Article number: 24.3.a28
Copyright Paleontological Society, September 2021
Submission: 13 July 2020. Acceptance: 4 September 2021.
Two new genera have been identified in the Permian of Mexico: cf Bjuvia and Nilssonia. Along with previously-known Taeniopteris, these confirm the presence of Cycadophytes in the upper Paleozoic of Mexico. This substantially increases the geographical and temporal distribution of this group and provides information on the type of environment in which these plants developed. The new reports come from two localities of the Matzitzi Formation, in the state of Puebla, Mexico, called Carretera (Ca) and Coatepec (Co). In the first locality, we identified material characterized by the presence of a simple leaf of large size with veins perpendicular to the rachis and always parallel, as well as a stomatal apparatus with papillae. The fragmentary nature of the material from Puebla allows only an affinity to Bjuvia of the order Cycadales. Other specimens are assigned to Taeniopteris and Nilssonia. The Nilssonia reported from Carretera, has a segmented lamina attached to the rachis on the upper side. Taeniopteris is characterized by an entire lamina, generally narrow, with veins originating perpendicularly to the rachis that dichotomizes one or several times. The species T. lentriculiformis and T. crassinervis are reported for the first time from Coatepec. Together with these genera, the orders Equisetales, Gigantopteridales, Glossopteridales, Lepidodendrales, Marattiales, Osmundales, Peltaspermales, and Voltziales were also identified. Future studies will aim to confirm the taxonomic affinity of these leaves.
Miguel Angel Flores-Barragan. Paleontology collection, Facultad de Estudios Superiores, Zaragoza, Universidad Nacional Autónoma de México, Guelatao avenue, Ejército de Oriente, Iztapalapa town hall, Mexico City, 09230, Mexico. Posgrado en Ciencias Biologicas, Universidad Nacional Autónoma de México, Mexico City, 04510, Mexico.
María Patricia Velasco-de Leon. Paleontology collection, Facultad de Estudios Superiores, Zaragoza, Universidad Nacional Autónoma de México, Guelatao avenue, Ejército de Oriente, Iztapalapa town hall, Mexico City, 09230, Mexico.
Keywords: upper Paleozoic; taxonomy; Cycadophyte; Taeniopteris
Final citation: Flores-Barragan, Miguel Angel and Velasco-de Leon, María Patricia. 2021. New records of Bjuvia and Nilssonia from the Permian of Mexico. Palaeontologia Electronica, 24(3):a28. https://doi.org/3447-cycadophytas-of-the-permian
Copyright: September 2021 Paleontological Society.
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Mexico has an extensive plant fossil record that spans from the Paleozoic to the Cenozoic (Silva, 1970, 1984; Velasco-de León and Ortiz-Martínez, 2010). In Mexico, the Paleozoic flora is represented in the Matzitzi (Puebla), Patlanoaya (Puebla), Paso Hondo (Chiapas), and the Tuzancoa Formations (Hidalgo) (Silva, 1970; Rosales-Lagarde et al., 2005; Ramos-Arias et al., 2007). Undoubtedly, the most studied and best known is the Matzitzi Formation, which has been analyzed intermittently since the middle of the century. Silva (1970) conducted the first paleobotanical study in this formation, where she described 25 plant species (mostly Lepidodendrales and Calamitales). Later, Reinhard Weber (1997) described a new genus, Lonesomia Weber of the order Gigantopteridales.
Magallón-Puebla (1991) conducted a morphological analysis of the Marattiales and described Fascipteris Gu et Zhi, which is currently known to correspond to Diplazites Goeppert (Cleal, 2015). Galván (2000) accomplished a paleobotanical study in Los Reyes Mezontla and Santiago Coatepec, Puebla, and recorded nine genera and 13 species, including new records of Annularia Sternberg, Sphenophyllum Brongniart, and Taeniopteris Brogniart.
Reports of possible cycadophytes for the Matzitzi Formation are scarce, with only one report of the fossil taxon Taeniopteris sp. (Galván, 2000, figure 19). The author mentions 18 specimens collected between the towns of Los Reyes Mezontla and Santiago Coatepec, Puebla. However, the description is poor, as well as the quality of the figures, which does not allow the observation of diagnostic characters and raises doubts about identification of the material as Taeniopteris.
We use the concept Cycadophyta in the sense of Pott et al. (2012), which refers only to the degree of leaf organization (type of leaf, margin, and venation) and does not imply a phylogenetic relationship. This is because the lack of characters, such as type of stomata or reproductive structures in most cases, complicates the specific assignment of the leaves to any orders of the Cycadophytes.
The Matzitzi Formation crops out in the north area of the state of Puebla and has an estimated thickness of 600 m (Figure 1A-B) (Calderón-García, 1956). There are still inconsistencies regarding its age, where assignment has varied from the upper Carboniferous (Silva, 1970), to the lower Permian (Weber et al., 1987), and to the upper Permian (Flores-Barragan, 2019). We agree with the proposal of the study from 2019 that considers our specimens as late Permian in age.
Sedimentological studies have proposed an anastomosed fluvial facies model with up to six facies associations (Centeno et al., 2009). The material examined in the present work belongs to two localities: Carretera and Coatepec (Figure 1C-D). The first one is located at kilometer #89 of the Tehuacán-Oaxaca federal highway, Mexico, and the second is located on the outskirts of the town of the same name (Santiago Coatepec, Puebla, Mexico).
MATERIALS AND METHODS
We conducted five visits to the localities of Carretera (Ca) and Coatepec (Co), where we collected a total of 497 specimens. The fossils are impressions in a lutite of fine- to medium-grained sandstone. The stratigraphic horizon was recorded for each specimen. The material is stored in the Paleontological Collection of the Facultad de Estudios Superiores Zaragoza of the National Autonomous University of Mexico under the acronym (CFZ-MTZ).
In order to obtain more precision in the morphological characters, which are of great importance for the identification (Artabe, 1985; Remy and Remy, 1975), we made detailed measurements of the specimens in the program Image J (version 1.8.0.). We also obtained cuticle using cellulose acetate peel as well as dispersed cuticles (Kerp, 1990; Kouwenberg et al., 2007) for fossils that were lustrous or carbonized. The cuticles were photographed with an Olympus E-620 camera and observed under an Olympus bx41 microscope for their description and measurement.
The taxonomic assignment is based on studies that used the morphological characters of the lamina, including Remy and Remy (1975), Artabe, (1985), and Van Konijnenburg-van Cittert et al. (2017).
In the Carretera locality, we measured a stratigraphic section of 24.5 m. At its base, there are 3.5 m of strata with a grain size of fine- to medium-grained sandstone and parallel lamination. The next 21 m are composed of medium-grained sandstone, with parallel, cross-planar, and ripple stratification. Between the sandstone strata, there are rock packages of up to 1 m in thickness with finer lithology (siltstone and lutite), and in this location is where most specimens were collected (Figure 2A).
In the Ca locality, we identified a total of 164 specimens, belonging to six different orders: Lepidodendrales, Equisetales, Marattiales, Glossopteridales, Peltaspermales, Voltziales, and Incertae sedis. Four of these orders had already been reported for this formation (Silva, 1970; Weber, 1987; Galván, 2000), and we add two new reports to these lists: Glossopteridales and Voltziales (Table 1).
In the Coatepec locality, we measured a stratigraphic section of 150 m. In the first 28 m, there is an alternating sequence of sandstone and lutite with plant fossils. Above this sequence, there is 52 m of massive strata of fine- to coarse-grained sandstone. Above this section, there are massive strata of conglomerates supported by matrix and round, with a thickness of 70 m (Figure 2B).
In this locality, we identified 333 specimens, belonging to nine orders Lepidodendrales, Equisetales, Osmundales, Marattiales, Glossopteridales, Gigantopteridales, Peltaspermales, Cycadales?, Voltziales, and one insertae sedis, being the possible Cycadophyte, which is our new record for this formation (Table 1).
Below we describe the new reports of Cycadophytes at the genus and/or species level for the Matzitzi Formation.
Class CYCADOPSIDA Brongniart, 1843
Order CYCADALES Dumortier, 1829
Genus BJUVIA Florin, 1933
cf. Bjuvia sp.
Material. CFZ-MTZ540, 551, 583.
Description. Entire lamina, lanceolate, with entire margins, the rachis is prominent and longitudinally striate; veins are fine, numerous, simple, and emanate perpendicularly from the rachis. Irregular to square and/or rectangular epidermal cells have generally straight walls. The stomata are arranged in irregular rows; stomatal apparatus is protected by simple digitate papillae.
Given the large size of the lamina, all specimens are preserved as fragments, with the best-preserved specimen measuring 15.0 cm in length and 18.55 cm in width at the mid-part (Figure 3A). The width of the leaf gradually decreases towards the apex and the base (Figure 3B). The shape of both is unknown. A rachis running along the lamina is longitudinally striated and 0.55 cm wide (Figure 3C). The leaf is laterally inserted into the rachis. The veins are perpendicularly inserted into the rachis. This venation is simple and has a density of 33 to 40 veins per centimeter in the proximal part to the margin (Figure 3D); the number of veins is constant along the entire lamina.
In the adaxial cuticle, the epidermal cells are rectangular to irregular in shape 80 to 90 µ long and 8 to 10 µ wide, with straight to slightly undulated anticlinal walls, 1 to 2 µ thick (Figure 3E). Crest distance is 6 to 8 microns, with a height of 3 microns. The epidermal cells are arranged parallel to the venation and also exhibit simple trichomes of up to 15 microns in length (Figure 3I).
In the abaxial cuticle, there are also irregular to square and/or rectangular epidermal cells, with straight anticlinal walls and a size between 50 and 100 µ (Figure 3F). The stomatal aperture is 10 to 15µ wide with 6-7 subsidiary cells on both sides surrounding the stoma. Four papillae are observed, which protrude from the stomatal aperture (Figure 3G and J). The stomata are arranged in irregular rows (Figure 3H).
Remarks. Entire leaves attached to a central rachis that lack epidermal and reproductive characters are generally located in the fossil taxon Taeniopteris (Van Konijnenburg-van Cittert et al., 2017). In this case, we observe seven subsidiary cells. The shape of the epidermal cells, the presence of trichomes, and the absence of dichotomies in the veins also suggest Bjuvia. Nevertheless, it is necessary to obtain better preserved material in order to be certain; thus, we consider the specimens CFZ-MTZ540, 551, and 583 as cf. Bjuvia sp.
Thus far, there are only three species of this genus, all located in the Triassic of Europe. Bjuvia simplex Florin is characterized by having large leaves of up to 1 m in length and a venation density of 12-14 veins per cm; the venation can dichotomize at the base of the veins. Even though the size of the specimen studied here is incomplete, the venation density completely differs from that observed in B. simplex. The same occurs with the species B. dolomitica Wachtler et Van Konijnenburg-van Cittert, which only has 14-18 veins per centimeter, as well as a larger leaf width and a thicker rachis with a constant width. Regarding the third species, B. thalensis Kustatscher et Van Konijnenburg-van Cittert, though it has a size relatively similar to that of the specimen from Puebla, it also differs in the venation density, as well as in the width of the rachis (Table 2).
In the case of the epidermal characters of the genus, the three reported species exhibit haplocheilic stomata, amphistomatic leaves, rectangular or square epidermal cells, and stomata generally in irregular rows with subsidiary cells and, in some cases, with papillae. The specimen from Puebla is similar to Bjuvia simplex in the shape of the abaxial epidermal cells, the size of the stomatal aperture, number of subsidiary cells and the presence of trichomes (Barbacka, 2001). With B. dolomitica it shares the characters of the adaxial cuticle, since both have rectangular to irregular epidermal cells with straight to slightly crenulated walls (Wachtler and Van Konijnenburg-van Cittert, 2000). Finally, with B. thalensis it shares the presence of papillae in the stomatal apparatus (Kustatscher and Van Konijnenburg-van Cittert, 2010).
Order INCERTAE SEDIS
Genus NILSSONIA Brongniart, 1825
Description. Leaf pinnate (segmented) is subdivided into numerous, regular oppositely positioned segments. The leaf is 6.3 cm long and 4.7 cm wide in the middle part. It has segments with a constant width from 1 to 1.2 cm wide at the base, and the leaf apex is unknown. The distance between the segments is relatively constant at about 0.2-0.3 cm. The lamina is attached to the upper edge of rachis and is completely covered by the rachis, which can measure up to 0.3 cm in width. The venation of the segments is inserted at an angle of 80-90°. The veins can dichotomize near the base then become parallel with a density of 12 to 17 veins per cm in the proximal part to the margin.
Remarks. Segmented leaves have been reported for the Permian from different parts of the world, such as Pterophyllum cotteanaum Gutbier from the lower Permian of Germany (Barthel et al., 2010), Pseudoctenis middridgensis Stonley from the upper Permian of England (Stonley, 1958), and/or Pseudoctenis samchokense, Kawasaki from the upper Permian of China (Pott et al., 2010). However, in these cases, the lamina segments are laterally attached to the rachis and are not similar to the Puebla specimen (Table 3). The leaf described in the present work is assigned to Nilssonia based on the leaf lamina clearly being attached to the upper edge of the rachis (Van Konijnenburg-van Cittert, et al., 2017). Nilssonia has some records for the upper Paleozoic (Tian and Zhang 1980; He et al., 1996), and the first reliable reports are from the Triassic. The species Nilssonia sturii Krasser from the upper Triassic of Austria (Pott et al., 2007) evinces some similarity to the specimen from Mexico but differs from it by having a lower number of veins, as well as the presence of dichotomies in the Mexican specimen.
It is important to mention that the dichotomies in the veins in the genus Nilssonia are not common in species from the Northern Hemisphere, but are common in species from Gondwana (Holmes et al., 2010). Therefore, it is not comparable to other species described for the Triassic of Europe (Barbacka, 2001; Kustatscher and Van Konijnenburg-van Cittert, 2010).
Genus TAENIOPTERIS Brongniart, 1828
Taeniopteris lentriculiformis (Etheridge) Walkom, 1917
Description. Entire lamina, with entire margins, probably oblong in shape, leaf width appears to be constant. The apex and base are not preserved. The leaf is 4.1 cm long and 2.5 cm wide. The lamina attaches laterally to the rachis. The rachis is slim, retaining its width throughout the whole leaf with a maximum width of 0.2 cm. The fine veins emanate from the rachis at 90°. The venation is simple, rarely dichotomous, with a density of 23 to 24 veins per cm at the middle-part of the leaf.
Remarks. Given the general morphology of the leaf, this specimen resembles an isolated pinna of the genus Danaeopsis Heer ex Schimper. However, this taxon is characterized by having strong secondary veins that anastomose near the margin. Even though there are species that can lack anastomoses, such as D. angustifolia and D. fecunda (Kustatscher et al., 2012a), the differences in leaf size, vein angle, and venation density do not allow assignation to these species. In addition, the lack of compound leaves and/or sporangia that determine the affinity of these specimens makes their comparison with this genus impossible. For this analysis, the specimen from Puebla was compared with 42 species of the fossil taxon Taeniopteris described for the Permian-Triassic (Table 4). The observations indicate a higher similarity with the species Taeniopteris lentriculiformis, which is characterized by the near absence of bifurcations in the veins. Yet the size of its lamina is comparable to that of T. vittata Brongniart, it does differ due to the lower venation density of T. lentriculiformis (Artabe, 1985). This species has been reported for the Triassic of Argentina, New Zealand, and Australia (Artabe, 1985; Rettallack, 1985).
Taeniopteris crassinervis (Feistmantel) Arber, 1917
Description. Entire lamina, with entire margins, 6.8 cm long and 5.3 cm wide at the mid-part. The leaf width appears to be constant. The shape of the base and apex are unknown. Undulations are observed in the lamina, which could be the result of desiccation and/or the fossilization process. The lamina attaches laterally to the rachis. The rachis is slim, retaining its width throughout the whole leaf with a maximum width of 0.3 cm. The veins emanate from the rachis at 90°. This venation divides at the proximal part of the rachis and then becomes parallel along it. It can have a density of up to 14 to 16 veins per centemeter at the mid-part of the leaf.
Remarks. After comparing it with 42 different species of the genus (Table 4), the specimen from Puebla was assigned to the species Taeniopteris crassinervis, since it exhibits strong veins with a similar venation density and perpendicular angle at which they are inserted regarding to the rachis. Another diagnostic characteristic of this species is the dichotomy of the veins in the contact area with the rachis (Figure 4E). This species has been reported for the Triassic of Argentina (Artabe, 1985), United States, India, Australia, New Zealand, and Africa (Beherensmeyer and Turner, 2019). This new report would correspond to the most southern record of North America.
The importance of epidermal characters has been emphasised for the taxonomic assignment of different plant groups, e.g., Cycadales (Pott et al., 2010). However, the cuticle is not always preserved since it depends on the fossilization process and the texture of the leaves. In most localities of Mexico, the preservation of cuticle in fossils is rare. There are reports of cuticles from the Permian of Hidalgo for the genera Taeniopteris and Comia Zalessky (Velasco et al., 2020). There are also informal records from the Jurassic, in the states of Puebla and Oaxaca, for some Bennettitalean genera: Zamites Brongniart and Otozamites Braun (Silva, 1969; Ortiz-Martínez, 2014). We add to these reports the cuticle obtained from the specimen of cf. Bjuvia sp., from which we were able to observe stomata and epidermal cells.
The genus Bjuvia has simple leaves, entire margins, rachis that runs through the entire lamina and veins almost perpendicular concerning to the rachis. The veins, most always, are not dichotomous. Based on the epidermal characteristics (haplochelic stomata), its assignment to the order Cycadales has been proposed (Wachtler and Van Konijnenburg-van Cittert, 2000). This genus has a stratigraphic range from the Triassic to the Jurassic. There are three described species thus far (Wachtler and Van Konijnenburg-van Cittert, 2000; Barbacka, 2001; Kustatscher and Van Konijnenburg-van Cittert, 2010), which completely differ from the specimen from Puebla. However, this assignment can only be corroborated by obtaining more cuticle fragments, which would be of great importance since they would confirm the geographic and temporal extension of this genus to the Permian of North America.
With regard to Nilssonia, there are other genera of Cycadophytes that have a segmented lamina, e.g., Pseudoctenis Seward, which differs from Nilssonia in having leaves laterally inserted into the rachis, never dorsally (Pott et al., 2010), and Ctenis Lindley et Hutton, which has an anastomosing venation (Pott et al., 2007). Given the insertion of the lamina into the rachis and the type of venation, it is possible to assign the specimen from Mexico to the genus Nilssonia. Nevertheless, poor preservation precludes proposing a new species or assigning it to an existing one.
From the Matzitzi Formation, we also studied leaves with an entire margin, a rachis, and less than 5 cm in width. We assigned these to Taeniopteris. However, it must be clarified that, thus far, Taeniopteris is considered an artificial genus with different taxonomic affinities and that should only be used for leaves that lack cuticular characters, which could ensure the taxonomic identity of the leaves (Pott and Launis, 2015). Thus, in the present work, they were not assigned to any order and remain in the category of Incertae sedis. Yet, the presence of two new reports for the Permian of Mexico is of great importance since, in addition to the record of Taeniopteris cf. T. magnifolia from the lower Permian of the state of Hidalgo, Mexico (Velasco et al., 2020), they confirm the presence of this morphotype of leaves in Mexico. These new reports demonstrate that only a few formal taxonomic studies have been conducted in the Matzitzi Formation. Therefore, the knowledge of the taxonomy is alpha level sensu Anderson and Anderson (2003).
The record of Taeniopteris cf. T. magnifolia occurs in a humid environment with periods of hydric stress in the Tuzancoa Formation (Velasco et al., 2020), which have characteristics very similar to those proposed for the Matzitzi Formation, where there is a mixture of both hygrophylic elements and those better adapted to water scarcity (Flores-Barragan, 2019). We propose that, in Mexico, this genus appears to be present at the end of the Paleozoic in environments with variable climate and intermittent periods of hydric stress.
Looy et al. (2014) mention that derived genera (recent appearance), such as these types of Cycadophyte leaves, evolved under conditions of environmental drought. This could be the case of the localities from the Permian of Mexico, with the prevalence of a sub-humid environment with seasonal rainfall, which indicates hydric stress in some strata (Flores-Barragan, 2019; Velasco et al., 2020). This condition limited the fossilization of the leaves, resulting in a sparse fossil record for these genera compared to those that inhabited more humid places. This would explain the isolated (geographically) and intermittent (chronologically) reports of these types of leaves during the Paleozoic.
Localities with reports similar to those recorded here are located in the Triassic of Europe, specifically in the middle Triassic of Italy and Germany (Wachtler and Van Konijnenburg-van Cittert, 2000; Kustatscher and Van Konijnenburg-van Cittert, 2010). In Italy, there is a prevalence of conifers over other plant groups, which, together with taxonomic and geological data, is interpreted as an environment with a sub-humid climate (Kustatscher and Van Konijnenburg-Van Cittert, 2005). On the other hand, Germany is considered to have had a generally more humid climate due to the abundance of hygrophilic elements such as Marattiales (Kustatscher et al., 2012b). The material from these environments is not floristically comparible with the Matzitzi Formation for it exhibits an abundance of genera typical of the upper Paleozoic, such as Asterotheca Presl and Corda, Calamites Brongniart, Cyperites Lindley and Hutton, and Sigillaria Brongniart. It appears that taxa with morphology similar to Cycadophyta have been established in partially sub-humid environments since the Permian-Triassic transition.
In the present work, we propose a sub-humid environment based on the floristic elements. However, studies on the edaphic and taphonomic conditions are still necessary in order to better understand the depositional environments of the Matzitzi Formation that allowed the establishment and coexistence of different floristic elements. New records, such as those reported in the present work, are important to answer questions on environmental, taxonomic, and distributional aspects. For example, does Bjuvia or Nilssonia have an earlier origin than that estimated based on the records in the literature? And did they have a larger geographic distribution? Much remains to be discovered in the localities of the end of the Paleozoic in what is now known as Mexico.
The presence of cf. Bjuvia sp, Nilssonia sp., Taeniopteris crassinervis, and T. lentriculiformis makes the existence of Cycadophytes in the Permian of Mexico conclusive. These records increase the described diversity for the Matzitzi Formation and have an impact on the spatial and temporal distribution of these genera. This will help to determine their origin and diversification.
The results of this work are part of the doctoral thesis MAFB, and he gives thanks for support to Postgraduate in Biological Sciences (Posgrado en Ciencias Biologicas, Facultad de Estudios Superiores Zaragoza) of the Universidad Nacional Autónoma de México and the scholarship CONACyT 762406. We also appreciate D. Lozano-Carmona, E.O. Chavez, and E, Ortiz-Martínez for their help in the development of the field work. We also thank reviewers of this article Dr. M. Pole, Dra. E. Kustatscher, and the anonymous reviewer for the comments and observations that contributed to the writing.
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