Monday, January 05, 2009

Triassic Pelycosaurs?!

Paper's a little old, but this is the first I found it. Very interesting if so. Pelycosaurs into the


A. Departamento de Paleontología, Facultad de Ciencias, Iguá 4225, CP 11400, Montevideo, Uruguay, , B. Museu de Ciências Naturais, Fundação Zoobotânica do Rio Grande do Sul. Av. Dr. Salvador França 1427, Jardim Botânico, CEP 90690-000, Porto Alegre, RS, Brasil

n their monograph Review of the Pelycosauria, Romer and Price (1940), proposed that the earliest synapsids (“pelycosaurs”) were cosmopolitan, despite the observation that amniotes appeared to be restricted to the paleotropics during the Late Carboniferous and Early Permian (290–282 Ma). Romer and Price (1940) accounted for the scarcity of terrestrial tetrapods, including “pelycosaurs,” in Lower Permian beds elsewhere to the absence of coeval continental deposits beyond North America and Europe. Indeed, most workers recognized a geographical and temporal gap between Permo-Carboniferous “pelycosaurs” and therapsid synapsids. Recent research has confirmed that varanopid and caseid “pelycosaurs” were components of therapsid-dominated Late Permian faunas preserved in Russia and South-Africa (Tatarinov and Eremina, 1975; Reisz, 1986; Reisz et al., 1998; Reisz and Berman, 2001).

In this note, we report the first record of basal synapsids for South America (Fig. 1) and discuss its paleogeographic and temporal implications. These remains come from outcrops assigned to the Buena Vista Formation (Goso et al., 2001; Fig. 2), which filled part of the Paraná Basin during Late Permian and probably Early Triassic (Bossi and Navarro, 1991). The Paranà Basin is one of the major sedimentary basins of Gondwana, covering an area of nearly 1.5 million km2, in Brazil, Argentina, Paraguay and Uruguay (França et al., 1995; Zalán et al., 1990). At the beginning of basin development the Devonian marine and brackish conditions prevailed, but subsequently, during the Late Permian, there was a gradual change to continental sedimentation and the deposition of fossil-bearing red beds. Buena Vista Formation is characterized by reddish fine sandstone interbedded with lenticular clay layers and intraformational conglomerates (Fig. 2), (Bossi and Navarro, 1991; Goso et al., 2001). The paleoenvironment is related to the final withdrawal of the sea, and the upper part of this section is characterized by continental and strong fluvial influences. The fossils described in this paper were recovered from the conglomerates in the middle part of the Buena Vista Formation.


Finally, the age of the Buena Vista Formation was based on correlation with Brazilian lithostratigraphic units (Rio do Rasto and Sanga do Cabral Formations), which have been considered as Upper Permian and Permo-Triassic by most authors (Andreis et al., 1980; Acevedo et al., 1985; Barberena et al., 1985; Faccini, 1989) and Sanga do Cabral Formation was recently assigned to the Lower Triassic (Cisneros and Schultz, in press).


there is no other evidence of “pelycosaurs” in strata younger the Upper Permian Tapinocephalus Assemblage Zone of South Africa, the presence of basal synapsids in the Buena Vista Formation could indicates that this unit was deposited initially during the Late Permian. However, if the Lower Triassic age of the Buena Vista Formation suggested by Bossi and Navarro (1991) can be substantiated, the presence of “pelycosaurs” could be explained by two alternative hypotheses: 1) Taking into account the geological setting discussed above, the “pelycosaur” remains could represent Upper Permian materials that have been reworked by the currents that generated the intraconglomerates; 2) the “pelycosaurs” were contemporaneous with the putatively Lower Triassic members of the fauna. The former hypothesis is plausible, given the damage to the extremities of the known elements. The latter hypothesis is equally plausible, yet it implies that the Uruguayan “pelycosaurs” are the youngest known representatives of an otherwise Paleozoic assemblage, greatly extending their temporal range into the beginning of the Triassic.

Look like we need a test for their age much like the one for the Cretaceous dicynodont. IF it is true, then we're likely to have seen some pretty kewl chronological extensions on the basal synapsid line.


ahem. That's a little profound.


Zach said...

Whoa. If this turns out to be valid, I sense a disturbance in the alt-Permian force...!

Will Baird said...

It definitely has some oddball implications. That it's SoAm is VERY interesting.

How are we doing with the alt-Permian?