Reanalysis of Wupus agilis (Early Cretaceous) of Chongqing, China as a Large Avian Trace: Differentiating between Large Bird and Small Non-Avian Theropod Tracks

Abstract

Trace fossils provide the only records of Early Cretaceous birds from many parts of the world. The identification of traces from large avian track-makers is made difficult given their overall similarity in size and tridactyly in comparison with traces of small non-avian theropods. Reanalysis of Wupus agilis from the Early Cretaceous (Aptian-Albian) Jiaguan Formation, one of a small but growing number of known avian-pterosaur track assemblages, of southeast China determines that these are the traces of a large avian track-maker, analogous to extant herons. Wupus, originally identified as the trace of a small non-avian theropod track-maker, is therefore similar in both footprint and trackway characteristics to the Early Cretaceous (Albian) large avian trace Limiavipes curriei from western Canada, and Wupus is reassigned to the ichnofamily Limiavipedidae. The reanalysis of Wupus reveals that it and Limiavipes are distinct from similar traces of small to medium-sized non-avian theropods (Irenichnites, Columbosauripus, Magnoavipes) based on their relatively large footprint length to pace length ratio and higher mean footprint splay, and that Wupus shares enough characters with Limiavipes to be reassigned to the ichnofamily Limiavipedidae. The ability to discern traces of large avians from those of small non-avian theropods provides more data on the diversity of Early Cretaceous birds. This analysis reveals that, despite the current lack of body fossils, large wading birds were globally distributed in both Laurasia and Gondwana during the Early Cretaceous.

An Ornithopod-Dominated Tracksite from the Lower Cretaceous Jiaguan Formation (Barremian–Albian) of Qijiang, South-Central China: New Discoveries, Ichnotaxonomy, Preservation and Palaeoecology

“…Xing et al [ 6 ] gave the first detailed description of the Pteraichnus tracks and evaluation of their paleoecological significance. Xing et al [ 4 ] reviewed Wupus agilis from the Lotus tracksite. Wupus , originally identified as the trace of a small non-avian theropod track-maker [ 2 ], is now considered to be the track of a large avian and referred to the ichnofamily Limiavipedidae.…”

“…The lithological association of the Jiaguan Formation consists of massive sandstones intercalated with thinner mudstone intervals, exposed at the Lotus site in an impressive near-vertical cliff face. The track-and wrinkle structure-bearing levels first occur in dark purple redquartz sandstone in the lower part of the Jiaguan Formation about 30–40 m above the base of the unit [ 2 , 4 , 6 ]. The beds are near-horizontal with the result that notches have been eroded horizontally into the steep vertical cliff faces by removal of the soft siltstones and mudstones.…”

“…The bird and pterosaur tracks have the same general orientation. Bird trackways run parallel to the interpreted direction of the river’s flow [ 4 ]. This suggests that the trackmakers may have been foraging, as has been observed in Goseongornipes isp.…”

“…Early discoveries of theropod and ornithopod tracks in Lower Cretaceous strata of south-central China offered a small glimpse of the Cretaceous fauna [ 1 ], but a more significant ichnological evidence was not reported until after 2007 [ 2 ]. Since then, multiple other Lower Cretaceous (Jiaguan Formation) tracksites have been found [ 3 , 4 ].…”

“…Xing et al [ 2 , 4 – 6 ] described dinosaur/pterosaur ichnoassemblages from the Lotus tracksite, Qijiang National Geological Park located in Qijiang District, south of Chongqing Municipality near the southeastern border of the Sichuan Basin. The Lotus tracksite includes over 300 tracks of ornithopods, non-avian theropods, birds, pterosaurs and sauropods [ 6 ].…”