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Euparkeria (Triassic archosaur) high bone growth rate

From: Ben Creisler

In the new JVP:

Lucas J. Legendre, Loic Segalen & Jorge Cubo (2013)
Evidence for high bone growth rate in Euparkeria obtained using a new
paleohistological inference model for the humerus.
Journal of Vertebrate Paleontology 33 (6):  1343-1350
DOI: 10.1080/02724634.2013.780060

The study of bone growth rate and metabolic rate evolution in
archosaurs (crocodiles, dinosaurs including birds, and pterosaurs) and
close outgroups has become a subject of major interest among
paleontologists in recent years. In this paper, we estimate the bone
growth rate of Euparkeria using a new statistical inference model for
the humerus. We modified the taxonomic range of extant species used in
previous studies, on which we performed quantitative measurements of
histological features and bone growth rates. Bone growth rate values
estimated for Euparkeria are crucial in understanding the ancestral
condition for archosaurs because this taxon is considered the closest
relative to the archosaur crown group. We obtained an instantaneous
growth rate of 6.12 μm/day, suggesting that Euparkeria shared with
other non-archosaurian archosauromorphs (Prolacerta, Proterosuchus,
and Erythrosuchus) a condition of high growth rate compatible with
endothermy. This derived state may have been inherited by some
Triassic crurotarsans, as suggested by the high instantaneous bone
growth rate (14.52 μm/day) estimated in this study for Postosuchus.
Jurassic crurotarsans may have lost endothermy during the transition
from terrestrial habitats and active predation to aquatic habitats and
sit-and-wait predation behaviors, so that Cretaceous crocodiles may be
secondarily ectothermic, as suggested by δ18O values. In conclusion,
we provide new evidence for the hypothesis of an ancestral endothermic
state for the last common ancestor of archosaurs, and show that
non-archosaurian archosauromorphs and Triassic crurotarsans may have
been characterized by a thermometabolism more similar to that of
dinosaurs than to that of lepidosaurs and turtles.