Elizabeth L. Nicholls

Paleobiogeography of the Cretaceous Western Interior Seaway of North America: the vertebrate evidence

Abstract Distribution patterns of marine vertebrates of the Cretaceous Western Interior Seaway of North America are analysed in a biogeographical context. The analysis is based on fossil vertebrate assemblages from the following Lower Campanian localities: (1) Anderson River fauna, N.W.T. (2) Pembina fauna, southern Manitoba (3) Sharon Springs fauna, South Dakota-Wyoming (4) Niobrara fauna, Kansas (5) Mooreville fauna, Alabama. Due to the cosmopolitan nature of many marine vertebrates, relative abundance is used in preference to presence-absence data in identifying faunal distribution patterns. The analysis demonstrates the presence of two faunal subprovinces in the seaway. The Northern Interior Subprovince is characterized by a low diversity in all groups and is dominated by plesiosaurs, hesperornithiforms and the mosasaur Platecarpus. The Southern Interior Subprovince is characterized by a high diversity in all groups and is dominated by sharks, turtles and the mosasaur Clidastes. These biogeographical subdivisions support the hypothesis of warm temperature and cool temperate zones in the seaway that have been proposed on the basis of invertebrate faunas.

NEW SPECIMEN OF BASILEMYS PRAECLARA HAY AND ITS BEARING ON THE RELATIONSHIPS OF THE NANHSIUNGCHELYIDAE (REPTILIA: TESTUDINES)

A new specimen of the Cretaceous trionychoid turtle Basilemys praeclara Hay, from the Frenchman Formation (Upper Maastrichtian) of Saskatchewan, confirms the validity of the species, previously known only from the type specimen. Basilemys praeclara is considered the sister taxon of Basilemys sinuosa , and the restriction of this clade to the late Maastrichtian reinforces the distinctiveness of the Lancian chelonian fauna from the older Judithian chelonian fauna. Basilemys, Nanhsiungchelys , and Zangerlia comprise the family Nanhsiungchelyidae, with Basilemys and Nanhsiungchelys being sister taxa within the family.

New material of Toxochelys latiremis Cope, and a revision of the genus Toxochelys (Testvoines, Chelonioidea)

ABSTRACT Toxochelys latiremis, a. species of Cretaceous marine turtle, is redescribed on the basis of an almost complete specimen from the Niobrara Chalk of Kansas (Upper Santonian-Lower Campanian). Two species of Toxochelys, T. latiremis Cope and T. moorevillensis Zangerl are recognized; T. browni (Hay), T. weeksi Collins, and T. barberi (Schmidt) are considered junior synonyms of Toxochelys latiremis. This revision extends the stratigraphic range of T. latiremis to the Lower Maastrichtian. The geographic range of this species now extends from southern Manitoba to Arkansas.