Olson's Extinction and the latitudinal biodiversity gradient of tetrapods in the Permian.

The terrestrial vertebrate fauna underwent a substantial change in composition between the lower and middle Permian. The lower Permian fauna was characterized by diverse and abundant amphibians and pelycosaurian-grade synapsids. During the middle Permian, a therapsid-dominated fauna, containing a diverse array of parareptiles and a considerably reduced richness of amphibians, replaced this. However, it is debated whether the transition is a genuine event, accompanied by a mass extinction, or whether it is merely an artefact of the shift in sampling from the palaeoequatorial latitudes to the palaeotemperate latitudes. Here we use an up-to-date biostratigraphy and incorporate recent discoveries to thoroughly review the Permian tetrapod fossil record. We suggest that the faunal transition represents a genuine event; the lower Permian temperate faunas are more similar to lower Permian equatorial faunas than middle Permian temperate faunas. The transition was not consistent across latitudes; the turnover occurred more rapidly in Russia, but was delayed in North America. The argument that the mass extinction is an artefact of a latitudinal biodiversity gradient and a shift in sampling localities is rejected: sampling correction demonstrates an inverse latitudinal biodiversity gradient was prevalent during the Permian, with peak diversity in the temperate latitudes.

Endocranial Casts of Pre-Mammalian Therapsids Reveal an Unexpected Neurological Diversity at the Deep Evolutionary Root of Mammals.

The origin and evolution of the mammalian brain has long been the focus of scientific enquiry. Conversely, little research has focused on the palaeoneurology of the stem group of Mammaliaformes, the Permian and Triassic non-mammaliaform Therapsida (NMT). This is because the majority of the NMT have a non-ossified braincase, making the study of their endocranial cast (sometimes called the "fossil brain") problematic. Thus, descriptions of the morphology and size of NMT endocranial casts have been based largely on approximations rather than reliable determination. Accordingly, here we use micro-CT scans of the skulls of 1 Dinocephalia and 3 Biarmosuchia, which are NMT with a fully ossified braincase and thus a complete endocast. For the first time, our work enables the accurate determination of endocranial shape and size in NMT. This study suggests that NMT brain size falls in the upper range of the reptilian and amphibian variation. Brain size in the dicynodont Kawingasaurus is equivalent to that of early Mammaliaformes, whereas the Dinocephalia show evidence of a secondary reduction of brain size. In addition, unlike other NMT in which the endocast has a tubular shape and its parts are arranged in a linear manner, the biarmosuchian endocast is strongly flexed at the level of the midbrain, creating a near right angle between the fore- and hindbrain. These data highlight an unexpected diversity of endocranial size and morphology in NMT, features that are usually considered conservative in this group.

When and how did the terrestrial mid-Permian mass extinction occur? Evidence from the tetrapod record of the Karoo Basin, South Africa.

A mid-Permian (Guadalupian epoch) extinction event at approximately 260 Ma has been mooted for two decades. This is based primarily on invertebrate biostratigraphy of Guadalupian-Lopingian marine carbonate platforms in southern China, which are temporally constrained by correlation to the associated Emeishan Large Igneous Province (LIP). Despite attempts to identify a similar biodiversity crisis in the terrestrial realm, the low resolution of mid-Permian tetrapod biostratigraphy and a lack of robust geochronological constraints have until now hampered both the correlation and quantification of terrestrial extinctions. Here we present an extensive compilation of tetrapod-stratigraphic data analysed by the constrained optimization (CONOP) algorithm that reveals a significant extinction event among tetrapods within the lower Beaufort Group of the Karoo Basin, South Africa, in the latest Capitanian. Our fossil dataset reveals a 74-80% loss of generic richness between the upper Tapinocephalus Assemblage Zone (AZ) and the mid-Pristerognathus AZ that is temporally constrained by a U-Pb zircon date (CA-TIMS method) of 260.259 ± 0.081 Ma from a tuff near the top of the Tapinocephalus AZ. This strengthens the biochronology of the Permian Beaufort Group and supports the existence of a mid-Permian mass extinction event on land near the end of the Guadalupian. Our results permit a temporal association between the extinction of dinocephalian therapsids and the LIP volcanism at Emeishan, as well as the marine end-Guadalupian extinctions.

Physiological implications of the abnormal absence of the parietal foramen in a late Permian cynodont (Therapsida).

The third eye (pineal eye), an organ responsible for regulating exposure to sunlight in extant ectotherms, is located in an opening on the dorsal surface of the skull, the parietal foramen. The parietal foramen is absent in extant mammals but often observed in basal therapsids, the stem-group to true mammals. Here, we report the absence of the parietal foramen in a specimen of Cynosaurus suppostus, a Late Permian cynodont from South Africa (SA). Comparison with Procynosuchus delaharpeae, a contemporaneous non-mammalian cynodont from SA, demonstrates that the absence of this foramen is an abnormal condition for such a basal species. Because seasonality was marked during the Late Permian in SA, it is proposed that the third eye was functionally redundant in Cynosaurus, possibly due to the acquisition of better thermoregulation or the evolution of specialized cells in the lateral eyes to compensate for the role of the third eye.

Carnivorous dinocephalian from the Middle Permian of Brazil and tetrapod dispersal in Pangaea.

The medial Permian (~270-260 Ma: Guadalupian) was a time of important tetrapod faunal changes, in particular reflecting a turnover from pelycosaurian- to therapsid-grade synapsids. Until now, most knowledge on tetrapod distribution during the medial Permian has come from fossils found in the South African Karoo and the Russian Platform, whereas other areas of Pangaea are still poorly known. We present evidence for the presence of a terrestrial carnivorous vertebrate from the Middle Permian of South America based on a complete skull. Pampaphoneus biccai gen. et sp. nov. was a dinocephalian "mammal-like reptile" member of the Anteosauridae, an early therapsid predator clade known only from the Middle Permian of Russia, Kazakhstan, China, and South Africa. The genus is characterized, among other features, by postorbital bosses, short, bulbous postcanines, and strongly recurved canines. Phylogenetic analysis indicates that the Brazilian dinocephalian occupies a middle position within the Anteosauridae, reinforcing the model of a global distribution for therapsids as early as the Guadalupian. The close phylogenetic relationship of the Brazilian species to dinocephalians from South Africa and the Russian Platform suggests a closer faunistic relationship between South America and eastern Europe than previously thought, lending support to a Pangaea B-type continental reconstruction.

Unique trackway on Permian Karoo shoreline provides evidence of temnospondyl locomotory behaviour.

Large-bodied temnospondyl amphibians were the dominant predators in non-marine aquatic ecosystems from the Carboniferous to the Middle Triassic. In the Permian-aged lower Beaufort Group of the main Karoo Basin, South Africa, temnospondyls are represented exclusively by the family Rhinesuchidae and are well represented by body fossils, whereas trace fossils are scarce. Accordingly, most interpretations of the behaviour of this family are based on skeletal morphology and histological data. Here we document the sedimentology and palaeontology of a late Permian palaeosurface situated immediately below the palaeoshoreline of the Ecca Sea (transition from the Ecca Group to the Beaufort Group) near the town of Estcourt in KwaZulu-Natal Province. The surface preserves numerous ichnofossils, including tetrapod footprints and fish swim-trails, but most striking are seven body impressions and associated swim trails that we attribute to a medium-sized (~1.9 m long) rhinesuchid temnospondyl. These provide valuable insight into the behaviour of these animals. The sinuous shape of some of the traces suggest that the tracemaker swam with continuous sub-undulatory propulsion of the tail.

A lamprey from the Devonian period of South Africa.

Lampreys are the most scientifically accessible of the remaining jawless vertebrates, but their evolutionary history is obscure. In contrast to the rich fossil record of armoured jawless fishes, all of which date from the Devonian period and earlier, only two Palaeozoic lampreys have been recorded, both from the Carboniferous period. In addition to these, the recent report of an exquisitely preserved Lower Cretaceous example demonstrates that anatomically modern lampreys were present by the late Mesozoic era. Here we report a marine/estuarine fossil lamprey from the Famennian (Late Devonian) of South Africa, the identity of which is established easily because many of the key specializations of modern forms are already in place. These specializations include the first evidence of a large oral disc, the first direct evidence of circumoral teeth and a well preserved branchial basket. This small agnathan, Priscomyzon riniensis gen. et sp. nov., is not only more conventionally lamprey-like than other Palaeozoic examples, but is also some 35 million years older. This finding is evidence that agnathans close to modern lampreys had evolved before the end of the Devonian period. In this light, lampreys as a whole appear all the more remarkable: ancient specialists that have persisted as such and survived a subsequent 360 million years.

South African Lagerstätte reveals middle Permian Gondwanan lakeshore ecosystem in exquisite detail.

Continental ecosystems of the middle Permian Period (273-259 million years ago) are poorly understood. In South Africa, the vertebrate fossil record is well documented for this time interval, but the plants and insects are virtually unknown, and are rare globally. This scarcity of data has hampered studies of the evolution and diversification of life, and has precluded detailed reconstructions and analyses of ecosystems of this critical period in Earth's history. Here we introduce a new locality in the southern Karoo Basin that is producing exceptionally well-preserved and abundant fossils of novel freshwater and terrestrial insects, arachnids, and plants. Within a robust regional geochronological, geological and biostratigraphic context, this Konservat- and Konzentrat-Lagerstätte offers a unique opportunity for the study and reconstruction of a southern Gondwanan deltaic ecosystem that thrived 266-268 million years ago, and will serve as a high-resolution ecological baseline towards a better understanding of Permian extinction events.

Computed Tomography elucidates ontogeny within the basal therapsid clade Biarmosuchia.

Biarmosuchia is a clade of basal therapsids that includes forms possessing plesiomorphic 'pelycosaurian' cranial characters as well as the highly derived Burnetiamorpha which are characterised by cranial pachyostosis and a variety of cranial bosses. Potential ontogenetic variation in these structures has been suggested based on growth series of other therapsids with pachyostosed crania, which complicates burnetiamorph taxonomic distinction and thus it is essential to better understand cranial ontogeny of the Burnetiamorpha. Here, three new juvenile biarmosuchian skulls from the late Permian of South Africa are described using X-ray micro computed tomography (CT). We found that juvenile biarmosuchians are distinguished from adults by their relatively large orbits, open cranial sutures, and incomplete ossification of the braincase and bony labyrinth. Also, they manifest multiple centres of ossification within the parietal and preparietal bones. CT examination reveals that the holotype of Lemurosaurus pricei (BP/1/816), previously alleged to be a juvenile, shows no evidence of juvenility and is thus probably an adult. This suggests that the larger skull NMQR 1702, previously considered to be an adult L. pricei, may represent a new taxon. This study provides, for the first time, a list of characters by which to recognise juvenile biarmosuchians.

A new specimen of Biseridens qilianicus indicates its phylogenetic position as the most basal anomodont.

A new well-preserved basal therapsid skull from the Xidagou Formation, Middle Permian of China, is identified as Biseridens qilianicus. The following synapomorphies distinguish Biseridens as an anomodont and not an eotitanosuchian as previously described: short snout; dorsally elevated zygomatic arch and septomaxilla lacking elongated posterodorsal process between nasal and maxilla. The presence of a differentiated tooth row; denticles on vomer, palatine and pterygoid; contact between tabular and opisthotic; lateral process of transverse flange of pterygoid free of posterior ramus and absence of mandibular foramen exclude it from other anomodonts. Our cladistic analysis indicates Biseridens to be the most basal anomodont, highlights separate Laurasian and Gondwanan basal anomodont clades and suggests that dicynodonts had their origins in the Gondwanan clade. The co-occurrence of the most basal anomodont (Biseridens) together with the most basal therapsid (Raranimus), basal anteosaurid dinocephalians, bolosaurids and dissorophids suggests that the earliest therapsid faunas are from China.

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.

Evolution of facial innervation in anomodont therapsids (Synapsida): Insights from X-ray computerized microtomography.

Anomodontia was the most successful herbivorous clade of the mammalian stem lineage (non-mammalian synapsids) during the late Permian and Early Triassic. Among anomodonts, Dicynodontia stands apart because of the presence of an osseous beak that shows evidence of the insertion of a cornified sheath, the ramphotheca. In this study, fourteen anomodont specimens were microCT-scanned and their trigeminal canals reconstructed digitally to understand the origin and evolution of trigeminal nerve innervation of the ramphotheca. We show that the pattern of innervation of the anomodont "beak" is more similar to that in chelonians (the nasopalatine branch is enlarged and innervates the premaxillary part of the ramphotheca) than in birds (where the nasopalatine and maxillary branches play minor roles). The nasopalatine branch is noticeably enlarged in the beak-less basal anomodont Patranomodon, suggesting that this could be an anomodont or chainosaur synapomorphy. Our analyses suggest that the presence or absence of tusks and postcanine teeth are often accompanied by corresponding variations of the rami innervating the caniniform process and the alveolar region, respectively. The degree of ossification of the canal for the nasal ramus of the ophthalmic branch also appears to correlate with the presence of a nasal boss. The nasopalatine canal is absent from the premaxilla in the Bidentalia as they uniquely show a large plexus formed by the internal nasal branch of the maxillary canal instead. The elongated shape of this plexus in Lystrosaurus supports the hypothesis that the rostrum evolved as an elongation of the subnarial region of the snout. Finally, the atrophied and variable aspect of the trigeminal canals in Myosaurus supports the hypothesis that this genus had a reduced upper ramphotheca.

Synchrotron scanning reveals the palaeoneurology of the head-butting Moschops capensis (Therapsida, Dinocephalia).

Dinocephalian therapsids are renowned for their massive, pachyostotic and ornamented skulls adapted for head-to-head fighting during intraspecific combat. Synchrotron scanning of the tapinocephalid Moschops capensis reveals, for the first time, numerous anatomical adaptations of the central nervous system related to this combative behaviour. Many neural structures (such as the brain, inner ear and ophthalmic branch of the trigeminal nerve) were completely enclosed and protected by bones, which is unusual for non-mammaliaform therapsids. The nearly complete ossification of the braincase enables precise determination of the brain cavity volume and encephalization quotient, which appears greater than expected for such a large and early herbivore. The practice of head butting is often associated with complex social behaviours and gregariousness in extant species, which are known to influence brain size evolution. Additionally, the plane of the lateral (horizontal) semicircular canal of the bony labyrinth is oriented nearly vertically if the skull is held horizontally, which suggests that the natural position of the head was inclined about 60-65°to the horizontal. This is consistent with the fighting position inferred from osteology, as well as ground-level browsing. Finally, the unusually large parietal tube may have been filled with thick conjunctive tissue to protect the delicate pineal eye from injury sustained during head butting.

Reappraisal of the envenoming capacity of Euchambersia mirabilis (Therapsida, Therocephalia) using µCT-scanning techniques.

Euchambersia mirabilis is an iconic species of Permo-Triassic therapsid because of its unusually large external maxillary fossa linked through a sulcus to a ridged canine. This anatomy led to the commonly accepted conclusion that the large fossa accommodated a venom gland. However, this hypothesis remains untested so far. Here, we conducted a µCT scan assisted reappraisal of the envenoming capacity of Euchambersia, with a special focus on the anatomy of the maxillary fossa and canines. This study shows that the fossa, presumably for the venom-producing gland, is directly linked to the maxillary canal, which carries the trigeminal nerve (responsible for the sensitivity of the face). The peculiar anatomy of the maxillary canal suggests important reorganisation in the somatosensory system and that a ganglion could possibly have been present in the maxillary fossa instead of a venom gland. Nevertheless, the venom gland hypothesis is still preferred since we describe, for the first time, the complete crown morphology of the incisiform teeth of Euchambersia, which strongly suggests that the complete dentition was ridged. Therefore Euchambersia manifests evidence of all characteristics of venomous animals: a venom gland (in the maxillary fossa), a mechanism to deliver the venom (the maxillary canal and/or the sulcus located ventrally to the fossa); and an apparatus with which to inflict a wound for venom delivery (the ridged dentition).

New Late Permian tectonic model for South Africa's Karoo Basin: foreland tectonics and climate change before the end-Permian crisis.

Late Permian Karoo Basin tectonics in South Africa are reflected as two fining-upward megacycles in the Balfour and upper Teekloof formations. Foreland tectonics are used to explain the cyclic nature and distribution of sedimentation, caused by phases of loading and unloading in the southern source areas adjacent to the basin. New data supports this model, and identifies potential climatic effects on the tectonic regime. Diachronous second-order subaerial unconformities (SU) are identified at the base and top of the Balfour Formation. One third-order SU identified coincides with a faunal turnover which could be related to the Permo-Triassic mass extinction (PTME). The SU are traced, for the first time, to the western portion of the basin (upper Teekloof Formation). Their age determinations support the foreland basin model as they coincide with dated paroxysms. A condensed distal (northern) stratigraphic record is additional support for this tectonic regime because orogenic loading and unloading throughout the basin was not equally distributed, nor was it in-phase. This resulted in more frequent non-deposition with increased distance from the tectonically active source. Refining basin dynamics allows us to distinguish between tectonic and climatic effects and how they have influenced ancient ecosystems and sedimentation through time.

Oxygen isotopes suggest elevated thermometabolism within multiple Permo-Triassic therapsid clades.

The only true living endothermic vertebrates are birds and mammals, which produce and regulate their internal temperature quite independently from their surroundings. For mammal ancestors, anatomical clues suggest that endothermy originated during the Permian or Triassic. Here we investigate the origin of mammalian thermoregulation by analysing apatite stable oxygen isotope compositions (δ18Op) of some of their Permo-Triassic therapsid relatives. Comparing of the δ18Op values of therapsid bone and tooth apatites to those of co-existing non-therapsid tetrapods, demonstrates different body temperatures and thermoregulatory strategies. It is proposed that cynodonts and dicynodonts independently acquired constant elevated thermometabolism, respectively within the Eucynodontia and Lystrosauridae + Kannemeyeriiformes clades. We conclude that mammalian endothermy originated in the Epicynodontia during the middle-late Permian. Major global climatic and environmental fluctuations were the most likely selective pressures on the success of such elevated thermometabolism.

Cranial Bosses of Choerosaurus dejageri (Therapsida, Therocephalia): Earliest Evidence of Cranial Display Structures in Eutheriodonts.

Choerosaurus dejageri, a non-mammalian eutheriodont therapsid from the South African late Permian (~259 Ma), has conspicuous hemispheric cranial bosses on the maxilla and the mandible. These bosses, the earliest of this nature in a eutheriodont, potentially make C. dejageri a key species for understanding the evolutionary origins of sexually selective behaviours (intraspecific competition, ritualized sexual and intimidation displays) associated with cranial outgrowths at the root of the clade that eventually led to extant mammals. Comparison with the tapinocephalid dinocephalian Moschops capensis, a therapsid in which head butting is strongly supported, shows that the delicate structure of the cranial bosses and the gracile structure of the skull of Choerosaurus would be more suitable for display and low energy combat than vigorous head butting. Thus, despite the fact that Choerosaurus is represented by only one skull (which makes it impossible to address the question of sexual dimorphism), its cranial bosses are better interpreted as structures involved in intraspecific selection, i.e. low-energy fighting or display. Display structures, such as enlarged canines and cranial bosses, are widespread among basal therapsid clades and are also present in the putative basal therapsid Tetraceratops insignis. This suggests that sexual selection may have played a more important role in the distant origin and evolution of mammals earlier than previously thought. Sexual selection may explain the subsequent independent evolution of cranial outgrowths and pachyostosis in different therapsid lineages (Biarmosuchia, Dinocephalia, Gorgonopsia and Dicynodontia).

Fossorial Origin of the Turtle Shell.

The turtle shell is a complex structure that currently serves a largely protective function in this iconically slow-moving group [1]. Developmental [2, 3] and fossil [4-7] data indicate that one of the first steps toward the shelled body plan was broadening of the ribs (approximately 50 my before the completed shell [5]). Broadened ribs alone provide little protection [8] and confer significant locomotory [9, 10] and respiratory [9, 11] costs. They increase thoracic rigidity [8], which decreases speed of locomotion due to shortened stride length [10], and they inhibit effective costal ventilation [9, 11]. New fossil material of the oldest hypothesized stem turtle, Eunotosaurus africanus [12] (260 mya) [13, 14] from the Karoo Basin of South Africa, indicates the initiation of rib broadening was an adaptive response to fossoriality. Similar to extant fossorial taxa [8], the broad ribs of Eunotosaurus provide an intrinsically stable base on which to operate a powerful forelimb digging mechanism. Numerous fossorial correlates [15-17] are expressed throughout Eunotosaurus' skeleton. Most of these features are widely distributed along the turtle stem and into the crown clade, indicating the common ancestor of Eunotosaurus and modern turtles possessed a body plan significantly influenced by digging. The adaptations related to fossoriality likely facilitated movement of stem turtles into aquatic environments early in the groups' evolutionary history, and this ecology may have played an important role in stem turtles surviving the Permian/Triassic extinction event.