Mujal, Eudald

Tetrapod diversity in Permian terrestrial ecosystems of southwestern Europe is poorly recorded by bone specimens, but it is better represented by an important tetrapod ichnological record that is relevant to our understanding of vertebrate communities in the equatorial Pangaea. Herein, two tetrapod ichnoassociations from three new ichnosites, within Cisuralian and Guadalupian volcanosedimentary terrestrial successions (the Lower Red Unit and the Upper Red Unit deposits) of the Castellar de n’Hug sub-basin (Catalan Pyrenees, NE Iberian Peninsula) are presented. Tetrapod ichnology in combination with stratigraphic and facies analyses permit a characterisation of these ecosystems. The sedimentary deposits show an evolution from fluvial meandering systems to playa-lake floodplains, denoting increased aridification and seasonality under a monsoonal regime. The ichnofossil record shows how tetrapod assemblages shifted from a prevalence of non-amniotes and eureptiles to a dominance of therapsids, eureptiles and parareptiles. The reported ichnotaxa are distributed in two ichnoassociations. The first preserves Batrachichnus, Dromopus, Hyloidichnus, Characichnos and an indeterminate tetrapod morphotype, whereas the second is defined by the presence of Dromopus, Hyloidichnus, Brontopus antecursor and Pachypes. The stratigraphically older ichnoassociation, preserved in volcaniclastic and fluvial deposits, presents features of the early Erpetopus biochron, whereas the stratigraphically younger one, preserved in playa-lake deposits, is constrained to the Brontopus sub-biochron. Biostratigraphic and magnetostratigraphic data suggest a late Cisuralian to middle Guadalupian age for the whole succession. The ichnoassemblage highlights a palaeobiogeographical connection between the Pyrenean Basin and other peri-Tethyan basins, which allows us to expand our knowledge about the palaeoecology and palaeobiodiversity of the Cisuralian to Guadalupian terrestrial ecosystems.

The Cisuralian–Guadalupian (early–middle Permian) was a period of climate transition between the Carboniferous icehouse conditions to the latest Permian–Early Triassic hothouse. The landmasses had coalesced in the supercontinent Pangaea and the climate was progressively becoming more arid, especially in a belt over the palaeoequator. The deposits of present-day Mallorca (Balearic Islands, western Mediterranean) were located in those low palaeolatitudes, in the western margin of the Tethys Sea, and correspond to alluvial systems with meandering rivers. The present study divides the stratigraphic succession into three main units, formally described herein as the Bec de s’Àguila Formation, Port des Canonge Formation and Pedra de s’Ase Formation. Based on an exhaustive review of the literature and new magneto- and biostratigraphic data, the sequence has been dated between the early and middle Permian (Artinskian–Wordian). Moreover, the detailed study of the fossils has provided a complete account of the denizens of those ecosystems. Tetrapod tracks occur abundantly in the Port des Canonge Formation, with morphotypes attributed to moradisaurine captorhinid eureptiles, araeoscelidian diapsids/non-varanodontine varanopids, possible pareiasauromorph parareptiles, “pelycosaur”-grade synapsids and indeterminate synapsids. Spores and pollen grains from the Pedra de s’Ase Formation indicate an overall dominance of conifers, accompanied by sphenophytes, ferns and seed ferns. Overall, apart from providing the first detailed interpretation of the ecosystems of the Permian of Mallorca, these new data have made it possible to improve the characterisation of the Permian–Triassic tectonosedimentary cycle in the Balearic Islands, which contribute to the understanding of the evolution of the western peri-Tethys ecosystems.

Tetrapod ichnology is a powerful tool to reconstruct the faunal composition of Middle Triassic ecosystems. However, reconstructions based on a single palaeoenvironment provide an incomplete and impoverished picture of the actual palaeodiversity. In this paper, we analyse Middle Triassic tetrapod ichnoassociations from the detrital Muschelkalk facies of the Catalan Basin of northeast Spain, ranging from terrestrial to coastal settings. We identified two main tetrapod ichnoassociations, preserved in two different palaeoenvironments, comprising the following ichnogenera and morphotypes: Procolophonichnium, Chelonipus, Rhynchosauroides, Rotodactylus, Chirotherium, Isochirotherium, Sphingopus, and indeterminate chirotheriids. We also statistically analyse a database of all known Middle Triassic tetrapod footprint localities worldwide; this database includes, for each track locality, the precise age, the palaeoenvironment and the presence/absence of ichnotaxa. Our results on the composition of ichnofauna within the palaeoenvironments of the Catalan Basin are integrated into this database. This approach allows us to revisit the palaeoenvironmental bias linked to the marine transgression that affected the Western Tethys region. Tetrapod ichnoassociations reveal the following palaeoenvironmental patterns: (1) in coastal settings, ichnoassociations are Rhynchosauroides-dominated and diversity is relatively low; (2) in terrestrial settings and those with less marine influences, ichnoassociations are non-Rhynchosauroides-dominated, usually characterised by more abundant chirotheriid tracks and, generally, a higher track diversity. The correlation between tetrapod ichnoassociations and sedimentary facies reveals how palaeoenvironmental constraints influenced faunal assemblages, especially those of the Middle Triassic of the Western Tethys region. Ichnoassociations allow the ecological response of tetrapod faunas to the environmental changes to be inferred for this critical time interval. Marine transgressions strongly influenced tetrapod ecosystems: environmental conditions were key for the faunal recovery in the aftermath of the end-Permian extinction, with the settlement of the so-called modern faunas and the rise of the dinosaur lineage.

Ronchi et al. (in press) comment on the stratigraphic, sedimentological, mineralogical and palaeontological analyses performed in the recently described Coll de Terrers Permian–Triassic terrestrial succession from the Catalan Pyrenees by Mujal et al. (2017a). The comment debates our interpretation of a succession of red-beds as Permian (Upper Red Unit, URU). Instead, the comment infers that the analysed succession is part of the regional upper Buntsandstein facies unit (Triassic), debating the proposed stratigraphic scheme by using the tectonic evolution as the main argument. Here, we clarify and present more details on the interpretation published in Mujal et al. (2017a). Based on this clarification and taking into account the comment, we arrive to the conclusion that the interpretation and inferences presented in Mujal et al. (2017a) are sound and justified.

The Carboniferous–Permian terrestrial successions record a global climatic shift from icehouse to hothouse conditions. Our multidisciplinary study documents an aridification trend throughout the ~ 1000 m thick composite terrestrial succession of the western Catalan Pyrenees (NE Iberian Peninsula), representing this time period. The detailed stratigraphic framework integrates sedimentology, paleopedology, biochronology (plant fossils and tetrapod footprints) and geochronology (paleomagnetism). Additional absolute age correlation is also carried out. The new and reviewed data show that the late Carboniferous wet environments (with short drought periods) progressively changed to a strong seasonal semi-arid and arid climate (with short humid periods) through the early Permian. This paleoclimatic trend supports the previously suggested aridification of the Pangean pan-tropical belt, and supports the hypothesis of the influence of the recurrent climatic fluctuations in Central Pangea, being tentatively correlated to the Southern Gondwanan glaciation-deglaciation periods. Therefore, the Carboniferous–Permian terrestrial succession from the Catalan Pyrenees emerges as a continuous record that can help to constrain late Paleozoic paleoenvironmental events.

The most severe biotic crisis on Earth history occurred during the Permian–Triassic (PT) transition around 252 Ma. Whereas in the marine realm such extinction event is well-constrained, in terrestrial settings it is still poorly known, mainly due to the lack of suitable complete sections. This is utterly the case along the Western Tethys region, located at Pangaea's equator, where terrestrial successions are typically build-up of red beds often characterised by a significant erosive gap at the base of the Triassic strata. Henceforth, documenting potentially complete terrestrial successions along the PT transition becomes fundamental. Here, we document the exceptional Coll de Terrers area from the Catalan Pyrenees (NE Iberian Peninsula), for which a multidisciplinary research is conducted along the PT transition. The red-bed succession, located in a long E-W extended narrow rift system known as Pyrenean Basin, resulted from a continuous sedimentary deposition evolving from meandering (lower Upper Red Unit) to playa-lake/ephemeral lacustrine (upper Upper Red Unit) and again to meandering settings (Buntsandstein facies). Sedimentary continuity is suggested by preliminary cyclostratigraphic analysis that warrants further analysis. Our combined sedimentological, mineralogical and geochemical data infer a humid-semiarid-humid climatic trend across the studied succession. The uppermost Permian strata, deposited under an orbitally controlled monsoonal regime, yields a relatively diverse ichnoassemblage mainly composed of tetrapod footprints and arthropod trace fossils. Such fossils indicate appropriate life conditions and water presence in levels that also display desiccation structures. These levels alternate with barren intervals formed under dry conditions, being thus indicative of strong seasonality. All these features are correlated with those reported elsewhere in Gondwana and Laurasia, and suggest that the Permian–Triassic boundary might be recorded somewhere around the Buntsandstein base. Consequently, Coll de Terrers and the whole Catalan Pyrenees become key regions to investigate in detail the Permian extinction event and the Triassic ecosystems recovery.