West bank of Missouri River near Bailey Island (Cretaceous to of the United States)

Where: Lyman County, South Dakota (43.6° N, 99.4° W: paleocoordinates 48.6° N, 67.1° W)

• coordinate based on nearby landmark

• outcrop-level geographic resolution

When: Baculites sp. (smooth) - Baculites perplexus ammonoid zone, Sharon Springs Member (Pierre Shale Formation), Early/Lower Campanian to Early/Lower Campanian (83.5 - 70.6 Ma)

• The Sharon Springs Member extends from Baculites sp. (smooth) - Baculites perplexus ammonite zones in South Dakota according to Gill et al. (1972) [Lower-Middle Campanian]

• bed-level stratigraphic resolution

Environment/lithology: marine; lithified, bentonitic, concretionary, black, gray shale and lithified, hematitic, black, gray shale

• "The Sharon Springs is composed largely of dark gray to black shales and is divisible into two zones on the presence or absence of fish remains. The lower part, called the Fish Scale zone, consists of a dark-gray, fissile, somewhat bituminous shale that always exhibits an abundance of fish scales and fragmentary fish skeletal remains. The top of the Fish Scale zone is marked by a

•thin layer of small, white, hard concretions. The upper part, known as the Upper Shale zone, has no fish fossils; and it is usually darker in color and generally contains small specks of red hematite. This zone is also somewhat less resistant to weathering than the lower one. The plesiosaur skeleton was found just a few feet above the base of the Fish Scale zone."

Size class: macrofossils

Collected by Bump, H. E. Martin in 1945

Collection methods: surface (float), surface (in situ),

Primary reference: S. P. Welles and J. D. Bump. 1949. Alzadasaurus pembertoni, a new elasmosaur from the Upper Cretaceous of South Dakota. Journal of Paleontology 23(5):521-535 [M. Carrano/H. Street]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 102092: authorized by Matthew Carrano, entered by Hallie Street on 08.01.2011

Creative Commons license: CC BY (attribution)

Taxonomic list

• unspecified fish material found in association with the plesiosaur fossils
Show authors, comments, and common names
Reptilia
 Plesiosauria - Elasmosauridae
"Alzadasaurus pembertoni n. sp." = Styxosaurus snowii
"Alzadasaurus pembertoni n. sp." = Styxosaurus snowii Williston 1890 elasmosaur
SDSM 451 (holotype nearly complete skeleton)