Digit-only sauropod pes trackways from China – evidence of swimming or a preservational phenomenon?

Abstract

For more than 70 years unusual sauropod trackways have played a pivotal role in debates about the swimming ability of sauropods. Most claims that sauropods could swim have been based on manus-only or manus-dominated trackways. However none of these incomplete trackways has been entirely convincing, and most have proved to be taphonomic artifacts, either undertracks or the result of differential depth of penetration of manus and pes tracks, but otherwise showed the typical pattern of normal walking trackways. Here we report an assemblage of unusual sauropod tracks from the Lower Cretaceous Hekou Group of Gansu Province, northern China, characterized by the preservation of only the pes claw traces, that we interpret as having been left by walking, not buoyant or swimming, individuals. They are interpreted as the result of animals moving on a soft mud-silt substrate, projecting their claws deeply to register their traces on an underlying sand layer where they gained more grip during progression. Other sauropod walking trackways on the same surface with both pes and manus traces preserved, were probably left earlier on relatively firm substrates that predated the deposition of soft mud and silt . Presently, there is no convincing evidence of swimming sauropods from their trackways, which is not to say that sauropods did not swim at all.

“Keep your feet on the ground”: Simulated range of motion and hind foot posture of the Middle Jurassic sauropodRhoetosaurus browneiand its implications for sauropod biology

“…In this hypothetical scenario, we would expect the trackmaker to leave impressions of only the cranial‐most portion of the pes (i.e., of its phalanges; Figure ). However, few known sauropod pedal tracks reflect morphologies that corresponds with this scenario (Xing et al, ). For Rhoetosaurus brownei , there is a lack of spatiotemporal proximate sauropod tracks, which might have otherwise provided inferences on its general pedal morphology.…”

Three-Dimensional Image Surface Acquisition in Vertebrate Paleontology: A Review of Principal Techniques

“…Because of this advancement in ease-of-use and affordability, photogrammetry is now commonly used throughout paleontology branches, being applied to trace (Bennett et al, 2013;Xing et al, 2016;Falkingham et al, 2018), individual bones (White et al, 2013), mounted skeletons (Bates et al, 2016), invertebrates (Schlüter, 2016) and even entire sites or outcrops (Klein et al, 2016). The method has even been applied to recreate lost fossils based on historical photographs Lallensack et al, 2015), or to SEM (Scanning Electron Microscope)…”

“…3D imaging of fossils including internal structure information (whole 3D imaging) can be achieved via computeraided X-ray tomography (CT; e.g., Brochu, 2002;Domínguez Alonso et al, 2004;Sereno et al, 2007;Paulina-Carabajal et al, 2014;Knoll et al, 2015;Stocker et al, 2016). Whereas CT Scanning demands the researcher take the fossil specimens to the scanning device facility (i.e., medical tomograph, micro-tomograph, synchroton microCT), surface scanning can be achieved by means of portable devices, which can be taken where the fossils are housed or even to the field where the fossils are still in situ (e.g., Wilhite, 2003;Vizcaíno et al, 2011;Falkingham and Gatesy, 2014;Xing et al, 2016;Otero et al, 2017). Ultimately, the nature of the fossil material being analyzed (e.g., size, weight, accessibility) and the purpose of the study to be undertaken (i.e., with or without internal structure information) will determine the final choice of either whole or surface 3D imaging.…”

The first theropod tracks from the Middle Jurassic of Gansu, Northwest China: new and rare evidence of quadrupedal progression in theropod dinosaurs

“…In Gansu, the Yanguoxia tracksites yielded the most abundant and diverse track records, including well-preserved sauropod, ornithopod, dromaeosaur, theropod, pterosaur, and bird tracks and trackways (Zhang et al 2006;Xing et al 2013aXing et al , 2016aXing et al , 2016bLi et al 2015). In the Honggu (Xing et al 2014a), Zhongpu (Xing et al 2014b, Guanshan (Xing et al 2016a), and Changma (Xing et al 2017) areas, some non-avian dinosaur and bird tracks were discovered.…”