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Abstract
A new genus and species of titanosauriform sauropod is erected based on a partial
skeleton found in the Lower Cretaceous Sasayama Group of Hyogo Prefecture, SW Japan.
The new taxon is here named as Tambatitanis amicitiae gen. et sp. nov., which is diagnosed
by the following features of the caudal vertebrae, chevrons and braincase: the postzygapophysis
and the summit of the neural spine of the anterior caudal vertebrae are located beyond
the posterior border of the centrum, the spine of the anterior caudal vertebrae is
curved strongly anteriorly and bow-shaped in lateral view, the summit of the neural
spine is expanded and hemispherical with its anterior face excavated by the posterodorsal
extension of a deep and narrow SPRF, the transverse process of the anterior caudal
vertebrae are short and L shaped, the anterior chevron is the longest among sauropods
in proportion to body size, the distal ends of the anterior chevrons are rod-shaped,
the distal ends of the mid chevrons are transversely thin and anteroposteriorly long
without cranial processes, and the dorsal border of the shaft of the paroccipital
process that forms the ventral margin of the posttemporal fenestra is short mediolaterally
and V-shaped in posterior view. A phylogenetic analysis suggests that T. amicitiae
is a basal titanosauriform, possibly belonging to the East Asian endemic clade Euhelopodidae.
The caudals and chevrons are described in detail in order to document highly autapomorphic
features of the new taxon as well as potentially phylogenetically informative characters.
The discovery of T. amicitiae suggests that East Asian basal titanosauriforms were
diverse not only in the number of the taxa but also in the morphological variation
of the caudal elements.