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.

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Evidence of seasonal torpor in an Early Triassic Antarctic Lystrosaurus.

Antarctica is today the coldest and driest continent with extreme variation in light availability throughout the year, restricting vertebrate life to coastal regions and rendering most of the continent uninhabitable. These modern environmental conditions are anomalous, however, considering the deep history of life in Antarctica when flora and fauna occupied large regions of the continent. Although more habitable with a warmer climate than today, Antarctica remained at a high latitudinal position for much of the Phanerozoic, subjecting its inhabitants to extreme photoperiod seasonality. Extant Vertebrates living in highly seasonally variable climates have evolved a variety of mechanisms to curb the effects of regular intervals of stress including daily torpor, hibernation, and brumation. These adaptations are largely behavioral thus rendering them difficult to study directly in the fossil record. Importantly, however, these adaptations reflect underlying metabolic changes in response to resource limitations, and therefore should be recognisable in fossil hard tissues that preserve chronological records of physiology.

Geological data from the Early Triassic document prolonged and unfavorable environments following the Permo-Triassic mass extinction. Permo-Triassic mass extinction survivors and newly evolved species would have had to adapt to high global temperatures, oceanic anoxia, and low nutrient availability that created unstable and highly variable environmental conditions. Polar regions are thought to have shielded their inhabitants from the extremes of these conditions both during the Permo-Triassic mass extinction and subsequently in recovery. The Fremouw Formation of Antarctica provides some of the earliest records of terrestrial Vertebrates of Early to Middle Triassic age (roughly 250–230 million years old). Furthermore, the flora and fauna of the Fremouw Formation is taxonomically similar to those found in non-polar regions of southern Pangaea, especially the Karoo Basin of South Africa, facilitating direct comparisons of polar and nonpolar populations.

In a paper published in the journal Communications Biology on 27 August 2020, Megan Whitney of the Museum of Comparative Zoology at Harvard University, and Christian Sidor of the Department of Biology and Burke Museum at the University of Washington, compare the frequency and patterns of growth marks in tusks of the Early Triassic non-Mammalian Synapsid Lystrosaurus, from polar Antarctica to those from the non-polar Karoo Basin of South Africa.

Dentine, a major tissue of the Vertebrate dentition, is deposited during times of regular incremental growth as well as times of arrested growth reflecting metabolic stress. Compared to bone or enamel, dentine acts as a particularly sensitive recorder of daily-to-monthly physiological activity providing a robust chronology of both regular and stressed growth and has previously been used to assess responses to environmental change. Despite this, the lack of sufficient experimental data on dentine deposition in extant Tetrapods makes specifying the absolute amounts of time recorded by each growth mark (i.e. daily growth, yearly growth, etc.) difficult. Instead, Whitney and Sidor adopt an agnostic terminology reflective of growth patterns where fine-scale, regular marks denote baseline or routine growth and thicker more pronounced growth marks are referred to as stress marks.

 

Measurements for stress and regular growth were recorded from the tusks of Lystrosaurus. (a) A cross-section of Antarctic specimen UWBM 118025 with a 'hibernation zone' highlighted at a higher magnification. Scale bars are 1000 μm. (b) Well-preserved regular incremental growth marks from the South African specimen UWBM 118028, lacking 'hibernation zones'. Arrows denote individual lines with an average spacing of 16–20 μm. Scale bar is 100 μm. Whitney & Sidor (2020).

The tusks of Lystrosaurus serve as particularly extensive markers of seasonality because they have been shown to be evergrowing. Such tusks can therefore capture extended periods of time and control for the developmental stage of the tooth, reducing any bias toward rapid growth in newly erupted teeth. Furthermore, ever-growing dentitions such as incisors of modern Rodents are known to preserve evidence of seasonal stress and hibernation as well as in fossil Rodents and the tusks of Mammoths. Previous descriptions of a 'hibernation zone' in these dentitions are recorded as episodes of shortened intervals between stress lines and as such, we accordingly employ these characteristics in testing for torpor in our Early Triassic sample.

Whitney and Sidor found evidence of prolonged and repeated metabolic stress events in the tusks of Antarctic Lystrosaurus that differ from the relatively steady growth observed in South African Lystrosaurus tusks. The patterns of stress found in polar Lystrosaurus are similar to previously described 'hibernation zones' suggesting that Antarctic Lystrosaurus experienced seasonal torpor, likely similar to hibernation. This preliminary finding supports the growing body of evidence that Lystrosaurus was endothermic and highlights the role of polar regions in the recovery of terrestrial vertebrates from the Permo-Triassic mass extinction.

Whitney and Sidor found that the spaces between regular, incremental growth marks in the tusks of Antarctic Lystrosaurus were not significantly different from those of South African Lystrosaurus indicating that although geographically separated by over 900 km in the Triassic, the baseline physiology and growth was generally similar in both populations and across individuals in our sample. These baseline indicators of physiology allowed Whitney and Sidor to control for alternative sources of variation in growth patterns between the two populations (i.e. differences in growth rate due to ontogeny or species/individual variance). In modern ever-growing dentitions, these regular growth marks have been demonstrated to vary with factors such as age, species of varying metabolisms, and dentine deposition is sensitive to nutrient inputs. Completely controlling for alternative sources of variation was particularly difficult given the small and fragmentary nature of the specimens that were available for destructive sampling, however, Whitney and Sidor consider these regular growth marks to be at least a general control for those sources of variation in growth that are unrelated to seasonality.

 

Stress and regular incremental data for Antarctic (blue) and South African (orange) Lystrosaurus tusks. (a) The mean distance between regular incremental growth marks was insignificantly different between the two populations suggesting similar baseline metabolic activity in Antarctic and South African Lystrosaurus populations. (b) The distance between growth marks was significantly greater in South African specimens indicating longer durations of uninterrupted growth. (c) The thickness of stress lines in Antarctic specimens was significantly greater than South African specimens indicating longer periods of inactive growth. (d)–(f) Measurements averaged in (a)–(c) separated by data collected for each specimen. Considerable variation was observed, but even with outliers removed, the average significant differences remained consistent. Whitney & Sidor (2020).

While Whitney and Sidor's sample contained individuals of similar baseline metabolic activity, indicators of metabolic stress were different between Antarctic and South African specimens. Quantitatively, both the duration of stress and the short intervals between stressful events suggest that Antarctic Lystrosaurus experienced relatively frequent and pronounced metabolic strain. The amount of growth between stressful events was, on average, significantly greater in South African Lystrosaurus suggesting longer durations of regular growth without stressful interruptions for non-polar populations that inhabited the Karoo Basin. Furthermore, stressful events appear to have lasted for longer durations in Antarctic fossils as suggested by the significantly thicker lines observed in tusks from the Fremouw Formation. Antarctic tusks preserve stressed growth marks akin to previous descriptions of a 'hibernation zone' where a series of thick stress marks are found close to one another while South African specimens typically display a single stress mark followed by regular growth that constitutes the majority of the growth record of this population.

 

Summary of stress mark data from a selection of South African (orange) and Antarctic (blue) specimens of Lystrosaurus. These graphs represent transects collecting the thickness (μm) of stress lines moving from the pulp cavity (to left) to the outer edge of the tusks (to right). Green boxes highlight durations without visible stress lines and gray boxes highlight portions of the tusk with closely spaced stress lines suggesting a stressful interval. The height of the boxes represents the thickest stress line during such period. Whitney & Sidor (2020).

Substantial variation within localities does exist. However, even when outliers are removed from Whitney and Sidor's quantitative analyses, statistically significant differences in stress marker measures persist. In fact, this variation is an important consideration given that not every stress line necessarily represents torpor, even in the Antarctic populations. Short periods of metabolic reduction may be caused by a variety of factors, but the unique patterns here observed in Antarctic tusks, where occurrences of closely spaced stress lines are present, are consistent with torpor at high latitudes.

 

Comparative measurements of stress lines in Antarctic (blue) and South African (orange) tusks. There is substantial variability within each population, however, South African stress lines tend to be thinner and farther apart than Antarctic specimens which are more likely to occur closer together and more frequently. This is apparent as individual data points (a) and when specimens are assigned a mean value for these measurements (b). Whitney & Sidor (2020).

From their exploratory study, Whitney and Sidor find evidence of severe and prolonged periods of stress in Antarctic Lystrosaurus tusks that support the conclusion that polar populations adapted to their high-latitude environment by means of seasonal reduction in metabolic activity, otherwise referred to as torpor. The 'hibernation zones' denoted here by temporarily reduced dentine deposition between stress lines are quantitatively and qualitatively akin to heterothermic activity observed in modern endotherms. Heterothermic ectotherms reduce their metabolic activity from at least half of to nearly complete quiescent metabolic activity. Heterothermic endotherms, on the other hand, can enter a state of torpor generally reducing metabolic activity by at most a third although most reduce by no more than 10% of normal activity. Generally, ectothermic heterotherms are not able to reactivate metabolic activity during unfavorable environmental conditions and enter times of brumation whereas endothermic heterotherms, even hibernators, frequently will come out of metabolic dormancy either daily, weekly, or monthly. The zones of stress observed here in Antarctic Lystrosaurus are marked by iterative reactivation of metabolic activity similar to those seen in torpor patterns of modern endotherms. This contributes additional support for a growing body of evidence that Dicynodonts like Lystrosaurus were likely endothermic.

These data also shed light on Antarctica’s role as a refugium during the Permo-Triassic mass extinction. Antarctic rocks have yielded Early Triassic Tetrapod taxa that are missing from other contemporaneous, but otherwise much better sampled localities such as the Karoo Basin of South Africa. These discrepancies in otherwise very similar faunal assemblages, have supported the hypothesis that the Antarctic portion of Pangaea was a high-latitude refugium from the global climatic events marked by the Permo-Triassic mass extinction. Furthermore, geologic data suggest that polar regions were, in fact, the first to begin a prolonged recovery in the Early Triassic. With its relatively temperate climate, Antarctica may have acted as a haven for terrestrial vertebrates through an extinction boundary and subsequent recovery.

Although more insulated from the effects of global climate change, tetrapods living in Antarctica during the Early Triassic would have had to adapt to extreme seasonality with long periods of limited light availability. A Permian Tetrapod assemblage has yet to be recorded from Antarctica, however, Lystrosaurus tusks from both the Permian and Triassic of the Karoo Basin do not record patterns of hibernation-like reductions in their metabolic activity. Thus, these data suggest that upon expanding its geographic range to the Antarctic portion of southern Pangaea Lystrosaurus adapted with extended periods of reduced metabolic activity, although continued testing of this initial observation is required.

Lystrosaurus survivorship through the Permo-Triassic mass extinction and its subsequent abundance in the fossil record of the earliest Triassic was likely predicated on a flexible physiology that could modulate typically elevated metabolic activity according to the limiting resources of a fluctuating environment. This agrees with James Valentine's suggestion that more stable environments tend to select for narrow niche partitioning among species, whereas those with unstable resources, such the Early Triassic, tend to select for species with greater flexibility and generalisation. Indeed, the near-global distribution of Lystrosaurus, with records known from China, Russia, India, Africa, and Antarctica, implies a remarkable ecological breadth for this lineage. Furthermore, Triassic rocks from both South Africa and Antarctica preserve fossil evidence of tetrapod burrowing, including for Lystrosaurus. Whitney and Sidor suggest that a combination of a flexible physiology and burrowing served as exaptations to the acquisition of torpor for Antarctic populations of Lystrosaurus.

Whitney and Sidor show preliminary evidence that Lystrosaurus used torpor to respond to the seasonal stress incurred specifically in the polar regions of southern Pangaea during the Early Triassic. It was this ability to sustain activity in a variety of stressful environmental conditions that may have served as a critical adaptation in surviving and recovering from the largest mass extinction the Earth has experienced to date. The Fremouw Formation preserves a diverse assemblage of tetrapod taxa with presumably an array of metabolic adaptations to the extremes of seasonal light availability. Continued testing of seasonal responses in Lystrosaurus, other non-Mammalian Synapsids, early Reptiles, and the abundant Temnospondyl fossils recovered from these localities can reveal how this polar ecosystem evolved despite unstable environmental conditions and eventually facilitated postextinction recovery.

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Tetrapod fossils from the Late Permian of Shanxi Province, China.

Chinese Permian Tetrapods have been known for decades. Dicynodon sinkianensis, now revised as Jimusaria sinkianensis, from the Guodikeng Formation of Xinjiang was the first to be reported 1934. Later, Dicynodonts were reported from the Quanzijie Formation and Wutonggou Formation of Xinjiang as well. In North Qilian area, a Dicynodont species, Dicynodon sunanensis, was described from the Sunan Formation and revised as Turfanodon bogdaensis or Turfanodon sunanensis subsequently. However, no Pareiasaur fossils have been reported from Xinjiang. In Inner Mongolia, many Tetrapod specimens have been discovered and at least four Dicynodont species and one Pareiasaur species are present in  Daqingshan County. In North China, the upper Permian Sunjiagou Formation and Shangshihezi (Upper Shihhotse) Formation have the widest exposure of all contemporaneous deposits, and their distributions are adjacent to the Daqingshan area. Many Pareiasaur species have been named for the specimens from the above formations, however, no Dicynodonts have been reported. The only known Tetrapod locality in the Shangshihezi Formation of Henan Province is dominated by the Pareiasaur Honania. In 2014, a tusked dicynodont snout was collected from the Sunjiagou Formation in Baode, Shanxi, which confirmed the presence of dicynodonts in this stratum. In 2013, a fossil hunter, Bai Zhi-Jun, discovered some bones from Shouyang and Yangquan, Shanxi Province. His initial work led to subsequent discovery of Pareiasaur and Dicynodont specimens from both the Sunjiagou Formation and Shangshihezi Formation.

In a paper published in the journal Vertebrata PalAsiatica on Yi Jian and 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, the Center for Excellence in Life and Paleoenvironment, and the College of Earth and Planetary Sciences of the University of Chinese Academy of Sciences, briefly describe a new Pareiasaur specimen and a new Dicynodont specimen from Shouyang in Shanxi Province and discuss their implications for biostratigraphy and biogeography.

 

The Permian tetrapod fossil localities and stratigraphic column of the fossil horizon in Shouyang, Shanxi. Yi & Liu (2020).

The Shangshihezi Formation is late Guadalupian to early Lopingian in age, while the Sunjiagou Formation is approximately late Lopingian in age. Both formations are composed of fluvial and lacustrine deposits, although the Sunjiagou Formation has interbedded by marine facies in southern margin of the North China Block. The Shangshihezi Formation is characterised by purple-colored mudstone, and the Sunjiagou Formation is dominated by dark red mudstone.

The specimens studied in this paper were collected from a valley eroded by the tributary of the Taohe River, near the border of Shouyang and Yangquan and close to the intersection of the Yun-Wen Road with the G5 Highway. SXMG 2017-YQ-01, including a right ilium, some vertebrae and ribs, was collected from purple sandy mudstone near the top of Shangshihezi Formation (Locality 17P), whereas IVPP V 26043, a broken skull, was collected from the dark red mudstone from the lower part of the Sunjiagou Formation (Locality 18P5). Another Dicynodont specimen, IVPP V 25335, was produced from near the base of the Sunjiagou Formation (Locality 18P3), which will be described elsewhere. The three localities are close in their stratigraphic level and geographic distance.

Speciomen SXMG 2017-YQ-01 comprises a right ilium, several dorsal vertebrae and ribs considered to have come from a Pareiasaur, from a purple sandy mudstone; near the top of the Shangshihezi Formation at locality 17P in  Shouyang County.

The vertebrae and ribs are poorly preserved, therefore, only the ilium is worthy of description. The right ilium is nearly complete aside from the anterodorsal margin of blade. The blade is thin and nearly flat, with a posterior process much shorter than the anterior one. The anterodorsal portion of the blade is fragmentary, and the posterior iliac margin is pointed posteroventrally. The dorsal margin of the blade is convex dorsally. The lateral surface of the anterior process is concave, but the anteroventral margin is slightly everted. The ilium narrows at the neck, the anterior margin of neck is nearly straight whereas the posterior margin is sharply concave. In medial view, the crista sacralis is not well developed, therefore the number of sacral ribs cannot be determined.

 

Comparison of ilia of Pareiasaurs (A)–(B) SXMG 2017-YQ-01 from Shouyang, Shanxi; (C)–(D) HGM 41HIII0434 (Honania complicidentata) from Jiyuan, Henan; (E)–(F) IVPP V 2717 (holotype of Shihtienfenia permica) from Baode, Shanxi (A), (C), (E) in medial views; (B), (D), (F) in lateral views. Yi & Liu (2020).

The supraacetabular buttress of the ilium is well developed, forming a prominent tuber on the lateral side. Anterior to the acetabulum, a shallow rugose groove is present. The dorsal outline of the acetabulum is approximately circular. The ventral side of ilium is slightly projecting medioventrally.

Although there are seven named Chinese Pareiasaur species, complete ilia are known only for Honania complicidentata and Shihtienfenia permica. In Honania complicidentata, the anterior iliac process is laterally concave and its anteroventral margin is slightly everted, the dorsal margin is slightly convex. In Shihtienfenia permica, the anterior portion of the iliac process is strongly everted as a convex surface and the dorsal margin is slightly concave. Anterodorsal expansion of the iliac blade is seen in many derived Cynodont and Dicynodont Synapsids from the Permian and Triassic. The iliac blade is greatly expanded anteriorly in Bradysaurus, Embrithosaurus, Pareiasuchus, Shihtienfenia, Pareiasaurus, Scutosaurus and Elginia. In Pareiasuchus, Shihtienfenia, Pareiasaurus, Scutosaurus and Elginia, the anteroventral margin of iliac blade is very strongly everted. 

The ilium of SXMG 2017-YQ-01 is identical as the ilium of Honania complicidentata in features mentioned above although its neck is slightly wider, so this specimen is more similar to the ilium of Honania than that of Shihtienfenia, and thus it may represent a species closely related to Honania complicidentata. So this new specimen indicates that Honania or a closely related taxon may be present in Shouyang, but precise identification requires more informative material.

Specimen IVPP V 26043 is an incomplete skull of a Cryptodont Dicynodont, from a dark-red sandy mudstone in the lower part of the Sunjiagou Formation at location 18P5 in Shouyang County.

The only preserved specimen is an incomplete anterior portion of a skull. The anterior tip of the premaxilla and tusks are incomplete. The preserved length is 12 cm, and a complete skull basal length is estimated as 25 cm. The external naris is anteroposteriorly elongated and it forms an oval concave area with an excavation which lies ventral and slightly posterior to the external naris.

 

A ‘Cryptodontian’ Dicynodont from the Sunjiagou Formation, Shouyang, Shanxi, IVPP V 26043 (A) lateral view; (B) posterior view; (C) dorsal view; (D) ventral view Abbreviations: cp, cultriform process; Ec, ectopterygoid; F, frontal; J, jugal; L, lacrimal; lf, lacrimal foramen; M, maxilla; N, nasal; pcc, postcaniniform crest; Pl, palatine; Pm, premaxilla; Prf, prefrontal; Sp, sphenoid; Sq, squamosal; V, vomer. Yi & Liu (2020).

The premaxilla is incomplete, and it is uncertain whether paired anterior ridges on palatal surface were present. The posterior median ridge increases in height and breadth posteriorly, with maximal size achieved immediately anterior to the palatine pads. This ridge continues into the interpterygoid region as the mid-ventral plate of the vomer. There are paired elongate depressions lateral to the ridge, without trace of the lateral anterior ridge. In lateral view, the premaxilla contacts the maxilla below the external naris. Posterodorsally, it forms a V-shaped suture with the nasal. The border of the septomaxilla is unclear.

The maxilla bears a well-developed caniniform process housing a broken tusk of about 15 mm in diameter. The caniniform process slightly bulges outwards along its lateral surface. Dorsally, the maxilla contacts the lacrimal and the nasal. Posteriorly, it contributes to the lateral surface of the anterior part of the zygomatic arch, which is formed together with the jugal dorsally and the squamosal ventromedially. The squamosal seems have no lateral exposure here. A sharp postcaniniform crest is present on the right side while this structure is incomplete on the left side. Anterior to the left caniniform process is an incomplete, but sharp palatal rim. Posteriorly and dorsally, there are two straight sutures with the jugal. Medially, the maxilla sutures with the palatine and the ectopterygoid. The labial fossa is absent.

The nasal is almost complete except for the broken dorsal surface. It has a long mid-nasal suture which separates the premaxilla from the frontals. A long and narrow boss is partially present on the right side, but the left one is not preserved. It is unclear if the two bosses were confluent or well separated. The nasal boss is only slightly beyond the posterior border of the external narial excavation, and is far from the orbit rim. Posteriorly, the nasal has a slightly curved suture with the frontal. The ridge across the nasofrontal border is absent.

The lacrimal is a concave bone on the snout surface that only forms small part of the anterior orbital margin. Its ventral margin sutures with the maxilla and forms an anteroposteriorly directed ridge, and a fossa is formed mainly by the lateral surface of the lacrimal. Anteriorly, it is separated from contacting the naris by the nasal. Within the orbit, the lacrimal is perforated by a single, large lacrimal foramen.

The prefrontal is a small triangular bone that is limited to the anterodorsal orbital margin. It is thickened as a boss, protruding more laterally than the lacrimal. The posterior parts of the frontals are not preserved, and their dorsal surfaces are weathered. The frontal is narrow and restricted to the interorbital region. It forms most part of the dorsal margin of the orbit.

The jugal is incomplete, only the portion making up the ventral wall of the orbit is preserved. It is bordered mainly by the maxilla and medially by the palatine.

The vomer is exposed as a narrow, rod-like element within the interpterygoid vacuity in ventral view. The posterior portion is not preserved. The palatine is exposed ventrally in the form of a palatine pad. Anteriorly, it contacts the maxilla, approaches the premaxilla but does not reach it. The choanal portion of the palatine extends dorsally to meet the vomer. The ectopterygoid is a small element lateral to the palatine.

This fossil can be distinguished from all Chinese Dicynodonts other than Daqingshanodon by the presence of postcaniniform crest and distinct nasal boss near the posterodorsal margin of external nares. The postcaniniform crest was alleged to be present in Daqingshanodon, but it is only weakly developed on the left side, and is less distinct than in this specimen. These two features are present in all ‘Cryptodontian’ other than Bulbasaurus. Although sometimes Daqingshanodon was referred to a monophyletic Cryptodontia, it usually occupies a stemward position in the clade and never falls within Geikiidae, Oudenodontidae, or Rhachiocephalidae. IVPP V 26043 has long nasal bosses like ‘Cryptodonts’ such as Australobarbarus, Oudenodon, Odontocyclops, and Aulacephalodon, and could be the first representative of the three main ‘Cryptodont’ subclades from China.

The pareiasaur from the Shangshihezi Formation may expand the distribution of the Jiyuan Fauna (Honania Assemblage Zone), but the presence of Honania needs to be confirmed by additional material. Also, this assemblage might extend to the lower part of the Sunjiagou Formation, but additional specimens are needed to confirm this. The younger Shihtienfenia Assemblage is only known from the upper part of the Sunjiagou Formation. The boundary between the two assemblage zones is still uncertain, but could be within the Sunjiagou Formation.

This first Dicynodont from the Sunjiagou Formation may represent an occurrence of a ‘Cryptodont’ subclade that was previously unknown in China. Recently, some new Dicynodonts were reported from the Naobaogou Formation of Inner Mongolia, and some could be referred to Jimusaria or even Jimusaria sinkianenis from Guodikeng Formation of Xinjiang. The Naobaogou Formation is generally regarded as a synchronous deposition as the Sunjiagou Formation. If this is true, there is the potential to find taxa such as Jimusaria and Daqingshanodon in Shanxi.

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Lystrosaurus murrayi & Lystrosaurus declivis: One species or two?

Dicynodonts of the genus Lystrosaurus are one of the few large terrestrial animals to have made it through the End Permian Extinction. The genus was quite diverse in the Late Permian of Southern Africa, and is also known from the Late Permian of Russia. In the Triassic two species are known from South Africa, with other specimens recorded from China, India and Antarctica. The first of the Triassic South African species, Lystrosaurus murrayi, was first described by Thomas Henry Huxley in 1859, the second Lystrosaurus declivis, was described by Richard Owen in 1860. It was later suggested by the prominent South African palaeontologist Robert Broom that these were likely to be the same species, though most recent studies of the group have still regarded them as separate species.

A specimen of Lystrosaurus murrayi in the Musee d'Histoire Naturelle in Paris. Wikimedia Commons.

In a paper published in the South African Journal of Science on 27 March 2018, Francis Thackeray of the Evolutionary Studies Institute at the University of the Witwatersrand challenges the assumption that the two Triassic South African Lystrosaurus species are separate, on the basis of morphometric analysis. 

Morphometric analysis is a tool used by palaeontologists, archaeologists, anthropologists and forensic pathologists to analyse and compare specimens. It relies on taking numerous measurements of an object such as a bone or shell, and comparing both these measurements and ratios between measurements to those obtained from other specimens in order to establish relationships between them. Traditionally these measurements have been obtained using tape measures and callipers, but modern scientists often use more sophisticated tools such as structured light scanners, which are capable of building highly detailed three dimensional models of specimens. 

 Specimen of Lystrosaurus declivis in the Musee des Confluences in Lyon. Wikimedia Commons.

Thackeray bases his analysis upon data previously published by Jennifer Botha-Brink, Daryl Codron, Adam Huttenlocker, Kenneth Angielczyk and Marcello Ruta in a paper published in the journal Scientific Reports in April 2016. This paper did not challenge the assumption that the two species were separate, but rather concentrated on the apparent breeding strategy of these species, noting that both had populations in which the largest specimens were rare, something often indicative of being able to breed before they reached full size, and suggests that this may have been a key adaptive trait that enabled these species to survive the End Permian Extinction.

Using the data provided by Botha-Brink et al., Thackeray takes this reasoning a step further and argues that the small difference in average size between the two species (with skulls averaging 0106.7 and 118.1 mm in length respectively) combined with the fact that most, if not all, specimens had not reached their maximum size, rules out any differentiation of the two species on the basis of size. He therefore suggests that all of these specimens should be referred to as Lystrosaurus murrayi, which was the first described and therefore has precedence.


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Kannemeyeriiforme Dicynodonts from the Middle Triassic of Shanxi Province, China.

Triassic deposits are widespread in Northern China, but Tetrapod fossil producing locations are very rare. Those that are known are restricted to the Heshanggou, Ermaying and Tongchuan formations, with the Ermaying producing the most abundant and diverse assemblages.

In a paper published in the journal Vertebrata PalAsiatica on 12 January 2015, Liu Jun of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences describes a series of Kannemeyeriiforme Dicynodont remains from two new Triassic localities in Liulin and Linxian counties in Shanxi Province.

The first set of remains comprise the front part of a skull with an associated jawbone, a cervical vertebra, a rib, a left humerus, radius, femur and tibia and an incomplete right ilium from an exposure of the Tongchuan Formation at Baidaoyu in Linxian County. These remains are placed in the genus Sinokannemeyeria, due to the wide low shape of the skull, the short anterior end of the premaxilla, a shallow depression on the anterior of the premaxilla, long dentary symphysis and a wide femur, and described as a new species, Sinokannemeyeria baidaoyuensis, meaning ‘from Baidaoyu’, due to an extension of the prefrontal bone level with the posterior margin (back) of the postnarial excavation.

Sinokannemeyeria baidaoyuensis: Skull in dorsal (A), ventral (B), anterior (C), and lateral (D) views; lower jaws in dorsal (E), lateral (F) and ventral (G) views. Abbreviations: L, lacrimal; M, maxilla; N, nasal; Pf, prefrontal; Pm, premaxilla; Sm, septomaxilla. Lui (2015).

Lui also notes that the caniniform tooth of the specimen is not completely wrapped by the caniniform process, and that this does not appear to be as a result of post-mortem damage. Since this state would weaken the tooth and has no apparent useful function it is thought to be a pathology suffered by the animal in life. The specimen also has weakly sutured skull bones and poorly ossifies ends on the humerus and femur, which may indicate it was a sub-adult.

Sinokannemeyeria baidaoyuensis: (A) A cervical vertebra in anterior view; (B) distal portion of left humerus in ventral (B1) and dorsal (B2) views; (C) left radius in anterior (C1) and posterior (C2) views; D. partially right ilium in lateral (D1) and medial (D2) views; (E) left femur in posteroventral (E1) and anterodorsal (E2) views; (F) left tibia in proximal (F1), anterior (F2) and posterior (F3) views. Abbreviations: cn.c, cnemial crest; ect, ectepicondyle; ent, entepicondyle; ent. f, entepicondyle foramen; ipp, iliac posterior process. Lui (2015).

The second set of remains comprise an occiput, a quadrate, a quadratojugal; a right caniniform process with tusk, one centrum, five neural arches, four sacral vertebrae with ribs; a right ilium, a left and right radius, a left and right tibiae and one claw, also from the Baidaoyu exposure of the Tongchuan Formation. These remains are assigned to the genus Parakannemeyeria on the basis of the caniniform process and occiput, but due to the poor preservation of the skull is not classified to species level.

Parakannemeyeria sp: (A) Right caniniform process with tusk in lateral (A1) and medial (A2) views; (B) right quadrate and quadratojugal in anterior (B1) and posterior (B2) views; (C) occiput in anterior (C1) and posterior (C2) views; (D) neural arch of axis in anterior (D1) and posterior (D2) views; (E) neural arch of a cervical in anterior (E1) and posterior (E2) views; (F) four sacral vertebrae with ribs in dorsal (F1) and ventral (F2) views; (G) ventral portion of right ilium in lateral (G1) and medial (G2) views; (H) left radius in anterior (H1) and posterior (H2) views; (I) left tibia in anterior (I1) and posterior (I2) views; (J) a claw in dorsal (J1) and ventral (J2) views.

The third set of remains comprises some vertebrae including an axis (the first vertebra, which connects to the skull), a tibia and some bone fragments, from an exposure of the Tongchuan Formation at Sanjiao in Liulin County. These remains are thought to belong to either Sinokannemeyeria or Parakannemeyeria; the axis is very similar to those of Sinokannemeyeria and a dorsal vertebra resembles that of Sinokannemeyeria yingchiaoensis, while the narrow centrum of the specimen resembles those of Parakannemeyeria and the general shape of the tibia resembles Parakannemeyeria youngi and most of the other bones could belong to members of either genus.

Unidentified Kannemeyeriid: (A) Axis in anterior (A1), lateral (A2) and posterior (A3) views; (B) a dorsal vertebra in lateral (B1) and posterior (B2) views; (C) incomplete left precoracoid in medial view; (D) proximal portion of left ulna in anterior (D1) and posterior (D2) views; (E) left tibia in anterior view. Scale bars equal 2 cm. Abbreviations: cn.c, cnemial crest; n.s, neural spine; od, odontoid; pap, parapophysis; przp, prezagapophysis; pzp, postzagapophysis; s.n, sigmoid notch; tr.p, transverse process. Lui (2015).

The final set of remains comprises an incomplete skull, an axial neural arch, a cervical, one incomplete hand and some bone fragments from Sanjiao in Liulin County. This is poorly preserved, and not assigned to any genus or species, however some observations are made. The premaxila has a smooth surface lacking the lateral extension seen in Sinokannemeyeria and Parakannemeyeria. The external naris is small, there is no postnarial excavation and the caniform process extend laterally, not ventrally, all character states seen in Rhadiodromus, Kannemeyeria and Shaanbeikannemeyeria, but not Sinokannemeyeria or Parakannemeyeria. The size of the snout suggests the living animal was considerably larger than Shaanbeikannemeyeria. Based upon this the specimen is excluded from Sinokannemeyeria and Parakannemeyeria, suggesting that at least three species are present in the total assemblage.

Unidentified Kannemeyeriid: (A) Incomplete skull in lateral (A1) and ventral (A2) views; (B) one metacarpal and two manual phalanges (possible same digit) in dorsal (B1) and ventral (B2) views; (C) a cervical in posterior (C1), lateral (C2) and anterior (C3) views; (D) left half of axial neural arch in anterior view; (E) an incomplete hand in dorsal view. Lui (2015).

See also…

Scavenging on the body of a Dicynodont Therapsid in the Late Permian of the Karoo Basin.

Therapsids were a group of Synapsid Amniotes (the group of terrestrial vertebrates that include the...

A Caseid Synapsid from the Late Pennsylvanian of Kansas.

Synapsids, the group which gave rise to and includes the modern Mammals (and which are sometimes misleadingly known as ‘Mammal-like Reptiles’) diverged from the other early Amniotes (fully terrestrial Vertebrates) about 315 million years ago in the Late Carboniferous, and went on to become the dominant large vertebrates in Permian ecosystems, though...

 Strange bedfellows in an Early Triassic burrow from the Karoo.

The Early Triassic Karoo Basin contain numerous preserved burrows of small Tetrapods, interpreted as adaptations to a harsh, seasonally dry, climate...

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Scavenging on the body of a Dicynodont Therapsid in the Late Permian of the Karoo Basin.

Therapsids were a group of Synapsid Amniotes (the group of terrestrial vertebrates that include the modern Mammals which are sometimes, misleadingly, known as ‘Mammal-like Reptiles), that reached great diversity in terrestrial ecosystems throughout Pangea (the ancient supercontinent of the time, which included all the modern continents joined together) in the Permian and Triassic, before being  largely replaced by more successful Archosaur groups, notably the Dinosaurs and Crocodylomprphs. The group is particularly well known from the Karoo Basin of South Africa.

In a paper published in the South African Journal of Science on 29 October 2012, Nicholas Fordyce of the Department of Zoology at the University of Cape Town, Roger Smith of the Iziko South African Museum in Cape Town and Anusuya Chinsamy, also of the Department of Zoology at the University of Cape Town, describe evidence of scavenging on the body of a Dicynodont Therapsid (a group of herbivorous Theraspids which often reached large sizes that had both beaks and tusks, and which may have survived as late as the Cretaceous) from mudrocks of the Tropidostoma Assemblage Zone of the Late Permian Beaufort Group, near Loxton in Northern Cape Province by John Nyaphuli in 1984, and prepared at the Iziko South African Museum in Cape Town by Annelise Crean. It has never been formally described and named, but is affectionately known as ‘Mamafura’.

The partially articulated Dicynodont ‘Mamafura’; the arrow indicates the left femur. Fordyce et al. (2012).

The skeleton of ‘Mamafura’ has articulated foreparts, but the hindquarters are more-or-less totally disarticulated. The bones show a level of weathering that is consistent with about two years spent exposed on the surface prior to complete burial. Sedimentary evidence suggests they originally lay on a semi-arid floodplain, and underwent three or four flood events before being finally buried, during which time some of the smaller bones of the animals feet were lost, either to water transportation or scavenging.

The left tibia of ‘Mamafura’ has two elongate grooves, which are thought to be the result of the actions of a scavenging or predatory animal. There is also a single circular indentation, 18 mm in diameter, on the left femur. 

(b and c) A large spherical puncture on the left femur, and (d) tooth scratch marks on the left tibia of ‘Mamafura’. Fordyce et al. (2012).

A broken canine tooth, 3.5 cm in length, was found with the skeleton. This has distinctive serrations on its lateral margins. Two Therapsid groups present in the fauna of the Karoo basin at the time of ‘Mamafura’ could produce a canine tooth of this size, the Therocephalians and Gorgonopsians, but no known Therocephalian has the sort of serrations seen on the tooth, suggesting that it came from a Gorgonopsian, probably Aelurognathus or possibly Cyonosaurus.

(a) The unidentified canine associated with the Dicynodont skeleton and (b) its serrations. (c) A Cyonosaurus specimen and (d) the 0.2-mm long serrations on the canine of Cyonosaurus and (e) an Aelurognathus specimen. (f) A silicon cast showing details of the serrations on a canine of Aelurognathus. Note the square serrations of (b) and (f) compared to the somewhat more rectangular serrations in (d). Fordyce et al. (2012).

Fordyce et al. suggest that soon after death ‘Mamafura’ was scavenged by a pack of Aelurognathus, acting in a similar way to modern Canids (Dogs). These preferentially attacked the rear and underbelly of the corpse, disarticulating the bones of the hindquarters, but not opening the ribs. Neither Aelurognathus nor Cyonosaurus appears to have been well adapted for durophagy (crushing bones or other hard foods), so it is doubtful that capable of making the marks found on the bones of the left hindlimb of ‘Mamafura’. Fordyce et al. suggest that these marks were either made by some other, unidentified, predator, possibly the animal responsible for the initial kill, or are the result of some other taphonomic process (post-mortem bone modification) that resembles tooth damage.

See also….

 A Caseid Synapsid from the Late Pennsylvanian of Kansas.









 Strange bedfellows in an Early Triassic burrow from the Karoo.

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