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GEOREF RECORD

Taphonomy of a juvenile lambeosaurine bonebed from the Two Medicine Formation (Campanian) of Montana, United States

Benjamin A. Scherzer and David J. Varricchio
Taphonomy of a juvenile lambeosaurine bonebed from the Two Medicine Formation (Campanian) of Montana, United States
Palaios (December 2010) 25 (12): 780-795

Abstract

The Sun River Bonebed is a monodominant assemblage of late juvenile lambeosaurine elements from the Upper Cretaceous Two Medicine Formation of north-central Montana, United States. Detailed excavation revealed an unusual paleobiologic and depositional signature. Although the bonebed occurs in a succession of beds representing anastomosing stream deposits in a seasonal paleoenvironment, the assemblage consists of a conglomerate of bone and calcareous clasts in a matrix of silty mud and free-floating sand grains. Internally, the bed exhibits normal grading of bone and calcareous clasts, poor sediment sorting, and preferred orientation of elongate elements, all characteristics common to debris flow deposits. The mud-rich matrix, poor sorting, and graded clasts of the bonebed suggest the assemblage was entrained and deposited by a cohesive debris flow, perhaps initiated through entrainment of fine overbank sediment by a seasonal flood. Nearly complete skeletal disarticulation and weathering of some bones indicate a brief period of postmortem exposure prior to debris flow entrainment. Fracture styles suggesting fresh breaks and frequent abrasion may reflect pre-flow trampling or chaotic flow transport. A significant number of elements also exhibit wet rot. The uniformity in taphonomic effects among elements suggests a mass mortality event, a rarity for debris-flow-hosted bonebeds, though the specific cause of death is uncertain. The age class dominance is interpreted to reflect original paleobiology, rather than abiotic postmortem selection, and establishes the Sun River Bonebed as the first bonebed of predominantly late juvenile material, with no adult material, in the Two Medicine Formation.


ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 25
Serial Issue: 12
Title: Taphonomy of a juvenile lambeosaurine bonebed from the Two Medicine Formation (Campanian) of Montana, United States
Affiliation: Montana State University, Department of Earth Sciences, Bozeman, MT, United States
Pages: 780-795
Published: 201012
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 97
Accession Number: 2011-006710
Categories: Vertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. col., 4 tables, sketch map
N47°30'00" - N48°08'60", W113°01'00" - W111°25'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 201104
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