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Re: Tyrannosaurus abundant in Hell Creek dino census

Interesting, truly, the great proportion of Tyrannosaurus suggests
that the ecosystem would be better sustained in time if Tyrannosaurus
focused in killing juveniles instead of adults, which would take more
time to recover in order to reproduce. Whatever the mechanical physics
of the attack and defense (discussed in the thread on sauropod
gigantism), if Tyrannosaurus ate adults, it seems it was at risk of
extinguishing its prey. In fact, killing prey when they are still
young is something also done by us with cattle, as some agronomist
once told me, which is a way to permit prey biomass production per
time unit to be greater, for near adultness, biomass growth rate
becomes slower.

2011/2/10  <bh480@scn.org>:
> From: Ben Creisler
> bh480@scn.org
> In case this paper in PLoS One has not been mentioned yet:
> Horner, J.R., Goodwin, M.B., Myhrvold, N.(2011). Dinosaur
> Census Reveals Abundant Tyrannosaurus and Rare
> Ontogenetic Stages in the Upper Cretaceous Hell Creek
> Formation (Maastrichtian), Montana, USA.
> PLoS ONE 6(2): e16574. doi:10.1371/journal.pone.0016574
> http://www.plosone.org/article/info%3Adoi%2F10.1371%
> 2Fjournal.pone.0016574
> Dinosaur Census Reveals Abundant Tyrannosaurus and Rare
> Ontogenetic Stages in the Upper Cretaceous Hell Creek
> Formation (Maastrichtian), Montana, USA
> A dinosaur census recorded during the Hell Creek Project
> (1999–2009) incorporates multiple lines of evidence from
> geography, taphohistory, stratigraphy, phylogeny and
> ontogeny to investigate the relative abundance of large
> dinosaurs preserved in the Upper Cretaceous Hell Creek
> Formation of northeastern Montana, USA. Overall, the
> dinosaur skeletal assemblages in the Hell Creek Formation
> (excluding lag-influenced records) consist primarily of
> subadult or small adult size individuals. Small juveniles
> and large adults are both extremely rare, whereas
> subadult individuals are relatively common. We propose
> that mature individuals of at least some dinosaur taxa
> either lived in a separate geographic locale analogous to
> younger individuals inhabiting an upland environment
> where sedimentation rates were relatively less, or these
> taxa experienced high mortality before reaching terminal
> size where late stage and often extreme cranial
> morphology is expressed.
> Tyrannosaurus skeletons are as abundant as Edmontosaurus,
> an herbivore, in the upper Hell Creek Formation and
> nearly twice as common in the lower third of the
> formation. Smaller, predatory dinosaurs (e.g., Troodon
> and dromaeosaurids) are primarily represented by teeth
> found in microvertebrate localities and their skeletons
> or identifiable lag specimens were conspicuously absent.
> This relative abundance suggests Tyrannosaurus was not a
> typical predator and likely benefited from much wider
> food choice opportunities than exclusively live prey
> and/or specific taxa. Tyrannosaurus adults may not have
> competed with Tyrannosaurus juveniles if the potential
> for selecting carrion increased with size during ontogeny.
> Triceratops is the most common dinosaur and isolated
> skulls contribute to a significant portion of this
> census. Associated specimens of Triceratops consisting of
> both cranial and postcranial elements remain relatively
> rare. This rarity may be explained by a historical
> collecting bias influenced by facies and taphonomic
> factors. The limited discovery of postcranial elements
> may also depend on how extensive a fossil quarry is
> expanded after a skull is collected.