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Hadrosauriform dental architecture from Early Cretaceous of China



Ben Creisler
bcreisler@gmail.com


A new online paper in open access:





Michael Pittman, Xing Xu, Jason R Ali, Rui Pei, Waisum Ma, Jin Meng &
Shundong Bi (2015)
Insights into iguanodontian dental architecture from an Early
Cretaceous Chinese basal hadrosauriform maxilla (Ornithischia:
Iguanodontia).
PeerJ PrePrints 3:e1636
doi: https://dx.doi.org/10.7287/peerj.preprints.1329v1
https://peerj.com/preprints/1329/



Basal hadrosauriform iguanodontian dinosaurs have been invaluable
towards understanding the evolution of the complex and highly
efficient advanced hadrosauriform tooth battery dental system. Here we
report a new basal hadrosauriform maxilla specimen - IVPP V22529 -
from the Dashuiguo Formation of Maortu, Nei Mongol, China that
preserves a corrugated middle ventrolateral margin that differs from
the straight and undulating ventral margins found in most iguandontian
and non-iguanodontian dinosaurs. The uniqueness of this ventrolateral
margin relates to a new dental structure - cementum ‘jackets’ that
wrap about the labial sides of the teeth. To our knowledge this is the
first time that cementum has been described migrated onto the tooth
crowns of iguandontians (and other dinosaurs), but this trait is
common amongst mammals. This dental morphology - seen in a similar
form in the basal hadrosauriform Equijubus – therefore broadens our
knowledge of iguanodontian maxillary anatomy and shows that the basal
hadrosauriform dental system was more morphologically complex than
previously thought. IVPP V22529 resembles maxillae specimens of
Probactrosaurus gobiensis, a contemporaneous taxon known from the same
locality in North China, in sharing an inferred subtriangular shape, a
relatively flat lateral surface bearing a low row of foramina as well
as similar-looking teeth. However, the presence of a unique corrugated
middle ventrolateral margin in IVPP V22529, a low row of foramina on
its lateral surface that also open anteriorly and increase in size
posteriorly as well as a prominent medial shelf suggests that this
specimen does not belong to P. gobiensis. However, these differences
could conceivably be related to ontogenetic and sexual variation,
which have not been fully documented in P. gobiensis. More detailed
comparisons of IVPP V22529 and Probactrosaurus are also hampered by
the missing posterior portion of IVPP V22529 as well as the missing
anterior ramii in Probactrosaurus maxillae specimens. It is clear
though that IVPP V22529 is different from the more advanced Northern
Chinese hadrosauriforms Bactrosaurus and Gilmoreosaurus. The latter
lack well-developed maxillary grooves on their medial shelves, unlike
IVPP V22529, but all three taxa possess less-developed ones on the
medial surfaces of the anteromedial processes of the anterior ramii.
Different to IVPP V22529, Gilmoreosaurus also has foramina that are
more highly-positioned on the lateral surface of its maxilla as well
as a row of larger and more circular ‘special’ foramina on its medial
surface. Thus, at this time, IVPP V22529 is identified as a basal
hadrosauriform and not as a new genus or as a new species of
Probactrosaurus.