August 31 , 2016

A small tetrapod footprint assemblage from the Anning Formation (Upper
Jurassic–Lower Cretaceous) at Konglongshan Town, Yunnan Province,
China, contains possible swim traces attributable to theropod
dinosaurs based on their tridactyl and mesaxonic pes morphology.
Morphotypes are tentatively assigned to the ichnogenera Characichnos
and Wintonopus, a third one is similar to Hatcherichnus. Due to the
inherent variability observed in tetrapod swim tracks, the names are
used here informally describing footprints that reflect a distinct
trackmaker behavior rather than anatomically accurate images of the
pes anatomy. Variation of the imprint shape is obviously due to
extramorphological effects and does not indicate taxonomic diversity
of trackmakers. Elongate, slender impressions associated with these
tracks are discussed here as possible tail traces. Trackmakers were
possibly buoyant and active swimming individuals touching and
scratching the bottom of deeper waterbodies with the distal ends of
their digits. The orientation of the traces perpendicular to preserved
ripples suggest cross-current movement and activities.

Li-Da Xing, Martin G. Lockley, Hendrik Klein, Jian-Ping Zhang, Tao Wang, W. Scott Persons IV & Zhi-Ming Dong (2016)
A tetrapod footprint assemblage with possible swim traces from the Jurassic–Cretaceous boundary, Anning Formation, Konglongshan, Yunnan, China.
Palaeoworld 25(3): 444–452
doi:10.1016/j.palwor.2015.06.002