First records of Permian trilobites from Perú

VACCARI, N. E; HUACALLO PACHECO, E·.; WAISFELD, B.G

Mendoza

Congreso; thInternational Palaeontological Congress: The History of Life: A view from the Southern Hemisphere; 2014

International Palaeontological Association

Despite the great thickness and geographic coverage of upper Paleozoic successions of South America, trilobite records are sparse and poorly known. Until not long ago Australosutura argentinensis Hahn and Hahn was the only trilobite reported from Carboniferous strata in Argentina (Tepuel-Genoa Basin, Patagonia). Only recently an assemblage composed of the proetine Pudoproetus Hessler associated with Cummingellinae indet. of Tournasian age have been recorded in La Rioja Province. In Brazil records of upper Paleozoic trilobites are restricted to three Carboniferous species included in the genus Ameura Weller: A. tapajotensis (Katzer), A. plummeri (Kegel), and A. duartei (Kegel) from the Amazon and Parnaíba basins. Furthermore, three taxa are so far known from Bolivia: Pseudophillipsia (Carniphillipsia) yampupatensis (Arellano), Triproetus dereimsi (Arellano), and Ditomopyge sp. indet. that come from the upper Carboniferous -lower Permian Copacabana Formation (Moscovian to Sakmarian). Here we report for the first time Peruvian trilobites derived from the Copacabana Formation exposed in the town of San Salvador in the vicinity of Cusco. In this locality the Copacabana Formation is about 600 m thick and is composed of dominantly massive limestone, alternating with bituminous shales, and subordinate dolomites, siltstones, and sandstones. The early Permian age of this succession has been constrained upon the Triticites opimus foraminifera zone. Trilobites are moderately abundant, occur either as isolated sclerites or as articulated specimens, occasionally enrolled, or as moult ensembles. They largely preserve their cuticle in unweathered limestone and occur as external and internal moulds in weathered limestones. Associated fauna include bryozoans, brachiopods, gastropods, and foraminifera. In our preliminary study at least four different taxa have been assessed. Relatively complete material allows the identification of a new species of Ditomopyge, and several well preserved pygidia are referred to Triproetus cf. T. dereimsi. Additional pygidia in the collection suggest the presence of two different morphotypes that still remain unidentified. The presence of T. cf. T. dereimsi favors a tentative correlation with the Yaurichambi section (La Paz Department, Bolivia). Overall, this finding suggests that trilobite diversity is considerably higher than previously addressed for the Permian of South America. From a paleogeographic viewpoint the taxa so far recorded largely display a widespread distribution; however, the presence of the swollen median preoccipital lobe in Ditomopyge n. sp. points to a closer link with the North American D. scitula group. Further studies of Peruvian trilobites will be of particular significance to unravel paleogeographic connections of this part of Gondwana during the late Paleozoic.