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Fwd: Cranial ontogenetic variation in early saurischians (free pdf)

Apparently this post did not get through. I'll try again...

---------- Forwarded message ----------
From: Ben Creisler <bcreisler@gmail.com>
Date: Fri, Jun 19, 2015 at 8:46 AM
Subject: Cranial ontogenetic variation in early saurischians (free pdf)
To: dinosaur@usc.edu

Ben Creisler

A new online paper:

Christian Foth, Brandon P Hedrick & Martin D Ezcurra (2015)
Cranial ontogenetic variation in early saurischians and the role of
heterochrony in the diversification of predatory dinosaurs.
PeerJ PrePrints 3:e1445
doi:  https://dx.doi.org/10.7287/peerj.preprints.1185v1

Non-avian saurischian skulls underwent at least 165 million years of
evolution and shapes varied from elongated skulls, such as in
Coelophysis, to short and box-shaped skulls, such as in Camarasaurus.
A number of factors have long been considered to drive skull shape,
including phylogeny, dietary preferences and functional constraints.
However, heterochrony is increasingly being recognized as a major
factor in dinosaur evolution. In order to quantitatively analyse the
impact of heterochrony on saurischian skull shape, we have analysed
five ontogenetic trajectories using two-dimensional geometric
morphometrics in a phylogenetic framework. This allowed for the
evaluation of how heterochrony affected overall skull shape through
both ontogenetic and phylogenetic trajectories and how it impacted
modular changes within the skull. Using principal component analyses
and multivariate regressions, it was possible to quantify different
ontogenetic trajectories in light of heterochrony. The results
recovered here indicate that taxa underwent a combination of local
paedomorphosis and peramorphosis within the skull along individual
ontogenies and phylogenies, but that either peramorphosis or
paedomorphosis dominated when the skull was considered as a whole. We
found that the hypothetical ancestor of Saurischia led to basal
Sauropodomorpha mainly through paedomorphosis, and to Neotheropoda
mainly through peramorphosis. Paedomorphosis then led from Orionides
to Avetheropoda, indicating that the paedomorphic trend previously
found in advanced coelurosaurs may extend back into the early
evolution of Avetheropoda. Not only are changes in saurischian skull
shape complex due to the large number of factors that affect shape,
but heterochrony itself is complex, with a number of reversals
throughout non-avian saurischian evolution. The sampling of
ontogenetic trajectories is considerably lower than the sampling of
adult species and the current study represents a first exploratory
analysis. To better understand the impact of heterochrony on cranial
evolution in saurischians, the data set we present must be expanded
and complemented with further sampling from future fossil discoveries,
especially of juvenile taxa.