Fig. 1. Map showing Khuren-Dukh Formation, Mongolia and localities where long-necked choristoderes have been found. 1, Shokawa ikoi, Okurodani Formation, Barremian–Aptian (Evans and Manabe 1999); 2, Hyphalosaurus baitaigouensis, Baitaigou, Yixian Formation, Barremian–Aptian (Ji et al. 2004); 3, Hyphalosaurus sp., Luojiagou, Yixian Formation, Barremian–Aptian (Zhang et al. 2012; the Tianyu specimens with locality information are all from Badaoyingzi, Luojiagou); 4, Hyphalosaurus lingyuanensis, Dawangzhangzi, Yixian Formation, Barremian–Aptian (Fanzhangzi) (Gao et al. 1999; Gao and Ksepka, 2008); 5, Khurendukhosaurus orlovi and Khurendukhosaurus sp., Khuren-Dukh Formation, middle–late Albian (Sigogneau-Russell and Efimov 1984; Efimov and Storrs 2000); 6, Khurendukhosaurus sp., Mogoito, Murtoi Formation, Barremian?–Aptian (Efimov 1996; Skutschas 2008; Skutschas and Vitenko 2017); 7, cf. Khurendukhosaurus sp., Bol'shoi Kemchung 3, Ilek Formation, Early Cretaceous (Skutschas and Vitenko 2017).