The First Freshwater Mosasauroid (Upper Cretaceous, Hungary) and a New Clade of Basal Mosasauroids
1. Attila Ősi (a)
2. Michael W. Caldwell (b)
3. László Makádi (c)
a. MTA-ELTE Lendület Dinosaur Research Group, Eötvös University Department of Physical and Applied Geology, Pázmány Péter sétány 1/c, Budapest, Hungary
b. Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
c. Department of Paleontology and Geology, Hungarian Natural History Museum, Budapest, Hungary
Mosasauroids are conventionally conceived of as gigantic, obligatorily aquatic marine lizards (1000s of specimens from marine deposited rocks) with a cosmopolitan distribution in the Late Cretaceous (90–65 million years ago [mya]) oceans and seas of the world. Here we report on the fossilized remains of numerous individuals (small juveniles to large adults) of a new taxon, Pannoniasaurus inexpectatus gen. et sp. nov. from the Csehbánya Formation, Hungary (Santonian, Upper Cretaceous, 85.3–83.5 mya) that represent the first known mosasauroid that lived in freshwater environments. Previous to this find, only one specimen of a marine mosasauroid, cf. Plioplatecarpus sp., is known from non-marine rocks in Western Canada. Pannoniasaurus inexpectatus gen. et sp. nov. uniquely possesses a plesiomorphic pelvic anatomy, a non-mosasauroid but pontosaur-like tail osteology, possibly limbs like a terrestrial lizard, and a flattened, crocodile-like skull. Cladistic analysis reconstructs P. inexpectatus in a new clade of mosasauroids: (Pannoniasaurus (Tethysaurus (Yaguarasaurus, Russellosaurus))). P. inexpectatus is part of a mixed terrestrial and freshwater faunal assemblage that includes fishes, amphibians turtles, terrestrial lizards, crocodiles, pterosaurs, dinosaurs and birds.
Note: one of the things I've seen is that Pannoniasaurus is reconstructed with terrestrial style legs. THe authors caution that the legs aren't really known.