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Ornithischian dinosaurs--systematic relationships and biogeographic history (free pdf)

Ben Creisler

A new paper:

Clint A. Boyd (2015)
The systematic relationships and biogeographic history of
ornithischian dinosaurs.
PeerJ 3:e1523
doi: https://doi.org/10.7717/peerj.1523

The systematic relationships of taxa traditionally referred to as
‘basal ornithopods’ or ‘hypsilophodontids’ remain poorly resolved
since it was discovered that these taxa are not a monophyletic group,
but rather a paraphyletic set of neornithischian taxa. Thus, even as
the known diversity of these taxa has dramatically increased over the
past two decades, our knowledge of their placement relative to each
other and the major ornithischian subclades remained incomplete. This
study employs the largest phylogenetic dataset yet compiled to assess
basal ornithischian relationships (255 characters for 65 species level
terminal taxa). The resulting strict consensus tree is the most
well-resolved, stratigraphically consistent hypothesis of basal
ornithischian relationships yet hypothesized. The only
non-iguanodontian ornithopod (=basal ornithopod) recovered in this
analysis is Hypsilophodon foxii. The majority of former
‘hypsilophodontid’ taxa are recovered within a single clade
(Parksosauridae) that is situated as the sister-taxon to Cerapoda. The
Parksosauridae is divided between two subclades, the Orodrominae and
the Thescelosaurinae. This study does not recover a clade consisting
of the Asian taxa Changchunsaurus, Haya, and Jeholosaurus
(=Jeholosauridae). Rather, the former two taxa are recovered as basal
members of Thescelosaurinae, while the latter taxon is recovered in a
clade with Yueosaurus near the base of Neornithischia.The endemic
South American clade Elasmaria is recovered within the
Thescelosaurinae as the sister taxon to Thescelosaurus. This study
supports the origination of Dinosauria and the early diversification
of Ornithischia within Gondwana. Neornithischia first arose in Africa
by the Early Jurassic before dispersing to Asia before the late Middle
Jurassic, where much of the diversification among non-cerapodan
neornithischians occurred. Under the simplest scenario the
Parksosauridae originated in North America, with at least two later
dispersals to Asia and one to South America. However, when ghost
lineages are considered, an alternate dispersal hypothesis has
thescelosaurines dispersing from Asia into South America (via North
America) during the Early Cretaceous, then back into North America in
the latest Cretaceous. The latter hypothesis may explain the dominance
of orodromine taxa prior to the Maastrichtian in North America and the
sudden appearance and wide distribution of thescelosaurines in North
America beginning in the early Maastrichtian. While the diversity of
parksosaurids has greatly increased over the last fifteen years, a
ghost lineage of over 40 myr is present between the base of
Parksosauridae and Cerapoda, indicating that much of the early history
and diversity of this clade is yet to be discovered. This new
phylogenetic hypothesis provides a comprehensive framework for testing
further hypotheses regarding evolutionary patterns and processes
within Ornithischia.