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[dinosaur] How Utahraptor death assemblage became trapped and buried in artesian spring system

Ben Creisler

A new paper:

James I. Kirkland, Edward L. Simpson, Donald D. DeBlieux, Scott K. Madsen, Emily Bogner & Neil E. Tibert (2016)
Depositional constraints on the Lower Cretaceous Stikes Quarry dinosaur site: Upper Yellow Cat Member, Cedar Mountain Formation, Utah.
Palaios 31(9): 421-439
DOI: 10.2110/palo.2016.041 

A new mass death assemblage in Lower Cretaceous strata of east-central Utah contains well-preserved skeletons representing an ontogenetic series of individuals of Utahraptor, and at minimum two iguanodont grade ornithischian skeletons. The dinosaurs were entombed in ovoid-lensoidal, fine-grained sandstone sills linked by sandstone pipes and/or dikes and another basal lensoidal mass with scattered and broken iguanodont and sauropod bones and to an underlying gravelly sandstone bed. Exposed in the excavation high-walls are syndepositional normal-faults bounding graded ripple strata. Multiphased fluid over-pressurization in an artesian setting creating the structures. Trapping, killing, and subsequent burial mechanism was generated by variations of pressure in a localized artesian spring system that breached the surface and is the first such mechanism documented with numerous dinosaur victims.