Scientists writing in the academic journal “PeerJ” have reported the discovery of an extensive pterosaur trackway from the Lower Cretaceous Shengjinkou Formation in the Xinjiang Uygur Autonomous Region in north-western China. The trackway consists of 114 small pterosaur tracks (57 handprints and 57 footprints). Analysis of these trace fossils has led to the erection of a new pterosaur ichnospecies – Pteraichnus wuerhoensis, although the researchers speculate that these tracks could have been made by the dsungaripterid pterosaur Noripterus complicidens.

Pteraichnus pterosaur tracksite
A photograph of the tracksite with an interpretative line drawing. The tracks have been assigned to the new pterosaur ichnospecies Pteraichnus wuerhoensis. Picture credit Wei Gao.

A Complicated Trackway to Interpret

As 57 handprints (manus) and 57 footprints (pes) have been preserved on the same slab of finely-grained sandstone, the researchers confidently assert that the trackmaker was quadrupedal, but they can’t say for certain whether these prints were all produced at the same time. It is presumed that they would have been made over a short period of time on a muddy shoreline close to a large lake, as they would have needed to be covered by sediment quite quickly to permit their preservation. The lack of ripple marks or invertebrate trace fossils in the slab suggest that this surface was rapidly buried after only being exposed for a short period.

The handprints range in size from 1.9 cm long to 5.15 cm, whilst the feet impressions range in size from 2.68 cm to 5.71 cm. This suggests that the tracks were made by pterosaurs of different ages. This indicates that both adult and juvenile forms may have congregated at this location.

Gregarious Pterosaurs

The density of the Wuerho small pterosaur tracks was also remarked upon. The density is high, the assemblage would represent a density of tracks of around 365 per square metre. Generally, high densities of tracks (in excess of 100 per square metre), have often been cited as evidence of gregarious behaviour or high activity levels.

A detailed comparison with other pterosaur tracks suggests that these prints belong to the ichnogenus Pteraichnus, this is the tenth ichnospecies to be assigned to this ichnogenus. It being distinguished from the others by several traits, for example in these tracks the length of the toes on the foot are equal to the length of the metatarsal part of the foot. The ratio between the length of the toes and the rest of the foot is 1:1, this ratio is different from other reported pterosaur tracks assigned to the ichnogenus Pteraichnus.

Pteraichnus ichnospecies could be Noripterus complicidens
The foot of the dsungaripterid pterosaur Noripterus complicidens (left) with outline drawing of N. complicidens foot (middle) and interpretative drawing of a track made by a foot (right). The researchers infer that these tracks were probably made by N. complicidens. The length of the digital part of the foot (Di) is equal to the length of the metatarsal part of foot (Me). The ratio between the length of the toes and the rest of the foot is 1:1 this ratio is different from other reported pterosaur tracks assigned to the ichnogenus Pteraichnus and therefore supports the theory that these tracks represent a new ichnospecies. Picture credit: Li et al with additional notation by Everything Dinosaur.

Tracks Possibly Made by Noripterus complicidens

The researchers from the Chinese Academy of Sciences (Centre for Excellence in Life and Palaeoenvironment), postulate that the tracks may have been made by the dsungaripterid pterosaur Noripterus complicidens. To date only two genera of pterosaur have been identified from fossils found in the Shengjinkou Formation in north-western China. They are both members of the Dsungaripteridae family, a group of advanced pterodactyloid pterosaurs with robust, stout skulls and strong limbs. The two genera are Dsungaripterus (D. weii) and the slightly smaller Noripterus (N. complicidens). By comparing the tracks to the foot bone of Noripterus, the researchers concluded that these tracks were made by Noripterus, a pterosaur with a wingspan of approximately 2 metres that probably fed on shellfish, hence the congregation of pterosaur tracks at this site, although no feeding traces could be identified.

An incomplete specimen of the dsungaripterid pterosaur Noripterus compliciden
An incomplete specimen of the dsungaripterid pterosaur Noripterus complicidens. Picture credit: Junchang Lü.

The scientific paper: “A new pterosaur tracksite from the Lower Cretaceous of Wuerho, Junggar Basin, China: inferring the first putative pterosaur trackmaker” by Yang Li, Xiaolin Wang and Shunxing Jiang published in PeerJ.

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