Advances in the knowledge of the macroflora of the Tuzancoa Formation, Hidalgo, Mexico, lower Permian

Abstract

The paleoflora of the Tuzancoa Formation has been studied since the middle of the last century. However, the constant discovery of new floristic elements and/or localities makes it necessary to re-evaluate the current knowledge of the paleoflora of this formation. Therefore, the objective of this work is to present new paleofloristic reports of three localities of the Tuzancoa Formation, as well as to analyze their geographical and chronological distribution and their relationship with other contemporary floras of Mexico. The localities studied are named Calnali 2, La Virgen, and San Mateo 2, the latter being a new locality. In the first locality, six orders were identified (Equisetales, Glossopteridales, Lepidodendrales, Marattiales, Peltaspermales and Voltziales), while in The Virgin and San Mateo 2, four orders were identified (Equisetales, Lepidodendrales, Marattiales, and Peltaspermales). The new reports correspond to one family, two affinities, five genera, and seven species; of this set, five taxa stand out as new reports for the Mexican Republic and/or as taxonomically important, and these correspond to Majonicaceae, Odontopteris cf. Brardii, Mariopteris, Taeniopteris feddeni and T. tenuis. Majonicaceae is represented by a female reproductive structure probably related to the species Calnalia hidalguensis; Odontopteris cf. Brardii is a fern characterized by the absence of a middle vein in its pinnules; Mariopteris is a fern with pinnules with varying degrees of fusion; Taeniopteris feddeni corresponds to a large entire leaf, more than five cm wide with a density of 20 to 22 secondary veins per cm; finally, Taeniopteris tenuis is an entire leaf less than 5 cm wide that presents a unique arrangement in its secondary venation with a density of 28 to 30 veins per cm. These new findings substantially increase the floristic diversity of the formation and allow to establish, together with lithology, a transitional environment in Calnali 2 and a continental environment in La Virgen and San Mateo 2. The stratigraphic and distribution ranges of the taxa, suggest an age for the plant-carrying strata of the Pennsylvanian–lower Permian; in addition, an inferred geographical affinity with the Euromerican kingdom is considered. Finally, when comparing the floristic list of the Tuzancoa Formation with other contemporary units with reports of fossil flora such as Matzitzi (Mt), Paso Hondo (Ph), Olinalá (Ol) and Patlanoaya (Pt), a minimal similarity is observed for the latter (Po, Ol and Pt) due to the poor records in relation to the Tuzancoa Fm. Regarding the Matzitzi Formation, in this case the plants indicate characteristics of different environments: Continental and humid for Matzitzi, and transitional in the locality of Calnali of the Tezuncoa Formation, while in the locality of the Virgin and San Mateo the environment is sub-humid. All these new contributions help us to better understand the terrestrial ecosystems of the late Paleozoic in the western equatorial margin of Euromerica.