Bonitasaura, new sauropod with beak-like jaws

[bh480@scn.org]

From: Ben Creisler bh480@scn.org

In case this has not been mentioned yet, the online 
version of Naturwissenschaften has a new titanosaur from 
Argentina with beak-like edges in the middle and back 
sections of its jaws.

Bonitasaura salgadoi gen. et sp. nov.: a beaked sauropod 
from the Late Cretaceous of Patagonia 
Sebastián Apesteguía1 
(1) Museo Argentino de Ciencias Naturales Bernardino 
Rivadavia, Av. Ángel Gallardo 470, 1405 Buenos Aires, 
Argentina

Received: 29 April 2004 Accepted: 4 August 2004 Published 
online: 10 September 2004
Abstract: Ornithischian and theropod dinosaurs were 
morphologically diverse during the Cretaceous. In 
contrast, sauropods were relatively more conservative. The 
anatomy of Bonitasaura salgadoi, a new 9-m titanosaurian 
sauropod from Upper Cretaceous beds of Patagonia, suggests 
that sauropod anatomical diversity would have included 
unexpected items. Its unusual, rectangular lower jaw 
possesses narrow, anteriorly restricted teeth and shows 
evidence of a sharp keratinous sheath over the non-
dentigerous region that probably worked to guillotine 
plant material. This discovery definitely demonstrates 
that titanosaurs acquired a mandibular configuration 
similar to that of some basal diplodocoids, as had already 
been suggested by the lower jaw of the controversial genus 
Antarctosaurus. This oral configuration, plus the beak-
like structure and the skull shape, resemble some traits 
more commonly seen in Laurasian ornithischians, mostly 
unexpressed in southern continents. A high sauropod 
morphological diversity seems to be in agreement with the 
poorly represented ornithischian clades of the southern 
hemisphere. ......


TEXT HIGHLIGHTS:

-       Sauropoda Marsh 1878       
-       Titanosauria Bonaparte and Coria 1993      
-       Bonitasaura salgadoi gen. et. sp. nov.   

Etymology 
The generic name is derived from the  La Bonita  hill, the 
name of the quarry, and saura, a female reptile. The 
species, salgadoi, honors Leonardo Salgado, the 
Argentinian paleontologist who gave new perspectives to 
sauropod research.

Holotype 
MPCA 300 (Museo Provincial  Carlos Ameghino , Cipolletti, 
Río Negro, Argentina), consists of a partially 
articulated, subadult skeleton (Fig. 1a-c). The material 
includes a left frontal, left parietal, right dentary with 
15 teeth, lacking at least three or four alveoli distal to 
the symphysis, two cervical, six dorsal, and 12 caudal 
vertebrae, two chevrons, several cervical and dorsal ribs, 
humerus, radius, two metacarpals, femur, tibia, two 
metatarsals.

Locality and geological setting 
 La Bonita  hill fossil quarry, Cerro Policía, Río Negro 
Province, NW Patagonia, Argentina. The specimen was found 
in a fluvial sandstone (Hugo and Leanza 1999) which 
belongs to the uppermost layers of the Bajo de la Carpa 
Formation (Santonian; Hugo and Leanza 1999).

Diagnosis 
Bonitasaura differs from other titanosaurs in the 
following combination of features: dentary alveoli reduced 
in number (three in the main ramus, one in the angle, and 
up to seven in the anterior region); middle and posterior 
region of the dentary edentulous and forming a sharp 
dorsal edge, with a profusely vascularized lateral side; 
very robust, diagonal neural arch pillars and bulging 
neural spine summits on anterior dorsal vertebrae....

The new titanosaur Bonitasaura constitutes the first 
sauropod dinosaur yet recorded that not only possesses 
squared jaws, with narrow-crowned teeth arranged in 
continuous series that include at least three replacement 
elements per alveolus, but additionally also a keratinous 
beak to aid in cutting plant material. A keratinous 
cutting structure in addition to the aforementioned 
nemegtosaurid features has previously been reported only 
in Late Cretaceous ornithischians, particularly hadrosaurs 
(Morris 1970), and has been proposed as an adaptive 
response to the rise and diversification of flowering 
plants (Bakker 1986; Salgado and Calvo 1997). However, the 
beak of ornithischians differs from that of Bonitasaura in 
that it is at the tip of the mouth, and there are teeth in 
the cheeks. Functional anatomical studies are necessary in 
order to evaluate how these differences reflect different 
ways of living in the two taxa. Furthermore, the dental 
mechanism seems to be less complex by far. The 
configuration shown by Bonitasaura is thus unique in 
having a posteriorly placed beak.
.....