Thursday, March 13, 2008

Two new Taphonomy papers

The March 2008 issue of Palaios has two interesting taphonomy articles:

Lauters, Pascaline, Yuri L. Bolotsky, Jimmy Van Itterbeeck, and Pascal Godefroit. 2008. Taphonomy and Age Profile of a Latest Cretaceous Dinosaur Bone Bed in Far Eastern Russia. Palaios 23(3): 153-162. [link]

Abstract: A large dinosaur bone bed has been investigated in the Udurchukan Formation (?late Maastrichtian) at Blagoveschensk, Far Eastern Russia. The observed mixture of unstratified fine and coarse sediments in the bone bed is typical for sediment-gravity-flow deposits. It is postulated that sediment gravity flows, originating from the uplifted areas at the borders of the Zeya-Bureya Basin, reworked the dinosaur bones and teeth as a monodominant bone bed. Fossils of the lambeosaurine Amurosaurus riabinini form >90% of the recovered material. The low number of associated skeletal elements at Blagoveschensk indicates that the carcasses were disarticulated well before reworking. Although shed theropod teeth have been found in the bone bed, Amurosaurus fossil assemblage. It is tentatively postulated that the absence of fossils attributable to nestling or early juvenile individuals indicates that younger animals were segregated from adults and could join the herd only when they reached half of the adult size.

Tapanila, Leif, Eric M. Roberts, Mohamed L. BouarĂ©, Famory Sissoko, and Maureen A. O'Leary. Phosphate Taphonomy of Bone and Coprolite Conglomerates: A Case Study from the Eocene of Mali, NW Africa. Palaios 23(3): 139–152. [link]

Abstract: Repeated sequences of carbonate and shale are punctuated by condensed sections of phosphatic conglomerate in the epeiric deposits of the Trans-Saharan Seaway in northeastern Mali. To characterize the taphonomic and depositional setting of these phosphates, a thick Eocene conglomerate from the area of Tamaguélelt was targeted for quantitative analysis. Systematic grid sampling demonstrates that nearly all of the clasts are derived from vertebrate sources (bones = 27%, coprolites = 20%, probable coprolites = 53%), and invertebrate body fossils are nearly absent. Bony and cartilaginous fish dominate the bone assemblage, which also includes minor reptilian elements from sea turtles, sea snakes, and dyrosaurid crocodilians. Coprolites are of five distinct varieties, including three spiral forms probably produced by separate fish taxa. Repeated episodes of abrasion and minor bioerosion with modest levels of sorting characterize the taphonomy of the phosphate conglomerate and are consistent with a shallow-marine-to-brackish-water depositional environment between fair-weather and storm-wave base. Early phosphogenesis strongly favored the preservation and lithification of phosphate-rich bones and coprolites, probably during periods of marine transgression and sediment starvation. Combined with evidence from sedimentology, these vertebrate-dominated fossil assemblages appear extensively reworked and highly time averaged as a result of amalgamation and concentration by storm activity during periods of marine transgression.

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