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RE: New review of bird origins and evolution in Naturwissenschaften
Ben Creisler wrote:
The online version of Naturwissenschaften has posted a
prepublication online article that reviews recent work on
Mesozoic birds and related dinosaurs. I could only access
the text in html form, not pdf.
The same issue also features a short communication that describes a new
Sebastián Apesteguía (2004) _Bonitasaura salgadoi_ gen. et sp. nov.: a
beaked sauropod from the Late Cretaceous of Patagonia
"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
The type specimen (MPCA 300), consists of a partially articulated,
incomplete subadult skeleton recovered from the uppermost layers of the Bajo
de la Carpa Formation (Santonian), at "La Bonita" hill, in Río Negro
Province, northwest Patagonia, Argentina.
The posited beak of _Bonitasaura_ would have been present *behind* the front
of the snout, not at the tip of the snout as in beaked ornithischians and
theropods. Its presence is inferred by the morphology of the lower jaw (a
stepped edentulous region behind the tooth-bearing front of the jaw), and a
corresponding gullotine blade is assumed for the upper jaw (not recovered).
_Bonitasaura_ appears to reinforce the titanosaur affinities of
_Antarctosaurus_, which also exhibits a squared snout convergent on
diplodocoids; there was a suggestion that _Antarctosaurus wichmannianus_ is
a chimera of titanosaurid and diplodocoid material (e.g., Upchurch, 1999).
Apesteguía suggests that _Bonitasaura_ might be most closely related to the
nemegtosaurids within the Titanosauria.
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