A new Mississippian hexactinellid sponge from the western Gondwana: Taxonomic and paleobiogeographic implications MARCELO G. CARRERA, JUAN JOSE RUSTÁN, N. EMILIO VACCARI, and MIGUEL EZPELETA Carrera, M.G., Rustán, J.J., Vaccari N.E., and Ezpeleta, M. 2018. A new Mississippian hexactinellid sponge from the western Gondwana: Taxonomic and paleobiogeographic implications. Acta Palaeontologica Polonica 63 (1): 63–70. A Mississippian hexactinellid sponge from the western Argentina improves the extremely poor late Paleozoic sponge records from Gondwana. The sponge is included in the subfamily Thysanodictyinae of family Dictyospongiidae. The new genus and species Minitaspongia parvis is erected, and its well-preserved spicular structure is described in detail repre- senting the first approximation of the spicule assemblage in Thysanodictyinae. The skeleton is clathrate, three-dimensional with at least two ranks of rectangular openings. This first report of this subfamily outside North America represents the best-known hexactinellid and the first dictyosponge record from the Carboniferous of Gondwana. Unlike the occurrences of Thysanodictyinae in North America, with thick skeletons linked to high-energy shallow water settings, Minitaspongia occurs in low-energy water siliciclastic settings related to a cold climate and glacimarine deposits. Accordingly, the complex wall structure of this sponge should not be invoked as a necessary adaptation to high energy and shallow water settings. Key words: Porifera, Hexactinellida, Reticulosa, Carboniferous, Mississippian, Argentina. Marcelo G. Carrera [[email protected]], CICTERRA-CONICET Universidad Nacional de Córdoba, Facultad de Ciencias Exactas Físicas y Naturales, Av. Vélez Sarfield 1611, Ciudad Universitaria, 5016, Córdoba, Argentina. Juan José Rustan [[email protected]], N. Emilio Vaccari [[email protected]], and Miguel Ezpeleta [[email protected]], CICTERRA-CONICET Universidad Nacional de Córdoba and Universidad Nacional de La Rioja, Av. Luis M. de la Fuente s/n, Ciudad Universitaria, 5300, La Rioja, Argentina. Received 23 June 2017, accepted 18 September 2017, available online 6 February 2018. Copyright © 2018 M.G. Carrera et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. position, which allows describing in detail the elusive, and Introduction poorly known, spicule pattern of dictyosponges. Some environmental insights are provided about the new The worldwide records of Carboniferous sponges show a genus Minitaspongia, in order to better interpret the recog- particular abundance of sphinctozoans, the lithistid rhizo- nized paleobiogeographic patterns. morines and the hexactinellid dictyosponges, mainly con- centrated in North America, China, United Kingdom, and Institutional abbreviations.—PULR-I, Museo de Ciencias Spain (García-Bellido and Rodríguez 2005 and references Antropológicas y Naturales at Universidad Nacional de La therein). Such a distribution, almost excluding Gondwana, Rioja, La Rioja, Argentina. suggests a sampling bias rather than a true paleobiogeo- graphic pattern. As a consequence any new record outside these areas significantly contributes to the global diversity Geographic and geological setting and biogeographic knowledge. This contribution reports the find of a new genus of The stratigraphic record surveyed corresponds to a series of hexactinellid dictyosponge in the very limited record of late late Paleozoic basins developed in southwestern Gondwana Paleozoic sponges from Gondwana. The sponge was found linked to an active tectonic margin (Limarino and Spalletti in Carboniferous marine periglacial deposits of western 2006). In the context of the Central Andean foreland basin Argentina and represents one of a few examples of high-lat- (Caminos et al. 1993), we focused on the Mississippian fill- itude occurrences, linked to glacial deposits. The finding ing of the Río Blanco basin, a high paleolatitude southern also documents the first well-preserved spicule mesh com- basin (> 60° according to Isaacson et al. 2008). Strata sur- Acta Palaeontol. Pol. 63 (1): 63–70, 2018 https://doi.org/10.4202/app.00403.2017 64 ACTA PALAEONTOLOGICA POLONICA 63 (1), 2018 La Rioja N A Province B 68˚34'54" C Cerro 5km Mudadero B N 400 km ARGENTINA SOUTH AMERICA 28°03 45’ ” Lower Missipian Agua de Lucho Formation vestruces 2 initas Pampa de los A 1 ierra del las 20 SM 10 0 ierra de mango SU sponges fossiliferous nodules striated and bullet clasts glacial records Mulas Muertas Formation (Permian) ripples Río del Penón Formation (Pennsylvanian) Devonian–Mississippian dykes dropstones Devonian–Mississippian units parallel lamination Punta del AguaFormation (Mississippian) (Jagüel Formation sensu lato) diamictite Lower–Middle Devonian Cerro Tres Cóndores Formation (Mississippian) conglomerate Agua de Lucho Formation (Mississippian) basement(Sierra Umango) sandstone fault with indication of dip 1 2 fossil localities black mudstone Fig. 1. A. Geographic location of the studied area. B. Geological map and location of the studied section. The west flank of the Agua Quemada Syncline is divided in some tectonic blocks (1 and 2) by inverse and dextral strip faults. Sponges come from nodules of equivalent fine-grained dark stratigraphical intervals of the Agua de Lucho Formation (Tournaisian), cropping out under glacigenic diamictitic in both tectonic blocks. C. Stratigraphic column of the Agua de Lucho Formation and the location of the sponge-bearing levels. veyed crop out at the Sierra de las Minitas to the northwest productive levels are correlated with the Agua de Lucho of the small town of Jagüé, in central western Argentina Formation, the main stratigraphic unit recording low (northern Argentine Precordillera). Fossils come from the (Tournaisian) Mississippian records in the area (González southwestern region of the Sierra de Las Minitas (Fig. 1), and Bossi 1987). In the studied sections, the Agua de Lucho to the west of de Agua Quemada syncline (see Fauqué and Formation is approximately 800 m thick, without visible Limarino 1991 and Prestianni et al. 2015). base, and it is composed of dominantly pelitic facies with The studied material was recovered from two strati- thick interbedded diamictitic bodies yielding dropstones, graphically equivalent fossil localities, separated by a fault and the succession is characteristic of a deltaic front and a (tectonic block 1 and tectonic block 2), and located on the prodelta, related to storm-dominated glacio-marine envi- western flank of the Agua Quemada syncline (Fig. 1). The ronments. A similar environmental interpretation was pro- CARRERA ET AL.—MISSISSIPPIAN HEXACTINELLID SPONGE FROM ARGENTINA 65 posed by González and Bossi (1987) in the northern region structure of the wall as an important characteristic in its of the basin. definition. However, as we pointed earlier, the dictyopon- Specifically, the specimens described herein come from gids need a major revision which is beyond the scope of this a greenish-black pelitic interval of about 100 m thick, lo- work. cated immediately below a diamictite bed, laterally equiva- lent to the one reported in the base of the column of the Agua Subfamily Thysanodictyinae Hall, 1882 Quemada Syncline by Prestianni et al. (2015). In these dark, Genus Minitaspongia nov. fine-grained fossiliferous interval, dropstones are recog- Type species: Minitaspongia parvis gen et. sp. nov.; monotypic; see nizable in the uppermost part while a significant number of below. siliceous nodules occur in the sampled middle-lower por- Etymology: From the Sierra de las Minitas locality. tion. Fossil remains are diverse and well-preserved (usually articulated) either in the shales or in the nodules. In addition Diagnosis.—As for type species by monotypy. to the sponges studied here, brachiopods, bryozoans, hyo- Minitaspongia parvis sp. nov. litids, conularids, bivalves, gastropods, nautiloids, crinoids, Figs. 2, 3. corals, fishes, and plant remains are also present. These sed- imentological and taphonomic features largely suggest that Etymology: From Latin parvis, small, young. suspension processes dominated over tractive ones, so that Type material: Holotype: PULR-I 4 nearly complete sponge specimen. this succession is interpreted as a marine shelf environment Paratype: PULR-I 5, fragmentary specimen. with glacial influence. Type locality: Sierra de las Minitas section, La Rioja Province, Argen- tina. Holotype comes from tectonic block 1 at GPS: 28° 47 43 S/ 68° Since the Gondwanan palynomorph Waltzispora lan- 45 22 W . Paratype comes from tectonic block 2 at GPS 28° 46 28 S/ zonii Daemon, 1974, indicative of a Tournaisian age, has 68° 44 40 W (Fig. 1). been recorded nearly 50 m above the overlying diamictites Type horizon: Agua de Lucho Formation, Tournaisian. The sponge (see Prestianni et al. 2015), the sponge bearing levels are comes from nodules within a thick black fossiliferous mudstone in- considered Tournaisian. terval, approximately 100–150 m underlying a diamictitic, glacigenic bed, and approximately 200–250 m below the record of the Tournaisian guide spore Waltzispora lanzonii Daemon, 1974 (see Prestianni et al. Systematic palaeontology 2015). Material.—Type material only. Class Hexactinellida Sollas, 1887 Diagnosis.—Obconical to palmate thysanodictyine