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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 titanosaur.


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 hemisphere."


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.


Tim

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