Along Corral Creek, Milne Ranch, southwest Muddy Mountain (Triassic of the United States)

Where: Wyoming (42.6° N, 106.3° W: paleocoordinates 10.3° N, 31.8° W)

• coordinate estimated from map

• small collection-level geographic resolution

When: Alcova Limestone Member (Crow Mountain Formation), Spathian (251.3 - 247.2 Ma)

• Alcova (Limestone) Member, Crow Mountain Formation, Chugwater Group

•The stratigraphic correlation and hence determination of the relative geological age of the Alcova Limestone is rendered difficult by the general paucity of fossils, vertebrates (Corosaurus) and invertebrates alike (for a review see Storrs, 1991). The presence of the nothosauriform reptile Corosaurus has led some workers (Colbert, 1957; Zangerl, 1963) to assign the Alcova to the Upper Triassic. Storrs (1991:101) accepted a late Lower Triassic (Scythian, Spathian) or, perhaps, an early Middle Triassic (Anisian) age for the Alcova Limestone

Environment/lithology: shallow subtidal; lithified, dolomitic, stromatolitic, shelly/skeletal, gray, silty, carbonaceous limestone

• The Alcova is a very hard, dense, resistant, microsparitic limestone in beds approximately 2-25 cm thick...The limestone is microlaminated, slightly fossiliferous, and locally dolomitic. Clastic content is generally low but vriable; quartz silt particles are locally common, increasingly so near pinchout boundaries. This silt is good evidence for natural lateral termination in these areas. Carbonate-pebble conglomerate is occasionally present in the unit. The Alcova limestone is usually grey in color, but can exhibit mottling of pink, red, yellow, and brown as a result of staining by ferric iron (hematite). Algal stromatolites are abundant in the lower portion of the unit...The limestone is ubiquituously petroliferous but is particularly high in organic content in the Alcova area where the rock is dark grey in color... The horizontal-to-wavy algal laminations of the Alcova are the principal bedding structures of the unit.

Size class: macrofossils

Collected in 1983; reposited in the YPM

Collection methods: surface (float),

• Most of the Yale Peabody Museum specimens were discovered in talus blocks beneath cliffs of the horizontal Alcova Limestone

Primary reference: G. W. Storrs. 1991. Anatomy and relationships of Corosaurus alcovensis (Diapsida: Sauropterygia) and the Triassic Alcova Limestone of Wyoming. Bulletin of the Peabody Museum of Natural History 44:1-151 [R. Benson/R. Benson]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 138081: authorized by Roger Benson, entered by Roger Benson on 04.01.2013

Creative Commons license: CC BY (attribution)

Taxonomic list

 Sauropterygia -
Corosaurus alcovensis Case 1936 diapsid