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Baurusuchus (Crocodyliformes) fossil taphonomy from the Adamantina Formation of Brazil



From: Ben Creisler
bcreisler@gmail.com

A new online paper:

Hermínio Ismael de Araújo Júnior & Thiago da Silva Marinho (2013)
Taphonomy of a Baurusuchus (Crocodyliformes, Baurusuchidae) from the
Adamantina Formation (Upper Cretaceous, Bauru Basin), Brazil:
implications for preservational modes, time resolution and
paleoecology.
Journal of South American Earth Sciences (advance online publication)
doi: http://dx.doi.org/10.1016/j.jsames.2013.07.006,
http://www.sciencedirect.com/science/article/pii/S0895981113000941


Upper Cretaceous vertebrate accumulations from the Adamantina
Formation are known due to their high taxonomic diversity. On the
other hand, taphonomic analyses still are rare, limiting the
understanding of processes related to the biostratinomic and
fossildiagenetic histories of this lithostratigraphic unit. In 2005,
fossils were collected from an outcrop located at Jales municipality,
state of São Paulo, southeastern Brazil. From this outcrop, a
well-preserved Baurusuchus was recovered, which displays a peculiar
set of taphonomic signatures. This paper identifies and interprets
taphonomic features of a specimen of Baurusuchus (Crocodyliformes,
Baurusuchidae; UFRJ DG 418-R) from the Adamantina Formation (Upper
Cretaceous of the Bauru Basin), in Jales municipality, state of São
Paulo. Brief taphonomic comparisons with other specimens previously
studied (crocodiles and dinosaurs) and a lithofaciological analysis of
the outcrop were undertaken in order to enhance the knowledge of the
stratigraphy and paleoenvironment and improve the time resolution for
the Adamantina Formation in the region of Jales. Furthermore,
paleoecological data were interpreted based on the taphonomic
analysis.

The fossil is composed of an articulated segment of vertebral column,
ribs, part of the pelvic girdle and gastralia. There is no hydraulic
equivalence between both the specimen of Baurusuchus and the size of
quartz grain predominant in the fossiliferous layer, suggesting death
in situ or short transport as a “water carcass”. Teeth marks
identified on the pubes were assigned to a small/juvenile baurusuchid
crocodyliform or a theropod dinosaur. The repositioning of some
elements (ribs and dorsal osteoderms) is suggestive of mummification.
Desiccation marks were observed and attributed to the stage 1 of
weathering. These features suggest subaerial exposure of the carcass
prior to burial, however, probably after the mummification. On the
other hand, the subaerial exposure was short, because the individual
was not fully disarticulated. Furthermore, the degrees of articulation
and preservation of the specimen nullify the hypothesis of reworking.

Lithofaciological and taphonomic analyses suggest a well-drained
floodplain as the burial environment and an arid or semi-arid climate
in the region of Jales outcrop. In addition, the taphonomic signatures
seem to indicate a time resolution about 100-104 years for the layer
where the crocodyliforms were collected, but it seems to have, within
this time limit, temporal-mixing among terrestrial crocodiles and
dinosaurs collected from the same layer, suggesting time-averaging in
this outcrop.