Late Permian terrestrial faunal connections invigorated: the first whaitsioid therocephalian from China

The record of therocephalian therapsids from the late Permian of China has recently been greatly expanded by the discovery of severalnew taxa of Akidnognathidae, a group previously known principally from South Africa and Russia. Continuing this string of discoveries,we present here the first Chinese record of a whaitsiid therocephalian. This is also the first record published of a tetrapod fromJingtai, Gansu, a late Permian locality that also yields remains of other groups such as dicynodonts, captorhinids, and chroniosuchians.This is the third taxon of whaitsiid therocephalian recognized in North Pangea. The new therocephalian is similar to the RussianMoschowhaitsia vjuschkovi in overall appearance, and although they are only recovered as sister-taxa in 6 out of 30 most parsimonioustrees in our phylogenetic analysis, it is tentatively referred to Moschowhaitsia as a new species,M. lidaqingi. The phylogeny obtained islargely similar to previous hypotheses, recovering three main lineages of Eutherocephalia: Akidnognathidae, Whaitsioidea andBaurioidea. However, it differs from previous analyses in finding Chthonosauridae (comprising the Russian Chthonosaurus andZambian Ichibengops) to be deeply nested within Whaitsioidea. Therocephalians were among the largest carnivores in the late Permianof North China, and may have represented the top predators in some faunas.Fil: Liu, Jun. Chinese Academy of Sciences; República de ChinaFil: Abdala, Nestor Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; Argentina. University of the Witwatersrand; Sudáfric

The emblematic South African therocephalian Euchambersia in China: A new link in the dispersal of late Permian vertebrates across Pangea

Therapsids were widely distributed in Pangea in the late Permian. South Africa in Gondwana and Russia in Laurasia are the principal areas recording tetrapods (including therapsids) of this age. More recent field explorations have increased the importance of Chinese late Permian fossil assemblages. This is clearly reflected in the discovery of several new therocephalians from the Naobaogou Formation in Nei Mongol. Here, we report a therocephalian from that unit identified as a new species of the emblematic South African taxon Euchambersia. The new species, Euchambersia liuyudongi, is represented by a well-preserved skull and mandible showing a well-developed maxillary fossa and the absence of postcanine teeth. This is the third akidnognathid therocephalian recovered from the Naobaougou Formation, but oddly, the two basal Chinese akidnognathids previously known were recovered from a younger unit of the formation than the derived E. liuyudongi. This is the first time that the same therocephalian genus has been recorded in northern and southern continents, making the record of the Naobaougou Formation key to understanding the evolution of late Permian continental fauna in general, and of akidnognathid therocephalians in particular.Fil: Liu, Jun. Chinese Academy of Sciences; República de ChinaFil: Abdala, Nestor Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; Argentina. Fundación Miguel Lillo; Argentina. University of the Witwatersrand; Sudáfric

Late Permian terrestrial faunal connections invigorated: the first whaitsioid therocephalian from China

The record of therocephalian therapsids from the late Permian of China has recently been greatly expanded by the discovery of severalnew taxa of Akidnognathidae, a group previously known principally from South Africa and Russia. Continuing this string of discoveries,we present here the first Chinese record of a whaitsiid therocephalian. This is also the first record published of a tetrapod fromJingtai, Gansu, a late Permian locality that also yields remains of other groups such as dicynodonts, captorhinids, and chroniosuchians.This is the third taxon of whaitsiid therocephalian recognized in North Pangea. The new therocephalian is similar to the RussianMoschowhaitsia vjuschkovi in overall appearance, and although they are only recovered as sister-taxa in 6 out of 30 most parsimonioustrees in our phylogenetic analysis, it is tentatively referred to Moschowhaitsia as a new species,M. lidaqingi. The phylogeny obtained islargely similar to previous hypotheses, recovering three main lineages of Eutherocephalia: Akidnognathidae, Whaitsioidea andBaurioidea. However, it differs from previous analyses in finding Chthonosauridae (comprising the Russian Chthonosaurus andZambian Ichibengops) to be deeply nested within Whaitsioidea. Therocephalians were among the largest carnivores in the late Permianof North China, and may have represented the top predators in some faunas.Fil: Liu, Jun. Chinese Academy of Sciences; República de ChinaFil: Abdala, Nestor Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; Argentina. University of the Witwatersrand; Sudáfric

Evolution and identity of synapsid carpal bones

To date there is little information on carpal bone homology in late Palaeozoic and Mesozoic Synapsida. Crucial to the understanding of homology in synapsid carpal elements is the fact that different nomenclatures are used for the carpals of non-mammaliamorph Synapsida (Gegenbauer?s canonical nomenclature) and Mammaliaformes (mammalian nomencla-ture). The homologies of the carpals of non-mammaliamorph synapsids and mammals were established early last century and have not been reviewed since then. Here we provide a detailed study of the carpal bones of synapsids ranging in age from the early Permian to Late Cretaceous. The mammaliamorph lunate, previously considered the homologue of the intermedium of non-mammaliamorph synapsids, is interpreted here as homologous to their lateral centrale. We interpret the single mammaliamorph centrale as a homologue of the medial centrale of non-mammaliamorph synapsids. In some synapsid specimens, we found that one or two centralia are fused to the radiale (e.g., the gorgonopsian Arctognathus and tritylodontid Bienotheroides), supporting a digging habit. A third centrale is present in the therocephalian Theriognathus, very likely an abnormal duplication. An additional medial bone in a biarmosuchian was interpreted as a prepollex/sesamoid. A cartilaginous prepollex/sesamoid may also have been present in several non-mammaliamorph synapsids, which have an open space proximal to distal carpal I. Distal carpal V is completely lost in dicynodonts and it is mainly fused to distal carpal IV in the adult stage of most other therapsid groups, but showed a delayed development in most non-mammaliamorph cynodonts. In mammaliamorphs, distal carpal V is not present. Our observations provide an up-dated revision of synapsid carpal homologies, mainly on the basis of position and anatomical contacts and also taking into account the results of embryological studiesFil: Kummell, S.. University Witten/herdecke; AlemaniaFil: Abdala, Nestor Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; ArgentinaFil: Sassoon, J.. University Of Bristol; Reino UnidoFil: Abdala, Virginia Sara Luz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Biodiversidad Neotropical. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Instituto de Biodiversidad Neotropical. Instituto de Biodiversidad Neotropical; Argentin

New insights on the cranial anatomy of Exaeretodon: intraspecific variation and taxonomic implications

Exaeretodon is a very abundant non-mammalian cynodont from the Upper Triassic found in South America and India. Presently, two species are considered valid: E. argentinus (Cabrera, 1943) from Argentina and E. riograndensis Abdala et al. 2002 from Brazil. We studied several unpublished specimens tentatively assigned to E. argentinus from the Ischigualasto Fm. (San Juan Province, Argentina) that range from ~130mm to ~400mm in basal skull length. Regardless of the individual size, two morphotypes were identified on the basis of differences in the zygomatic region, including: the presence/absence of a process of the jugal; the shape, relative orientation, and posterior extension of the dorsal and ventral zygomatic rami of the jugal; and the morphology and orientation of the zygomatic portion of the squamosal. The holotype of E. argentinus (formerly Belesodon argentinus Cabrera, 1943) is an incomplete left lower jaw. Only the holotypes of the once valid E. frenguelli Cabrera, 1943 and Theropsis robusta Cabrera, 1943 (presently considered junior synonyms of E. argentinus) and E. riograndensis preserve the relevant portions of the zygomatic region. These specimens represent only one of the morphotypes whereas the second morphotype has not been previously recognized. In addition, there are differences among the specimens of the first morphotype that were originally interpreted to be due to preservational artifacts but could instead account for intraspecific variation. Our preliminary results suggest that the second morphotype might characterize a new taxon, highlighting the importance of an integral re-evaluation of Exaeretodon Cabrera, 1943 considering all the evidence available.Fil: Gaetano, Leandro Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Martínez, Ricardo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Instituto y Museo de Ciencias Naturales. Área de Paleontología de Vertebrados; ArgentinaFil: Abdala, Nestor Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; ArgentinaReunión de Comunicaciones de la Asociación Paleontológica ArgentinaPuerto MadrynArgentinaAsociación Paleontológica Argentin

Craniodental anatomy in Permian-Jurassic Cynodontia and Mammaliaformes (Synapsida, Therapsida) as a gateway to defining mammalian soft tissue and behavioural traits

Mammals are diagnosed by more than 30 osteological characters (e.g. squamosal-dentary jaw joint, three inner ear ossicles, etc.) that are readily preserved in the fossil record. However, it is the suite of physiological, soft tissue and behavioural characters (e.g. endothermy, hair, lactation, isocortex and parental care), the evolutionary origins of which have eluded scholars for decades, that most prominently distinguishes living mammals from other amniotes. Here, we review recent works that illustrate how evolutionary changes concentrated in the cranial and dental morphology of mammalian ancestors, the Permian-Jurassic Cynodontia and Mammaliaformes, can potentially be used to document the origin of some of the most crucial defining features of mammals. We discuss how these soft tissue and behavioural traits are highly integrated, and how their evolution is intermingled with that of craniodental traits, thus enabling the tracing of their previously out-of-reach phylogenetic history. Most of these osteological and dental proxies, such as the maxillary canal, bony labyrinth and dental replacement only recently became more easily accessible - thanks, in large part, to the widespread use of X-ray microtomography scanning in palaeontology - because they are linked to internal cranial characters. This article is part of the theme issue 'The mammalian skull: development, structure and function'.Fil: Norton, Luke A.. University of the Witwatersrand; SudáfricaFil: Abdala, Nestor Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; Argentina. University of the Witwatersrand; SudáfricaFil: Benoit, Julien. University of the Witwatersrand; Sudáfric

Ontogenetic growth in the crania of Exaeretodon argentinus (Synapsida: Cynodontia) captures a dietary shift

Background. An ontogenetic niche shift in vertebrates is a common occurrence where ecology shifts with morphological changes throughout growth. How ecology shifts over a vertebrate’s lifetime is often reconstructed in extant species—by combining observational and skeletal data from growth series of the same species—because interactions between organisms and their environment can be observed directly. However, reconstructing shifts using extinct vertebrates is difficult and requires well-sampled growth series, specimens with relatively complete preservation, and easily observable skeletal traits associated with ecologies suspected to change throughout growth, such as diet. Methods. To reconstruct ecological changes throughout the growth of a stem-mammal, we describe changes associated with dietary ecology in a growth series of crania of the large-bodied (∼2 m in length) and herbivorous form, Exaeretodon argentinus (Cynodontia: Traversodontidae) from the Late Triassic Ischigualasto Formation, San Juan, Argentina. Nearly all specimens were deformed by taphonomic processes, so we reconstructed allometric slope using a generalized linear mixed effects model with distortion as a random effect. Results. Under a mixed effects model, we find that throughout growth, E. argentinus reduced the relative length of the palate, postcanine series, orbits, and basicranium, and expanded the relative length of the temporal region and the height of the zygomatic arch. The allometric relationship between the zygomatic arch and temporal region with the total length of the skull approximate the rate of growth for feeding musculature. Based on a higher allometric slope, the zygoma height is growing relatively faster than the length of the temporal region. The higher rate of change in the zygoma may suggest that smaller individuals had a crushing-dominated feeding style that transitioned into a chewing-dominated feeding style in larger individuals, suggesting a dietary shift from possible faunivory to a more plant-dominated diet. Dietary differentiation throughout development is further supported by an increase in sutural complexity and a shift in the orientation of microwear anisotropy between small and large individuals of E. argentinus. A developmental transition in the feeding ecology of E. argentinus is reflective of the reconstructed dietary transition across Gomphodontia, wherein the earliest-diverging species are inferred as omnivorous and the well-nested traversodontids are inferred as herbivorous, potentially suggesting that faunivory in immature individuals of the herbivorous Traversodontidae may be plesiomorphic for the clade.Fil: Wynd, Brenen. No especifíca;Fil: Abdala, Nestor Fernando. Fundación Miguel Lillo; Argentina. University of the Witwatersrand; Sudáfrica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; ArgentinaFil: Nesbitt, Sterling J.. No especifíca

Mesozoic fossil vertebrates from northwestern Argentina

En la presente contribución se detalla el registro de fósiles vertebrados mesozoicos en el noroeste de Argentina. El mismo se compone de una parte triásica y otra cretácica, pero hay también un registro puntual del Jurásico. El Triásico se presenta en la cuenca de Ischigualasto-Villa Unión en las provincias de San Juan y La Rioja y en la cuenca de Marayes-El Carrizal al sur de San Juan, mientras que el Jurásico Inferior existe en la última cuenca y en la Formación Cañón del Colorado en el centro de la provincia de San Juan. El Cretácico está documentado en la Formación Los Llanos de La Rioja y en la cuenca del Noroeste en Jujuy y Salta. El Triásico Superior es el mejor representado mostrando una buena diversidad de arcosauromorfos. El mejor registro de dinosauriformesno dinosaurianos es en la Formación Chañares, mientras que los dinosaurios más antiguos del mundo aparecen ya bien diversifi cados en la Formación Ischigualasto y se vuelven abundantes en Los Colorados. Dicinodontes son componentes residuales (poco diversos y abundantes), mientras que los cinodontes son abundantes en la Formación Chañares y abundantes y más diversifi cados en la fauna de Ischigualasto. Registros antiguos detortugas existen en las formaciones Los Colorados y Quebrada del Barro, y en esta última hay también esfenodontes. En el Cretácico de la Formación Los Llanos se documentaron nidadas de huevos de saurópodos y restos fragmentarios de cocodrilos. En la cuenca del Noroeste, la Formación Las Curtiembres registra peces teleósteos, ranas pípidas, tortugas pleurodiras, mesoeucrocodilidos, dinosaurios terópodos y enantiornites; mientras queen la Formación Los Blanquitos fueron hallados dinosaurios titanosaúridos y terópodos y un diente de cocodrilo. La Formación Lecho está dominada por dinosaurios titanosaurios y también se hallaron terópodos y enantiornites. Finalmente, en la Formación Yacoraite hay peces y cocodrilos, así como también huellas atribuidas a diferentes grupos de dinosaurios.We present a synthesis of the vertebrate fossil record from northwestern Argentina. The Triassic is represented in the Ischigualasto-Villa Unión Basin in La Rioja and San Juan provinces and in the Marayes-El Carrizal Basin in the south of San Juan, whereas the Lower Jurassic crops out in the latt er basin and in the Cañón del Colorado Formation in the center of San Juan Province. Cretaceous fossils are documented in the Los Llanos Formation in La Rioja Province and in the Noroeste Basin in Jujuy and Salta provinces. The Upper Triassic is best represented in the Ischigualasto-Villa Union Basin, featuring well-diversifi ed archosauromorphs. Non dinosaur dinosauriforms are well diversifi ed in the Chañares Formation, and the world’s oldest dinosaurs are already well diversifi ed in the Ischigualasto Formation and become abundant in Los Colorados. Ancient records of terrestrial turtles exist in the Los Colorados and Quebrada del Barro formations. Sphenodontians are also represented in the latt er unit. A nesting site of sauropods and fossils of a crocodile are documented in the Cretaceous Los Llanos Formation. In the Noroeste Basin, the Las Curtiembres Formation has records of teleost fi sh, pipid frogs, pleurodire turtles, mesoeucrocodiles, theropod dinosaurs and enantiornithes birds; whereas in the Los Blanquitos Formation were found titanosaurid and theropod dinosaurs, as well as a crocodile tooth. The Lecho Formation is dominated by titanosaurid dinosaurs and also record theropod dinosaurs and enantiornithes. Finally, in the Yacoraite Formation there are fish and crocodiles, as well as tracks att ributed to diff erent groups of dinosaurs.Fil: Abdala, Nestor Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; Argentina. University of the Witwatersrand; SudáfricaFil: Bertelli, Sara Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; ArgentinaXX Congreso Argentino de GeologiaSan Miguel de TucumánArgentinaAsociación Geológica ArgentinaUniversidad Nacional de Tucumán. Facultad de Ciencias Naturale

Tooth replacement patterns in the Early Triassic epicynodont Galesaurus planiceps (Therapsida, Cynodontia)

Sixteen specimens of the Early Triassic cynodont Galesaurus planiceps (including eight that were scanned using micro-computed tomography) representing different ontogenetic stages were assembled to study the dental replacement in the species. The growth series shows that the incisors and postcanines continue to develop and replace, even in the largest (presumably oldest) specimen. In contrast, replacement of the canines ceased with the attainment of skeletal maturity, at a basal skull length of ~90 mm, suggesting that Galesaurus had a finite number of canine replacement cycles. Additionally, the functional canine root morphology of these larger specimens showed a tendency to be open-rooted, a condition not previously reported in Mesozoic theriodonts. An alternating pattern of tooth replacement was documented in the maxillary and mandibular postcanine series. Both postcanine series increased in tooth number as the skull lengthened, with the mandibular postcanine series containing more teeth than the maxillary series. In the maxilla, the first postcanine is consistently the smallest tooth, showing a proportional reduction in size as skull length increased. The longer retention of a tooth in this first locus is a key difference between Galesaurus and Thrinaxodon, in which the mesial-most postcanines are lost after replacement. This difference has contributed to the lengthening of the postcanine series in Galesaurus, as teeth continued to be added to the distal end of the tooth row through ontogeny. Overall, there are considerable differences between Galesaurus and Thrinaxodon relating to the replacement and development of their teeth.Fil: Norton, Luke A.. University of the Witwatersrand; SudáfricaFil: Abdala, Nestor Fernando. University of the Witwatersrand; Sudáfrica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; ArgentinaFil: Rubidge, Bruce S.. University of the Witwatersrand; SudáfricaFil: Botha, Jennifer. Free State University; Sudáfrica. Karoo Palaeontology; Sudáfric

A new large cynodont from the Late Permian (Lopingian) of the South African Karoo Basin and its phylogenetic significance

The Karoo Basin of South Africa has the best global record of Lopingian (Late Permian) non-mammaliaform cynodonts, currently represented by five species. We describe Vetusodon elikhulu gen. et sp. nov., documented by four specimens from the Daptocephalus Assemblage Zone. With a basal skull length of ~18 cm, it is the largest Lopingian cynodont and is also larger than Induan representatives of the group. Vetusodon elikhulu has a cranial morphology that departs notably from that previously documented for Permo-Triassic cynodonts. It features a short and extremely wide snout, resembling that of the contemporaneous therocephalian Moschorhinus, and has large incisors and canines that contrast with the small unicusped postcanines, suggesting a more important role of the anterior dentition for feeding. The dentary is extremely long and robust, with the posterior margin located closer to the craniomandibular joint than in other Lopingian and Induan cynodonts (e.g. Thrinaxodon). The secondary palate morphology of V. elikhulu is unique, being short and incomplete and with the posterior portion of the maxilla partly covering the vomer. A phylogenetic analysis suggests that V. elikhulu is the sister taxon of Eucynodontia and thus the most derived of the Lopingian to Induan cynodonts yet discovered.Fil: Abdala, Nestor Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; ArgentinaFil: Gaetano, Leandro Carlos. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; ArgentinaFil: Smith, Roger M. H.. Evolutionary Studies Institute; SudáfricaFil: Rubidge, Bruce. Evolutionary Studies Institute; Sudáfric