A rare new Pliensbachian plesiosaurian from the Amaltheenton Formation of Bielefeld in northwestern Germany

Abstract

Sachs, S. & Kear, B.P. November 2018. A rare new Pliensbachian plesiosaurian from the Amaltheenton Formation of Bielefeld in northwestern Germany. Alcheringa 42, 487-500. ISSN 0311-5518.We describe a new plesiosaurian from the upper Pliensbachian Amaltheenton Formation of Bielefeld in northwestern Germany. The taxon is based upon an incomplete associated skeleton comprising part of the right mandibular ramus, several teeth, a series of cervical, pectoral, dorsal and caudal vertebrae, as well as ribs, limb girdle elements including a nearly complete right scapula, and various distal limb bones. A unique character state combination serves to distinguish the Amaltheenton Formation remains from other previously documented Early Jurassic plesiosaurians. The most important features are the presence of a longitudinal notch incising the posterior rim of the glenoid fossa and retroarticular process, and a pronounced ventrolateral shelf on the scapula, both of which constitute derived states otherwise shared with Early Cretaceous leptocleidians. However, phylogenetic analysis using a ‘total group’ Plesiosauria data-set that specifically accommodates for Pliensbachian taxa unanimously placed the Amaltheenton Formation plesiosaurian among Early–Middle Jurassic pliosaurids. This discovery is significant because it reveals unexpected homoplasy, but also because it establishes what is only the third formally named plesiosaurian taxon thus far documented from Pliensbachian strata worldwide.Sven Sachs* [sachs.pal@gmail.com], Naturkunde-Museum Bielefeld, Abteilung Geowissenschaften, Adenauerplatz 2, 33602 Bielefeld, Germany and Im Hof 9, 51766 Engelskirchen, Germany; Benjamin P. Kear [benjamin.kear@em.uu.se] Museum of Evolution, Uppsala University, Norbyvägen 16, Uppsala SE-752 36, Sweden.