The first record of Purussaurus (Crocodylia, Alligatoridae) in the Late Miocene of Argentina

: Herein we report the first record of Purussaurus Barbosa-Rodrigues, 1892 for the Neogene of Argentina. This genus is recorded in Miocene beds of different localities in Colombia, Venezuela, Brazil, and Perú, and includes at least three different species with total body lengths ranging from 8 to 13 m. The material reported here is a partially preserved tooth (MAS-PV 386) found at the locality Toma Vieja (Paraná, Entre Ríos Province, Argentina), in strata informally known as “Conglomerado osífero” or “Mesopotamiense” (Late Miocene) and traditionally regarded as the basal levels of the Ituzaingó Formation. The material corresponds to the apical portion of a conical crown, slightly compressed, lingually curved, and with a subrounded apex. The enamel is ornamented with thin apicobasal ridges that are anastomosed and separated by shallow grooves. These ridges are transversely crossed by shallow lines that give the enamel surface a crackled aspect. The crown has a continuous carina formed by the enamel that runs along the mesial and distal surface of the tooth, which divides the vestibular (or labial side of the tooth) and lingual faces of the crown that are subequal in size. The carina is ornamented with fine enamel wrinkles that are parallel to each other and perpendicular to the mesiodistal carina. This condition, known as pseudoziphodonty, together with the enamel structure and overall shape of the crown, allow referring the specimen MAS-PV 386 to Purussaurus sp. This finding represents the southernmost record of one of the largest predatorial neosuchian crocodylians which inhabited the wetlands that developed during the Late Miocene in South America.

We present herein the first record of Purussaurus in the Late Miocene of Argentina together with a detailed description of this material and a discussion of its paleogeographic and paleoenvironmental implications.

Geological and Paleontological Settings
In the Entre Ríos Province, the "Conglomerado osífero" crops out discontinuously in the river banks of the Paraná River and its tributaries, from the city of Paraná northwards to Hernandarias (Fig. 1A). The tooth here described was collected in the Toma Vieja locality (31° 42' 10''S, 60° 28' 35''W), where this conglomerate is clearly distinguished by a visible erosive unconformity from the mudstone and sandstone beds of the underlying Paraná Formation (Fig. 1B). The "Conglomerado osífero" is characterized by well consolidated levels of fine cross stratified gravel sandstone and well sorted fine to coarse grained cross stratified sandstone beds, and clayed mudstone lenses, which concentrated abundant fossil bones and teeth of fragmented and disassociated vertebrates (Brandoni & Noriega, 2013). These skeletal fragments are heavy and well mineralized and belong mostly to continental vertebrates, although a few mostly reworked marine forms can be represented (e.g., Cione et al., 2000). Traditionally, the "Conglomerado osífero" was considered as part of the fluvial system of the Ituzaingó Formation that outcrops in Entre Ríos Province (Frenguelli, 1920;Aceñolaza, 1976Aceñolaza, , 2000Brunetto et al., 2013;Schmidt et al., 2020). Particularly, Brunetto et al. (2013) and Brandoni et al. (2019) regarded the "Conglomerado osífero" as part of the Lower Member of the Ituzaingó Formation and interpreted that it corresponds to a continental paleoenvironment dominated by a braided fluvial succession. However, Pérez (2013a) considered that these levels correspond to fluvial tide influenced channels of a marginal marine paleoenvironment and assigned them to the upper levels of the Paraná Formation.

MATERIAL AND METHODS
MAS-PV 386 was described macro and microscopically. For the macroscopic anatomical analysis comparisons with teeth of extant and Miocene caimanines were made, with first hand materials, photographs taken from literature (Tab. 1), or own photographs. Terminology used for the spatial orientation of the tooth follows Smith & Dodson (2003); however, we decided to add the term "vestibular" as synonym of "labial", since reptiles do not have lips. The microscopic analysis was made by the Environmental Scanning Electron Microscope ESEM-FEI Quanta 200 of the LIMF. In addition, chemical element mapping tools (major elements) were used, and Backscattered Electrons (BE) method. The latter, based on the detection of the atomic number (Z), provides an image of the distribution of chemical elements in the material that makes up the entire piece, with the darkest areas being those with the lowest Z and the lightest and bright ones with higher Z (Fig. 2) CROCODYLIFORMES Hay, 1930(Benton & Clark, 1988) CROCODYLIA Gmelin, 1789ALLIGATORIDAE Gray, 1844CAIMANINAE Brochu, 1999 Purussaurus Barbosa-Rodrigues, 1892 Purussaurus sp.

Type species.
Purussaurus brasiliensis Barbosa-Rodrigues, 1892. Referred material. MAS-PV 386, incomplete tooth preserving the apex sector of an almost well preserved crown (Fig. 3). Locality and horizon of the new specimen. Toma Vieja locality, near Paraná City (Entre Ríos Province, Argentina), "Conglomerado osífero" (traditionally considered as the base of Ituzaingó Formation, Brunetto et al., 2013), Late Miocene (Brandoni, 2013;Brunetto et al., 2013;Schmidt et al., 2020). Description. MAS-PV 386 consists of a fragmentary tooth that preserves most of the apical sector of the crown, which is conical but slightly compressed and lingually curved. In lingual and vestibular views, the mesial and distal margins are straight in the apical region but more curved in the base of the preserved part of the crown, where the tooth is subcircular in transverse section, with a vestibular-lingual width equal to 16.6 mm, and a mesiodistal width equal to 19.7 mm (both measured at the base of the piece). This minimal but abrupt increase in tooth width due to curving of the mesial and distal margins is present, although more marked, in other teeth assigned to Purussaurus (e.g., DGM 1128, Souza et al., 2016, figure 3 F-H).
The tooth apex is rounded, showing a partial wear of the enamel apical surface, a condition commonly seen in worn or shed teeth of all crocodiles. The enamel of the lingual and vestibular (or labial, sensu Smith & Dodson, 2003) surfaces of the crown are uniformly ornamented with fine anastomosed striae or ridges separated by smooth grooves, extending from the apex to the base along the entire surface of the crown. These fine apicobasal ridges are transversely crossed by thin irregular lines, which observed under magnification give the enamel a cracked appearance.
The crown shows a conspicuous carina that extends continuously along the mesial and dis-tal faces of the tooth dividing the crown into a vestibular and a lingual subequal sectors. This crenulated carina is preserved in several sectors of the mesial and distal margins, it is exclusively formed by the enamel and bears fine but very marked parallel crenulations, oriented perpendicularly to the carina. Under magnification (SEM) it can be verified that these crenulations are formed by rounded parallel short crests separated by a shallow valley of enamel, distributed on both the labial and lingual surfaces of the carina (Figs. 2B-C, 3C). The density of these carinae is 5 per millimeter. This condition is called pseudoziphodonty (or false ziphodonty; Prasad & de Broin, 2002) and differs from the ziphodont condition (serrated teeth) present in other archosaurs, in which the crenulations are formed by both the dentine and the enamel (Prasad & de Broin, 2002).
Several features acquired during the fossilization and depositional processes of MAS-PV 386 can be observed. In a macroscopic view, damaged areas are present at the base and the mesial and distal margins of the tooth, with worn surfaces and fractures (Fig. 3). Under magnification (SEM) an evident wear can be observed at the apex of MAS-PV 386, and several excoriations associated with longitudinal microfractures running from the apex to the base and connected to each other with finer subhorizontal microfractures ( Fig. 2A). The longitudinal micro fractures are arranged in the smooth grooves or valleys between the apicobasal striae that constitute the general ornamentation of the crown (Figs. 2A,  3). The vestibular surface of the tooth shows a process of micro alveolarization, identified from the presence of small depressions distributed all over the surface of the enamel. Finally, the tooth is broken at the base and, given the nature of this fracture, it can be inferred that it was separated from the skull after fossilizing. Comparisons. Teeth preserved implanted in the upper and lower jaws are scarce in the crocodylian fossil record. In the case of Purussaurus, few teeth were recovered in situ and described in the literature (e.g., Langston, 1965;Aguilera et al., 2006;Aureliano et al., 2015;Souza et al., 2021). A gradual transition in the shape and size of teeth has also been described for this taxon, from taller and pointed anterior teeth to broader, lower, and more bulbous posterior ones (Langston, 1965;Aureliano et al., 2015). The teeth of Purussaurus have been described as rounded in a basal section but with crowns tending to be compressed (Langston, 1965) and bearing pseudoziphodont ridges. Anteriormost, larger, conical and sharp teeth of both upper and mandibular series of Purussaurus have been described as slightly compressed and lingually and distally curved (Langston, 1965;Aguilera et al., 2006;Aureliano et al., 2015). In P. mirandai the premaxillary teeth are sharp, anteroposteriorly and labiolingually curved; these teeth are relatively compressed as MAS-PV 386 (with a vestibular-lingual width of 15-30 mm and a mesiodistal width of 19-39 mm, sensu Aguilera et al., 2006). Due to its dimensions and proportions, MAS-PV 386 is more similar to the premaxillary second tooth of P. mirandai (e.g., AMU-CURS-135, described by Aguilera et al., 2006), although given that MAS-PV 386 is an isolated tooth, its relative size and position in the tooth row cannot be specified since the body size of the individual is unknown. Some posterior maxillary teeth of P. mirandai are preserved in some specimens (e.g., AMU-CURS-135, MCC URU-115-72V) and as in most of caimanines, these teeth are blunt, more rounded and lower than the anterior ones, with a general morphology clearly different from MAS-PV 386. The dentary teeth arrangement of P. mirandai is similar to other caimanines with the anterior teeth larger, taller and sharper, being the mandibular tooth 4 the tallest of the first teeth preserved (e.g., AMU-CURS-135). In this species mandibular teeth are more compressed than the teeth of the upper jaw and than in MAS-PV 386. Following this reasoning, MAS-PV 386 could correspond to a tooth of the upper series.
In relation to the crown ornamentation, the teeth of Purussaurus have been described as pseudoziphodont (see below). All these teeth pres-ent mesiodistal carinae, sometimes incompletely preserved and with fine striations perpendicular to the surface of the crown. In P. mirandai, the third premaxillary teeth of MCC URU-115-72V and some isolated teeth associated with AMU-CURS-135 show a striae density of 3 per 5 mm, different from MAS-PV 386 in which the density of these striae is 5 per millimeter. Finally, the enamel of isolated teeth assigned to Purussaurus has been described by several authors (e.g., Langston, 1965;Aguilera et al., 2006;Aureliano et al., 2015;Souza et al., 2016Souza et al., , 2021 which conclude that in smaller teeth (especially in the posterior and more bulbous ones), the enamel is generally wrinkled whereas larger teeth generally show smooth enamel but with longitudinal and transverse lines along the crown, conditions similar to those of MAS-PV 386.
The general morphology of MAS-PV 386 is like the anterior teeth of specimens assigned to Purussaurus from northern regions (e.g., Brazil, Colombia), in which the anterior teeth have slightly flattened crowns subcircular at their bases (Langston, 1965;Aguilera et al., 2006;Aureliano et al., 2015;Souza et al., 2016Souza et al., , 2021. Considering the general structure of the enamel of MAS-PV 386, it also resembles specimens assigned to Purussaurus in having longitudinal and transverse striae along the crown (e.g., DGM 1128-R and DGM 1194-R, Souza et al., 2016, figure 3 F-I;Aureliano et al., 2015, figure 5). The pseudoziphodonty, the macro and microscopic appearance of the enamel, together with the general shape of the tooth, allows us to assign MAS-PV 386 to the genus Purussaurus. However, the lack of species level diagnostic features in the teeth of each species of this genus precludes assigning MAS-PV 386 to any of the known Purussaurus species. Furthermore, MAS-PV 386 differs from teeth assigned to P. mirandai, P. neivensis, and P. brasiliensis, which have been described as curving backwards and slightly inwards in these species (Langston, 1965;Aguilera et al., 2006;Aureliano et al., 2015;Souza et al., 2021). As occur in most generalist alligatorids, the dentition of Purussaurus is heterodont in shape and size, showing a general transition from taller conical pointed anterior teeth (with some hypertrophied  Aureliano et al. (2015) Purussaurus brasiliensis DGM 527-R Solimões Formation (Late Miocene; but see Souza et al. 2021 for other interpretations of provenance), "Petrópolis" outcrop, in the left side ofthe upstream Juruá River, between Porto Walter and the debouchment of Igarapé Ouro Preto (Price, 1967)   teeth such as the 4th dentary tooth, 3rd/4th premaxillary teeth and 2nd/3rd maxillary teeth) to lower and rounded posterior teeth which are more button like shaped (e.g., Aguilera et al., 2006;Aureliano et al., 2015). After the anatomical comparisons here made, MAS-PV 386 is within the range of size variation of Purussaurus and the morphology of the crown indicates that it is probably an anterior tooth. As it is an isolated tooth, the position of MAS-PV 386 in the teeth row cannot be specified. However, compared with the proportions of the less compressed upper teeth and the relatively more compressed lower teeth of Purussaurus mirandai, the proportions of MAS-PV 386 indicate that it could be a tooth from the upper series (premaxillary tooth or anterior maxillary tooth).
In addition to the anatomical features, the preservation traits observed in MAS-PV 386 allow us to recognize the effects of the taphonomic processes that affected the material. From the BE analysis of the SEM, differences in the chemical elements and density of the materials that compose the surface of the tooth are identified (Fig.  2 E H). By mapping the chemical elements that conform the surface of the tooth, it was possible to verify the typical presence of calcium (Ca2+) and phosphorus (P5+), which constitute the original components of the tooth (hydroxyapatite), but also the presence of silicon (Si) and iron (Fe). In MAS-PV 386, Si and Fe fill the fractures and probably come from the silicoclastic sediment of the conglomerate (terrigenous material) and from authigenic precipitation as ferruginous cement (hematite, Fe2O3), respectively, during the fossil-diagenetic processes (Figs. 2G -H). The presence of longitudinal, transverse, and perpendicular fractures (respect of the apicobasal axis of the tooth) ( Fig. 2A D) is characteristic of a fragile tooth that loses the organic component that gives it the resistance of the structure. These fractures together with the small depressions distributed all over the vestibular surface of the enamel (micro alveolarization) would indicate that the piece suffered some abrasion by roll of little magnitude generated by the silicoclastic granular sediment of the bottom of the fluvial channel where it was accumulated.
Analyzing crocodylian assemblages from other contemporary South American localities, such as Solimões and Urumaco formations, Purussaurus is one of the taxa that cohabited in the Late Miocene mega wetland systems. Within these associations, caimanines (such as Mourasuchus and different Caiman species) and gavialoids (such as Gryposuchus) are always registered showing differences in their sizes and snout, jaws and teeth shapes. This morphological variability has been interpreted as evidence of niche partitioning, which results in optimizing the availability of resources and avoiding competition (Aureliano et al., 2015). In addition to the large size of Purussaurus species, the pseudoziphodont teeth suggest that they would have been active predators that included large vertebrates in their diets (e.g., Pujos & Salas-Gismondi, 2020  The sedimentological characteristics observed in the "Conglomerado osífero" in the Toma Vieja locality are mainly given by channel fill deposits interpreted as a braided fluvial system (e.g., Brunetto et al., 2013;Brandoni et al., 2019). As mentioned above, these levels rest unconformably on the shallow marginal marine deposits of the Paraná Formation through an erosive boundary, interpreted by some authors as a regional erosive surface related to the basal section of the Ituzaingó Formation (Brunetto et al., 2013;Brandoni et al., 2019). The erosive coarsegrained deposits of the "Conglomerado osífero", together with the taphonomic characteristics of most of its fossils (which are disarticulated, fragmentary, and with evidence of transport) suggest that this association represents a mixture of faunas, mainly continental with few marine taxa of different ages (Cione et al., 2000;Schmidt et al., 2020). Beyond this scenario, the now documented presence of Purussaurus in the "Conglomerado osífero" suggests that ecosystems associated with the southernmost South American Miocene wetlands would have been taxonomically similar to those of lower latitudes (e.g., Hoorn et al., 2010Hoorn et al., , 2022Tineo et al., 2015;Tineo, 2020). Particularly the presence of Gryposuchus neogaeus and caimanines such as Mourasuchus arendsi, Purussaurus, and several species for the moment assigned to Caiman (Bona & Barrios, 2015; in the Late Miocene of Paraná (Tab. 2) proposes a wide geographic distribution of these Neogene fluvial systems with a similar ecological complexity for the entire region in South America. Among the fossil material of crocodylians of the "Conglomerado osífero", Gryposuchus neogaeus is the most complete specimen recovered so far (i.e., MLP 26-413, an almost complete skull; Gasparini, 1968). Caimanines, on the other hand, are represented by isolated skulls and postcranial fragments which would indicate that most of these specimens will have been transported from their source area. In this scenario, MAS-PV 386 is another example of this taphonomical features. Although a regional environmental reconstruction is necessary to interpret the different continental sub-environments that would have developed in this part of the basin, the taxonomic diversity of crocodylians recognized in the "Conglomerado osífero" indicates the presence of warm humid environments with large amounts of water, capable of to withstand large piscivores gavialoids and huge caimanines along the megapredator Purussaurus.

CONCLUSIONS
The record of the tooth MAS-PV 386 in the "Conglomerado osífero" in Entre Ríos Province allows us to propose for the first time the presence of Purussaurus in the Late Miocene of Argentina. Although isolated indeterminate remains of large crocodylians have been described in the "Conglomerado osífero" (such as cranial and postcranial fragments of vertebrae, ribs, long bones, and osteoderms; Bravard, 1858;Burmeister 1883Burmeister , 1885Rovereto, 1912;Rusconi, 1933), at the moment this genus was geographically restricted to Miocene beds of Brazil, Colombia, Perú, and Venezuela (Aguilera et al., 2006;Aureliano et al., 2015).
This new finding represents the southernmost record of one of the largest known predators of neosuchian crocodiles. The presence of this mega carnivore alligatorid suggests a greater taxonomic diversity for the huge caimanines in Late Miocene wetlands in northeast Argentina. The potential faunistic association of large crocodylians such as Gryposuchus, Purussaurus, and giant caimans allows to explore the hypothesis of a niche partitioning already inferred for other Miocene northernmost South American localities given by the coexistence of piscivorous and other animal eating crocodylians. This possible setting proposes the existence of more complex environments capable of sustaining all this crocodilian fauna and therefore a more complex scenario for inland wetland and fluvial ecosystems developed in the Late Miocene in the South American Chaco Parana Basin.