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Extinct archosaur bone growth rates



From: Ben Creisler
bcreisler@gmail.com


In the new issue of Paleobiology:

Jorge Cubo, Nathalie Le Roy, Cayetana Martinez-Maza, and Laetitia Montes (2012)
Paleohistological estimation of bone growth rate in extinct archosaurs.
Paleobiology 38(2):335-349. 2012
doi: http://dx.doi.org/10.1666/08093.1
http://www.bioone.org/doi/abs/10.1666/08093.1


The clade Archosauria contains two very different sister groups in
terms of diversity (number of species) and disparity (phenotypic
variation): Crurotarsi (taxa more closely related to crocodiles than
to birds) and Ornithodira (pterosaurs and dinosaurs including birds).
The extant species of Crurotarsi may constitute a biased sample of
past biodiversity regarding growth patterns and metabolic rates. Bone
histological characters can be conserved over hundreds of millions of
years in the fossil record and potentially contain information about
individual age at death, age at sexual maturity, bone growth rates,
and basal metabolic rates of extinct vertebrates. Using a sample of
extant amniotes, we have constructed a paleobiological model to
estimate bone growth rate from bone histological traits.
Cross-validation tests show that this model is reliable. We then used
it to estimate bone growth rates in a sample of extinct archosaurs
including Crurotarsi and Ornithodira. After testing for phylogenetic
signal, optimization of femoral growth rates through squared change
parsimony onto a time-calibrated tree of amniotes shows two divergent
evolutionary trends: whereas bone growth rates increase from the last
common ancestor of Ornithodira to extant birds, they decrease from the
last common ancestor of Crurotarsi to extant crocodiles. However, we
conclude, on the basis of recent evidence for unidirectional airflow
in the lungs of alligators, that crocodiles may have retained the
capacity of growing at high rates.