On the fossil Remains of Panochthus Burmeister, 1866 (Xenarthra, Cingulata, Glyptodontidae) from the Pleistocene of southern Brazil

The genus Panochthus represents the last lineage of “Panochthini” recorded in the Pleistocene. This genus has a wide latitudinal distribution in South America, and in Brazil it occurs in the southern and northeastern regions. In this paper we describe new material (isolated osteoderms and caudal tube fragments) assigned to Panochthus from the state of Rio Grande do Sul (southern Brazil) and discuss some taxonomic issues related to Panochthus tuberculatus and Panochthus greslebini based on this material . The occurrence of P. greslebini is the first for outside the Brazilian Intertropical Region. In addition, we describe new diagnostic features to differentiate the osteoderms of P. greslebini and P. tuberculatus. Unfortunately, it was not possible to identify some osteoderms at the species level. Interestingly, they showed four distinct morphotypes characterized by their external morphology, and thus were attributed to Panochthus sp. Lastly, we conclude that in addition to P.tuberculatus registered to southern Brazil, there is another species of the genus, assignable to P. cf. P. greslebini. Our analysis reinforce the reliability of caudal tube characters for the classification of species of Panochthus.

The fi rst record of Panochthus, for the territory of Brazil was mentioned by Ihering (1891), in correspondence to Florentino Ameghino, from the coastal plain of the state of Rio Grande do Sul, Santa Vitória do Palmar Municipality.Subsequently, Panochthus was reported from deposits in northeast Brazil (tanks) by Branner (1915) and by several authors (e.g.Moreira 1971, Bergqvist 1993).The fossil content of these tanks was deposited during the late Pleistocene, with available electron spin resonance (ESR) ages dating it to between 63,000 to 10,000 years BP (e.g.Kinoshita et al. 2005, Oliveira et al. 2009, Silva 2009, Dantas et al. 2011).In the northeastern region of Brazil, P. greslebini and P. jaguaribensis are considered endemic species (e.g.Bergqvist 1993, Porpino and Bergqvist 2002, Zamorano 2012, but see Chimento and Agnolin 2011).P. tuberculatus has only been recorded in Rio Grande do Sul (e.g.Bombin 1976, Ribeiro andScherer 2009).Another dubious record of Panochthus in the Amazon region is referred to by Paula Couto (1956); the material is a single isolated osteoderm collected in the Jurua River, in the state of Acre.
In this paper, we describe new material of the Panochthus from the state of Rio Grande do Sul (southern Brazil) and discuss some taxonomic aspects of the species reported.

MATERIALS AND METHODS
The material studied here belongs to the paleontological collections of the Museu de Ciências Naturais da Fundação Zoobotânica do Rio Grande do Sul (MCN/FZBRS), Museu de Ciências Tancredo Filho Melo (MCTFM), Laboratório de Geologia e Paleontologia da Universidade Federal de Rio Grande (LGP/ FURG) and Museu Nacional do Rio de Janeiro (MNRJ), Brazil.The anatomical nomenclature follows Porpino and Bergqvist (2002), while the scheme for the different regions of the carapace is based on; systematics follow Zamorano et al. (2013) (see.Zamorano and Brandoni 2013).The description and terminology for osteoderms follows Hill (2006).

PROVENANCE OF MATERIALS
The material was found in the municipalities of Uruguaiana (Touro Passo Creek), Santa Vitória do Palmar (Balneário Hermenegildo, coastal plain and Chui Creek) and Rosário do Sul (Rincão dos Fialho) (Fig. 2).
Balneário Hermenegildo (53°15′S, 33°42′W) comprises the southern portion of the coastal plain of Rio Grande do Sul, 20 km from Santa Vitória do Palmar.Over time, it has suffered modifications to its landscape related to sea level fluctuations (transgressive-regressive events), which developed four lagoon-barrier systems (Villwock and Tomazelli 1995).The fossil remains of the coastal plain are associated with deposits of lagoon-barrier system III, with an estimated age of 120,000 years BP (Villwock and Tomazelli 1995).The dates obtained for the coastal plain of Rio Grande do Sul show a wide variation from younger than 18,000 to 650,000 years BP (Lopes et al. 2008(Lopes et al. , 2010)).According to Lopes et al. (2010), the mixture of fossils from the middle and late Pleistocene is probably the result of reworking of several fossil beds by successive Quaternary transgressive events.
Chuí Creek (33°35′S; 53°20′W) is located in southernmost part of Rio Grande do Sul, in Santa Vitória do Palmar Municipality.The material was found in situ exposed along the banks of Chuí Creek.The plain through which the creek flows and where the fossil remains of Chuí Creek occur are associated with deposits of lagoon-barrier system III located between coastal barrier II (westwards) and barrier III (eastwards).The age of the fossils of Chuí Creek was estimated to be at least 120,000 years BP based on their location within the barrierlagoon system III (Lopes et al. 2005).However, subsequently it was demonstrated that these fossils are more recent (Lopes et al. 2010).A sample from the bank of Chuí Creek dated by ESR suggests an age between 42,000 and 33,000 years BP (Lopes et al. 2010).The mammal fossils collected are assigned to the Lujanian age (Oliveira et al. 2005).
Rincão dos Fialho is located in Rosário do Sul Municipality (30°12′S; 55°16′W).It is situated in the southwestern state of Rio Grande do Sul.The material was collected near the Fialho farmhouse, in a stream that cuts through layers of sandy sediments of variable thickness, of Pleistocenic age, that are directly in contact with the Triassic (Ferigolo et al. 1997).tuberculatus, and different from P. greslebini, which is heavily truncated, and P. subintermedius, which is pointed and subtriangular.In dorsal view, it is possible to distinguish two subapical figures, as in P. frenzelianus, P. jaguaribensis and P. tuberculatus.In P. greslebini and P. subintermedius there is just one dorsal figure.In dorsal view, the lateral figure can be seen to be of relatively large size as in P. frenzelianus, and distinct from P. jaguaribensis, P. subintermedius and P. tuberculatus, in which it is smaller.The terminal figure is oriented laterally as in P. frenzelianus and P. tuberculatus, while in P. jaguaribensis and P. greslebini it is oriented ventrally.The terminal figure is surrounded by a shallow slope, which differs from P. subintermedius and P. greslebini.Although the caudal tube is fragmented, it is possible to identify similar figures on the carapace.The morphology of the caudal tube are the most variable in this species (Zamorano et al. 2012).
The osteoderms of the postero-dorsal region of P. tuberculatus are thick and their tubercular figures are larger than in any other species of Panochthus (Fig. 3A).

GEOGRAPHIC PROVENANCE
Balneário Hermenegildo, coastal plain of Rio Grande do Sul.

DESCRIPTION
The caudal tube, MCN-PV32182, shows an apexian figure, considered an apomorphy of Panochthus greslebini, visible only on the dorsal surface and of subcircular outline (Fig. 4A-A'); however, the apexian figure of P. greslebini (DGM 1M) is less deep than in the specimen MCN-PV 32182.In this specimen, it is possible to identify the figure only in posterior view; in anterior view, it is poorly preserved, and it is not possible to describe it in more accurate details.Ferreira et al. (2013) observed that osteoderms of the lateral region of the carapace present distinctive features to P. greslebini: they are thinner and have smaller tubercles, which, in turn, show a greater distance between the radial sulci (Fig. 3B); the tubercular figures are small and have a flat surface, with a diameter of approximately 2-7 mm.Some osteoderms from the posterodorsal region show a slight concavity in the center of the plane figures, resembling in this respect P. subintermedius from the early Pleistocene of Argentina Ensenadan age.
P. greslebini is recorded in the Pleistocene of the northeast of Brazil, and is considered an endemic species of the Brazilian intretropical region (Bergqvist 1993, Porpino andBergqvist 2002).

DESCRIPTION
The caudal tube (Fig 4 E-F) has a distal, semioval extremity and has a subtriangular shape, ending in a conical tip.In dorsal view, the caudal tube presents only one dorsal figure, shared only by P. greslebini and P. subintermedius, and lacks a secondary dorsal figure, which differs from P. frenzelianus, P. jaguaribensis and P. tuberculatus.The terminal figure is oriented laterally as in P. frenzelianus and P. tuberculatus.Therefore, due to the fragmentary condition of the specimen MCN-PV 2960 and the absence of diagnostic features, its specific assignment is not possible.
All the carapace osteoderms analyzed are pentagonal, hexagonal, rectangular or subquadrangular form, with thicknesses ranging from17.2mm (MCN-PV 2016) to 42.8 mm (MCN-PV 4139), and show a tendency for merging between the osteoderms, especially those of the lateral side of the carapace.The osteoderms show the general ornamentation pattern of the dorsal region of the carapace of Panochthus, characterized by the presence of multiple polygons on the surface; these polygons are undefined and do not possess the formation of a distinct central figure.In a few osteoderms there is a distinct central figure, typical of the lateral edges of P. tuberculatus and P. frenzelianus (Zamorano 2012).In the south of Brazil, most of the records of glyptodonts are isolated osteoderms, which weakens the establishment of species identifications.Morphological differences that enable us to classify these isolated osteoderms into four main morphotypes were noted ( Morphotype III (MCN-PV 4988, Fig. 5C).This morphotype is distinguished by deep radial sulci and by clearly polygonal figures (pentagonal and hexagonal), flat and without any trabecular aspect.1943, Bombin 1976) are dubious.Oliveira (1996) in a study on the Xenartha of Rio Grande do Sul, analyzed the material assigned to P. tuberculatus and considered it as Panochthus sp. because the specimens were isolated and insuffi ciently preserved osteoderms, which were not enough to differentiate the species.In addition, Kerber and Oliveira (2008) revised the fauna of mammals from Touro Passo based on new materials, and proposed the presence of Panochthus sp.previously reported to the locality by Bombin (1976) as P. tuberculatus.Herein, we identify P.tuberculatus and P. cf.P. greslebini to the Balneário Hermenegildo, while for the other locations studied (Touro Passo Creek, Chuí Creek and Rincão dos fi alhos ) assigning Panochthus sp.
The caudal tubes, although very fragmented, are more informative than osteoderms, and they were cautiously used to identify Panochthus tuberculatus and P. cf.P. greslebini.Unfortunately, the caudal tubes are derived from the continental shelf, so they do not possess a stratigraphic context.Thus, a better identifi cation of these species is still dependent on new fi ndings from the continental Quaternary beds.
All other osteoderms despite having different shapes (quadrangular, pentagonal and hexagonal) show the same reticular pattern, characteristic of the genus.The depth of the radial sulci may vary considerably in Panochthus, according to its localition on the carapace so it cannot be used as a diagnostic feature.Most of the osteoderms found could not be assigned to a particular species; however, some individual were possible to be identified at level.An example of this are the osteoderms of P. frenzelianus located on the caudal edge of the carapace, which bear an opening that narrows down and closes with a rounded, almost cylindrical cross-section (Zamorano 2012).It has also been found that the osteoderms of the postero-dorsal region of P. tuberculatus and lateral osteoderms of P.greslebini can be used to distinguish these species (see Fig 3).
The species of Panochthus show the external surface of osteoderms i similar morphological pattern comprising small tubercles.Particularly, in P.intermedius (antero-dorsal and postero-dorsal regions) and P. jaguaribensis (dorsal region following Moreira 1971) the carapace shows the typical rosette pattern (Zurita et al. 2011);however, Costa Pereira et al. (2014) interpret this fragment of P.jaguaribensis as having similarities with the cephalic shield of other species of Panochthus.The pattern differs from that observed on the dorsal regions of the carapace of P. frenzelianus, P. tuberculatus and P. greslebini, in which a clear reticular pattern is observed (Zamorano 2012).Porpino and Bergqvist (2002) point out that the carapace of P.jaguaribens is less thick than in P. greslebini, and that this feature represents another distinguishing characteristic among the taxa.Costa Pereira et al. (2014) indicate the need detailed revision of P. jaguaribensis.
There are some diagnostic features at least for some species of Panochthus (presence of main figures in osteoderms from the antero and posterodorsal regions of carapace in P. intermedius and presence of an apexian figure in P. greslebini, for instance).Furthermore, some authors (e.g.Cruz et al. 2011) have argued that the species of Panochthus can be differentiated by unique combinations of carapace and caudal tube characteristics.Moreira (1971) observed a wide variation between specimens of P. greslebini, interpreted by him as ontogenetic.Chimento and Agnolin (2011) described a piece fragment of caudal tube from Santiago del Estero province, Argentina, this fragment described and figured by them, do not present evidence apexian figure, but a detailed note on the figure provided by these authors in view ventral is observed two ventral figure, which do not correspond to P.greslebini.It is noteworthy that that the fragment described here may actually represent the first occurrence of P. greslebini outside the Brazilian Intertropical Region.The presence of the species P. subintermedius (based in MCN-PV 2960) may not be ruled out either, although it is a taxon typical of the early-middle Pleistocene, while P. greslebini and P. jaguaribensis are from the Pleistocene sensu lato and considered endemic to the northeast of Brazil (Bergqvist 1993, Porpino andBergqvist 2002).
In Brazil, the fossil record of Panochthus is restricted to the southern and northeast of Brazil (see Fig 1 ); the fossils recorded between these regions are mainly in cave of karstic origin (see.Lund 1839, Salles et al. 2006, Castro and Langer 2011, Ghilardi et al. 2011, Silva et al. 2012).The glyptodonts previously reported for this type of depositional environment are Glyptodon and Hoplophorus.The absence of Panochthus in these localities may be due to the lack of further study in these regions, where the Pleistocene deposits are still poorly known.Zurita et al. (2005) suggested that the strong development of frontonasal sinuses and a strongly pneumatized skull in Neosclerocalyptus and Panocthus played a major rule in thermoregulation and would represent an adaptation for savannalike environments in a semiarid climate period.Carlini et al. (2004) suggest, based on the fauna of Mesopotamia Argentine, southern Brazil Panochthus FROM SOUTHERN BRAZIL and Uruguay West, would be associated an environmental conditions wetter and warm.
During the Quaternary, there were several glacial cycles, with cold and dry periods interrupted by hot and wetter periods (Haberle and Maslin 1999).Multiple pulses of expansion/contraction of the fields and regression/transgression of sea levels were recorded.According to Scillato-Yane et al. (2002) during mainly the last interglacial period there was development of an ecological corridor connecting the Mesopotamia region of Argentine with the intertropical region of Brazil.Sánchez et al. (2004) propose a corridor along the east of South America and some coastal areas of the Atlantic, which was formed during regression of sea level, and was used by mammals adapted to mesic environments.These pulses can justify the concurrent presence of genera from intertropical and pampean regions through the Pleistocene, for example: Panochthus, Pampatherium Gervais and Ameghino, 1880, Holmesina Simpson 1930, Glyptodon Owen, 1839and Notiomastodon Cabrera, 1929 in southern Brazil mainly in the plain coast of Rio Grande do Sul.The interesting thing is the simultaneous presence of purportedly endemic intertropical species and pampaean species belonging to those genera in the same area (see Oliveira and Pereira 2009).

Figure 1 -
Figure 1 -Map of the geographic distribution of Panochthus in the Pleistocene.
Figure 2 -Location map of fossiliferous localities. A. Panoramic view of banks exposing the TouroPasso Formation and stratigraphic sequences (modifi ed from Bombin 1976); B. BalneárioHermenegildo and transect of the coastal plain of Rio Grande do Sul, showing its main depositional systems (modifi ed from Tomazelli and Villwock 2005); C. Panoramic view of banks exposed at Chui Creek and stratigraphic sequences (modifi ed from Lopes 2013); D. Rincão dos Fialho, where the material of Panochthus sp was collected.
Fig 5).Morphotype I (MCN-PV 2043, Fig 5A).The contact area between osteoderms has a rough aspect; in the external view the osteoderm presents several subcircular and concave figures, which are separated from each other by shallow radial sulci and limited by shallow radial sulci with foramina in the connection between them.The morphotype I osteoderms are larger than the other morphotypes identified and were found only in the Chuí Creek locality (Fig 6).Morphotype II (MCN-PV 5659, Fig 5B).The contact area between osteoderms does not have a rough aspect as in morphotype I; in external view the osteoderms present several circular figures, small, prominent and trabecular in aspect.The figures are limited by wide and shallow radial sulci with relatively large foramina.The morphotype II osteoderms are smaller than the morphotypes I and IV, and were found in the Rosário do Sul, Rincão dos Fialho locality and Santa Vitória do Palmar, Balneário Hermenegildo locality (Fig. 6).

Figure 6 -
Figure 6 -Distribution of the morphotypes in localities of the study.