The evolutionary origins of turtles remain poorly understood. Molecular systematics posit a sister relationship between turtles and archosaurs, but morphological studies return conflicting hypotheses of turtle relationships both to other living reptiles and to their closest fossil relatives. The middle Permian Eunotosaurus africanus has been widely regarded as the oldest stem turtle, which makes it instrumental in recent discussions of the origins of turtles and their highly transformed anatomy. Here, we use anatomical observations derived from X-ray computed microtomography (μCT) of Eunotosaurus and candidate stem turtles to evaluate phylogenetic hypotheses of turtle origins. Eunotosaurus has many plesiomorphies and lacks synapomorphies of crown reptiles, whereas Proganochelys, one of the oldest uncontentious stem turtles, shares similarities with archosauromorphs, especially in the endocranium. Our comprehensive phylogenetic analysis recovers Eunotosaurus as a millerettid stem reptile not related to turtles. This indicates that features shared by Eunotosaurus and turtles, notably including broadened dorsal ribs, evolved independently. These similarities are better explained by convergent evolution of fossorial ecologies rather than shared ancestry. Furthermore, we find strong support for the molecular phylogenetic hypothesis that turtles are sister to Archosauria among living reptiles, resolving long-standing conflicts between morphological and molecular datasets. By placing turtle origins among the earliest archosauromorphs in the late Permian, we provide new insights into the anatomical transformations involved in the origins of the distinct turtle body plan.

Mozambique has become a focal point for numerous new discoveriesof dicynodont remains, contributing significantly to our knowledge on theanatomy and phylogeny of Dicynodontia of the Late Permian. Here wepresent a new dicynodont skull from the Metangula Graben in NorthernMozambique, collected in 2019, which has been subjected to synchrotronscanning and segmentation for anatomical description and future phylogeneticanalyses.

Permian members of the therocephalian clade Baurioidea remain much more poorly known than the extremely mammal-like Triassic representatives. Here, we describe the cranium of the single known specimen of the lycideopid baurioid Choerosaurus dejageri, based on high-resolution CT-imaging and provide comparisons with closely related taxa. Besides examining external anatomical characters like its characteristic cranial and dentary bosses, we provide important details on the previously obscure palatal morphology. The reconstruction of the holotype shows that this species represents an important transitional stage in the evolution of the therocephalian secondary palate. Complete secondary palates evolved independently three times in therapsids (incl. baurioid therocephalians and cynodonts). In Choerosaurus, the vomer plays the role of an important bracing element in the palate through a long suture with the maxillary shelves, known as the maxillo-vomerine bridge. This differs from the early cynodont condition and highlights different evolutionary origins of therocephalian and cynodont secondary palates. Moreover, similarities in the palatal morphology with Lycideops support the hypothesis of a close relationship between these two taxa.

Therapsids are early-diverging synapsids that thrived during the Permian and Triassic periods, and ultimately gave rise to mammals. They include six major groups, which already exhibited considerable diversity at their first appearance in the fossil record. Their early to middle Permian origins remain poorly understood due to a scarcity of fossils with clear therapsid morphology in the early Permian and the presence of an interval of poor fossil preservation near the early to middle Permian boundary (Olson's Gap). This limits our insight into the phylogenetic relationships among the main middle Permian groups. This study presents a novel approach to therapsid phylogeny, using probabilistic frameworks. In performing a phylogenetic analysis based exclusively on cranial characters, using both RevBayes and MrBayes, this study challenges understanding of the early diversification of Therapsida. We recover Neotherapsida, with Anomodontia branching as the sister taxon to Theriodontia. Biarmosuchia and Dinocephalia form a clade. The positions of taxa such as Sinophoneus and Biseridens are reconsidered. The application of Fossilized Birth-Death models suggests that while Therapsida originated in the early Permian, currently known therapsid groups diversified around 281 to 272 million years ago and subsequently underwent rapid radiation into five clades: Biarmosuchia, Dinocephalia, Anomodontia, Gorgonopsia, and Eutheriodontia.

The middle Permian represents a critical interval in therapsid evolution, when gorgonopsians emerged as some of the first specialized apex predators within terrestrial ecosystems. Despite their significance, the early diversification of Gorgonopsia in Gondwana remains poorly understood due to scarcity and fragmentary material. Here, we describe a nearly complete skull (BP/1/8260) with an occluded lower jaw from the lower Abrahamskraal Formation (Tapinocephalus Assemblage Zone). The specimen exhibits a distinctive combination of cranial features, including a transversely narrow snout, small orbital and temporal openings, V-shaped palatine bosses, and a vertically oriented occiput that distinguish it from all known gorgonopsians. Based on its unique morphology, a new taxon, Jirahgorgon ceto sp. nov., is established for this specimen. In our phylogenetic analysis, the new taxon forms a clade with Phorcys dubei, which is here named Phorcyidae fam. nov. Members of Phorcyidae are unique among basal African gorgonopsians in combining a vertical occiput and rubidgeine-like cranial proportions, indicating that large-bodied gorgonopsians were present in the Wordian and overturning notions that they were exclusively small carnivores until the Wuchiapingian. Basal skull length analyses indicate that body size evolution in Gorgonopsia, while largely random through time (Brownian motion evolutionary model), is nonetheless structured by shared ancestry. The discovery of Jirahgorgon illustrates the complexity of gorgonopsian evolution, showing an early appearance of large-bodied, robust morphotypes and highlighting the lower Abrahamskraal Formation as a key resource for understanding the initial radiation of theriodonts.

Brain size and encephalization are correlated with extinction risks, making them central to understanding evolutionary outcomes in the face of the climatic and ecological challenges posed by mass extinction events. Yet, the end-Permian mass extinction—the most significant extinction event in the history of Life—has received little attention from a paleoneurological perspective. Here we use Synchrotron Radiation and CT scanning to study the evolution of brain endocasts of mammalian forerunners, the Permo-Triassic Synapsida, across this extinction event. During mass extinction events, it is expected that the brain would adapt either by growing larger to enhance behavioral response to the challenges, or shrinking to save energy. To test these predictions, we conducted a broad phylogenetic survey of synapsids across the end of the Permian and, unexpectedly, found stasis of the encephalization quotient. Furthermore, analysis of evolutionary rates indicates that stabilizing selection does not account for the observed stasis. We hypothesize that a lack of resources may have impeded neuroplasticity and prolonged a period of stasis that began in the late Permian. Brain size resumed varying after the crisis, marking the first steps toward the evolution of the mammalian brain.

The maxillary canal system in Cynognathus and Diademodon is described. The hypothesis that expansion of the maxillary sinus represents a synapomorphy of the clade Cynognathia is supported. A trend towards the reduction of the inferior palpebral ramus is proposed.

Cynodontia is an important subclade of Therapsida that first occurred in the late Permian. It includes extinct subclades which are the non-mammaliaform cynodonts and Mammaliaformes, with the latter ultimately giving rise to crown mammals. The systematics of non-mammaliaform cynodonts has been extensively studied and is relatively well-resolved, however, there are still many problematic taxa that are difficult to identify and place confidently into the cynodont phylogenetic tree. Cistecynodon parvus is one such taxon, known only from a single specimen, the holotype skull which was found in the Middle Triassic Burgersdorp Formation of South Africa, in strata assigned to the Trirachodon-Kannemeyeria Subzone of the Cynognathus Assemblage Zone. Over the past century Cistecynodon has been variously referred to Eucynodontia (which includes the two major subclades Probainognathia and Cynognathia) and to non-eucynodont cynodonts, without any emerging consensus. Here the holotype of Cistecynodon parvus (BP/1/2520) is re-described based on computed tomography (CT) digital reconstruction of the specimen. This new data is applied to determine a phylogenetic matrix which supports that C. parvus is a basal (non-eucynodont) cynodont. This basal position is reflected in the anatomy of its secondary palate, which is not closed despite the specimen being a subadult. The inner ear, trigeminal canal, parietal foramen and carotid foramina are uniquely derived, likely as adaptations to an obligate fossorial lifestyle, confirming the validity of the taxon and its inferred subterranean habitat.

Oviparity was likely the plesiomorphic reproductive condition for non-mammalian Synapsida, the stem-mammal group. Yet, despite nearly two centuries of research, no definitive fossil eggs of late Palaeozoic or early Mesozoic synapsids have been discovered. Here, three perinate specimens of the dicynodont genus Lystrosaurus from the Early Triassic of the South African Karoo Basin are examined using high-resolution CT and synchrotron scanning. One specimen, NMQR 3636, displays a tightly curled posture suggestive of an in ovo position and completely lacks tusks. Crucially, the lower jaw symphysis remains unfused-a developmental trait found only in pre-hatching embryos of modern birds and turtles. No calcified eggshell is preserved, so the egg might have been soft and leathery. The large size of the reconstructed egg suggests a precocial, non-milk-feeding developmental strategy. As a non-cynodont synapsid, Lystrosaurus offers a rare and valuable glimpse into reproductive biology far removed from the mammalian crown group. Unlike the more derived, mammal-like cynodont Kayentatherium, whose egg size aligns with lactation, Lystrosaurus anchors the plesiomorphic condition deep within Synapsida. Its reproductive strategy may have played a crucial role in its resilience and ecological dominance following the end-Permian mass extinction.

The tapinocephalid dinocephalian Moschops is one of the most iconic taxa of the middle Permian, yet its paleobiology remains one of the least well-known. Here, we address some aspects of paleoneurology and paleobiology of Moschops using CT scanning of four well preserved skulls from the upper Abrahamskraal Formation of South Africa. Two of the specimens preserve articulated scleral ossicle rings, the dimensions of which are more consistent with a diel activity pattern, although intermediate between diurnal, nocturnal, and cathemeral. The bony labyrinth for the inner ear (preserved in one specimen) has comparatively short semicircular canals, and the agility score aligns with those of modern large herbivores that are able to swim. This is consistent with previous hypotheses inferring that some tapinocephalid dinocephalians may have been semi-aquatic. The four individuals form a partial ontogenetic series, and we show that the endocast grows markedly with body size in Moschops, as does the encephalization quotient. The latter is an unusual pattern for vertebrates. We also report the first possible evidence for the preservation of soft brain tissues in a non-mammalian synapsid, which sparks exciting perspectives for future studies of non-mammalian synapsid paleoneurology.

A subadult Moschognathus whaitsi from the Eastern Cape Province, South Africa, was scanned using synchrotron radiation X-ray computed tomography (SRXCT). Its subadult state allowed the cranial bones and teeth to be identified and individually reconstructed in 3D. A complete description of every preserved cranial bone is here produced, with special attention given to the braincase. An evaluation of a frontal abscess has provided insight into the potential behavior of Moschognathus, regarding the long-standing hypothesis of dinocephalian headbutting. The first 3D description of tapinocephalian dentition shows the unique talon-and-heel tooth morphology and expands our understanding of the replacement patterns in the dentition of basal therapsids. We report evidence of at least three successive replacement generations developing in the incisiform dentition of M. whaitsi simultaneously. The arrangement of these successive generations of replacement incisiform teeth is reminiscent of the complex dental batteries described in sauropod dinosaurs. Furthermore, an alternating pattern of replacement is apparent and suggests that the upper and lower rows of functional teeth were comprised of at least two tooth generations.

The pineal eye is a photoreceptive organ, sometimes called the "third eye", housed within the parietal foramen of some ectothermic vertebrates (Eakin 1973; Quay 1979). It is amongst the most enigmatic organs, and accordingly, concerns relating to its origin and evolution have long fascinated palaeontologists (Eakin 1973; Roth and Roth 1980; Benoit et al. 2016). In dicynodont synapsids, a parietal foramen is almost always present, with a few noticeable exceptions that have, so far, eluded explanations (Benoit et al. 2016; Kammerer 2019). Kombuisia frerensis is one such exception. There are two recognised species of Kombuisia: K. frerensis, from South Africa, and K. antarctica, from Antarctica. The two species are virtually undistinguishable except for the absence of a parietal foramen in the former, whereas the latter retains a slit-like opening on the skull roof (Fr & ouml;bisch et al. 2010). While describing K. frerensis, Hotton (1974) refrained from including the absence of a parietal foramen in the diagnosis of the species as very little was known about the intraspecific variability of this character. Intraspecific variation of the parietal foramen has since been documented in modern reptiles (e.g., Gundy and Wurst 1976; Roth and Roth 1980) and other synapsids (Benoit et al. 2016). As a result, the absence of a parietal foramen in K. frerensis has been treated with caution by subsequent authors (e.g., Kammerer 2019). In 2023, our research team found a new specimen referrable to K. frerensis: an almost undeformed skull with articulated lower jaw and associated postcrania (Fig. 1A). This new specimen confirms that the absence of a parietal foramen is diagnostic for K. frerensis. We here explore the physiological implications of this condition and propose that it may be the result of latitudinal gradient separating the two species of Kombuisia.

The anatomy of the enigmatic stem-reptile Galesphyrus capensis (Middle-Late Permian, South Africa) is redescribed in detail. The validity of G. capensis is confirmed based on its holotype, but the other previously referred specimen is excluded from G. capensis based on skeletal differences. The new anatomical data described here are included in an expanded phylogenetic dataset, designed to examine the relationships of Permian reptiles. Both specimens are recovered as early-diverging members of a clade which includes Millerettidae, traditionally considered 'parareptiles' and Neodiapsida. Consequently, Parareptilia is paraphyletic, as Millerettidae occupies a more crownward position than any other parareptile, themselves not forming a clade. Our results also demonstrate that neodiapsids originated at least in the late Capitanian, prior to the Capitanian Mass Extinction, and highlight the diversity of Younginidae, which includes three South African taxa. The exquisitely preserved postcranium of G. capensis sheds light on postcranial evolution in Late Permian stem-reptiles, bringing additional support for sister-group relationship between millerettids and neodiapsids. Our new data on G. capensis and other stem-reptiles demonstrate that the evolutionary history of the foot was remarkably complex close to the origin of Sauria, with some of the prerequisites to the evolution of the saurian foot and gait having already appeared by the late Capitanian. These overlooked Middle and Late Permian stem-reptiles have the potential to further our understanding of the origin of the reptilian crown group.

A century and a half of paleoneurological study of synapsids has provided invaluable insight into the evolution of their brain, sense organs, behavior, and physiology. Here, we review and discuss the evidence for parental care, brooding, intraspecific combat, display, and gregariousness, and conclude that evidence for higher levels of social interactions and communication is piling up and may soon push the origin of sociality in the mammalian lineage to the middle Permian. We also review the paleoneurological cues (the trigeminal canals, parietal foramen, and inner ear) that support a new evolutionary hypothesis in which the homeogene MSX2 mutated early in the probainognathian cynodonts and changed their biology towards a more mammalian condition. This includes the loss of the parietal foramen, inflation of the cerebellar vermis, maintenance of a fur pelt, and appearance of mammary glands, some 247 million years ago. This was followed by the origin of the ability to whisk 241 million years ago, and that of endothermy 233 million years ago, as indicated by the evolution of the trigeminal and semicircular canals, respectively. Finally, we review the immense progress made in the study of encephalization and support that probainognathians went through a neurosensory revolution during the Triassic. Their newly acquired small body size, fur, and nocturnal lifestyle generated sensory input that affected the evolution of all their sensory organs, leading up to the development of the modern mammalian brain.

The diversity of the fauna of the late Permian K6 Formation of the Metangula graben of northern Mozambique is coming to light thanks to recent discoveries made by the PaleoMoz Project. Here we describe the first diagnosable gorgonopsian remains from the K6a2 Member of the Metangula graben, specimen PPM2018-7Z. This specimen is a large-bodied gorgonopsian, and shows several features similar to the latest late Permian species Inostrancevia africana. PPM2018-7Z shares various autapomorphies with Inostrancevia africana including the extremely narrowed jugal ventral to the orbit, the pineal foramen being positioned far posteriorly, the anteroposteriorly expanded ventral portion of postorbital bar, the orbit being larger than the temporal fenestra and by having prefrontal rugosities and foramina. The tooth morphology of Inostrancevia africana is here accessed based on the left canine of PPM2018-7Z, which is characterised by low labial ridges, a short mesial carina and thick basal denticles of the mesial carina. PPM2018-7Z is phylogenetically recovered close to Inostrancevia africana within the “Russian clade gorgonopsians”. PPM2018-7Z and Inostrancevia africana do not possess an interorbital ridge that is present in some rubidgeines such as Clelandina and Dinogorgon. Furthermore, PPM2018-7Z and inostranceviines retain a postfrontal with a posterior process that extends posteriorly invading the parietal border, unlike in rubidgeines in which the posterior process of the postfrontal is absent. The presence of Inostrancevia africana in the K6a2 Member of the Metangula graben helps correlating this member to the Daptocephalus Assemblage Zone in the Karoo Basin of South Africa.

Hypercanines, or hypertrophied canines, are observed in a wide range of both extinct and extant synapsids. In non-mammaliaform cynodonts, the Permo-Triassic forerunners of mammals, long canines are not uncommon, appearing in several unrelated taxa within the clade. Among them is Trucidocynodon riograndensis , a carnivorous ecteniniid cynodont from the Late Triassic of Brazil, which exhibits a specialized dentition, including spear-shaped incisors, very long and narrow canines, and sectorial postcanines with distally oriented cusps, all of which have finely serrated margins. Recent synchrotron X-ray micro-computed tomography of a large specimen (CAPPA/UFSM 0029; Várzea do Agudo site, Brazil) provides new insights into its lower jaw and dentition, as well as offers the first digital endocast of an ecteniniid. Our study reveals the presence of (i) putatively opened-root canines in the adult stage and the possible presence of unresorbed remnant of an old canine, which may indicate that the specimen stopped replacing its canines; (ii) lower canines that are longer than the upper canines and, in occlusion, were kept inside deep paracanine fossae that perforated the dorsal surface of the rostrum; (iii) a diastema between the incisors and lower canine, which is absent in the holotype; (iv) advanced brain structures, such as the absence of a pineal body, presence of cerebral hemispheres divided by the interhemispheric sulcus and expanded laterally, and a higher encephalization quotient than non-mammaliaform prozostrodonts, reflecting the homoplastic evolution of relative brain sizes observed in Triassic cynodont lineages. Finally, the abundance of carnivorous and omnivorous species at the Várzea do Agudo site, where the specimen was found—including the archosauriforms Dynamosuchus collisensis and Stenoscelida aurantiacus —suggests a diverse predator guild that warrants further investigation from a paleoecological perspective.