Jordan C. Mallon, Donald M. Henderson, Colleen M. McDonough & W.J. Loughry (2018)
A 'bloat-and-float' taphonomic model best explains the upside-down preservation of ankylosaurs.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
In North America, upside-down ankylosaur occurrences are more common than not.
Frequency of overturned ankylosaurs is likely due to bloat-and-float.
Differential bloating behaviour of ankylosaurids and nodosaurids may explain why the latter are found more often in marine paleoenvironments.
Ankylosaur taphonomy may help to explain upside-down glyptodont occurrences.
It is widely held that, within the Cretaceous fluvial and marine deposits of North America, ankylosaur remains are typically preserved upside-down; however, this anecdotal observation has yet to be substantiated. Likewise, none of the various hypotheses that purport to explain the frequent occurrence of overturned ankylosaurs has been tested either. This study is the first to apply quantitative and modeling approaches to address these shortcomings. We find strong statistical support for the dominance of upside-down occurrences, and favour a âbloat-and-floatâ model to account for them. According to this model, ankylosaur carcasses become reworked into fluvial or marine settings where they bloat and overturn prior to their final deposition. Differential floating behaviour between ankylosaurids and nodosaurids may have implications regarding the occurrence of the latter in marine depositional environments. This consideration of ankylosaur taphonomy might similarly help to explain the purported frequency of overturned glyptodonts, which share a similar bauplan with ankylosaurs.