SVP 12 – Lotosaurus bonebed redated to Ladinian

Hagen et al. 2015 discuss the sedimentology of the Lotosaurus (now dated to Ladinian, Late Middle Triassic, Fig. 1) bone bed. This was suspected here three years ago and thankfully suspicions are now confirmed.

Figure 1. Lotosaurus, a finback poposaur.

Figure 1. Lotosaurus, a finback poposaur.

From the abstract
Lotosaurus adentus is a highly unusual, sail-backed, edentulous poposauroid pseudosuchian archosaur* known primarily from a single site in Sangzhi County, Hunan Province, south China. This locality, the Lotosaurus Quarry, is traditionally dated to the Anisian and is distinctive in being a dense bonebed from which dozens if not hundreds of individual bones and occasional partial skeletons of Lotosaurus have been collected since it was discovered in 1970. The site appears to have formed in a fluvial-floodplain depocenter with sediment derived from multiple sources, rather than in a tidal flat setting as previously suggested. The presence of a population of unexpectedly young detrital zircons from the bone bed unit indicates that Lotosaurus is likely to be Ladinian in age, rather than Anisian as previously reported. This result is more congruent with the phylogenetic position of Lotosaurus, which lies among or just outside a grouping of derived poposauroids known from the Upper Triassic of North and South America.”

*Poposaur, yes, but there is no such thing a pseudosuchian, which is not a monophyletic clade, and only crocs and dinos are archosaurs.

Previous to this reediting of the sediment, Lotosaurus was a chronological outlier and this date change comes as good news.

References
Hagen CJ et al.  2015. Taphonomy, age, and geological context of the original Lotosaurus adentus (Archosauria, Poposauroidea) bone bed in the Middle Triassic Badong Formation, Hunan China. Journal of Vertebrate Paleontology abstracts.

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