Fernando Abdala

The Chañares Formation in north-western Argentina has provided an impressive number of specimens of early archosauriforms, dicynodonts, and non-mammaliamorph cynodonts. However, there is a very low diversity of cynognathian cynodonts. Herein, we report on Pontognathus ignotus gen. et sp. nov., a small new traversodontid from the traditional Late Triassic Carnian levels of the unit. It differs from other traversodontids for lacking a maxillary platform lateral to the posterior postcanines and by presenting a unique combination of characters from the premaxilla, maxilla, and dentition (i.e., the precanine diastema; the placement of the paracanine fossa; the number of upper postcanines; the general outline of the upper postcanines crown in occlusal view; the shouldering between adjacent teeth; the expansion of the crown distolateral to the sectorial crest; the extension, limits and deepness of the occlusal basin; the distal ridge-like bulging at the base of the crown; the number and relative placement and development of the cusps). It is a relatively small taxon inferred to have occupied a specialized, small herbivorous/omnivorous role, which in this fauna is otherwise only shared by small individuals of the traversodontid Massetognathus pascuali.

Techniques for digital restoration of cranial elements on three-dimensional surface models

Pareiasaurs were an enigmatic and diverse group of parareptilian herbivores of the middle and late Permian. Nanoparialuckhoffi was erected in 1936 but remains the least well-known member of four “dwarf” pareiasaurs that comprise Pumiliopareiasauria. After new preparation of the holotype, we present the first detailed cranial description of Nanoparialuckhoffi and a new diagnosis for the taxon based on seven autapomorphies: (1) an additional bone on the posterior margin of the cheek flange between the squamosal and quadratojugal; (2) a pyramidal-shaped parietal; (3) a very short, square lacrimal; (4) paired prepalatal foramina positioned anterolaterally on the internal premaxillary palatal flange; (5) notch on anteromedial border of the choana; (6) a ventral flange formed by the lateral margin of the internal tabulars; and (7) tabulars that extend posteriorly further than the supratemporals. We find evidence supporting a juvenile ontogenetic state for the holotype, including small skull; unossified open cranial sutures; an unossified dorsal braincase; and fewer marginal teeth than most pareiasaurs. An updated phylogeny recovers Nanoparia as a sister taxon to Provelosaurusamericanus from Brazil and remains a constituent member of Pumiliopareiasauria. Keywords: Nanoparia, Pumiliopareiasauria, Pareiasauria, Parareptilia, late Permian, Gondwana.

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’.

Ontogenetic allometry, the covariation of shape with size over the course of development, represents a fundamental component of morphological diversification that can vary across species and in association with ecological factors. Ontogenetic allometry patterns for the skull have been described for species from several marsupial lineages, associated with common dietary niches, e.g., carnivory. We here conduct a novel detailed examination of cranial ontogeny in the numbat (Myrmecobius fasciatus), unique among marsupials in being myrmecophagous and adopting a strictly diurnal habit. We investigated ontogenetic allometry using multivariate analyses in a postnatal series (n = 28) of complete numbat skulls to estimate the rate of growth of its major constituent elements, described by 15 measurements. We find positive allometry for length of the nasals and palate, which relates directly to the remarkable rostral elongation in the species relative to other marsupials, in addition to several other ontogenetic changes. These comprise negative allometry of palate breadth, elongation of upper and lower toothrows that produces diastemata between weakly developed teeth, and decreasing muzzle height, all of which contribute to the development of a long, tapering, narrow rostrum, with limited mastication ability, as seen in the small temporal space and poor development of crests and processes associated with jaw musculature. Our specific allometric results and comparisons, together with qualitative observations, reveal a distinct imprint of myrmecophagy on skull ontogeny in the numbat and help explain the development and evolution of specialized feeding function of this species. Norberto P. Giannini [ngiannini@amnh.org], CONICET Fundacion Miguel Lillo, Unidad Ejecutora Lillo, UEL, Tucumán, Argentina, Facultad de Ciencias Naturales, Instituto Miguel Lillo, Universidad Nacional de Tucumán, Tucumán, Argentina, Department of Mammalogy, American Museum of Natural History, New York, NY, USA; Fernando Abdala [nestor.abdala@wits.ac.za], CONICET Fundacion Miguel Lillo, Unidad Ejecutora Lillo, UEL, Tucumán, Argentina, Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa; David A. Flores [dflores@macn.gov.ar], CONICET Fundacion Miguel Lillo, Unidad Ejecutora Lillo, UEL, Tucumán, Argentina, Instituto de Vertebrados, Fundación Miguel Lillo, Tucumán, Argentina; Laura A. B. Wilson [laura.wilson@anu.edu.au], School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia, School of Archaeology and Anthropology, The Australian National University, Canberra, ACT 2601, Australia.

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.

Pareiasaurs were relatively abundant, globally-distributed, herbivorous parareptiles of the mid to late Permian. The basal-most forms, all members of the Bradysauria, are restricted to the Guadalupian (mid-Permian) of South Africa and went extinct in the late Capitanian near the top of the Tapinocephalus Assemblage Zone. Currently four species are recognized in this group: Bradysaurus seeleyi, B. baini, Embrithosaurus schwarzi and Nochelesaurus alexanderi. These taxa have been poorly defined historically and based on a limited number of specimens, leaving the taxonomic diversity of the group open to doubt and limiting their utility in biostratigraphy. Here, we present our fourth and final contribution to improve the understanding of this group by providing a taxonomical and phylogenetic review, updated stratigraphical ranges, and updated diagnoses for each taxon within Bradysauria. Bradysaurus seeleyi is synonymized with Bradysaurus baini, resulting in three valid mid-Permian pareiasaur taxa: Bradysaurus baini, Embrithosaurus schwarzi and Nochelesaurus alexanderi. Our cladistic analysis of cranial and postcranial characters supports the monophyly of Bradysauria with five synapomorphies. Embrithosaurus schwarzi is recovered as the sister taxon to a clade containing Bradysaurus baini and Nochelesaurus alexanderi. By identifying 157 pareiasaur specimens in fossil collections we show that the Bradysauria are stratigraphically restricted to the Abrahamskraal Formation of the Beaufort Group and suggest a staggered appearance. Bradysaurus baini is first to appear, followed by Nochelesaurus alexanderi, and lastly by Embrithosaurus schwarzi. All three taxa perished during the Capitanian mass extinction, and have their highest occurrences near the top of the Abrahamskraal Formation.