Reappraisal of Europe's most complete Early Cretaceous plesiosaurian: Brancasaurus brancai Wegner, 1914 from the Wealden facies of Germany

The olotype of Brartcasaurus brancai is one of the most historically famous and anatomically complete Early Cretaceous plesiosaurian fossils. It derived from the Gerdernann & Co. brickworks clay pit near Gronau (Westfalen) in North Rhine-Westphalia, northwestern Germany. Stratigraphically this locality formed part of the classic European Wealden facies, but is now more formally attributed to the upper most strata of the Buckeberg Group (upper Berriasian). Since its initial description in 1914, the type skeleton of B. brancai has suffered damage both during and after WWII. Sadly, these mishaps have resulted in the loss of substantial information, in particular an structures of the cranium and limb girdles, which are today only evidenced from published text and/or illustrations. This non-confirmable data has, however,. proven crucial for determining the relationships of B. brancai within Plesiosauna. either as an early long-necked elasmosaund, or a member of the controversial Early Cretaceous leptocleidid radiation. To evaluate these competing hypotheses and compile an undated osteological. compendium, we undertook a comprehensive examination of the holotype as it now preserved, and also assessed other Buckeberg Group plesiosaurian fossils to establish a morphological hypodigm. Phylogenetic simulations using the most species-rich datasets of Early Cretaceous plesiosaurians incorporating revised scores for B. brancai, together with a second recently named Backeberg Group plesiosaurian Granausaurus wegneri (Ham pc,. 2013), demonstrated that referral of these taxa to Leptocleididae was not unanimous, and that the topological stability, of this Glade is tenuous. In addition, the trait combinations manifested by B. brancai and G. wegneri were virtually identical. We therefore conclude that these monotypic individuals are ontogenetic morphs and G. wegneri is a junior synonym of B. brancai. Finally, anomalies detected in the diagnostic features for other Wealden plesiosaurians have prompted reconsiderations of interspecies homology versus intraspecific variability. We therefore propose that the still unresolved taxonomy of B. brancai should emphasize only those character states evident in the examinable fossil material, and specifically accommodate for growth-related modifications delimited via osteologically mature referred specimens.