title: The paleoenvironments of azhdarchid pterosaurs localities in the Late Cretaceous of Kazakhstan.
abstract: Five pterosaur localities are currently known from the Late Cretaceous in the northeastern Aral Sea region of Kazakhstan. Of these, one is Turonian-Coniacian in age, the Zhirkindek Formation (Tyulkili), and four are Santonian in age, all from the early Campanian Bostobe Formation (Baibishe, Akkurgan, Buroinak, and Shakh Shakh). All so far collected and identifiable Late Cretaceous pterosaur bones from Kazakhstan likely belong to Azhdarchidae: Azhdarcho sp. (Tyulkili); Aralazhdarchobostobensis (Shakh Shakh); and Samrukianessovi (Akkurgan). These latter two taxa, both from the Bostobe Formation might be synonyms. Azhdarcho sp. from the Zhirkindek Formation lived in a tropical-to-subtropical relatively humid climate on the shore of an estuarine basin connected to the Turgai Sea. Known fossils were collected in association with brackish-water bivalves and so the overall paleoenvironment of this pterosaur was likely an estuarine marsh as indicated by the dominance of conifers and low relative counts of ferns and angiosperms. Aralazhdarchobostobensis, from the Bostobe Formation, lived on a coastal fluvial plain along the Turgai Sea. This paleoenvironment was either floodplain (Akkurgan, Buroinak, and Shakh Shakh) or estuarine (Baibishe). In the Santonian - early Campanian, shallow waters near this coastal plain were sites for the intensive accumulation of phosphates under upwelling conditions caused by strong winds from the ancient Asian landmass. These winds also caused significant aridization of the climate during this time. We speculate that pterosaurs may have been attracted to this area by the abundant resources in the bio-productive estuaries and nearshore upwelling waters.
authors.affiliation: Zoological Institute of the Russian Academy of Sciences, Universitetskaya nab. 1, 199034 Saint Petersburg, Russia ; Department of Sedimentary Geology, Geological Faculty, Saint Petersburg State University, 16 liniya VO 29, 199178 Saint Petersburg, Russia.
authors.forename: Alexander
authors.initials: A
authors.lastname: Averianov
authors.affiliation: Ocean and Earth Science, National Oceanography Centre, Southampton, University of Southampton, Southampton SO14 3ZH, UK ; MTA-DE Lendület Behavioural Ecology Research Group, Department of Evolutionary Zoology and Human Biology, University of Debrecen, 4032 Debrecen, Egyetem tér 1, Hungary.
authors.forename: Gareth
authors.initials: G
authors.lastname: Dyke
authors.affiliation: Zoological Institute of the Russian Academy of Sciences, Universitetskaya nab. 1, 199034 Saint Petersburg, Russia.
authors.forename: Igor
authors.initials: I
authors.lastname: Danilov
authors.affiliation: Department of Vertebrate Zoology, Biological Faculty, Saint Petersburg State University, Universitetskaya nab. 7/9, 199034 Saint Petersburg, Russia.
authors.forename: Pavel
authors.initials: P
authors.lastname: Skutschas
keywords: Azhdarchidae; Kazakhstan; Late Cretaceous; Pterosauria; distribution; paleoenvironments