The two vertebrate fossil assemblages from the ?Middle Triassic Ntawere Formation have been known since the 1960s, but little new work has been done since the description of novel taxa in the 1960s and 1970s. Three recent field seasons have increased vertebrate diversity in the upper Ntawere assemblage and expanded biostratigraphic connections between the lower and upper Ntawere assemblages and assemblages in fossiliferous basins across southern Pangea. The upper Ntawere contains hybodontoid sharks, ptychoceratodontid lungfish, large- and small-bodied stereospondyl amphibians (Cherninia, ‘Stanocephalosaurus’ Batrachosuchus, a new taxon), stahleckeriid dicynodonts (Sangusaurus, Zambiasaurus), traversodontid and trirachodontid cynodonts (Luangwa, a new species, Cricodon), and at least four archosauromorphs, including a large loricatan pseudosuchian, a shuvosaurid poposauroid, and silesaurid dinosauriforms (Lutungutali), whereas the lower Ntawere contains the cynodonts Cynognathus and Diademodon and species of the dicynodont Kannemeyeria. The lower and upper Ntawere assemblages have been correlated with the middle and upper subzones of the Cynognathus Assemblage Zone of the Karoo Basin, South Africa, into a network of connections between assemblages in modern day Tanzania, Argentina, Brazil, Namibia, Antarctica, and India. Although lower Ntawere correlations are reinforced by the occurrence of Cynognathus, new observations from the upper Ntawere, in combination with field work in Tanzania, Namibia, and Brazil, have shifted the geographic focus of biostratigraphic connection away from the Karoo later in the Triassic. A recent radiometric date from Argentina from below the horizon correlated with both the Karoo and the lower Ntawere places these, and all higher assemblages, into the Carnian Stage of the Late Triassic.

The partial skull and postcranial skeleton of a subadult Cricodon metabolus is described as the first record of a trirachodontid cynodont from the upper Ntawere Formation of northeastern Zambia. On the basis of features in the type and referred specimen, Cricodon metabolus can be diagnosed by the presence of a posterior cingulum in the lower postcanines that opens labially in a ‘V’-shaped notch between a large basal cuspule and the steeply descending posterior ridge of the principal labial cusp, and by a pair of large foramina on the maxillary shelf. The subadult specimen shows evidence for four series of postcanine teeth, including a wave of small gomphodont teeth being replaced by a younger wave of larger gomphodont teeth. Cladistic analysis of 75 characters in 27 cynodonts recovers Trirachodontidae as a clade that is the sister taxon of Traversodontidae. Trirachodontidae includes four species, with Langbergia modisei as the earliest diverging taxon. Our analysis also recovers ‘Trirachodon’ kannemeyeri as the sister taxon of Cricodon metabolus, leading us to transfer the former species to the genus Cricodon. Trirachodon berryi is determined to be a valid taxon that is sister to Cricodon. Two reputed trirachodontids from China, Sinognathus gracilis and Beishanodon youngi, do not appear as trirachodontids in our analysis but rather resolve as sister taxa within Traversodontidae. Although this hypothesis of relationships is not supported by the current analysis, we suggest that the two Chinese species might be probainognathians that convergently evolved expanded postcanine teeth rather than gomphodontians.

We report new data on the climate, paleoenvironments, and burial history of tetrapod fossils in the Middle Triassic Lifua Member of the Manda Beds (Songea Group) of southern Tanzania. Two bone-bearing intervals have been identified, both hosted by rubified floodplain mudrocks deposited alongside rivers that flowed from the Ruhuhu rift scarps into a series of subsiding basins under a warm, seasonally wet climate. The lower occurrence is a bonebed containing fossils of a large dicynodont (Dolichuranus), large cynodonts (Cynognathus), temnospondyls, small reptiles, and at least two archosauromorph reptiles. A chaotic melange of semiarticulated, disarticulated, and reworked bones associated with pedogenically mottled sandy siltstone is interpreted as having accumulated in a distal crevasse splay complex. The middle to upper Lifua bone accumulations are associated with floodplain pond and sheetwash deposits. Outcropping as isolated patches of strongly calcified rubified mudstones with lenses of reworked glaebule conglomerate, these accumulations contain partially articulated archosaur (Asilisaurus, Nundasuchus) and cynodont (Scalenodon) skeletons along with vertebrate coprolites and nonmarine bivalves (‘Unio’). Changes in floodplain facies, faunal assemblage, and taphonomic style between lower and middle to upper Lifua strata are similar to those recorded between the middle and upper Burgersdorp Formation (subzones B to C of the Cynognathus Assemblage Zone) of the main Karoo Basin of South Africa. We propose that an increase in mean annual temperature and rainfall in southwestern Gondwana during Early to Middle Triassic times resulted in vegetated, semipermanent water bodies in the floodplain depressions that supported a relatively diverse assemblage of herbivorous dicynodont, cynodont, and early archosaur populations.

A collaborative field work program in the Triassic of Tanzania and Zambia has produced a plethora of new fossil material. Parareptiles, however, are rare, with only one procolophonoid specimen found to date. In 2012, a new procolophonid parareptile, Mandaphon nadra, gen. et sp. nov., was discovered. The single specimen, consisting of a skull and partial postcranium, displays the autapomorphy of two raised, lozenge-shaped bosses on the quadratojugal. Whereas the posterior maxillary teeth are small, labiolingually expanded, and vaguely bicuspid, the premaxillary teeth are much larger and conical, a trait more commonly found in leptopleuronine procolophonids. The large, lozenge-shaped bosses on the quadratojugal do not correspond to additional ossification in other areas in the skull. In a phylogenetic analysis of procolophonoid relationships consisting of 59 characters and 28 procolophonoid taxa, Mandaphon appears within a poorly supported but monophyletic Leptopleuroninae, the first of this clade found in Africa. The presence of Mandaphon along with the procolophonoid Ruhuhuaria in the Manda Beds is only the third known co-occurrence of members of these two groups, with most non-procolophonid procolophonoids restricted to the Permian and Early Triassic.

During the recovery from the end-Permian extinctions in the Middle Triassic, small reptiles (<50 cm) are exceptionally rare, and this gap in the fossil record inhibits our understanding of small reptile ecology and evolution during such a critical transition in Earth history. Here, we fully describe two fragments of left and right hemimandibles of a small sauropsid (UMZC T1162) that likely belonged to the same individual. The specimen bears anteriorly enlarged dentary teeth and labiolingually expanded crown bases, two character states unique to Ruhuhuaria reiszi (Procolophonoidea: Owenettidae), a taxon recently described from the same locality. From this, we tentatively assign UMZC T1162 to Ruhuhuaria reiszi. Micro-computed tomography (CT) and scanning electron microscopy (SEM) were employed to fully examine the morphology of the new specimen and illuminate details of the teeth not available in the holotype. The dentition of UMZC T1162 is better preserved than that of the holotype and shows that the more posterior teeth of this animal were chisel-shaped rather than pointed, that at least some of the teeth were transversely expanded at the base, and that tooth implantation is acrodont in the posterior portion and pleurodont in the anterior portion of the dentary. This potential second specimen of Ruhuhuaria reiszi complicates the previously hypothesized relationships of the taxon and further illustrates the difficulties in assigning small sauropsids to various clades in the Triassic Period. If UMZC T1162 does represent another specimen of Ruhuhuaria reiszi, it would show that small Triassic sauropsids had more variation in their tooth implantation and tooth disparity than previously appreciated.

The diverse assemblage of extinct archosaur species known from the Manda Beds of Tanzania has provided key insights into the timing and tempo of the early part of the archosaur radiation during the Middle Triassic. Several archosaur specimens were collected from the Manda Beds in 1933 by F. R. Parrington, and three of these were subsequently described and made the basis of a new genus, ‘Mandasuchus,’ in a 1956 doctoral dissertation. However, this important fossil material was never formally published, and >60 years later ‘Mandasuchus’ and ‘Mandasuchus tanyauchen’ remain nomina nuda, despite frequent references to them in the literature. Here, we provide a detailed description of this material, provide the first formal diagnosis of Mandasuchus tanyauchen, gen. et sp. nov., and assess its phylogenetic position. The holotype of M. tanyauchen includes a well-preserved partial postcranial skeleton and fragmentary cranial remains. Four referred specimens include two partial skeletons, consisting primary of postcranial remains, a partial maxilla that was previously assigned to the dinosaur clade Saurischia, and a well-preserved astragalus and calcaneum that may belong to the holotype individual. Mandasuchus tanyauchen is diagnosed by a unique combination of character states, as well as by two possible autapomorphies (ascending process of maxilla thin and compressed from anterolateral to posteromedial; femur with distinct pit lateral to the distal-most expression of the posteromedial tuber). Our phylogenetic analysis recovered M. tanyauchen within Paracrocodylomorpha, as the sister taxon to all other sampled members of Loricata.

The evolution of the braincase and brain of early pseudosuchians through to the earliest crocodylomorphs is poorly understood given the paucity of specimens, lack of well-preserved material, and lack of consensus on the phylogenetic relationships of the major clades of Pseudosuchia. Here, we describe three differently sized braincases diagnosable as belonging to the archosaur Parringtonia gracilis from the Middle Triassic Manda Beds of Tanzania. One of them, a nearly complete and exceptionally preserved braincase, possesses a complex set of character states typically present in early-diverging Pseudosuchia, but it also possesses nearly all of the character states previously hypothesized to represent synapomorphies exclusive to aetosaurs and crocodylomorphs. Details of the internal anatomy and a reconstructed endocast were obtained through high-resolution computed tomographic data and show a high degree of conservation of brain architecture across Pseudosuchia, in stark contrast to the extensive shifts observed within Theropoda to crown Aves. Integrating cranial and postcranial data into a phylogenetic analysis, we find Parringtonia gracilis to be closely related to a Revueltosaurus-Aetosauria clade at the base of Suchia and distantly related to crocodylomorphs. No matter which pseudosuchian clade is the most closely related to crocodylomorphs, we deduce that homoplasy in the braincase appears to be common across Pseudosuchia.

Bird-line archosaurs (= Avemetatarsalia, the clade containing birds, dinosaurs, pterosaurs, and their kin) originated in the Triassic Period. However, the earliest evolution of this group is poorly documented because fossils are extremely rare and consist mostly of postcrania. Here, we document the osteology of Teleocrater rhadinus, an early avemetatarsalian from the lower portion of the Middle Triassic Lifua Member of the Manda Beds of the Ruhuhu Basin, southwestern Tanzania. Material of Teleocrater rhadinus includes the holotype partial skeleton comprising a single individual, including cervical, trunk, and caudal vertebrae, pectoral, pelvic, forelimb, and hind limb material, and referred specimens representing parts (skull elements, vertebrae, pectoral, pelvic, and limb elements) of at least three other individuals collected from a bonebed. Character states of the skull elements, vertebrae, girdles, and limbs indicate that Teleocrater rhadinus represents the first documented non-ornithodiran avemetatarsalian known from well-preserved, associated material. Furthermore, Teleocrater rhadinus forms part of a newly recognized clade, Aphanosauria, which also contains formerly enigmatic archosaur taxa from across Pangea, including Dongusuchus efremovi from the Middle Triassic of Russia, Yarasuchus deccanensis from the Middle Triassic of India, and Spondylosoma absconditum from the ?Middle Triassic of Brazil. This new clade and other new discoveries from the Middle to Late Triassic elucidate the sequence of character acquisitions at the base of Avemetatarsalia and fill a crucial gap in the understanding of the anatomical transformations that enabled dinosaurs to flourish later in the Mesozoic.

A partial hind limb (femur and tibia) from the Triassic Lifua Member of the Manda Beds (Tanzania) is recognized as a new morphotype of kannemeyeriiform dicynodont. The femur of this specimen is the largest known dicynodont postcranial element from the Manda Beds and indicates an animal nearing the size of the Late Triassic Stahleckeria potens from Brazil and Namibia. This specimen also resembles both Stahleckeria and the related Argentine stahleckeriid Ischigualastia in having an unusually elongate, straight femoral shaft and a massive and bulbous femoral head, but it differs in its compact distal end of the femur and the relative gracility of both its femur and tibia. The recognition of this specimen as a novel form of Manda dicynodont indicates that as many as six distinct kannemeyeriiforms are present in the mid-to-upper Lifua Member fauna, equaling or exceeding the species richness of previously known Laurasian faunas and substantially exceeding the richness of coeval Gondwanan faunas.

The Triassic dicynodont Sangusaurus is poorly known because the holotype of the first species to be described (S. edentatus from Zambia) is fragmentary, and the description of the second species (S. parringtonii from Tanzania) is extremely brief. Nevertheless, the genus has played a role in Triassic biostratigraphy by linking the Ntawere Formation and the Manda Beds. Here, we redescribe Sangusaurus, including a new, nearly complete skull from Tanzania. The incomplete holotype of S. edentatus results in few characters diagnosing the genus. The skull of S. parringtonii, however, is highly autapomorphic. The snout is telescoped, with only a thin strip of frontals separating the nasals and the parietals. The external surfaces of the premaxilla, the maxillae, the nasals, and the prefrontals are extremely rugose; a sharp median crest extends from the premaxilla to the frontals, terminating in a thickened boss. The occiput is broader than the skull is long, and the adductor fossa on the squamosal is nearly vertical. Our phylogenetic analysis shows that Sangusaurus is not a kannemeyeriid but instead is a stahleckeriid. The feeding system of Sangusaurus emphasizes an orthal jaw motion. The articular surfaces of the jaw joint form a single posteroventrally sloping surface; translating the quadrate and the articular results in a primarily orthal movement of the jaw symphysis. The internal and external jaw adductors provide a strong, dorsally-directed component to the power stroke. Adductor mechanical advantage is similar to Stahleckeria, but Sangusaurus likely had a stronger transverse component of jaw movement because of the very lateral placement of M. adductor mandibulae externus lateralis.

Cynognathus crateronotus is a species of large carnivorous cynodont, first named and best known from the Triassic Burgersdorp Formation (Beaufort Group, Karoo Basin) of South Africa. Fossils of the genus have also been reported from the upper Fremouw Formation of Antarctica, the Upper Omingonde Formation of Namibia, and the Río Seco de la Quebrada Formation of Argentina. Without associated cranial material, however, distinguishing the postcrania of Cynognathus from that of the closely related cynognathian, Diademodon tetragonus, has proven difficult. Here we provide a more comprehensive diagnosis for Cynognathus crateronotus and describe two novel occurrences. First, parts of a medium-sized individual were recovered from a scrambled mass of dental and semiarticulated postcranial material from the lower Ntawere Formation of Zambia, a horizon that previously produced fossils of Diademodon and Kannemeyeria. Second, a large individual was collected from a recently discovered locality within the lower part of the Lifua Member of the Manda Beds of Tanzania. A large proportion of the postcranial skeleton, along with some craniodental remains, was found ex situ in a sandy streambed just downstream from a quarry that has produced the dicynodont Dolichuranus, an azendohsaurid archosauromorph, and the avemetatarsalian Teleocrater rhadinus. The widespread occurrence of Cynognathus across southern Pangea demonstrates its utility as a biostratigraphic marker, but recently published radiometric age estimates from Argentina suggest that either the genus persisted for over 10 million years or African strata traditionally interpreted as Middle Triassic are better understood as Late Triassic in age.

Stable carbon isotope analysis of coexisting soil calcite and organic matter sampled from modern, California soil profiles representing 18 different U.S. Department of Agriculture (USDA) official soil series yields 51 paired calcite–organic matter δ¹³C values (Δ¹³C_cc-om values). These paired values correspond to atmospheric pCO₂ estimates ranging from less than ~100 to 2200 ppm_v using standard assumed soil pCO₂ concentrations at temperatures spanning the typical range of modern soil calcite crystallization. Nevertheless, there is a strong negative correlation of Δ¹³C_cc-om values with mean annual precipitation (MAP) among these modern sites, offering a potential means to estimate paleo-MAP values from calcite and associated, occluded organic matter in paleosols. One hundred and twenty-five Δ¹³C_cc-om values from lower Permian–lower Middle Triassic paleosol profiles in the southwestern U.S.A., northwestern China, and Africa are presented as a proxy for paleorainfall over ~85° of paleolatitude. The results indicate substantial spatiotemporal variation in MAP and appear to reflect the development and strengthening of global megamonsoonal atmospheric circulation associated with assembly of the supercontinent Pangea. The data also indicate extremely low rainfall values in regions with endemic tetrapod fossil assemblages, suggesting that climate change was a principal driver of biogeography, biodiversity, and evolution of tetrapod faunas across continental landscapes during Permo-Triassic time.

The Permian-Triassic mass extinction (PTME) was one of the transformative events of the Phanerozoic, marked by extinction, post-Permian transformation of surviving ecosystems, and the formation of new communities. The South African Karoo Basin has served as the primary source of data on the terrestrial component of these events, but its global applicability remains poorly known. Here, we compare Permian-Triassic communities of the Karoo Basin with those from the Luangwa and Ruhuhu basins of Zambia and Tanzania, respectively, analyzing their functional structures and simulating dynamic responses to environmental perturbation. Results show that compositional similarities of late Permian communities among the basins underlie similarities in their dynamics and resistance to secondary extinction. The Karoo Basin ecosystem also displays evidence of a transformation to increased resistance during the late Permian. Although the Karoo Basin ecosystem was reduced significantly by the PTME, structural features of that resistance persisted into the Early Triassic, facilitated by a greater susceptibility to extinction of small-body-sized amniotes and large carnivorous amniotes. It was undone by the initial stages of postextinction restructuring. Continued evolution of the Triassic ecosystem led to a recovery of resistance, but in a community compositionally dissimilar from its Permian antecedents. Likewise, the upper part of the Lifua Member of the Manda Beds (Middle Triassic) of Tanzania was structurally distinct from the Karoo Basin communities but displayed similar dynamics. The recurrence and convergence of communities with different histories toward similar dynamics suggest that there are taxon-independent norms of community assembly and function operating on geological timescales.