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Taphonomy of three dinosaur bone beds in the Upper Cretaceous Two Medicine Formation of northwestern Montana; evidence for drought-related mortality

Raymond R. Rogers
Taphonomy of three dinosaur bone beds in the Upper Cretaceous Two Medicine Formation of northwestern Montana; evidence for drought-related mortality
Palaios (October 1990) 5 (5): 394-413

Abstract

Taphonomic and sedimentologic attributes of three dinosaur bone beds discovered within the Campanian Two Medicine Formation of Montana suggest drought-related mortality. Two bone beds, Canyon Bone Bed and Dino Ridge Quarry, have yielded the near-exclusive remains of a new species of Styracosaurus (Family Ceratopsidae); the third bone bed, Westside Quarry, is dominated by a new species of Prosaurolophus (Family Hadrosauridae). All three assemblages are mono/paucispecific, parautochthonous concentrations of disarticulated and dissociated skeletal debris. Evidence supporting a drought hypothesis includes: 1) a seasonal, semiarid paleoclimate, 2) associated caliche horizons, 3) aqueous depositional settings, 4) apparent age distributions characteristic of modern drought mortality (CBB and DRQ), and 5) the intraformational recurrence of low-diversity bone beds, Several alternative scenarios were considered, but drought proved most reasonable in light of the enhanced probability of preserving drought assemblages, and the species-selective and recurrent nature of modern drought mortality. Styracosaurus sp. and Prosaurolophus sp. may have been gregarious, water-dependent taxa; during drought these particular taxa may have obligatorily congregated, either in herds, familial groups, or seasonal aggregates, in the vicinity of persistent water sources, The mono/paucispecific natures of the bone beds may reflect ecological segregation due to varying degrees of water-dependency, resource partitioning, or territorial/resource defense within a Late Cretaceous dinosaur community. The preservational bias suggested by previous workers for drought assemblages is seemingly substantiated within the richly fossiliferous strata of the Two Medicine Formation.


ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 5
Serial Issue: 5
Title: Taphonomy of three dinosaur bone beds in the Upper Cretaceous Two Medicine Formation of northwestern Montana; evidence for drought-related mortality
Author(s): Rogers, Raymond R.
Affiliation: Univ. Mont., Dep. Geol., Missoula, MT, United States
Pages: 394-413
Published: 199010
Text Language: English
Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States
References: 89
Accession Number: 1991-019155
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, sect., strat. cols., sketch maps
N48°19'00" - N49°00'00", W114°04'60" - W112°10'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 1991
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