Dinosaur, Bird, and Pterosaur Footprints from the Lower Cretaceous Wuerhe Asphaltite Area, Junggar Basin, China
An assemblage featuring well-preserved dinosaur, bird, and pterosaur footprints has been identified within the deposits of the upper Tugulu Group (Lower Cretaceous) in the Wuerhe asphaltite area of the Junggar Basin, Xinjiang, northwestern China. This discovery reveals a complex interaction of trackmakers in a moist, plastically deformable substrate, providing significant insight into the Early Cretaceous fluvio-lacustrine ecosystems of the region.
Geological Setting and Stratigraphy
The Wuerhe asphaltite mine (46°5′6.25″ N, 85°45′49.97″ E) covers an area of approximately 0.78 km² on the edge of the Gurbantunggut Desert. Stratigraphically, the tracksite pertains to the Upper Layer of the Tugulu Group (Albian, Yu, 1990; or Aptian–Albian, Maisch et al., 2004), placing it higher than the previously documented Huangyangquan tracksite. The sedimentary sequence consists of fourteen documented layers characterized by grey sandy mudstones and light green-grey sandstones bordering the mined asphaltite. The footprints are localized at the interface of the first and second layers. The notable reddish hue of the sediments at this site suggests more extensive oxidation compared to adjacent localities.
Ichnological Analysis
Theropod Tracks
A collection of fourteen natural casts (MGCM.A1a, b; 2a, b; 3; 4a–f; 5a, c; 6) indicates a diverse range of theropod trackmakers. These specimens exhibit a significant size range, with footprint lengths spanning 6.6 to 15.1 cm. Morphological features, including digit proportions and pad configurations—particularly in specimen MGCM.A5a—show strong affinities with the ichnogenus Jialingpus. The presence of smaller, morphologically similar tracks (such as MGCM.A4d and A6) suggests the presence of juvenile individuals belonging to the same trackmaker group as the larger Jialingpus specimens.
Avian Tracks
Approximately ten bird tracks were recovered, varying in length from 3.0 to 5.5 cm. These small, tridactyl footprints are characteristic of shorebird-like trackmakers. Specimen MGCM.A4g serves as the primary reference, displaying a forward-directed Digit III as the longest, with Digit II being shorter than Digit IV and a total divarication angle of 81°. Other specimens, such as MGCM.A1c, demonstrate more robust digit traces but maintain the same diagnostic shorebird-like morphology.
Pterosaur Tracks
The assemblage includes a single tridactyl footprint (MGCM.A7) preserved in high relief. The trace is diagnostic of a pterosaur manus, characterized by a specific outline and a swollen, convex shape in the proximal area near the shorter digit traces (likely representing digits I and II). This isolated natural cast is tentatively assigned to the ichnogenus Pteraichnus, consistent with pterosaur tracks found elsewhere in the Junggar Basin.
Taphonomy and Overlapping Relationships
An exceptional feature of the Wuerhe site is the preservation of overlapping tracks on single slabs, such as MGCM.A1a–c. Analysis of these overlaps reveals that Digit II of MGCM.A1b was traversed and plastically deformed by the foot of the MGCM.A1a trackmaker. The deformation of Pad 1 into a U-shape without fracturing indicates that the sediment was moist and highly plastic at the time of impression. Such relationships allow for the determination of relative timing; for instance, when a smaller track is deeper than a larger overlapping track, it suggests the smaller track was produced first, effectively serving as a pre-existing depression in the substrate.
Paleoecology and Ichnofacies
The co-occurrence of various theropod size-classes, shorebird-like birds, and pterosaurs suggests a thriving, mixed-age community. The sedimentary facies indicate a deltaic lowland environment, likely providing abundant food resources along the shorelines of water bodies within a fluvio-lacustrine habitat. This faunal association is a representative example of the shorebird ichnofacies, illustrating a complex ecological niche where terrestrial dinosaurs and winged archosaurs frequently congregated.
Scientific Citation: Palaeoworld 22 (2013) 42–51. Received 17 December 2012; accepted 13 March 2013.
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Figure 1: Geographic location and stratigraphic position of the Wuerhe asphaltite tracksite within the Junggar Basin, Xinjiang.
Figure 2: Stratigraphic column of the asphaltite tracksite showing the grey sandy mudstones and the specific interface where the footprints were recovered.
Figure 3: Outline drawings of theropod and bird tracks (MGCM.A1–3) showing overlapping impressions and plastic deformation indicating moist sediment conditions.
Figure 4: Detailed natural casts of theropod footprints showing varying size classes, interpreted as representative of adult and juvenile individuals.
Figure 5: Morphological comparison of the Jialingpus-like theropod track MGCM.A5a with known ichnotaxa from the Huangyangquan tracksite.
Figure 6: High-relief natural cast of the pterosaur manus track MGCM.A7, tentatively assigned to the ichnogenus Pteraichnus.