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Dakotadon (Early Cretaceous ornithopod) redescribed

Ben Creisler

An open access preprint in PeerJ:

Clint A Boyd and Darrin C Pagnac (2015)
Insight on the anatomy, systematic relationships, and age of the Early
Cretaceous ankylopollexian dinosaur Dakotadon lakotaensis.
PeerJ PrePrints 3:e1649
doi: https://dx.doi.org/10.7287/peerj.preprints.1135v2

Knowledge regarding the early evolution within the dinosaurian clade
Ankylopollexia drastically increased over the past two decades, in
part because of an increase in described taxa from the Early
Cretaceous of North America. These advances motivated the recent
completion of extensive preparation and conservation work on the
holotype and only known specimen of Dakotadon lakotaensis, a basal
ankylopollexian from the Lakota Formation of South Dakota. That
specimen (SDSM 8656) preserves a partial skull, lower jaws, a single
dorsal vertebra, and two caudal vertebrae. That new preparation work
exposed several bones not included in the original description and
revealed that other bones were previously misidentified. The presence
of extensive deformation in areas of the skull is also noted that
influenced inaccuracies in prior descriptions and reconstructions of
this taxon. In addition to providing an extensive re-description of D.
lakotaensis, this study reviews previously proposed diagnoses for this
taxon, identifies two autapomorphies, and provides an extensive
differential diagnosis. Dakotadon lakotaensis is distinct from the
only other ankylopollexian taxon known from the Lakota Formation,
Osmakasaurus depressus, in the presence of two prominent,
anteroposteriorly oriented ridges on the ventral surfaces of the
caudal vertebrae, the only overlapping material preserved between
these taxa. The systematic relationships of D. lakotaensis are
evaluated using both the parsimony and posterior probability
optimality criteria, with both sets of analyses recovering D.
lakotaensis as a non-hadrosauriform ankylopollexian that is more
closely related to taxa from the Early Cretaceous (e.g.,
Iguanacolossus, Hippodraco, and Theiophytalia) than to more basally
situated taxa from the Jurassic (e.g., Camptosaurus, Uteodon). This
taxonomic work is supplemented by field work that relocated the type
locality, confirming its provenance from unit L2 (lower Fuson Member
equivalent) of the Lakota Formation. Those data, combined with
recently revised ages for the members of the Lakota Formation based on
charophyte and ostracod biostratigraphy, constrain the age of this
taxon to the late Valanginian to early Barremian.