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Big boys and girls rule soft seds (was Dino Death Pits)



"Rather, they appear to have been highly localized 
areas of liquefaction caused by large-dinosaur (possibly 
sauropod) trampling of saturated sediments. Evidence 
indicates that the small theropods, and some other small 
vertebrates, became mired and died in these mud-filled 
pits."

Thanks, Ben...

--- On Sun, 1/17/10, bh480@scn.org <bh480@scn.org> wrote:

> In case this paper has not been mentioned:
> 
> DAVID A. EBERTH, XU XING, and JAMES M. CLARK. 2010. 
> DINOSAUR DEATH PITS FROM THE JURASSIC OF CHINA 
> Palaios 25: 112-125 (Feb. 2010)
> 
>  
> Abstract
> Three newly discovered bonebeds from the Shishugou 
> Formation of Xinjiang, China, are unusual in preserving 
> vertically stacked and articulated to associated skeletons
> 
> of at least 18 small, non-avian theropod dinosaurs in pits
> 
> that are 1-2 m deep. The pits host a soft sediment-
> deformed mixture of alluvial and volcanic mudstone and 
> sandstone. There is no evidence that the pits were 
> discrete depressions in the topography that filled through
> 
> time. Rather, they appear to have been highly localized 
> areas of liquefaction caused by large-dinosaur (possibly 
> sauropod) trampling of saturated sediments. Evidence 
> indicates that the small theropods, and some other small 
> vertebrates, became mired and died in these mud-filled 
> pits. High quality skeletal preservation suggests that 
> most individuals were buried within days to months after 
> their deaths. Carcasses were buried successively, coming 
> to rest above previously buried individuals. In some 
> cases, skeletal body parts became separated or were 
> removed, probably during scavenging. Given the large sizes
> 
> of the pits relative to the small body sizes of the 
> vertebrates contained within them, we conclude that small 
> vertebrates (<3 m long and <1 m tall) were
> particularly 
> susceptible to miring at these sites. Although the small, 
> presumably herbivorous ceratosaur, Limusaurus 
> inextricabilis, dominates the combined small theropod 
> assemblage from these bonebeds (minimum number of 
> individuals [MNI] = 15), there is no evidence that any 
> biological features other than its small size and a large,
> and possibly, gregarious local population were responsible
> for its becoming mired in large numbers. A bias for small 
> theropods in these bonebeds, compared to their relatively 
> low abundance in the overall Shishugou Formation fauna, 
> underscores that small theropods are underrepresented in 
> Mesozoic fossil assemblages collected from other ancient 
> alluvial and paludal settings.