Taphonomy and Palaeoenvironments a new early Permian Tetrapod fauna from Brazil

Abstract

The Early Permian Pedra de Fogo Formation of Brazil accumulated in a large intracontinentalsag-basin (Parnaíba Basin) located in sub-tropical Gondwana around 20oS(palaeolatitude). With progressive climatic drying, palaeoenvironments changed from a large,shallow lake to expansive exposed mudflats surrounding a shrinking lacustrine wetland,culminating in isolated playas fed by ephemeral streams which finally became an aeoliandune field.Our team has collected over 500 fossils from this formation in northeastern Brazil. Theyinclude actinopterygians, dipnoans and chondrichthyans, together with two fully-articulatedcoelacanths, at least four temnospondyl taxa (the archegosaurid Prionosuchus, thetrimerorhachid Procuhy, the dvinosaur Timonya, and a rhinesuchid), small-to-mid-sizedcaptorhinid reptiles (cf. Captorhinus/Captorhinikos), and a small parareptile, as well asabundant fish-scale bearing spiral coprolites.Three gradationally superimposed sedimentary facies associations are recognized in the Pedrade Fogo Formation: offshore lacustrine, shoreline/carbonate mudflats and finally anephemeral stream/dune complex. The taphonomic style of vertebrate fossils varies withdepositional facies reflecting different modes of post mortem burial.Offshore facies comprise thick beds of massive siltstone and finely-laminatedsiltstone/mudstone couplets showing algal crenulations but no infaunal burrowing, indicativeof an anoxic lake bed. Scattered actinopterygian fish skeletons with scales are rare, but somefine sandstone turbidite/inundate interbeds contain more fully-articulated aquatic tetrapods,some with soft tissue preservation, indicative of death and burial caused by storm induceddensity underflows.The carbonate mudflats facies association contains silicified algal-laminated limestonesdisplaying stromatolite mounds, tepee and desiccation structures typical of alkaline lakeshorelines. Clusters of coprolites and fish-hash lenses comprising masses of isolated teeth andscales are suggestive of heavy predation within drying ponds and channels.The ephemeral stream/dunite facies contains most of the plant material, mainly tree trunksand in places at the top of the formation rare 3-D petrifications of leaves and fructifications.We are revealing a previously unknown diversity of early Permian (+/-280 Mya) tetrapods inGondwana. While some aspects of the fauna (e.g., caporhinids, trimerorhcachids) are similarto those known from the classic Permian redbeds of the southwestern United States, thepresence of taxa such as rhinesuchids suggest that the Gondwanan tropics were an importantcradle of later Permo-Triassic biodiversity. Dvinosaurian temnospondyls were a majorcomponent of these Gondwanan tetrapod communities that originated, and diversified in andaround tropical saline to brackish water lakes and wetlands.