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Age of the Tacuarembó Formation

Why do you think is provisional?
I think that current fossil record and radiometric dates are consistent
with a Late Jurassic-Early Cretaceous age for the Tacuarembó Formation.
Let's see: the ocurrences of the hybodontid shark Priohybodus (Perea et
al., 2001), the fushunograptid conchostracan Migransia ferrandoi (Yanbin
et al., in press), the indeterminated mesosuchian Meridiosaurus vallisparadisi
(Mones, 1997; Mones, pers. com.) and an indeterminated ceratodontiform dipnoan
(Da Silva, 1990; Soto, in prep.) precludes a Triassic age, being far more
probable a Late Jurassic-Early Cretaceous age.
The radiometric dates from the overlying (and sometimes interbedded) Arapey
Formation make more probable that the Tacuarembó Formation is not older
than Kimmeridgian and not younger than Hautevirian in age (see Perea et
al., 2001).
I think that nowadays, a Late Jurassic-Early Cretaceous age for the Tacuarembó
Fm., first proposed by Mones and Figueiras (1981), is the best explanation.

I don't have the complete references at hand, but if you are interested
feel free to contact me.


Matias Soto

>>Perea, D., Ubilla, M. & Rojas, A. (2003): First report of theropods
>>from the Tacuarembó Formation (late Jurassic-Early Cretaceous), Uruguay.
>>Alcheringa, 27 (2): 79-83, 3 Abb.; Sydney
>A late Jurassic-Early Cretaceous age for the Tacuarembó Formation is, as
>understand, provisional. The Tacuarembó Formation used to be considered
>Middle Triassic-Early Jurassic, but was re-dated to a younger age by Perea
>et al. (2001) based on the record of _Priohybodus_ from this formation.

>remains (teeth, spine) closely resembles those of the Late Jurassic-Early
>Cretaceous hybodont _Priohybodus arambougi_, which is known from north

>Africa and the Arabian pensinsula.
>Perea, D., Ubilla, M., Rojas, A., and Goso, C.A. (2001). The West Gondwana
>occurrence of the hybodontid shark _Priohybodus_, and the Late
>Jurassic-Early Cretaceous Age of the Tacuarembo Formation, Uruguay.
>Palaeontology 44 (6), 1227-1236.
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