An embryonic Synapsid from the Early Triassic of South Africa.

 The persistence of egg-laying in modern Monotremes has led evolutionary biologists to conclude that this is likely to have been the ancestral state in the Synapsids, the group from which the Mammals arose. However, fossil evidence for this has been surprisingly absent. The earliest known potential fossil amniotic egg comes from the Permian of South America, and has been attributed to a Mesosaurid Sauropsid (a group not closely related to Synapsids of Mammals). This specimen preserves an immature skeleton curled in a position consistent with having been in an egg at the time of death, but no actual eggshell (not altogether surprising, as the earliest amniote eggs are not predicted to have been mineralised). The earliest amniotic egg fossils with both embryonic remains and eggshell come from Sauropodomorph dinosaurs from the Early Jurassic of Gondwana. Some potential eggs associated with Synapsid Pelycosaurs from the Early Permian of North America are not considered to be reliable, as neither embryos nor shell structures are preserved.

The Late Triassic-Early Jurassic Elliot Formation of South Africa's Karoo Basin has produced numerous Dinosaur egg fossils with embryos, as well as the skeletal remains of many non-Mammalian Cynodonts, something which has led to questions about whether Permo-Triassic Synapsids laid eggs at all. This is a serious consideration; Synapsids, particularly groups such as Lystrosaurus and Diictodon, are extremely common in the Permian and Triassic of the Karoo, with perinate specimens (specimens thought to have died around the time of birth or hatching) being found here and elsewhere, but no eggs are known. The preservation of Dinosaur eggs in the Karoo suggests there was no taphonomic process here producing a bias against the preservation of eggs, and palaeontologists have been active in the Karoo Basin for over 180 years, suggesting that if such eggs were present, there should have been a good chance of their being found. Egg-laying and bearing live young are found in closely related Snakes and Lizards, and it appears that this group has been able to switch back-and-forth between these conditions fairly easily. It is therefore conceivably possible that Synapsids developed the ability to bear live young very early in their history, and that Monotremes have secondarily switched back to egg-laying.

However, this has wider implications than Synapsid palaeontology. Current theories on the origin of lactation in Mammals have been built on the assumption that this preceeded the switch to live-birth (largely because Monotremes produce both eggs and milk). It is now generally accepted that the purpose of lactation was not originally to feed the young, but rather started as skin secretions used to either moisturise the eggs, provide nutrients, protect them against fungi and bacterial infections, or for hormonal signalling through the egg membrane. Should it be found that the Synapsids from which Mammals evolved bore live young, then these theories would have to be abandoned.

In a paper published in the journal PLoS One on 9 April 2026, Julien Benoit of the Evolutionary Studies Institute at the University of the Witwatersrand, Vincent Fernandez of the European Synchrotron Radiation Facility, and Jennifer Botha of the Evolutionary Studies Institute and Centre of Excellence in Palaeosciences at the University of the Witwatersrand, describe three perinate specimens of the Dicynodont Synapsid Lystrosaurus from the Early Triassic of Xhariep Municipal District in Free State Province, South Africa, one of which appears to have been preserved within an egg.

The specimens examined are the three smallest specimens attributed to Lystrosaurus. They include BP/1/4011, an isolated skull measuring 43.0 mm, discovered by James Kitching in the upper Palingkloof Member of the Balfour Formation at Orangia on Tweefontein 508, BP/1/9332, an almost complete articulated skeleton with a skull length of 44.0 mm, discovered by Brandon Stuart in the upper Palingkloof Member of the Balfour Formation at Nooitgedacht 68 Farm near Spitskop, and NMQR 3636, a complete skeleton with a skull length of 34.5 mm, found by John Nyaphuli at Rheeboksfontein 5 Farm in 2008, probably from the upper Palingkloof Member of the Balfour Formation or the lower Katberg Formation.Each of these fossils was a scanned at the European Synchrotron Radiation Facility in Grenoble, France, with three dimensional models being reconstructed with the Avizo Software Package.

The isolated skull BP/1/4011 was described by Kitching as the smallest known skull attributed to Lystrosaurus in 1964, and attributed to either Lystrosaurus murrayi or Lystrosaurus curvatus by a study in 2006. Benoit et al. are more cautious, attributing it to Lystrosaurus sp. but suggesting it shows affinities to Lystrosaurus curvatus.

The first of the articulated skeletons, BP/1/9332, is considered to be an early juvenile of Lystrosaurus sp., with affinities to Lystrosaurus murrayi. It is preserved in a splayed out position, similar to that of most larger Lystrosaurus specimens from the Karoo Basin, with most bones perfectly articulated, and synchrotron images show that no loose elements are preserved in the surrounding matrix. It appears to be the most developmentally advanced of the three specimens, because its splenials are co-ossified at the mandibular symphysis, although its occipital and basicranial bones remain loose. From the splayed out position in which it was found, Benoit et al. determine that it had hatched before dying, probably moving some distance from its hatching site before death.

Photograph of BP/1/9332 in dorsal view. Benoit et al. (2026).

The final specimen, NMQR 3636, is also considered by Benoit et al. to be an early juvenile of Lystrosaurus sp., with affinities to Lystrosaurus murrayi. However, unlike BP/1/9332, this specimen is curled into a fetal position, consistent with having been within an egg at the time of death. It also appears to be the most developmentally immature of the specimens, lacking tusk buds in its maxillary alveolae, something present in both the other specimens, or a mesethmoid bone, the structure that supports the olfactory bulbs in life, which is again present in the other two specimens. 

Most notably, the lower jaw of NMQR 3636 has an incompletely co-ossified symphyseal suture between the two paired bones in the lower jaw. This is completely co-ossified in both the other specimens, as well as in modern beaked Amniotes such as Turtles and Birds at the time of hatching. Modern Monotremes do hatch with an unfinished intermandibular symphysis, but these feed on milk provided by their mothers for some time after hatching, something Lystrosaurus is not thought likely to have been able to produce. 

Based upon this, Benoit et al. conclude that the early developmental stage of the skeleton, combined with a posture which would be expected of a perinate prior to hatching and a jaw which had not developed to the stage where it could feed on the hard foodstuffs likely to have been consumed by juvenile Lystrosaurus. is indicative of an Animal which died within the egg and was subsequently preserved, albeit without preservation of the egg itself.

Specimen NMQR 3636 in left lateral view. (a) Photograph of the specimen; (b) 3D digital reconstruction of the segmented bones; (c) live reconstruction by artist Sophie Vrard. Colour code for (b): vertebral elements in shades of green, ribs in blue, forelimb elements in red, femur in yellow, pelvic girdle elements in grey, skull in light red, mandible in light orange. Benoit et al. (2026).

Based upon the position of the embryo, it is estimated that the original egg was 3.65 cm long and 2.75 cm in diameter, with an internal mass of 115 cm³ and a mass of 115 g. While size estimates for adult Lystrosaurus vary, this is clearly larger compared to the size of an adult than either living Monotremes or most non-Avian Reptiles, although comparatively smaller than the eggs of Birds. This is probably indicative of a large yolk, which can feed the embryonic Animal for longer, allowing it to develop further within the egg. 

Modern Monotremes produce small eggs compared to the size of an adult, which contain comparatively little yolk material. This is possible because the young hatch at an early developmental stage, and are then nourished with milk. Interestingly, the Jurassic Tritylodontid Cynodont Kayentatherium produced eggs which were even smaller compared to the size of an adult. While Kayentatherium has been reconstructed as being quite Reptile-like in physiology, the small egg size could be a sign that it was capable of a form of lactation. It has also been suggested that Kayentatherium probably had hair, something which is known to be linked genetically to the formation of mammary glands (which produce milk), and it has also been shown that there is a genetic link between the reduction in egg yolk production and the ability to produce milk. All of which suggests that Kayentatherium may have been more Mammal-like than previously reconstructed, and that the appearance of the ability to produce milk may have been closely linked to the emergence of the Mammaliamorpha.

See also...

Inostrancevia africana: An Inostranceviine Gorgonopsian from the Metangula Graben of Northern Mozambique.

The Gorgonopsians were a distinctive group of Therapsid Reptiles known from the Middle-to-Late Permian. They were exclusively terrestrial, had binocular vision, a Crocodile-like, semi-erect gait, and are interpreted as having been homeothermic (capable of maintaining a constant internal temperature through a mixture of behavioural and metabolic processes), and possibly to have had fur and the ability to sweat. The jaws of Gorgonopsians have been reconstructed to have been able to open to more than 90°, and to have been able to deliver a powerful bite, making them formidable predators. The dentition of Gorgonopsians is particularly interesting, as they had Mammal-like heterodont dentition, with distinctive incisor, canine, and molar teeth, but retained Reptile-like polyphyodont tooth-replacement (i.e., new teeth constantly replacing older, worn, teeth throughout their lives). The canine teeth of Gorgonopsians were greatly enlarged compared to the other teeth, giving them a 'sabre-toothed' gape, and serrated in a similar way to the teeth of predatory Theropod Dinosaurs.

The earliest Gorgonopsians were small Animals, with skulls 10-15 cm in length, found in European Russia. The group split into two clades quite early on, one persisting in European Russia and the other spreading to Africa, where they became a successful and diverse group best known from the Karoo Basin of South Africa. Both groups grew steadily over the remainder of the Permian, with the largest being the Late Permian Inostranceviines, a group of 'Russian' Gorgonopsians which spread into Africa for a second time, the largest of which had skulls 60 cm in length, and are interpeted as having had body-lengths of up to 3.5 m and body masses of around 300 kg.

The Metangula Graben of northern Mozambique has produced a range of Late Permian fossils comparable to those found in the Karoo Basin of South Africa, including pollen, Plants, and Vertebrate Animals, notably Dicynodonts such as Dicynodon angielczyki, Daptocephalus leoniceps, Dicynodontoides/Kingoria, Endothiodon mahalonobisi, and Lystrosaurus. However, despite their importance in the Karoo ecosystems, only fragmentary and unidentifiable Gorgonopsian remains have been described from the Metangula Graben to date.

In a paper published in the Swiss Journal of Palaeontology on 6 March 2025, Zanildo Macungo of the Museu Nacional de Geologia in Maputo, and the Evolutionary Studies Institute at the University of the Witwatersrand, Julien Benoit, also of the Evolutionary Studies Institute at the University of the Witwatersrand, and Ricardo Araújo of the Centro de Recursos e Ambiente & Instituto de Plasmas e Fusão Nuclear at the Universidade de Lisboa, describe a Gorgonopsian specimen from the Metangula Graben of Northern Mozambique. 

The described specimen, PPM2018-7Z, was collected along one of the branches leading to the Maluízo River, about 3 km to the northwest of the town of Mepoche in Lago District. This exposure is considered to belong to the K6a2 Member of the K6 Formation, which has produced Therapsid taxa such as Daptocephalus cf. Daptocephalus leoniceps and Dicynodontoides/Kingoria, and is therefore considered to be equivalent to the Daptocephalus Assemblage Zone of the Karoo Basin, making it 254.5–251 million years old.

Geology and geographical location of the described specimen, PPM2018-7Z. Macungo et al. (2025).

Specimen PPM2018-7Z is a partial skull which has undergone dorsoventral compression and mediolateral shearing. The skull roof, occiput, and a small portion of the posterior part of the basicranium are preserved, although fractures pass through the parietal-frontal suture and the separation between the occiput from the dorsal half of the foramen magnum. The crushing and fracturing has led to the loss of fine structures such as the nuchal ridge, pila antoticae, and most of the parasphenoid rostrum.

Specimen PPM2018-7Z in (A) right lateral view, (B) closer view of the zygomatic arch, (C) medial view of the zygomatic arch. Abbreviations: Fr, frontal; ju., jugal; jutp, jugal temporal process; la, lacrimal; na, nasal; op, opisthotic; opc, opisthotic condyle; pa, parietal; po, postorbital; pold, postorbital bar depression; pof, postfrontal; pr, prootic; prf, prefrontal; sq, squamosal; sqs, squamosal sulcus; sqz, zygomatic process of the squamosal; su, supraoccipital. (C) Not in scale. Macungo et al. (2025).

A small portion of the left maxilla is still attached to the skull, with a larger fragment of the right maxilla being found associated with the skull. Also found in association was large, mediolaterally compressed left canine, and a badly preserved cross-section of the right canine. The preserved left canine is 113 mm long and 32 mm wide at the base; the root is not preserved.

Canine of PPM2018-7Z in (A) distal, (B) mesial, (C) lingual, (D) labial, views. (E) Closer view of the basal-lingual surface, (F) closer view of the apico-lingual surface. Abbreviations: apr, apicobasal ridges; de, denticles; dic, distal carina; lafa, labial surface; lid, lingual depression; lifa, lingual surface; mec mesial carina. Panels (E) and (F) are not in scale. Macungo et al. (2025).

Specimen PPM2018-7Z is assigned to the species Inostrancevia africana, on the basis of  the presence of rugosity and small foramina on the lateral face of the prefrontal, an orbit larger than the temporal fenestra (11  cm vs. 9 cm, respectively), extreme narrowing of the jugal below the orbit, a far posterior position of the pineal foramen, a reduced contribution of the frontal to the orbital margins, the presence of a deep parietal depression, an anteroposteriorly greatly expanded postorbital bar ventrally, the protrusion of the postfrontal onto the parietal, and the laterally facing temporal bar of the squamosal.

This represents the fourth specimen of Inostrancevia africana described, with two previously described specimens from the Daptocephalus Assemblage Zone of the Karoo Basin in South Africa, and one from the Usili Formation of the Ruhuhu Basin in Tanzania. This distribution is noteworthy because Inostrancevia africana belongs to the Russian clade of the Gorgonopsian group, with all of its close relatives, including the co-generic Inostrancevia alexandri being found exclusively in European Russia.

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Jiucaiyuangnathus confusus: A new species of Baurioid Therocephalian from the Eartly Triassic of Xinjiang Province, China.

The Bogda Mountains of northeastern Xinjiang Province, China, preserve a Permian-Triassic sequence which has produced a broad range of terrestrial Vertebrates, including non-Mammalian Therapsids such as Dicynodonts, Gorgonopsians, and Therocephalians. Two Therocephalians have been described from this sequence to date, Urumchia lii from the Early Triassic Jiucaiyuan Formation, and Dalongkoua fuae from the Late Permian Guodikeng Formation, although several other species are known from elsewhere in North China, including Shiguignathus wangi, Jiufengia jiai, Euchambersia liuyudongi, and Caodeyao liuyufengi from the Late Permian Naobaogou Formation of Inner Mongolia, Moschowhaitsia lidaqingi from the Late Permian Wufoshi Formation of Gansu Province, Hazhenia concava from the Early Triassic Heshanggou Formation of Inner Mongolia, Ordosiodon lincheyuensis, Ordosiodon youngi and Nothogomphodon sanjiaoensis from the Early Triassic Ermaying Formation of Shanxi Province, Yikezhaogia megafenestrala. from the Early Triassic Ermaying Formation of Inner Mongolia, and Traversodontoides wangwuensis from the Middle Tirassic Ermaying Formation of Henan Province.

In a paper published in the journal Vertebrata PalAsiatica on 20 July 2024, Lui Jun of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences and the College of Earth and Planetary Sciences of the University of the Chinese Academy of Sciences, and Fernando Abdala of the Área de Paleontología at Unidad Ejecutora Lillo and the Evolutionary Studies Institute at the University of the Witwatersrand, describe a new species of Baurioid Therocephalian from the Early Triassic Jiucaiyuan Formation of Jimsar County in Xinjiang Province, China.

The new species is described from a slab on which a partial snout and several postcranial skeletal elements were visible on the surface. When X-ray microcomputed tomography was applied to this slab it was discovered that two largely disarticulated partial skeletons were present within. The partial skeleton is designated as the holotype of the new species (in taxonomy, a specimen is named as the holotype when an new species is discovered, and any other specimens are deemed to belong to that specie species if the can be shown to belong to the same species as the holotype), which is given the name Jiucaiyuangnathus confusus, where 'Jiucaiyuangnathus' means 'Jiucaiyuan-jaw', in reference to the Jiucaiyuan Formation, and 'confusus' means 'confusing' in reference to the difficulty had deciphering the specimens. It is thought that the snout is derived from one of the post-cranial skeletons, but it is impossible to tell which.

Jiucaiyuangnathus confusus (IVPP V32945, holotype) from Jimsar, Xinjiang. (A)–(C) photo (A) and 3D rendering (B) of the left side of the snout in lateral and 3D rendering of the medial view of the left side of the snout (C); (D). 3D rendering of the snout in posterior view showing the bones as preserved. Abbreviations: afo. anteriormost foramen; cc. christa choanalis; F. frontal; L. lacrimal; l.c. lacrimal canal; M. maxilla; m. maxillary tooth; m.a. maxillary antrum; msf. maxillo-septomaxillary foramen; pdl. dorsal layer of palatine; pit. maxillary round pit; PL. palatine; PM. premaxilla; pml. medial layer of palatine; sH, sinus Highmore; SM. septomaxilla; V. vomer. Lui & Abdala (2024).

The preserved portion of the jaws has five surviving incisors and lacks canines. There is a diastema (gap) between the last incisor in the upper jaw and the first maxillary tooth, but no equivalent gap is present in the dentition of the lower jaw, traits consistent with Jiucaiyuangnathus confusus being a Baurioid Therocephalian.

3D rendering of Jiucaiyuangnathus confusus (IVPP V32945, holotype) from Jimsar, Xinjiang . (A) The preserved snout in ventral view; (B), (C) vomer in dorsal (B) and ventral (C) views, vomer is reconstructed in the natural position in (C); (D) left dentary in lateral view; (E), (F) mandibles in dorsal (E) and ventral (F) views. Abbreviations: 1st ic. first incisor; ch. choana; D. dentary; d. dentary tooth; F. frontal; for vn. place for vomeronasal organ; M. maxilla; N. nasal; PL. palatine; PM. premaxilla; SP. splenial; V. vomer; v.f. vomerine foramen. Lui & Abdala (2024).

The two partial skeletons are given the designations IVPP V32946-1 (which is marginally the smaller of the two) and IVPP V32946-2 (which is marginally the larger). While both are largely disarticulated, most of the bones are close to their original positions, making it possible to assign them to one of the two skeletons wirh confidence. In both skeletons, the neural arches are separate from the centra of the vertebrae, making it likely that they were juveniles at the time of death.

Posterior skeletons of Jiucaiyuangnathus confusus (IVPP V32946) from Jimsar, Xinjiang  (A), (B) photo of the slab; (C), (D) 3D rendering of bones. Gray (IVPP V32946-1) and light purple (IVPP V32946-2) are bones of each specimen. Light blue uncertain. Lui & Abdala (2024).

Specimen IVPP V32946-1 has ten presacral vertebrae preserved, the the atlas and axis, five thoracics, and three lumbars, as well as three sacral vertebrae and a series of at least 11 caudal vertebrae, five of them being rod-like. There are three short, curved cervical vertebrae, and five incomplete ribs on the left side and seven nearly complete ribs on the right side of the thoracic vertebrae. An almost complete pelvic girdle lacks only the left ischium. A right femur, lacking a proximal end and with an incomplete distal end, probably belongs to this skeleton.

3D rendering of Jiucaiyuangnathus confusus  (IVPP V32946-1) from Jimsar, Xinjiang.  (A), (B) The preserved skeleton in dorsal (A) and ventral (B) views; (C) right femur in distal view; (D)–(F) atlas and axis in anterior (D), left (E), and right (F) lateral views; (G) four thoracic vertebrae in right lateral view; (H), (I) sacral region in lateral (H) and dorsal (I) views; (J) caudal vertebrae Abbreviations: aic. atlas intercentrum; cdr. caudal rib; cdv. caudal vertebra; cr. cervical rib; FE. femur; lv. lumbar vertebra; ns. neural spine; sr. sacral rib; sv. sacral vertebra; tp. transverse process; tr. thoracic rib; tv. thoracic vertebra. Lui & Abdala (2024).

Specimen IVPP V32946-2 has ten continuous vertebrae, interpreted as thoracics, as well as 13 complete long left thoracic ribs and the proximal side of eight right thoracic ribs. The head of the first sacral rib is considerably expanded dorsoventrally with a short, stout shaft curving ventrally and a very expanded distal end to contact the ilium. This specimen has a nearly complete left scapula and the dorsal portion of the right scapula, as well as a separated procoracoid, which lies close to the ventral side of the scapula. An incomplete interclavicle appears as a broad flat bone that gently curves ventrally, and the sternum is preserved as a large, thin, longer than wide flat plate. Again, the pelvic girdle is almost complete, in this case lacking the left pubis. The proximal parts of both femurs are preserved, with the right being more complete.

3D rendering of Jiucaiyuangnathus confusus (IVPP V32946-2) from Jimsar, Xinjiang. (A), (B) Skeleton in dorsal (A) and ventral (B) views; (C) part of thoracic vertebrae in left lateral view; (D) two sacral and three anterior caudal ribs; (E)–(H) sacral ribs of (D) in dorsal (E), (G) and ventral (F), (H) views; (I)–(L) two smaller sacral ribs in dorsal (I), (K) and ventral (J), (L) views Abbreviations: cdr. caudal rib; mt. metatarsal; sr. sacral rib. Liu & Abdala (2024).

Neither of the skeletons has neural arches fused to the centra, suggesting that they were both juveniles when they died, but the neural arches of the smaller skeleton are more distant from the centra than in the larger, possibly suggesting that it was younger and less developed. There are also differing degrees of ossification in the bones of the pelvic girdle of the two skeletons, which again suggest different levels of development. 

See also...

Pseudotherium argentinus: A (possible) Mammaliamorph Cynodont from the Late Triassic Ischigualasto Formation of Argentina.

One of the major transformations in vertebrate evolution occurred in a series of events leading up to the origin of the Mammals. The transformation, which occurred by or before the Middle Jurassic, took place as several pulses of expansion of the relative size of the brain (encephalization) and the emergence of the uniquely mammalian neocortex.The shift in position and function of mammalian auditory ossicles were also part this transition. From their original position at the jaw joint and dual function in feeding and audition, the auditory ossicles became detached from the jaw and decoupled from feeding to take their characteristic mammalian position suspended beneath the otic capsule and functioned solely in hearing. The closest extinct relatives of the Mammals among the Cynodonts  extremely small, and it was not until the Cainozoic that the independent evolution of large body size began to are characterise various Mammal groups. Owing to their small size these fossils have proven difficult to prepare and to study in detail using conventional methods.

In a paper published in the journal PLoS One on 7 August 2019, Rachel Wallace of the Jackson School of Geosciences at the University of Texas at Austin, Ricardo Martínez of the División Paleontologia de Vertebrados at the Universidad Nacional de San Juan, and Timothy Rowe, also of the School of Geosciences at the University of Texas at Austin, describe a new species of Cynodont from the early Late Triassic Ischigualasto Formation of Valle Pintado in Ischigualasto Provincial Park, San Juan Province, Argentina.

The Ischigualasto Formation outcrops out in northwestern Argentina and forms part of the Ischigualasto-Villa Unión Basin. It comprises a sequence of fluvial channel sandstones with well-drained floodplain sandstones and mudstones. Interlayered volcanic ash layers above the base and below the top of the formation provide chronostratigraphic control and yielded ages of 231 and 226 million years old. The Ischigualasto Formation is divided into four members. The La Peña Member forms the lowest 40 m of the formation and consists of multistory channel sandstones and conglomerates covered by poorly-drained floodplain mudstones. The Cancha de Bochas member forms the next 140 m and is composed of thick, well-drained floodplain mudstones interbedded with high-sinuosity channel sandstones. The Valle de la Luna Member forms the next 470 m, and is mostly characterised by amalgamated high-sinuosity channels, abandoned channels and marsh deposits. Finally, the Quebrada de la Sal Member forms the uppermost 50 m of the Ischigualasto Formatio, and consists of tabular fluvial deposits.

 Geographic and geologic maps of the southern portion of the Ischigualasto-Villa Unión Basin. Wallace et al. (2019).

The Ischigualasto Formation is also divided from base to top into three abundance-based biozones. The Scaphonyx-Exaeretodon-Herrerasaurus biozone, which is characterised by a predominance of the Rhynchosaur Scaphonyx, the Cynodont Exaeretodon, and the Dinosaur Herrerasaurus, but also includes the majority of known fossils and the highest taxonomic diversity. The Exaeretodon biozone is characterised by low diversity and high relative abundance of the Cynodont Exaeretodon. The Jachaleria biozone is almost devoid of vertebrate fossils except for scarce specimens of the Dicynodont Jachaleria.

The specimen from which the new Cynodont species is described was found in 2006 by Ricardo Martínez during a field trip to the Ischigualasto Formation carried out by the Instituto y Museo de Ciencias Naturales of the Universidad Nacional de San Juan. It was found at the Valle Pintado locality, which is located in the upper levels of the La Peña Member and in the lower portion of the Scaphonyx-Exaeretodon-Herrerasaurus biozone, n a fossiliferous layer 40 m above the base of the Formation. This is one of the most fossiliferous horizons known in the Ischigualasto Formation, and a diverse and abundant fauna has been recovered from the same level, including several specimens of the Theropod Dinosaur Herrerasaurus, the type specimen of the basal Sauropodomorph Dinosaur Panphagia, plus various carnivorous and herbivorous Cynodonts, Rhynchosaurs, and Pseudosuchian Archosaurs.

The new species is named Pseudotherium argentinus, where 'Pseudotherium' means 'false beast' in Greek (the suffix '-therium', meaning 'beast' is commonly used to indicate Mammals in palaeontology), and 'argentinus' indicates the area where it was found. It is described from a single specimen which comprises an isolated skull that is missing the mandibles, most of the premaxillae, zygomatic arches, and quadrates. One incomplete stapes and one quadratojugal are preserved. Much of the superficial surface of the skull was exposed through manual preparation. Anatomical investigation of the interior utilise micro-computed tomography, and from these scans 3D printouts of enlarged models of the specimen were made to augment and extend observation of its surficial anatomy.

Pseudotherium argentinus, a comparison of image processing methods based on utilize micro-computed tomography scans. (A) Isosurface rendering; (B) volume rendering, scattering algorithm, no digital matrix removal. Wallace et al. (2019).

Pseudotherium argentinus is considered to be a Probainognathian Cynodont (the goup that includes all Mammals, as well as some non-Mammalian groups). It has a lacrimal bone that contributes extensively to the floor of the orbit; the frontal bone has a long orbital process that contacts a short orbital process of the palatine near the floor of the orbit; the orbital process of the palatine is low and contributes little to the orbital wall; the prefrontal bone is superficially large and extends anteriorly (forwards), medial to (inside) the lacrimal, contributing to the lateral wall of the nasopharyngeal passage (nasal trumpet); a vestige of the postorbital bone is preserved behind the orbit, but lacks an ossified postorbital bar; the interpterygoid vacuities (openings in the palete) remained open throughout life; laterally flaring parasphenoid alae (ridges on the paraspenoid bone) intersect at an obtuse angle between their contacts with the petrosal promontorium (protusion on the petrosal bone); there is a longitudinal ventral process on the basisphenoid; the lambdoidal crest strongly overlaps the occipital plate; there is a large, open spaces within the spongy bone of the parietal, petrosal, squamosal, basioccipital, basisphenoid, supraoccipital, and exoccipital surrounding the braincase; the vertical margin of the petrosal (prootic) lateral flange is notched; the upper canines are long, laterally compressed and non-serrated with a ridge on both their labial and lingual surfaces; there are nine upper postcanine teeth with the first postcanine consisting of a single cusp, while blunt, indistinct cusps form the crowns of the remaining postcanines.

Pseudotherium argentinus, digitally colored 3D volume renderings of the holotype. Skull in dorsal (top), right lateral (middle), and ventral (bottom) views. Abbreviations: al, alisphenoid; alqr, quadrate ramus of alisphenoid; bo, basioccipital; ce, cavum epiptericum; eo, exoccipital; fr, frontal; if, incisive fossa; ju, jugal; la, lacrimal; mx, maxilla; na, nasal; os, orbitosphenoid; pal, palatine; par, parietal pbc, parabasisphenoid complex; pet, petrosal (= periotic); pf, prefrontal; po, postorbital; pt, pterygoid; ptqr, quadrate ramus of pterygoid; smx, septomaxilla; so, supraoccipital; sq, squamosal; st, stapes; tb, tabular; vo, vomer. Wallace et al. (2019).

A number of features suggest that the holotype was approaching full skeletal maturity at time of death. The sagittal and lamdoidal crests are well developed; the orbit is relatively small compared to other skull proportions; the prootic and opisthotic are fused to form the petrosal; and extensive fusion has occurred between the basioccipital and exoccipitals, and between the tabular, supraoccipital, and interparietal. Additionally, a short diastema between the canine and the first postcanine suggests that a tooth had been shed and not replaced. There are also irregular wear facets on all of the postcanine tooth crowns. The only suggestions of immaturity include the presence of a pair of small un-erupted replacement postcanine crowns situated at the base of the right and left fourth postcanine roots, visible in the computed tomography scans, and possibly the presence of an interpterygoid vacuity.

Because the premaxillae and lower jaw of Pseudotherium are not preserved, the form and number of incisors are unknown. The upper canines are long and curved. The canines were displaced postmortem, and the fossil is distorted on its left side, further displacing the left canine. As a result, the long roots of the canines appear to erupt through the overlying maxilla where their roots are broken and eroded. The crown morphology of the canines is distinctive, being buccolingually compressed, and with ridges running nearly the length of the crown on both labial and lingual surfaces.

Line drawings of Pseudotherium argentinus holotype. (Top) Reconstructive drawing of fossil in dorsal view. Zygomatic arches depicted with dashed lines. Major cracks in the fossil specimen were avoided in the drawing. The more complete right half of the fossil was mirrored to reconstruct the less complete left half. Drawings of fossil in its original, preserved condition, depicted in right lateral (middle) and ventral (bottom) views. Abbreviations: al, alisphenoid; alqr, quadrate ramus of alisphenoid; bo, basioccipital; ce, cavum epiptericum; eo, exoccipital; fr, frontal; if, incisive fossa; ipv: interpterygoid vacuity; ju, jugal; la, lacrimal; mx, maxilla; na, nasal; os, orbitosphenoid; pal, palatine; par, parietal pbc, parabasisphenoid complex; pet, petrosal (periotic); pf, prefrontal; po, postorbital; pt, pterygoid; ptqr, quadrate ramus of pterygoid; smx, septomaxilla; so, supraoccipital; sq, squamosal; st, stapes; tb, tabular; vo, vomer. Wallace et al. (2019).

Pseudotherium and some related taxa of interest display a special kind of transitional mammalian characters. These are features such as the complex pattern of pterygopalatine troughs and ridges around the choana or the bifurcation of the paroccipital process, that are seen in the earliest fossil members of crown Mammalia, but that are subsequently so entirely transformed that nothing quite like them is found in extant Mammals. 

Wallace et al. conclude that Pseudotherium should lie within Mammaliamorpha, but also that it lacks a number of features that have been considered diagnostic of Mammaliamorpha in other analyses. Such features include several diagnostic derived character states that are present in the Tritylodontidae (a Cynodont group closly related to the Mammaliaformes) and basal Mammaliaformes, but which are lacking in Pseudotherium. For example, Pseudotherium retains vestigial prefrontal and postorbital bones, which are entirely absent within Mammaliamorpha. In the palate, Pseudotherium lacks the anterior extension of the ventral pterygoid keel onto the vomer, as is seen in Tritylodontids, Morganucodon (an early Mammaliaforme which is well known from a large number of specimens), and other mammaliaforms. Pseudotherium lacks fully divided postcanine tooth roots, another condition generally considered diagnostic of Mammaliamorpha. Additionally, Pseudotherium has an ossified medial orbital wall (as in Mammaliamorphs), but this wall fails to extend posteriorly to enclose the orbital fissure behind the orbit. The orbital fissure in basal Mammaliamorpha is almost completely closed by the orbitosphenoid and alisphenoid. Pseudotherium also lacks a floor beneath the cavum epiptericum (which held the trigeminal ganglion), which is at least partially present in Tritylodontids, and fully present in Mammaliaformes.

Despite this Pseudotherium shares a number of derived character states widely recognized as diagnostic of the Mammaliamorpha. The presence of such features in Pseudotherium may indicate that these character states are more widely distributed than previously believed, that they may be homoplastic (gained or lost independently in separate lineages over the course of evolution), or that their distribution is equivocal because of incompleteness of some of the other relevant taxa. In several
cases, these features can only be identified with certainty from computed tomography scans. Probably the most significant resemblance Pseudotherium shares with Mammaliamorphs is in its cranial endocast in which the cerebral hemisphers form tall, elongated domes separated by a deep interhemispheric sulcus. Pseudotherium shares with Mammaliamorpha ossification of the orbital wall (anterior portion of the orbital fissure), in which sheets of bone from the frontal and palatine join to provide a solid orbital wall (although it fails to fully close the orbital fissure behind the orbit). The Tritheledontids preserve a more plesiomorphic condition (condition closer to the ancestral state) in which both the orbital wall and orbital fissure remain broadly open. Pseudotherium also shares with Mammaliamorphs the loss of an intact postorbital arch that separates the orbit from the temporal fenestra (although Pseudotherium retains a vestigial postorbital bone).

As in mammaliamorphs, Pseudotheriuim has a secondary palate that extends to the back of the tooth row. The arrangement of bones surrounding the choana takes on a distinct configuration in which parabasisphenoid and pterygoid no longer form a single continuous ventral parasagittal ridge, and instead form parallel parasagittal ridges (pterygopalatine ridges) separated by a shallow trough which may mark the passage of the auditory (eustacean) tube from the nasopharynx to the middle ear. Broad parasphenoid alae are also present in Pseudotherium and in basal Mammaliamorphs. The condition of these characters in Tritheledontids has not been reported, but should be observable in computed tomography scans.

The discovery of Pseudotherium argentinus underscores the diversity of small Cynodonts in the Mid- to Late Triassic and highlights the acquisition of growing numbers of mammalian features as a distinctive feature of this radiation. Although the phylogenetic position of Pseudotherium is not fully resolved, it shares with the other ‘taxa of interest’ a number of novelties that link it closely to the origin and early diversification of Mammaliamorpha. Current evidence suggests that the evolution of endothermy, lactation, parental care, prolonged activity, and the beginnings of encephalization were the products of this segment of history, and that it played out in miniaturized Cynodonts.The current uncertainty on phylogenetic relationships among those taxa that have been referred to as Tritheledontids and Brasilodontids is based in part on incompleteness, and also on differing strategies for sampling taxa for analysis. It seems clear that resolving this phylogenetic ambiguity will more precisely elucidate the sequence of events culminating in the origin of Mammalia, and that computed tomography may be a key technology in providing character evidence for this phylogeny.

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Vertebrate remains from the Late Permian of Xinjiang Province, China.

The Dalongkou Section of the Guodikeng Formation in Jimsar County in northern Xinjiang Province, China, is one of the few terrestrial sections that preserve the transition from the Permian to the Triassic periods, one of the most important biological turnovers in the fossil record. This section has produced a variety of Vertebrate fossils, adding to our knowledge of a variety Vertebrate groups known only from this time interval.

In a paper published in the journal Vertebrata PalAsiatica on 28 November 2016, Liu Jun of the Key Laboratory of Vertebrate Evolution and Human Origins at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences and the University of Chinese Academy of Sciences and Fernando Abdala of the Evolutionary Studies Institute at the University of the Witwatersrand describe two new Late Permian Vertebrate specimens from the Dalongkou Section of the Guodikeng Formation.

The first new specimen is identified as a Eutherocephalian, a group of Theraspids (the wider group that includes living Mammals and their ancestors) known from the Middle Permian to the Middle Triassic, and described as a new species, Dalongkoua fuae, where 'Dalongkoua' refers to the location where the specimen was found (the Dalongkou Section) and 'fuae' honours Fu Hua-Lin, who prepared the specimen. The specimen comprises an incomplete left premaxilla with three teeth, an incomplete right premaxillae with four teeth, the snout and part of the orbital region with the maxilla on both sides featuring functional and replacement canines, some isolated vertebrae, a left humerus, two phalanges and some bone fragments.

Dalongkoua fuae: Skull, including premaxilla in left lateral (A), right lateral (B) and ventral (C) views; right premaxilla in dorsal view (D); the second preserved right incisor in lingual view (E) Abbreviations: F. frontal; J. jugal; M. maxilla; N. nasal; Pf. prefrontal; Pm. premaxilla; Po. postorbital; r.c. replacing canine; t.f. temporal fenestra; V. vomer. Scale bar equals 1 cm. Lui & Abdala (2016).

The second specimen is identified as a Chroniosuchian (a group that may either be either Stem Tetrapods - a group that split off from other Tetrapods before the split between Lisamphibians and Amniotes - or Reptiliomorphs - Amniotes that split off from other groups before they diverged), but not described to species level due to the fragmentary nature of the material. This specimen comprises five vertebrae, a rib, some gastral scales, a partial ilium, a left femur, and a partial fibula.

Chroniosuchian specimen sterior (C), dorsal (D) and ventral (E) views; one caudal vertebra in anterior (F), left lateral (G), posterior (H), and ventral (I) views; J. gastral scales; caudal intercentrum in anterior (K), left lateral (L), and ventral (M) views Abbreviations: dp. diapophysis; ha. haemal atch; ic. intercentrum; nc. neural canal; ns. neural spine; pc. pleurocentrum; pnc. paraneural canal; poz. postzygapophysis; pp. parapophysis; prz. prezygapophysis; tp. transverse process. Scale bar equals 1 cm. Lui & Abdala (2016).

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