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Skull Sutures Are Ambiguous Maturity Indicators for Dinosauria

Ben Creisler

New in PLoS ONE:

Alida M. Bailleul, John B. Scannella, John R. Horner& David C. Evans (2016)
Fusion Patterns in the Skulls of Modern Archosaurs Reveal That Sutures
Are Ambiguous Maturity Indicators for the Dinosauria.
PLoS ONE 11(2): e0147687.
http: // journals.plos.org/plosone/article?id=10.1371/journal.pone.0147687

The sutures of the skulls of vertebrates are generally open early in
life and slowly close as maturity is attained. The assumption that all
vertebrates follow this pattern of progressive sutural closure has
been used to assess maturity in the fossil remains of non-avian
dinosaurs. Here, we test this assumption in two members of the Extant
Phylogenetic Bracket of the Dinosauria, the emu, Dromaius
novaehollandiae and the American alligator, Alligator
mississippiensis, by investigating the sequence and timing of sutural
fusion in their skulls. As expected, almost all the sutures in the emu
skull progressively close (i.e., they get narrower) and then
obliterate during ontogeny. However, in the American alligator, only
two sutures out of 36 obliterate completely and they do so during
embryonic development. Surprisingly, as maturity progresses, many
sutures of alligators become wider in large individuals compared to
younger, smaller individuals. Histological and histomorphometric
analyses on two sutures and one synchondrosis in an ontogenetic series
of American alligator confirmed our morphological observations. This
pattern of sutural widening might reflect feeding biomechanics and
dietary changes through ontogeny. Our findings show that progressive
sutural closure is not always observed in extant archosaurs, and
therefore suggest that cranial sutural fusion is an ambiguous proxy
for assessing maturity in non-avian dinosaurs.