Revision of the Devonian Acritarch Genus Pyloferites Quadros 1999 Based on Palynomorph Assemblages from Brazil

ABSTRACT A large population of the acritarch genus Pyloferites Quadros 1999 was recovered from the Devonian strata of the Paraná Basin, Alto Garças Sub-basin (Brazil), at the Jaciara section. Based on a literature review and the examination of new material, including morphometric analyses, Pyloferites shows wide morphological variability, and, therefore, is herein emended. Additionally, a species emendation and a new species are instituted: Pyloferites escobaides (Cramer 1964) Daners et al. 2017 emend. nov., and Pyloferites paranaensis sp. nov. The stratigraphical distribution of P. escobaides is extended from the middle–late Pragian to the Famennian, while P. paranaeinsis is restricted to the Pragian to early Emsian, or possibly middle Emsian, of the Paraná Basin. The presence of Pyloferites in Brazil, Bolivia, Uruguay, and Spain supports a Gondwanan and Perigondwanan palaeobiogeographical distribution.


Introduction
Organic-walled microfossils termed acritarchs are considered an informal and probably polyphyletic group of unknown biological affinities (i.e. incertae sedis) (Servais et al. 2004 and references therein). They are present throughout the geological column, although they are more widespread in the Lower-Middle Palaeozoic. Acritarchs are a valuable tool mainly for dating and the correlation of strata, but also for contributing to palaeoenvironmental and palaeobiogeographical interpretations. As an example of their usefulness as palaeobiogeographical markers, genera such as Bimerga, Winwaloeusia, Cordobesia, and Schizocystia are exclusively reported from Devonian Gondwanan and Perigondwanan strata (e.g. Deunff 1977Deunff , 1980Steemans et al. 2008;Garc ıa Muro et al. 2017 and references therein; Rubinstein et al. 2018).
The acritarch genus Pyloferites was described by Quadros (1999) from the Famennian of the Amazon Basin of Brazil. A central body more or less pentagonal in outline, with processes well differentiated from the vesicle arising from each angle, and a pylome as excystment aperture, are its diagnostic features (Quadros 1999). Previously, Cramer (1964) had erected Baltisphaeridium escobaides, from the Pragian-Emsian of the La Vid Shale Member, in the Le on province of Spain. He described this species as a polygonal vesicle formed by the broad bases of the processes, and the frequent presence of an ellipsoidal opening. Eisenack et al. (1973) transferred Baltisphaeridium escobaides to the genus Multiplicisphaeridium, noting the presence of a pylome. Later, Daners et al. (2017) reassigned Multiplicisphaeridium escobaides to the genus Pyloferites due to the presence of the pylome. However, they retained Pyloferites pentagonalis, described by Quadros (1999), as a separate species. Daners et al. (2017) recorded P. escobaides in Pragian-Emsian strata of the Paran a Basin in Uruguay.
The specimens from the Brazilian part of the Paran a Basin studied herein display a variety of morphologies that enable their inclusion in the genus Pyloferites. The aim of this contribution is to comprehensively analyse the morphological variability of the specimens herein assigned to the genus Pyloferites, and using statistical methods, to determine whether it corresponds to intraspecific variability within Pyloferites escobaides emend. nov. or indicates more than one species. Accordingly, the genus Pyloferites is emended, and the species already assigned to the genus are discussed, and synonymised. The stratigraphical range and geographical distribution of the genus are also reviewed in order to understand its biostratigraphical and palaeobiogeographical potential. maceration techniques (Traverse 2007). The residues were oxidised with a Schulze solution [nitric acid (HNO 3 ) þ potassium chlorate (KClO 3 )] and then screened on a 12 lm sieve.
Specimens of the genus Pyloferites were measured, and light photomicrographs were taken under Nomarski differential interference contrast illumination with an Olympus BX51 microscope and an Infinity 1 digital camera. Specimen locations are referred to in the text and plate captions using England Finder coordinates, which are given in parentheses. The palynological slides are housed in the EDDy Lab/Palynology repository. Sample numbers are detailed in Figure 1.
The following morphological variables were considered for bivariate and multivariate statistical analyses: length, width, and number of processes, type of ramification (digitated, second order, third order), vesicle major and minor diameter, wall ornamentation (psilate, scabrate, striate), pylome diameter, and the presence or lack of a thickened rim surrounding the pylome. Principal component analysis (PCA) was applied to the dataset of morphological variables measured from 181 specimens, recorded throughout the section, to display relationships among specimens. Additionally, a linear regression analysis, using InfoStat V R 2018 (Di Rienzo et al. 2018), was performed to identify any relationships among the morphological variables. Histograms, including kernel density plots, were performed for the width and length of the processes, using the software PAST (Harper 1999;Hammer et al. 2009). These morphological variables are the ones that best support a separation into two species.

Results
Taking into account all measured features, the PCA biplot does not contribute to a separation into two species. The first two principal component axes represent 24.9% and 18.5%, respectively, of the variance (Figure 3). However, a new PCA was conducted considering only the width and length of the processes, and the analysis showed that these two parameters were the most appropriate characteristics with which to separate the specimens into two species. The  first two principal component axes represent 61.3% and 38.7%, respectively, of the variance ( Figure 4). Aditionally, the histogram of process width shows a bimodal pattern that allows us to differentiate the Pyloferites escobaides emend. nov. population with thinner processes from the P. paranaensis sp. nov. population with broader processes (Figure 5, 1). The histogram of process length, however, shows more variability. A bimodal distribution can be observed and enables a separation between specimens with processes longer than 5 lm (P. escobaides emend. nov.) and those with processes shorter than 5 lm (P. paranaensis sp. nov.) ( Figure 5, 2). The species are described in detail below.
The regression analysis of the various morphological characteristics does not reveal a clear relationship, since the linear correlation analyses are not statistically significant (p > .05). As an example, the presence of a thickened rim around the pylome is not generally related to either the size of the vesicle or its ornamentation. Nevertheless, there is an expected linear correlation between the diameter of the vesicle and the diameter of the pylome (p < .0001). Interestingly, the most remarkable relationship is a weak positive linear regression between the width of the processes and the presence of a thickened rim around the pylome (p < .0001) (Figures 6 and  7). The data supporting the findings of this study are available within the article and the Supplementary material.
Original diagnosis (Quadros 1999, 19). Vesicle approximately pentagonal in outline, psilate or slightly micropunctate; pylome in the proximal face, occupying from the central part up to 2/3 of the central body. The processes, perfectly differentiated from the central body, extend radially from the pentagon angles, and freely communicate with the vesicle cavity. In addition to these processes, other processes may also occur, irregularly distributed on the distal and proximal faces, giving a total of eight to 10 processes. They are branched up to second or third order. (Translated from the original diagnosis in Portuguese.) Emended diagnosis. Vesicle of variable shapetriangular, square, polygonal, or roundedwith three to 23 processes. Process hollow, freely communicating with the vesicle cavity, broad-based and terminally digitated or branched up to third order. In some cases, the junctions of the process bases define the vesicle shape; processes can be arranged around the pylome or irregularly on the vesicle. Occasionally, processes are short (up to 10% of the vesicle diameter), simple, with rounded tips or digitated from or beginning very close to their bases. Vesicle wall 1-1.5 lm thick, psilate, slightly microspinose, and/or finely striate. Excystment by a rounded to elliptical, frequently deformed pylome that encompasses 75-95% of the vesicle diameter. Around the pylome, a thickened rim 1-2 lm thick may be present.
Plates 1-3 Figure 3. Principal component analysis (PCA). P. length: length of processes; p. width: width of processes; p. ramification: type of ramification (digitate, second order, third order); p. number: number of processes; major diam.: vesicle major diameter; minor diam.: vesicle minor diameter; w. ornamentation: wall ornamentation (psilate, scabrate, striate); py. diameter: pylome diameter; thickened rim: presence or lack of a thickened rim surrounding the pylome. Original diagnosis (Cramer 1964, 294). 'Central body and basal part of the processes hollow, moderately thin walled and transparent. The walls are psilate at Â1200 magnification. The processes have very broad bases giving the central body a roughly polygonal form. The processes may be bifurcated several times at the top; the final parts of the processes are solid. A round to ellipsoidal opening is often present. Number of processes in optical section 5 to 10 (7)'.
Emended diagnosis. Vesicle polygonal to rounded, bearing three to 20 broad-based processes, hollow, freely communicating with the vesicle cavity, distally digitated or irregularly branched up to third order. In some cases, the confluence of the process bases defines the vesicle shape. Processes are disposed around the pylome or irregularly distributed on the vesicle. Sometimes, the branches arise close to the base. Vesicle wall 1-1.5 lm thick, slightly microspinose and/or scabrate, frequently finely striate. Excystment by a circular to elliptical, frequently deformed pylome that encompasses 75-95% of the vesicle diameter. Around the pylome, there may be a rim 1-2 lm thick.
Distribution. Pragian-Emsian of the Cantabrian Mountains, Spain (Cramer 1964 Discussion. Pyloferites pentagonalis was described by Quadros (1999) for the Upper Devonian of Brazil, and Multiplicisphaeridium escobaides was described by Cramer (1964) for the Lower Devonian of Spain. Although these   authors illustrated quite different morphological entities, the specimens of the Jaciara section studied herein evidence wide intraspecific variability, including forms displayed by both these authors and a complete gradation between them. This justifies the integration of them all into a single species, with the specimens illustrated by Quadros and Cramer as possible extreme representatives of a single taxon. Furthermore, the different morphologies were recorded in almost all the samples of the Jaciara section, thus suggesting that the variability of the species is stratigraphically   independent. Wicander et al. (2011, 79) also observed the similarity of the two taxa, informally considering them synonyms: 'Pyloferites pentagonalis (¼ Multiplicisphaeridium escobaides Cramer 1964)'.
2013 Multiplicisphaeridium escobaides Cramer 1964, Grahn et al.: 39, pl Diagnosis. Vesicle polygonal to rounded. The base of the processes is markedly broad, with no clear differentiation from the central body. Processes can be arranged around the pylome or irregularly distributed on the vesicle. Processes hollow, freely communicating with the vesicle cavity, frequently digitate. Vesicle wall psilate, slightly microspinose and/or ornamented with fine striation. Excystment by a large pylome. A thickened rim may be present around the pylome.
Description. Vesicle triangular, polygonal, or rounded, with three to 23 processes (frequently around seven). The confluence of process bases may define the vesicle shape. Processes hollow, freely communicating with the vesicle cavity, broadly based, often wider than long, distally branched up to second order or digitate. Short processes (up to 10% of the vesicle diameter) are digitated from or very close to their bases, or rarely simple, with rounded tips. Processes can be arranged around the pylome or irregularly distributed on the vesicle. Vesicle wall 1-1.5 lm thick, slightly microspinose and/or finely striate. Excystment by a broad rounded to elliptical pylome, sometimes surrounded by a rim 1-2 lm thick.
Comparison. Pyloferites escobaides has longer processes than P. paranaensis that are never broader than they are high. The genus Papulogabata presents a discoidal thickening on the vesicle, which is opposite to the cyclopyle (Playford and Dring 1981). Nanocyclopia has a smaller pylome in relation to the vesicle diameter; the vesicle is always rounded, without processes.
Distribution. Pyloferites paranaensis sp. nov. is only recognised in the Paran a Basin of Brazil and Uruguay, from the parastratotype section of the Ponta Grossa Formation, Tibagi-Telêmaco Borba section (Grahn et al. 2013), as reworked from Devonian rocks in the Permian of the Paran a Basin, Uruguay (Guti errez et al. 2015).
Discussion. Pyloferites paranaensis specimens from the lower levels of the Jaciara section have fewer processes and, in general, simpler branching types (e.g. specimens illustrated in Plate 4). Specimens with more processes and those that are more digitated tend to be more frequent towards the upper part of the section (e.g. Plate 6, figures 1, 3, 7, 15). Although some specimens could be considered transitional forms between P. escobaides and P. paranaensis (e.g. Plate 1, figure 11; Plate 2, figure 18; Plate 3, figure 6), their processes are longer than those of P. paranaensis and are also longer than they are wide.

Discussion
According to the morphometric analysis carried out in this contribution, a wide intraspecific variability was recognised and all forms were grouped into two species. Taking into account all previous records, both species are present from the middle or late Pragian, and the record of P. escobaides emend. nov. now extends to the Famennian (Quadros 1999). The morphology of P. escobaides emend. nov. seems to be more variable in the Lower Devonian, while the Upper Devonian records of the species exhibit vesicles that are mostly pentagonal to square in outline (Quadros 1999;Wicander et al. 2011;Lakin et al. 2021). Towards the end of the Devonian, global palaeoenvironmental changes took place, which could have driven morphological changes in P. escobaides. However, the Late Devonian records are still scarce, and more research is needed before a conclusive interpretation can be reached. The Jaciara section was deposited under shallow-platform conditions in a progressive flooding model, in which three facies associations, organised in four metre-scale coarseningupwards cycles limited by flooding surfaces, were recognised (Garc ıa Muro et al. 2020 and references therein). Pyloferites escobaides emend. nov. and P. paranaensis sp. nov., as well as all their morphological varieties herein analysed, were recorded in all the outcrop samples except for sample 23, where no representatives of the genus were found ( Figure  2). Thus, the intraspecific variability and the different species of Pyloferites do not seem to be ecophenotypic responses to locally varying ecological conditions. In fact, they appear to evidence high adaptability to a changing environment represented by coarsening-upward cycles limited by flooding events. Additionally, both species, with representatives of all transitional morphologies, were documented in the southern and northern parts of the Paran a Basin, with different sedimentological histories during most of the Devonian Period (e.g. Grahn et al. 2010b;Rodrigues de Vargas et al. 2020; and references therein). More detailed palynological contributions on the Brazilian and other Gondwanan basins are needed to corroborate the stratigraphical ranges of both Pyloferites species, and their morphological variability over time.
Even though the stratigraphical distribution of the genus Pyloferites apparently spans almost the entire Devonian, it is not a common taxon in acritarch assemblages. According to Cramer (1964), Baltisphaeridium escobaides is rarely recorded in the Pragian-Emsian of the La Vid Shale Member (Spain). Daners et al. (2017), who proposed a new combination for the species, measured only three specimens from the Pragian-Emsian of the Paran a Basin, in Uruguay, without specifying whether this low number of specimens was due to their rare occurrence. Quadros (1999), who created the monospecific genus Pyloferites, with P. pentagonalis as its type species (herein interpreted as a junior synonym of B. escobaides Cramer 1964), only measured four specimens recorded from the Famennian strata of the Amazon Basin. Lakin et al. (2021) mentioned the uncommon presence of 'P. pentagonale' in the Late Famennian of Bolivia.
Pyloferites escobaides emend. nov. and P. paranaensis sp. nov. are particularly frequent in the late Pragian-Emsian of the Jaciara section herein studied. Large populations of both species were found, which allowed us to measure 181 of the better preserved Pyloferites specimens for the morphometric analysis. The overrepresentation of Pyloferites in the Jaciara section, compared with its presence in other localities, may be due either to particular ecological or taphonomic conditions in the studied area, or to the scarcity of detailed taxonomic investigations of Devonian organic-walled phytoplankton from other regions of Gondwana, particularly South America and Spain. Notably, this taxon has not been recorded from North Gondwana (North Africa, Saudi Arabia), where Devonian acritarch assemblages have been extensively studied (e.g. B€ ar and Riegel 1974; Jardine et al. 1974;Moreau Benoit 1984;Le H eriss e 2002;Bougara et al. 2017). This is also the case for other Gondwanan taxa, such as Bimerga and Cordobesia, that are restricted to South American basins (e.g. P€ othe de Baldis 1977;Wood 1995;Daners et al. 2017;Garc ıa Muro et al. 2017, 2018 andreferences therein;Rubinstein et al. 2018).
The presence of P. escobaides emend. nov. in Bolivia, Brazil, and Uruguay suggests a Gondwanan distribution for this species. Its record in the Lower Devonian of Spain (Armorica) supports its connection with Gondwana. It also suggests that there were probably no significant barriers between Armorica (formerly a Perigondwanan terrane) and Gondwana at that time, possibly because the Palaeotethys Ocean that separated them had only recently begun to open up (Torsvik and Cocks 2013). Records of P. escobaides from the Middle and Late Devonian are restricted to Gondwana, probably because Armorica was moving away from Gondwana during this period. The highly diverse and very well-preserved organicwalled phytoplankton assemblage from Devonian sediments of the Jaciara section (unpublished data), together with spores (Garc ıa Muro et al. 2020), also supports close palaeogeobiographical relationships with other Devonian South American basins in Brazil, Argentina, Bolivia, and Uruguay.

Conclusions
The genus Pyloferites is emended in the light of its abundance and high variability recognised in the Lower Devonian Jaciara section, Paran a Basin, Brazil. Statistical analyses of the morphological variables allowed us to distinguish two species: Pyloferites escobaides emend. nov. and Pyloferites paranaensis sp. nov. Pyloferites escobaides emend. nov. displays a South American distribution from the middle-late Pragian to the Famennian, while it is constrained to the Lower Devonian in Spain. This species exhibits a wide morphological variability in the Lower Devonian. However, it seems to evolve morphologically into a square or pentagonal shape towards the Upper Devonian. The presence of P. escobaides in Spain, restricted to the Lower Devonian, could be related to the separation of Armorica from Gondwana during the Middle-Late Devonian. Pyloferites paranaensis sp. nov. shows a more restricted stratigraphical and geographical distribution, from the late Pragian to possibly the middle Emsian in the Paran a Basin. In summary, the genus Pyloferites proves to be a useful biostratigraphical and palaeobiogeographical marker for the Devonian, especially for west Gondwana.