Aaron W. HUNTER1, Neal L. LARSON2, Neil H. LANDMAN3, Jamie BREZINA4, and Tatsuo OJI5

1Department of Applied Geology, Western Australian School of Mines, Curtin University, GPO Box U1987, Perth, WA 6845, Australia; 2Black Hills Museum of Natural History, PO Box 614 Hill City, SD 57745, USA; 3Divi sion of Paleontology (Invertebrates), American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024-5192, USA; 4South Dakota School of Mines & Technology, 501 East Saint Joseph Street, Rapid City, SD 57701 USA; 5Nagoya University Museum, Nagoya University, Furo-cho, Nagoya 464-8601, Japan.

Corresponding author: aaron.hunter@curtin.edu.au

Despite a rich and varied record, Mesozoic stalked crinoids are relatively rare in the Western
Interior Seaway of North America compared to those found in Northern Europe. A unique example
of Mesozoic stalked crinoid is described from cold methane seeps (hydrocarbon seep mounds
also called “tepee buttes”) from the Upper Cretaceous (upper Campanian) of the Northern Great
Plains of the United States; the first crinoids to be described from such an environment. The Late
Cretaceous Western Interior Seaway has never before yielded any identifiable stalked crinoid remains.
Nevertheless, there have been significant studies on both free living and stalked crinoids
from other locations in the Upper Cretaceous of North America that provide a good basis for comparison.
This new species is characterized by a tapering homeomorphic column with through-going
tubuli and lacks any attachment disc. The arms are unbranched and pinnulate, with muscular
and syzygial articulations. The unique morphology of the column justifies the establishment of a
separate family. A new suborder is also proposed as there exists no corresponding taxon within
the Articulata that can accommodate all the characteristics of this new genus. This new crinoid
shares many features with other members of the articulates, including bathycrinids, bourgueticrinids
and guillecrinids within the order Comatulida, as currently defined in the revised Treatise of
Invertebrate Paleontology. Reconstructing the entire crinoid using hundreds of semi-articulated
and disarticulated fossils reveals a unique paleoecology and functional morphology specifically
adapted to living within this hydrocarbon seep environment. However, the function of the most
notable feature of this crinoid, the through-going tubuli, remains a mystery.