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Dinosaur fossil size bias in Dinosaur Park Formation (Alberta)

From: Ben Creisler

A new online paper:

Caleb Marshall Brown, David C. Evans, Nicolás E. Campione, Lorna J.
O'Brien & David A. Eberth (2012)
Evidence for taphonomic size bias in the Dinosaur Park Formation
(Campanian, Alberta), a model Mesozoic terrestrial alluvial-paralic
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)

A study of the distribution of dinosaurian body masses in the Dinosaur
Park Formation (DPF; Campanian; southern Alberta), reveals a prominent
negative skew; a pattern distinct from those of modern terrestrial
faunas. We find a direct and robust correlation between taxon size
(estimated live body mass) and known completeness. There is a clear
dichotomy between large and small-bodied taxa at around 60 kg, in
which taxa less than 60 kg are significantly less complete (mean
completeness = 7.6%) than those with an estimated mass of 60 kg or
greater (mean = 78.2%). Along with completeness, there is also a
strong association of body size and taphonomic mode, with small taxa
known largely from isolated and occasionally associated remains, and
large taxa known from articulated skeletons. In addition there is a
significant correlation between taxon body mass and both date of
discovery and of description, with taxa < 60 kg taking an average of
60.5 and 74.8 years to discover and describe, respectively, compared
to 29.6 and 35.9 years for taxa > 60 kg. The rates of both cumulative
discovery and description for large taxa are best described by a
logarithmic curve nearing an asymptote, whereas small taxa show either
a linear or power increase though time. This suggests our current
knowledge of the large-bodied dinosaur assemblage is reasonably
representative of the true biological fauna with few discoveries
likely to be made in the future. However, small taxa are greatly
underestimated in both their diversity and abundance, with many more
potential discoveries to be made. Given that (1) the sedimentary
deposits and fossil assemblages at DPF together represent one of the
best studied examples of a Mesozoic alluvial-paralic (terrestrial)
'palaeoecosystem,' and (2) similar patterns have been suggested (but
not documented) for other Mesozoic terrestrial ecosystems in the
Western Interior of North America. We suggest this pattern of size
bias may typify vertebrate fossil assemblages in terrestrial Mesozoic
systems. If so, such biases must be considered before patterns of
diversity in dinosaur communities through time can be considered
accurate, or used to compare and interpret Mesozoic palaeoecosystems.