A PERMIAN MIXOHALINE OSTRACOD ASSOCIATION OF THE TERESINA FORMATION, PARANÁ BASIN, BRAZIL

– New ostracod species are described for Middle to Upper Permian (Guadalupian) rocks of the Teresina Formation, Paraná Basin, from two localities in the São Paulo State, southwestern Brazil: Xavante Dam and Pau Preto Quarry. Paranacythere nigripallus gen. nov. and sp. nov., Velatomorpha xavante sp. nov., and Velatomorpha pseudoaltilis sp. nov. are herein described. The association Velatomorpha– Paranacythere is proposed as typical of Permian mixohaline environments of the Teresina Formation, and is the most abundant in the two studied localities. Paranacythere nigripallus gen. nov. and sp. nov. is proposed to accommodate a very abundant species with typically cytheroidean characteristics, and tentatively ascribed to the family Cytheruridae. Some ecological remarks are presented based on ostracod population age structure, biostratinomy and taxonomic composition of assemblages. The diagnosis of Velatomorpha Tibert & Dewey is emended.


INTRODUCTION
Ostracods constitute the arthropod lineage with the most abundant and diversified fossil record, which ranges from the Ordovician to the Holocene (Rodriguez-Lázaro & Ruiz-Munhoz, 2012).Marine faunas were dominated initially by paleocopids, but towards the Late Paleozoic podocopids and platycopids became gradually more diverse, while paleocopids became extinct at the end-Permian extinction (EPE).By the Early Carboniferous these crustaceans began to colonize marginal marine and lacustrine waters, reaching considerable diversity in these environments in the Late Carboniferous and afterwards (Williams et al., 2006;Bennett et al., 2011;Iglikowska, 2014).Horne (2003) and McGairy et al. (2021), however, argue that the colonization of mixohaline environments by paleocopids, platycopids and leperditicopids might have begun during the Silurian.
The ecological diversity of ostracods allows their use as reliable environmental proxies (Carbonel et al., 1988), which requires detailed taxonomic knowledge.In South America, research on Permian ostracods lags behind the post-Paleozoic one, and taxonomic knowledge is, therefore, very limited.Studies in Chile (Breitkreuz et al., 1992), Paraguay (Zabert, 1985), and Uruguay (Díaz-Saravia & Herbst, 2001), revealed typical lacustrine assemblages.In Brazil, Sohn & Rocha-Campos (1990), Maranhão & Petri (1996) and Bergue et al. (2020), on the other hand described the occurrence of assemblages with some degree of marine influence in the Passa Dois Group.Those papers supply invaluable data for the understanding of non-marine ostracods diversification in southern Pangea.This paper aims to contribute towards the knowledge on Brazilian Paleozoic ostracods describing a new genus and three new species of the Teresina Formation, and presenting brief discussion on their evolutionary and paleoecological significance.

GEOLOGICAL SETTING
In this work, two localities in the southern São Paulo State corresponding to rocks of the Teresina Formation, Passa Dois Group, are studied (Figure 1).The Passa Dois Group records mainly Middle to Upper Permian rocks (Holz et al., 2010;Ng et al., 2019), and represents a complete cycle of continentalization divided in Irati, Serra Alta, Teresina and Rio do Rasto formations (Milani et al., 1998).
These units comprise mixed carbonatesiliciclastic microfacies where part of the carbonate rocks is associated to episodic marine incursions (Ng et al., 2019).Especially in the Teresina Formation, the limestones are more abundant at the middle and upper portions of the unit, and usually present cm to dm-scale layers of bivalve and ostracod bearing limestones and microbialites.The typically pure ones correspond to oolitic calcarenites (Ng et al., 2019) cemented by sparite, and calcilutites, which may present bivalves and ostracods with disarticulated shells (Rohn, 2001;Rohn et al., 2003).The ostracod assemblage described herein was recovered in peloidal calcisiltites from the Pau Preto Quarry and Xavantes Dam outcrops, correlated to middle to upper portion of the Teresina Formation, respectively (Mello & Sousa, 1985;Maranhão, 1995;Maranhão & Petri, 1996;Rohn & Fairchild, 2015;Bergue et al., 2020).
These fossil assemblages characterize marginal environments with variable marine influence.According to Bergue et al. (2020), the ostracod assemblages, at least in some levels, characterize mixohaline waters due to the low richness and high abundance of some taxa, particularly Velatomorpha.In the absence of reliable global marine biostratigraphic markers (e.g., conodonts), the position of the Teresina Formation is still not defined but lies possibly between either the Guadalupian-Lopingian or the Lopingian-Triassic boundaries (Ng et al., 2019).Isotopic analysis carried out in the Araguainha Dome and seismic structures coeval to the Teresina Formation reinforce a Guadalupian-Lopingian age for these stratigraphic interval (Tohver et al., 2012(Tohver et al., , 2018)).

MATERIAL AND METHODS
The 18 samples (approximately 500 g each) were obtained in exposed sections from two localities of the São Paulo State, southwestern Brazil, as follows: 11 samples from the Xavantes Dam (Fartura municipality, 23°19'52.22"S;49°36'7.07"W),and seven samples from the Pau Preto Quarry (Taguaí municipality, 23°17'28"S; 49°18'12"W) (Figure 1).The samples were disaggregated in oxygen peroxide, washed in meshes between 0.25 and 1.0 mm, and oven dried.All ostracod specimens were picked under stereomicroscope and assembled in micropaleontological slides for taxonomic analysis.SEM images were carried out in a Phenom XL equipment at Laboratório de Micropaleontolgia Aplicada of Departamento de Geologia, Universidade Federal de Pernambuco.The genus Velatomorpha Tibert & Dewey, 2006 is very abundant in the studied material, represented both as adult and juvenile specimens, but in many of them identification at species level was not possible due to poor preservation.So, only specimens that could be assigned to any of the species described herein or in previous studies are counted at the item "Material" on the taxonomy chapter.

SYSTEMATIC PALEONTOLOGY
The suprageneric taxonomy herein adopted follows mostly Tibert et al. (2013) Duplicature moderately wide at the anterior region.
Etymology.In allusion to the basin name (Paraná) + cythere, the first marine ostracode genus proposed (Müller,1785) in allusion to the Greek island Cythera.
Remarks.The monotypic genus Paranacythere is proposed to accommodate a very abundant species of the Teresina Formation.Paranacythere gen.nov.differs significantly from any Paleozoic or post-Paleozoic genera (e.g., Benson et al., 1961;Abushik, 1990).The impossibility of studying in detail the internal morphology does not permit to ascribe with certainty this genus to any family, although the conspicuous duplicature clearly indicates its podocopid affinity.Based on its chronostratigraphic position and general macroevolutionary aspects of podocopids, however, Paranacythere gen.nov. is probably among the Permianidae, Limnocytheridae, Bythocytheridae and Cytheruridae (Whatley & Moguilevsky, 1998;Whatley & Boomer, 2000).Permianids and limnocytherids are typically nonmarine taxa and characterized by a median sulcus in carapace.The marine bythocytherids also present a conspicuous median sulcus, which is absent in Paranacythere gen.nov.Therefore, Cytheruridae, seems to be a reasonable classification for the genus herein proposed.Despite being predominantly marine, and diversified from Mesozoic onwards, Whatley & Boomer (2000) argue that the earliest cytherurids might have inhabited marginal marine environments.
Paranacythere gen.nov., however, differs from the two Permian cytherurids discussed by Whatley & Boomer (2000).From Judahella Sohn, 1968 differs in outline and the absence of swellings and nodes on the surface.From Gruendelicythere Kozur, 1971 differs in the absence of reticulated nodes and sulci in the lateral surface.
Etymology.L. in allusion to the morphological similarity to V. altilis (Jones & Kirkby, 1889).Remarks.Velatomorpha pseudoaltilis sp.nov.differs from V. xavante sp.nov. in having the outline of the RV markedly oval.In spite of the similarity to V. altilis, these species differ in the posterior outline of the RV and in the outline of the LV.Another similar species, V. fittsi (Kellet, 1935), differs in having the LV completely enclosed by the RV.

ASSEMBLAGES COMPOSITION AND TAPHONOMIC REMARKS
Velatomorpha spp.and Paranacythere nigripallus gen.nov.and sp.nov.are the dominant taxa both in Xavantes Dam and Pau Preto Quarry.The Xavantes site is characterized by high incidence of Velatomorpha, whose specimens are usually preserved as two or three nested valves of several instars, possibly up to A-5.Carapaces, on the other hand, are very rare and exclusively juveniles.In the Pau Preto Quarry assemblages are dominated by Paranacythere nigripallus gen.nov.and sp.nov., but Velatomorpha spp.are also common.
Different from Velatomorpha, carapaces of Paranacythere nigripallus gen.nov.and sp.nov.are common, although valves are dominant.In part, the predominance of valves over carapaces in Velatomorpha is explained by the hinges poorly developed or even absent in most Paleozoic ostracods (Scott, 1961).In the species herein described hinge structures were not observed, and the valves junction occurs simply (at least in V. pseudoaltilis sp.nov.) through a smooth contact margin without interlocking devices.
The valve:carapace and adult:juvenile ratios in fossil assemblages might indicate environmental energy level and have, therefore, paleoecological potential.Reyment (1960) discussed briefly the adult:juvenile relation in ostracod assemblages, but this issue was detailed only some decades later by Whatley (1988), who represented population age structures in three histogram types (A, B, and C).Whatley's histogram type A represents assemblages composed both by adults and multiple instars indicating autochthony and low environmental energy.Types B and C, in turn, depict assemblages whose original composition has been altered by transport.The assemblages from Xavantes Dam composed by adults and several instars fit in Whatley's assemblage Type A (i.e., low environmental energy), which is consistent with marginal marine areas.In Pau Preto, the predominance of adults over juveniles of Paranacythere nigripallus gen.nov.and sp.nov.cannot be ascribed either to selective transport or preservation bias based on the available data.
Valve nesting (also called cup-in-cup), another conspicuous biostratinomic trait seen in several samples of both sections herein studied, is usually assumed as indicative of gentle water movements in very shallow marginal areas (Wakefield, 1995;Carignano & Varella, 2011;Bergue et al., 2011Bergue et al., , 2015)).Alternative explanation for the origin of this pattern is the stacking in the digestory tract of predators (Retrum & Kaesler, 2005).Notwithstanding, a more plausible explanation links nesting to two factors: size and abundance of valves, i.e., nesting would occur whenever high incidence of large valves takes place (Guernet & Lethiers, 1989;Wakefield, 1995).This reasoning is supported by Fontana & Ballent (2005) who observed in an ephemeral lake in the Buenos Aires Province (Argentina) the occurrence of nesting only in the largest species: Amphicypris argentinensis Fontana & Ballent, 2005.Last but not least, carapace incrustation must be pointed as another important thaphonomic feature in the studied assemblages.In most cases it hampered the morphological analysis of specimens and, consequently, their due identification.The incrusting mineral deposited over valves and carapaces produces in some instances honeycomblike structures, whose analysis through energy dispersive X-ray spectroscopy (EDS) revealed to be of carbonatic composition (Figure 4).The paleoenvironmental significance of these incrustations, however, could not be interpreted in the present study, and constitute a potential theme of investigation in future works.
The studies above mentioned supply important data on the origin and radiation of non-marine (i.e., mixohaline and freshwater) ostracod faunas in several parts of Pangea.Adaptative radiations, irrespective of the animal group considered, result mostly from opportunities.Species do not necessarily have fixed ecological traits, which would permit ecological shift and occupation of new niches (Mayr, 1963).Yet, opportunities do not ensure per se adaptative radiation, and factors such as lack of speciation, lack of ecological resources and lack of evolvability, might turn some clades more prone to radiating than others (Losos, 2010).The diversity of environments in marginal marine areas during the Late Paleozoic in different regions of Pangea lay the pathway for understanding the adaptative irradiation of ostracods (Bennett et al., 2011).
Although records of the initial phase of freshwater colonization by ostracods might be biased by preservational restraints, it is assumed that the oldest freshwater faunas date from Early Carboniferous (Horne, 2003;Williams et al., 2006;Bennet, 2008).Details and timing of these radiations -that might have occurred repeatedly (see Retrum & Kaesler, 2005) -are not completely known.Notwithstanding, they were certainly influenced both by intrinsic (e.g., physiologic adaptations) and extrinsic factors (e.g., sea level changes and coastal morphodynamics) during the Carboniferous and which continued along the Permian (Bennett et al., 2011;Iglikowska, 2014).
The absence of marine ostracod taxa (such as bairdiids, bythocytherids and healdiids) in the Teresina Formation might be explained by the evolutive phase of the Paraná Basin during the Carboniferous and Permian.After the Late Paleozoic Ice Age (Pennsylvanian), a sea level rise trend is registered in the Supersequence Gondwana I (Milani et al., 2007;Cagliari et al., 2016).The Serra Alta Formation represents its maximum marine influence, and the overlaid Teresina Formation registers pelites with tide influenced structures, which characterizes the inception of new ecological conditions (Milani et al., 2007).According to Simões et al. (2017) and Guerrini et al. (2020), these processes represent the establishment of a confined epeiric sea, followed by a trend of shallowing and continentalization in the basin.In marginal areas of this epeiric sea, several types of environments with variable salinity gradients might have been established (Ng et al., 2019), such as estuaries, bays, lakes, lakes with occasional marine influence, and lagoons as discussed by Bennett et al. (2011).
Hence, the absence of typical marine cytheroidean, and the freshwater lymnocytherids and darwinulids, permit to characterize the assemblages herein studied as mixohaline, where Velatomorpha-Paranacythere constitutes the typical association.This association is considered ecologically analogous to others composed by Cytherideidae in the Mesozoic and Cenozoic.Other occurrences in the northwesthern Pangea sustain Velatomorpha as a taxon widespread and diverse in mixohaline environments (Tibert & Dewey, 2006;Gray et al., 2012;Tibert et al., 2013).The continentalization trend observed in this sector of the Paraná Basin and the repeated events of climatic changes prompted the evolution of the endemic ostracod assemblage herein studied.

CONCLUSIONS
The association Velatomorpha-Paranacythere characterizes mixohaline environments of the Guadalupian Teresina Formation and is proposed as ecological analogous of the cytherideid associations Fossocytheridea-Perissocytheridea in the Mesozoic and Cyprideis-Perissocytheridea in the Cenozoic.Ostracod assemblages from the Teresina Formation record important evolutionary step on the diversification of non-marine ostracods in the southern Pangea.The genus Velatomorpha with three species formally described for the Teresina Formation represents an important ecological index for mixohaline environments.Other morphotypes of Velatomorpha, which could not be thoroughly studied in the present work due to the scarcity of specimens, possibly correspond to new species, and in this case a biostratigraphical potential for the genus might be expected.

Figure 1 .
Figure 1.Map of the Passa Dois Group outcrops between São Paulo and Paraná, location and stratigraphic position of study areas and samples.Sources: Ages and chronostratigraphic division according to Lucas & Shen (2018) and chronostratigraphic chart after Ng et al. (2019).Complementary radiometric age determination of bentonic ash falls beds from Irati Formation and Araguainha impact structure according to Santos et al. (2006) and Tohver et al. (2012), respectively.