Bonitasaura


Bonitasaura is a titanosaurian dinosaur hailing from uppermost layers of the Late Cretaceous Bajo de la Carpa Formation, Neuquén Group of the eastern Neuquén Basin, located in Río Negro Province, Northwestern Patagonia, Argentina. The remains, consisting of a partial sub-adult skeleton jumbled in a small area of fluvial sandstone, including lower jaw with teeth, partial vertebrae series and limb bones, were described by Sebastian Apesteguía in 2004.
The genus name Bonitasaura refers to the fossil quarry's name, "La Bonita", while the name of the type species, B. salgadoi, pays homage to Leonardo Salgado, a renowned Argentine palaeontologist.

Description

Bonitasaura measured in length, and had a skull similar to another group of sauropods, the diplodocids. The lower jaw had a distinctive, sharp ridge immediately behind a reduced set of teeth. This ridge supported in life a sharp, beak-like keratin sheath that probably paired with a similar structure in the upper jaw. The keratin sheath worked much like a guillotine to crop vegetation raked into the mouth by the peg-like front teeth. This animal also had a rather short neck and robust projections of the back vertebrae for muscle attachment, indicating that the neck was used in vigorous exertions, probably during feeding.
Bonitasaura also shows that some lines of titanosaurian evolution converged with diplodocids, namely low long skulls without the characteristic nasal arches of other macronarians and lower jaws that were squared off and contained comb-like teeth, reversed limb proportions and rudimentary whiplash tails. It also threw a wrench into the suggestion by some authors that the titanosaur Antarctosaurus is a chimera made up of a titanosaurian skull and body and a diplodocoid jaw.

Classification

Bonitasaura was originally classified as a member of Nemegtosauridae in the original description, but subsequent cladistic analyses and description found it to be nested among the titanosaur clade that includes Lognkosauria and Rinconsauria.