Bonitasaura

Bonitasaura is a titanosaurian dinosaur hailing from uppermost layers of the Late Cretaceous Bajo de la Carpa Formation, Neuquen Group, 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 Apesteguía in a short communication in mid-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.

Bonitasaura measured 9 metres (30 feet) 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.

B. salgadoi is further evidence that, after a purported extinction of diplodocid sauropods, some lines of titanosaurian evolution converged with them, exhibiting low long skulls without the characteristic nasal arches of other macronarians (such as Brachiosaurus or Argentinosaurus) and lower jaws that were squared off and contained comb-like teeth, reversed limb proportions (the front limbs shorter than the hind limbs, unlike the condition in most other macronarians) and rudimentary whiplash tails. This find also sheds light on some problematic aspects of the related dinosaur Antarctosaurus, sometimes viewed as a chimera made up of a titanosaurian skull and body and a diplodocid jaw.