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Mochlodon vorosi, new rhabdodontid species from Hungary



From: Ben Creisler
bcreisler@gmail.com


A new paper in PLoS ONE:


Attila Ősi, Edina Prondvai, Richard Butler & David B. Weishampel (2012)
Phylogeny, Histology and Inferred Body Size Evolution in a New
Rhabdodontid Dinosaur from the Late Cretaceous of Hungary.
PLoS ONE 7(9): e44318.
doi:10.1371/journal.pone.0044318
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0044318


Background

Rhabdodontid ornithopod dinosaurs are characteristic elements of Late
Cretaceous European vertebrate faunas and were previously collected
from lower Campanian to Maastrichtian continental deposits.
Phylogenetic analyses have placed rhabdodontids among basal
ornithopods as the sister taxon to the clade consisting of
Tenontosaurus, Dryosaurus, Camptosaurus, and Iguanodon. Recent studies
considered Zalmoxes, the best known representative of the clade, to be
significantly smaller than closely related ornithopods such as
Tenontosaurus, Camptosaurus, or Rhabdodon, and concluded that it was
probably an island dwarf that inhabited the Maastrichtian Haţeg
Island.

Methodology/Principal Findings

Rhabdodontid remains from the Santonian of western Hungary provide
evidence for a new, small-bodied form, which we assign to Mochlodon
vorosi n. sp. The new species is most similar to the early Campanian
M. suessi from Austria, and the close affinities of the two species is
further supported by the results of a global phylogenetic analysis of
ornithischian dinosaurs. Bone histological studies of representatives
of all rhabdodontids indicate a similar adult body length of 1.6–1.8 m
in the Hungarian and Austrian species, 2.4–2.5 m in the subadults of
both Zalmoxes robustus and Z. shqiperorum and a much larger, 5–6 m
adult body length in Rhabdodon. Phylogenetic mapping of femoral
lengths onto the results of the phylogenetic analysis suggests a
femoral length of around 340 mm as the ancestral state for
Rhabdodontidae, close to the adult femoral lengths known for Zalmoxes
(320–333 mm).

Conclusions/Significance

Our analysis of body size evolution does not support the hypothesis of
autapomorhic nanism for Zalmoxes. However, Rhabdodon is reconstructed
as having undergone autapomorphic giantism and the reconstructed small
femoral length (245 mm) of Mochlodon is consistent with a reduction in
size relative to the ancestral rhabdodontid condition. Our results
imply a pre-Santonian divergence between western and eastern
rhabdodontid lineages within the western Tethyan archipelago.