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Revueltosaurus and Krzyzanowskisaurus (Archosauria) tooth microstructure

From: Ben Creisler

A new paper in open-access Palaeontologia Electronica:

Andrew B. Heckert and Jessica A. Miller-Camp (2013)
Tooth enamel microstructure of Revueltosaurus and Krzyzanowskisaurus
(Reptilia:Archosauria) from the Upper Triassic Chinle Group, USA:
Implications for function, growth, and phylogeny.
Palaeontologia Electronica 16(1): 1A, 23p;

Tooth enamel microstructure can carry significant phylogenetic,
ontogenetic, and functional information within amniotes. Here we
provide the first descriptions of the tooth enamel microstructure of
two Late Triassic taxa, the crurotarsan Revueltosaurus callenderi Hunt
and the putative ornithischian Krzyzanowskisaurus hunti (Heckert),
which some consider closely related. To test the hypotheses that
enamel thickness corresponds to function and/or phylogeny we analyzed
the enamel of each at various scales, measuring enamel thickness and
examining microstructural features throughout both longitudinal and
cross-sectional thickness using previously established techniques to
facilitate comparisons. Both taxa possess thick (up to ~150 µm) enamel
for their size (< 20 mm crown height). Enamel in R. callenderi ranged
from ~5-152 µm across a premaxillary tooth in longitudinal section,
and ~42-92 µm in a maxillary/dentary tooth transverse section. K.
hunti enamel thickness was ~18-155 µm longitudinally and ~29-75 µm
transversely. Both also had well-developed basal unit layers (BUL) and
weakly developed columnar microstructure. Well-developed lines of
incremental growth (LIG) are present in both taxa, through which the
columnar enamel grades into parallel crystallite enamel. Their enamel
microstructure is therefore grossly similar to that of several
ornithischian taxa, especially ankylosaurs, with which they are
strongly convergent, and also compares well to rauisuchids and
tyrannosaurids. The relatively unique combination of microstructural
characteristics in the schmelzmuster of R. callenderi and K. hunti
supports the hypothesis that they are closely related, but does not
conclusively preclude a different taxonomic placement for K. hunti so
we retain its separate generic designation.