Abstract
The trackway of a swimming theropod (ichnogenus Characichnos) is reported from the Lower Cretaceous Feitianshan Formation of Sichuan, China. These swim tracks help confirm that non-avian theropods were capable of forging moderately deep bodies of water. The trackway occurs on the same surface as a typical walking trackway of a sauropod (ichnogenus Brontopodus). Both occurrences are the first reported from the Cretaceous of Sichuan, and the swim tracks are the first well-preserved example of a Characichnos trackway from China. Additionally, a theropod walking trackway and several ornithopod walking trackways (similar to the ichnogenus Caririchnium) occur in the same horizon. The ornithopod trackways show a parallel orientation, suggesting gregarious behavior of the trackmakers, which may have been iguanodontiforms and/or hadrosauriforms. The co-occurrence of theropod swim tracks and theropod walking tracks suggests a fluctuation of water depth within a distinct time span.
Highlights
Fossil tracks attributed to swimming tetrapods are substrate traces left by organisms as they propelled themselves through water
Tracksite I is an exposure of the Feitianshan Formation, a 302–1090-m-thick unit of fluvial facies comprised of red clastic sediments
Dinosaur tracks yielded from the upper member of the Feitianshan Formation, which consists of non-uniformly thick alternations of mixed purplish-red and grayish-purple feldspar-quartz sandstone, purplish-red and brick-red calcareous siltstone and mudstone
Summary
Tracksite I is an exposure of the Feitianshan Formation, a 302–1090-m-thick unit of fluvial facies comprised of red clastic sediments. The Feitianshan Formation was first assigned to the Late Jurassic, but has since been identified as Early Cretaceous [10]. Dinosaur tracks yielded from the upper member of the Feitianshan Formation, which consists of non-uniformly thick alternations of mixed purplish-red and grayish-purple feldspar-quartz sandstone, purplish-red and brick-red calcareous siltstone and mudstone. The base is formed by a thick (174–828 m) layer of feldspar-quartz sandstone, which is rich in copper [10]1). The tracksite II exposure is an approximately 1000 m2 sandstone bedding surface, with a steep (about 50°) northwest dip. Mudcracks suggest a change in water depth and a short-term exposure to the air.
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