long slender wings necessary for flight. Pterodactylus had numerous options for controlling flight such as morphing the size and shape of the wings, increasing or decreasing the camber, moving the feet, pteroid or fifth toe. Based on calculations, Pterodactylus was a very acrobatic flier capable of hovering, continuous flapping, and soaring flight. Losing the tail gave pterodactyloids two distinct advantages: better terrestrial mobility and more maneuverable flight. Elongation of the metacarpus, and a more posteriorly directed hindlimbs allowed pterodactyloids to have a more upright and erect stance than basal pterosaurs. This more upright posture allowed pterodactyloids to become bipedal, which is ideal for ground based takeoff and landings. It is believed that this more terrestrial lifestyle led to the higher diversity of pterodactyloids. Loss of the tail decreased the turning radius of pterodactyloids and coupled with the some very broad cranial crests allowed for very maneuverable flight. This more maneuverable flight was accompanied by an expansion of the brain, where the centers of coordination and balance were enhanced.

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Keywords

Pterosaur, Pterodactylus, Pterodactyl, Anatomy, Locomotion, Flight, Walking, Tail

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