A palynological investigation of plesiosaur-bearing rocks from the Upper Cretaceous Tahora Formation, Mangahouanga, New Zealand

High-palaeolatitude plesiosaur, mosasaur and, more rarely, dinosaur fossils are well known from the Maungataniwha Sandstone Member of the Tahora Formation in Mangahouanga Stream, Hawkes Bay, New Zealand. A palynological investigation of strata exposed along Mangahouanga Stream and of transported boulders hosting vertebrate fossils reveals well-preserved assemblages dominated by terrestrial pollen and spores but also including marine dinoflagellate cysts in some samples. The palynofacies are strongly dominated by wood fragments including charcoal; one outcrop sample and the sample taken from a boulder hosting plesiosaur vertebrae contain entirely terrestrially derived palynoassemblages, suggesting a freshwater habitat for at least some of the plesiosaurs. The host unit spans the Santonian to lowermost Maastrichtian, while the key pollen taxa Nothofagidites senectus and Tricolpites lilliei, together with the dinocyst Isabelidinium pellucidum and the megaspore Grapnelispora evansii, indicate a late Campanian to early Maastrichtian age for the fossiliferous boulders. The palynoflora indicates a mixed local vegetation dominated by podocarp conifers and angiosperms with a significant tree-fern subcanopy. The presence of taxa with modern temperate distributions, such as Nothofagus (southern beech), Proteaceae and Cyatheaceae (tree-ferns), indicates a mild-temperate climate and lack of severe winter freezing during the latest Cretaceous, providing an ecosystem that most probably made it possible for polar dinosaurs to overwinter in this part of the world.