Bonatitan reigi, new titanosaur from Argentina

[Tim Williams <twilliams_alpha@hotmail.com>]

Reference:

Martinelli, A.G. and Forasiepi, A.M. (2004).  Late Cretaceous vertebrates 
from Bajo de Santa Rosa (Allen Formation), Rio Negro province, Argentina, 
with the description of a new sauropod dinosaur (Titanosauridae).  Revista 
del Museo Argentino de Ciencias Naturales Nueva Serie. 6(2): 257-305

ABSTRACT: A large and diverse collection of vertebrate remains from the 
Campanian-Maastrichtian Allen Formation (Malargue Group) at the Bajo de 
Santa Rosa locality (Rio Negro Province, Argentina) is described here.  The 
vertebrates are represented by: chondrichthyans; diplomystid siluriform, 
lepisosteid, cf. percichthyid and dipnoid osteichthyans; pipid and 
leptodactylid anurans; chelid turtles; sphenodonts; elasmosaurid 
plesiosaurs; madtsoiid snakes; faveoolitid and megaloolithid eggshells; and 
hadrosaurid, cf carcharodontosaurid, and titanosaurid dinosaurs.  A new 
small saltasaurine titanosaurid, _Bonatitan reigi_ gen. et sp. nov., is 
described.  It is diagnosed by the following association of characters: 1) 
longitudinal groove located on the suture between parietals that continues 
posteriorly over the supraoccipital to the foramen magnum; 2) basisphenoid 
tubera long and narrow; 3) dorsal to middle caudal vertebrae with deep oval 
to circular pits present on both sides of the prespinal lamina; 4) anterior 
caudal vertebra with spino-postzygapophysial and spino-prezygapophysial 
laminae 5) neural arch of anterior caudals with deep interzygapophysial 
fossae with numerous pits; 6) anterior caudal vertebra with an accessory 
sub-horizontal lamina extending from the antero-ventral portion of the 
postzygapophysis to the mid-portion of the spino-prezygapophysial lamina; 
and finally, 7) anterior caudal vertebra with a prominent axial crest on the 
ventral surface of the cemtrum.  The first record of sphenodonts and cf 
carcharodontosaurid theropods is recognized for the upper Late Cretaceous of 
Patagonia, as well as the earliest record of percichthyids (Perciformes).  
The vertebrate record is mainly composed of terrestrial and freshwater taxa, 
but a few marine elements are found (elasmosaurids) indicating a marine 
influence during the deposition of the Allen Formation in the area of Bajo 
de Santa Rosa.  The vertebrate remains support, a Campanian-Maastrichtian 
age for the Allen Formation.  Comparisons with other South American 
Campanian-Maastrichtian localities suggest a similar fossil vertebrate 
composition, with relatively few differences between the Patagonian and 
extra Patagonian South American records.