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Maiasaura population biology and life history synthesis

Ben Creisler

A new online paper:

Holly N. Woodward, Elizabeth A. Freedman Fowler, James O. Farlow and
John R. Horner (2015)
Maiasaura, a model organism for extinct vertebrate population biology:
a large sample statistical assessment of growth dynamics and
Paleobiology  (advance online publication)
DOI: http://dx.doi.org/10.1017/pab.2015.19

Fossil bone microanalyses reveal the ontogenetic histories of extinct
tetrapods, but incomplete fossil records often result in small sample
sets lacking statistical strength. In contrast, a histological sample
of 50 tibiae of the hadrosaurid dinosaur Maiasaura peeblesorum allows
predictions of annual growth and ecological interpretations based on
more histologic data than any previous large sample study. Tibia
length correlates well (R2>0.9) with diaphyseal circumference,
cortical area, and bone wall thickness, thereby allowing longitudinal
predictions of annual body size increases based on growth mark
circumference measurements. With an avian level apposition rate of
86.4 μm/day, Maiasaura achieved over half of asymptotic tibia
diaphyseal circumference within its first year. Mortality rate for the
first year was 89.9% but a seven year period of peak performance
followed, when survivorship (mean mortality rate=12.7%) was highest.
During the third year of life, Maiasaura attained 36% (x=1260 kg) of
asymptotic body mass, growth rate was decelerating (18.2 μm/day),
cortical vascular orientation changed, and mortality rate briefly
increased. These transitions may indicate onset of sexual maturity and
corresponding reallocation of resources to reproduction. Skeletal
maturity and senescence occurred after 8 years, at which point the
mean mortality rate increased to 44.4%. Compared with Alligator, an
extant relative, Maiasaura exhibits rapid cortical increase early in
ontogeny, while Alligator cortical growth is much lower and protracted
throughout ontogeny. Our life history synthesis of Maiasaura utilizes
the largest histological sample size for any extinct tetrapod species
thus far, demonstrating how large sample microanalyses strengthen
paleobiological interpretations.