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Evidence for ectothermic growth rates in dinosaurs



From: Ben Creisler
bcreisler@gmail.com


A new paper in PLoS ONE:

Jan Werner and Eva Maria Griebeler (2014)
Allometries of Maximum Growth Rate versus Body Mass at Maximum Growth
Indicate That Non-Avian Dinosaurs Had Growth Rates Typical of Fast
Growing Ectothermic Sauropsids.
PLoS ONE 9(2): e88834.
doi:10.1371/journal.pone.0088834
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0088834

We tested if growth rates of recent taxa are unequivocally separated
between endotherms and ectotherms, and compared these to dinosaurian
growth rates. We therefore performed linear regression analyses on the
log-transformed maximum growth rate against log-transformed body mass
at maximum growth for extant altricial birds, precocial birds,
eutherians, marsupials, reptiles, fishes and dinosaurs. Regression
models of precocial birds (and fishes) strongly differed from Case's
study (1978), which is often used to compare dinosaurian growth rates
to those of extant vertebrates. For all taxonomic groups, the slope of
0.75 expected from the Metabolic Theory of Ecology was statistically
supported. To compare growth rates between taxonomic groups we
therefore used regressions with this fixed slope and group-specific
intercepts. On average, maximum growth rates of ectotherms were about
10 (reptiles) to 20 (fishes) times (in comparison to mammals) or even
45 (reptiles) to 100 (fishes) times (in comparison to birds) lower
than in endotherms. While on average all taxa were clearly separated
from each other, individual growth rates overlapped between several
taxa and even between endotherms and ectotherms. Dinosaurs had growth
rates intermediate between similar sized/scaled-up reptiles and
mammals, but a much lower rate than scaled-up birds. All dinosaurian
growth rates were within the range of extant reptiles and mammals, and
were lower than those of birds. Under the assumption that growth rate
and metabolic rate are indeed linked, our results suggest two
alternative interpretations. Compared to other sauropsids, the growth
rates of studied dinosaurs clearly indicate that they had an
ectothermic rather than an endothermic metabolic rate. Compared to
other vertebrate growth rates, the overall high variability in growth
rates of extant groups and the high overlap between individual growth
rates of endothermic and ectothermic extant species make it impossible
to rule out either of the two thermoregulation strategies for studied
dinosaurs.