A tapinocephalid dinocephalian (Synapsida, Therapsida) from the Rio do Rasto Formation (Paraná Basin, Brazil): Taxonomic, ontogenetic and biostratigraphic considerations
Authors:
Boos et al
Abstract:
Permian tetrapod fossils have been recovered from the Rio do Rasto Formation of Brazil since the 1970s. Previous studies of this fauna indicated strong affinities with the Guadalupian-Lopingian vertebrates of South Africa and Eastern Europe, suggesting biostratigraphic correlations between these areas. Here, a new dinocephalian specimen from the Rio do Rasto Formation in the Serra do Cadeado area (Paraná State, Brazil) is described based on fragmentary skull remains and an associated left lower jaw ramus. Despite the fragmentary nature of these remains, they represent the most complete tapinocephalid specimen known from South America. Comparison with other tapinocephalids indicates that the material described herein represents a juvenile or sub-adult specimen. Although it is not possible to identify this material to the genus level, it most closely resembles the ‘moschopines’ Moschops and Moschognathus from the Tapinocephalus Assemblage Zone of South Africa. As dinocephalians are known to be restricted to the Guadalupian, they are one of the best tetrapod biostratigraphic markers for the Rio do Rasto Formation, indicating that at least some of the strata in the areas where they occur [Serra do Cadeado (Paraná State), Fagundes farm and Boqueirão farm (Rio Grande do Sul State)] are Guadalupian. Vertebrate fossils from Rio do Rasto Formation occur in disperse, isolated and discontinuous outcrops, so that they have been grouped in ‘local faunas’. However, most of the specimens lack precise stratigraphic provenance data and even occurring in locations near each other they are not necessarily contemporary. Thus, until a more robust stratigraphic framework is developed, we suggest discontinuing use of ‘local faunas’ to this stratigraphic unit.
Tapinocephalids (Therapsida, Dinocephalia) from the Permian Madumabisa Mudstone Formation (Lower Karoo, Mid-Zambezi Basin) of southern Zambia
Authors:
Sidor et al
Abstract:
Permian tetrapods from Zambia are best known from the Luangwa Basin, which was the subject of sporadic geological and paleontological work throughout the 20th century (Wallace, 1907; Dixey, 1937; Drysdall and Kitching, 1962, 1963; Attridge et al., 1964; Kemp, 1975, 1979; Davies, 1981; King, 1981; King and Jenkins, 1997; Lee et al., 1997). Based on its fossil content, the rocks of the upper member of the Madumabisa Mudstone Formation in the Luangwa Basin are considered Late Permian in age and contemporaneous with those of the Cistecephalus Assemblage Zone (AZ) of the Karoo Basin of South Africa (Angielczyk et al., 2014). Recent field work has demonstrated that a broadly distributed and relatively homogenous tetrapod fauna can be found wherever rocks of Cistecephalus AZ age are exposed across southern Africa (e.g., Malawi, South Africa, Tanzania, Zambia, and likely Mozambique; Sidor et al., 2013; Sidor, 2013).
Until recently, older tetrapod fossils from southern Africa were much rarer, with only South Africa and Zimbabwe recognized as yielding Middle Permian taxa (Catuneanu et al., 2005; Rubidge, 2005). The Karoo Basin has produced the most diverse fauna with the Eodicynodon and Tapinocephalus AZs including dicynodonts, dinocephalians, gorgonopsians, pareiasaurs, and therocephalians (Smith et al., 2012), although new radiometric dating suggests that the base of the overlying Pristerognathus AZ should be considered Middle Permian as well (Rubidge et al., 2013). Boonstra (1946) described the first dinocephalians from Zimbabwe. Unfortunately, this material now appears to be lost (Van den Heever and Grine, 1981; King, 1988). More recently, Lepper et al. (2000) described newly recovered material from the upper part of the Madumabisa Mudstone Formation of Zimbabwe and recognized both anteosaurid as well as tapinocephalian occurrences. The most recent discovery of Middle Permian tetrapods was reported by Simon et al. (2010), who noted the presence of isolated tapinocephalid remains from the middle portion of the Ruhuhu Formation of southern Tanzania. Endothiodont dicynodonts and temnospondyl amphibian remains from the same locality are currently under study by our research group.
Between 1951 and 1953, geologists from the Geological Survey Department of Northern Rhodesia were assigned to map coal reserves in the Mid-Zambezi Valley. Vertebrate fossils discovered in the course of their work were sent to S. H. Haughton for identification, and were subsequently published by Gair (1959:36) as “Dinocephalian and typical of the Tapinocephalus zone, possibly even Tapinocephalus itself.” Later, Drysdall and Kitching (1963:38) suggested that the fossils were fragmentary and unidentifiable. Unfortunately, none of the fossils was formally described and the collection now appears to be lost.
In 2010, members of our team relocated Gair's fossil site, and in July 2011 and June 2012 we collected additional tetrapod fossils there (Fig. 1; Table 1). Among them are numerous teeth that can be unambiguously referred to the tapinocephalid Dinocephalia (Boonstra, 1962; King, 1988). The discovery of this novel tetrapod assemblage provides useful biostratigraphic data for this portion of the Madumabisa Mudstone Formation in the Mid-Zambezi Basin.
New specimens of Stenocybus acidentatus (Therapsida: Dinocephalia) from the Middle Permian Dashankou Fauna of China
Authors:
Jiang et al
Abstract:
The basal dinocephalian clade Stenocybusidae was known from two incomplete specimens representing one generus, Stenocybus, from Dashankou fanua in Yumen, Gansu Province of China. The holotype of Stenocybus acidentatus is laterally compressed, making some characters unclear. Here we describe two new specimens of Stenocybus acidentatus from the same locality, an anterior portion of skull with articulated jaws, and a right dentary with nearly complete dentition. They show some detailed features on the morphology of the premaxilla, maxilla, nasal, external nares and dentary. The phylogenetic relationship between Stenocybus acidentatus and the relatively large Sinophoneus yumenensis is still difficult to determine, and needs more new complete material and further evidences.
Insights into the habitat of Middle Permian pareiasaurs (Parareptilia) from preliminary isotopic analyses
Authors:
Canoville et al
Abstract:
Pareiasaurs were an abundant group of large herbivores during Middle and Late Permian times. The habitat of pareiasaurs has proven enigmatic, and ecological interpretations from anatomical and taphonomic data have included aquatic, semi-aquatic to fully terrestrial lifestyles. Insight into the ecology of extinct taxa can also be gained from stable isotope analyses, and interpretations benefit from studies of multiple, coeval groups. Here, we report the first stable carbon and oxygen isotope analyses from the enamel, dentine and bone of pareiasaurs and contemporaneous therapsids (dinocephalians and therocephalians), in specimens recovered from the Permian Tapinocephalus to lower Pristerognathus Assemblage Zones of South Africa. Previous ecological inferences for dinocephalians (riparian to terrestrial) and therocephalians (terrestrial) are less ambiguous than reconstructions for pareiasaurs and provide an independent reference for interpreting stable isotope measurements. Oxygen isotopes of enamel carbonate were indistinguishable between pareiasaurs and therocephalians, which had higher values than dinocephalians. The data suggest that dinocephalians and pareiasaurs (megaherbivores) inhabited different ecological niches and that pareiasaurs may have shared a terrestrial habitat with therocephalians (carnivores). Our results agree with earlier suggestions of a terrestrial lifestyle among pareiasaurs and provide evidence of niche partitioning among large coeval Capitanian herbivores of South Africa.
Osteology, ontogeny, and phylogenetic position of Sinophoneus yumenensis (Therapsida, Dinocephalia) from the Middle Permian Dashankou Fauna of China
Author:
Jun Liu
Abstract:
Sinophoneus yumenensis and Stenocybus acidentatus are the only dinocephalians from China, and the latter taxon has been proposed to be a junior synonym of the former. Here I confirm this synonymy on the grounds that the differences between the two putative taxa are due to ontogenetic variation. The osteology of Sinophoneus yumenensis is described in detail based on both previously described specimens and several new ones from the same locality. Sinophoneus yumenensis differs from all other anteosaurs in having premaxillary dorsal processes that are separated by relatively long nasal anteromedial processes, and vomers without raised, elongated edges; from all other anteosaurs except Archaeosyodon praeventor in having distinct frontal posterolateral processes, and a wide intertemporal region formed partly by long posterior processes of the postfrontals that approach the posterior edge of the skull roof; and from Archaeosyodon praeventor in having a well-developed midline ridge on skull roof. A revised phylogenetic analysis including the new material recovers Sinophoneus as the most basal known anteosaurid.
