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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Kermitops gratus: A new species of Amphibamiform Temnospondyl from the Early Permian Lower Clear Fork Formation of Texas.

Modern Lissamphibians (Frogs, Salamanders, and Caecillans) are considered to be descended from a group of small, lightly-built, terrestrial Temnospondyls called the Amphibamiforms, known from Carboniferous, Permian, and Triassic deposits. The assumed relationship between Amphibamiforms and Lissamphibians is based upon the presence of bicuspid, pedicellate teeth in some adult Amphibamiforms, one of few traits which is common to all modern Lisamphibian groups. The general skull shape of Amphibamiforms also tends to resemble that of Lissamphibians, though these, as with the skeletons in general, are more simplified in Lissamphibians than in Amphibamiforms, presumably as a result of changes in timing and rate of developmental processes in Lisamphibians.

In a paper published in the Zoological Journal of the Linnean Society on 21 March 2024, Calvin So of the Department of Biological Sciences at George Washington University, Jason Pardo of the Negaunee Integrative Research Center at the Field Museum of Natural History, and Arjan Mann, also of the Integrative Research Center at the Field Museum of Natural History, and of the Department of Paleobiology at the Smithsonian National Museum of Natural History, describe a new species of Amphibamiform Temnospondyl from the Early Permian Lower Clear Fork Formation of Texas.

The new species is described from a single partial skull comptising a near complete roof and  occiput with a partial braincase, and mandibles. It is given the name Kermitops gratus, where 'Kermitops' is a combination of the name 'Kermit', in reference to the famous Lissamphibian and beloved Muppets’ character created and originally performed by Jim Henson, and '-ops', the Greek for 'face', while 'gratus' means 'gratitude' in Latin, in thanks to the Smithsonian National Museum of Natural History vertebrate palaeontology curator Nicholas Hoton III, and other members of the Smithsonian National Museum of Natural History field party that were involved in the collection efort.

Photograph (A) and interpretive illustration (B) of Kermitops gratus (USNM PAL 407585) in dorsal view. So et al. (2024).

The skull is approximately 3 cm long along the midline and 2 cm wide at the level of the occiput. There is some taphonomic distortion on both sides, making the orbits appear slightly more ovoid than they would have in life, and the left orbit is partially disarticulated. The anterior palate and braincase are lost but the remainder of the skull is well-preserved, even showing a full arrangement of palpebral ossicles in place and showcasing fine dermal ornamentation on the dorsal skull. The margins of the orbit are slightly raised, resulting in a differentiation of the orbital margin from the rest of the skull roof surface. The snout is long and parabolic in shape, consistent with the morphology seen in Micropholids. 

Attempts to include Kermitops gratus in phylogenetic trees using different methods produced quite different results, suggesting that insufficient sampling of the group has been done to achieve a consensus hypothesis. Notably, So et al. failed to find a clear relationship between Lissamphibians and Amphibamiform taxa with pedicellate bicuspid teeth, which would seem to indicate either that the trait evolved separately numerous times within the Amphibamiformes, or that it was present in the earliest members of the group, and lost multiple times.

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Cycadodendron galtieri: Cycad wood from the Permian of Saxony, central-eastern Germany.

Cycads are a thought to have been among the earliest Gymnosperm Plants to have appeared, with molecular clock estimates suggesting that they diverged from other Gymnosperms in the Late Carboniferous or Early Permian. The group underwent a major evolutionary radiation in the Early Triassic, and fossils are abundant in Mesozoic and Cainozoic deposits. These fossils tend to closely resemble modern Cycads, despite these sharing a fairly recent common ancestor, suggesting a high degree of morphological conservatism within the group. Palaeozoic fossils are much less common, and can be more difficult to interpret. These comprise possible Cycad megasporophylls (leaves) from the Late Carboniferous and Early Permian, although it is difficult to be confident about the affinities of these.

In a paper published in the International Journal of Plant Sciences on 11 October 2023, Ludwig Luthardt of the Museum für Naturkunde at the Leibniz Institute for Evolution and Biodiversity Research, Ronny Rößler of the Museum für Naturkunde Chemnitz and the Department of Palaeontology at the Technische Universität Bergakademie Freiberg, and Dennis Stevenson of the New York Botanical Garden and the School of Integrative Plant Science at Cornell University, describe a new species of Cycad based upon a piece of stem wood from the Holocene gravel deposits of the Zwickauer Mulde river, which are known to produce silicified woods derived from the Permian Chemnitz Fossil Lagerstätte.

Geography and geology of the source area of the fossil Cycad stem, combining the catchment area of the Zwickauer Mulde River/Chemnitz River with the most important localities of mainly in situ found petrified wood and their stratigraphic affiliation. Abbreviations: NSVC, North SaxonyVolcanite Complex; ZVC, Zeisigwald Volcanic Complex. Luthardt et al. (2023).

The new species is named Cycadodendron galtieri, where 'Cycadodendron' means 'Cycad-tree' (the suffix '-dendron' is commonly used for fossil woods, on the basis that chunks of wood of any size must have come from a tree), and 'galtieri' honours Jean Galtier, a renowned palaeobotanist from Montpellier, France, for his significant contributions to the knowledge of the evolution and anatomy of Palaeozoic fossil Plants. It is described from a single piece of polished wood, K9883, roughly 69 mm by 56 mm, thought to have derived from a larger stem, as the outer parts, including the cortex and vestiges of leaf bases, are not preserved.

Overview of polished sections of Cycadodendron galtieri (K9883, holotype). (A) General view of the specimen in transverse section. K9883a. (B) Counterpart of the specimen, additionally cut in radial sections. K9883b, K9883c. (C), (D), Radial sections of the specimen; successivevascular cylinders are indicated by arrows and X1–X9 in (D). K9883b, K9883c. All specimens are at the same scale. Luthardt et al. (2023).

While foliage can be difficult to ascribe to a particular plant group, due to convergent evolution among plants living in similar environments, the wood of Cycads is highly distinctive, with vascular stands arranged in medullary bundles within a wide inner pith, surrounded by consecutive vascular segments each producing centripetal secondary xylem and centrifugal phloem. The presence of these features within Cycadodendron galtieri marks the specimen as an unequivocable Cycad, and therefore the oldest known fossil which can be confidently assigned to the group.

Anatomical sketches of Cycadodendron galtieri with the overall arrangement of stem tissues. (A) Transverse section showing the pith with medullary bundles and pith-peripheral bundles, successive vascular segments, and traversing medullary bundles. K9883a. (B) Radial section exhibiting vertical arrangement of stem tissues and indicating the number of successive vascular segments and phloem-parenchyma zones. K9883b. Luthardt et al. (2023).

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Secondary cratering from the Early Permian of Wyoming.

Many Solar System bodies, including our Moon, are covered by enormous numbers of impact craters. On Earth, in contrast, the total number of such craters discovered stands at 208. This is largely due to the Earth's active surface, with the continents and continental shelves being subjected to constant erosion and deposition of sediments, and the ocean floors being constantly recycled through subduction and seafloor spreading. However, the situation is more complicated than it seems at first sight; many of the craters seen on the Moon and other Solar System bodies are in fact secondary craters, formed by debris ejected from larger impact events. Once understood, such craters have been relatively easy to identify, frequently being elliptical rather than circular in shape, shallower than primary craters, and arranged radially around the initial impact crater. The implications of this are debatable, with some planetary scientists arguing that as many as 95% of small craters on some bodies may be secondary in origin, whereas others see them as a insignificant proportion of the total number.

In a paper published in the journal GSA Bulletin on 11 February 2022, Thomas Kenkmann and Louis Müller of the Institute of Earth and Environmental Sciences at Albert-Ludwigs-Universität Freiburg, Independent Consultants Allan Fraser and Doug Cook, Kent Sundell of the School of Science at Casper College, and Auriol Rae, also of the Institute of Earth and Environmental Sciences at Albert-Ludwigs-Universität Freiburg, describe the discovery of a secondary impact field comprising at least 31 craters, and possibly as many as 60 more, in southeastern Wyoming, USA. 

The presence of a field of impact craters in the Rocky Mountains in Wyoming was first reported in 2018 by Thomas Kenkman, Kent Sundall, and Douglas Cook. At the time they reported about 40 circular-to-elliptical structures on a tilted Permian exposure on the northeast flank of the Sheep Mountain, eight of which showed sufficient grain deformation to be confirmed as impact structures. These were initially interpreted as the result of a single large object which broke up as it entered the atmosphere, resulting in a group of closely clustered craters.

The new paper by Kenkman et al. describes the presence of several other craters on Sheep Mountain Ridge, and other exposures of the same age at Wagonhound Ridge, Mule Creek, Fetterman Ridge, Fetterman Road, and Palmer Canyon Road, as well as possible craters at several other locations. These range from 10 to 80 m in diameter, and while many are circular, some are as much as 1.7 times as long as they are wide. All of the structures which are firmly established as being craters lie at the top of the Casper Formation, which is immediately overlain by the Opeche Shale member of the Permian Goose Egg Formation, dating the impacts to about 280 million years ago, making them late Early Permian in origin.

 

Digital elevation model map of southeastern Wyoming, USA, and adjacent areas showing the exposure of Casper Formation and the locations of the secondary craters. Based on the intersection of trajectory fans, the proposed site of the possible primary crater is reconstructed. SM, Sheep Mountain; MC, Mule Creek; FR, Fetterman Ridge; FRX, Fetterman Road; PCR, Palmer Canyon Road; WR, Wagonhound Ridge; BE, Box Elder Canyon; MR, Manning Ridge. Kenkman et al. (2022).

The Casper Formation is made up primarily of aeolian sandstones (i.e. sands laid down in a terrestrial desert or dune environment), although the uppermost portion of the section, where the craters are preserved, represents a marine transgression into this environment, forming a lagoon or sabkha environment (a sabkha being a coastal saltpan regularly refilled by tidal waters and emptied by evaporation). The craters sometimes form pedestals standing above the eroded surface of this formation, resulting from lithification processes of associated with the impacts, such as shock fusion (welding together of particles by a sudden impact), and cementing by a glassy melt formed within the crater.

 

Remote sensing images of selected craters of the different crater fields. (A), (B), (D), and (E) are drone images; (C), (F), and (G) are Google Earth imagery. Crater locations: SM, Sheep Mountain; MC, Mule Creek; FR, Fetterman Ridge; FRX, Fetterman Road; PCR, Palmer Canyon Road. (A) Crater SM-1 has an elliptical outline, a pedestal morphology with a preserved proximal ejecta blanket, and a raised rim. The downrange (northwest) rim shows an overturned ejecta flap. The linear ejecta wall is interpreted as a herringbone pattern. (B) Craters SM-6-3-4-5 form a northwest-southeast–trending radial crater chain. The ovoid crater SM-2 shows an overturned ejecta flap downrange (northwest) and a linear ejecta wall. (C) Craters MC-1 and MC-2 represent eroded craters with very little topography but a concentric fracture pattern. (D) Strongly degraded craters FR-1 and FR-2 contain shock effects along their crater rims. (E) The deeply eroded crater SM-9 is circular and has a bright halo of quartzitic sandstone. (F) Crater FRX-20 is a strongly elliptical landform with a gently rising rim. (G) The western and northern rim of crater PCR-1 exposes steeply dipping rocks. PCR-2 shows an elliptical outline. Kenkman et al. (2022).

The Casper Formation, on the upper surface of which the craters are preserved, has very little surface exposure, 1% of in Converse County and only 4% in Albany County, suggesting that many more craters may be preserved buried beneath the centre. This area lies within the Laramide Mountains, an area within the wider Rocky Mountains where Late Cretaceous to early Eocene (~75-50 million years ago) reverse faulting and folding uplifted an area of Archean basement rocks and the material overlying it. Most of the known craters lie upon the Sheep Mountain flank of the Sheep Mountain anticline, an extended fold-ridge mountain running from northwest-to-southeast, where the Opeche Shale has eroded back revealing the upper surface of the Casper Formation; it has been calculated that about 2 km of overlying rocks have been eroded away here since the onset of the orogeny; strata that are still likely to be in place in other areas, covering up other craters associated with this field.

 

(a) Simplified geological map of the Wyoming state. (b) Aerial photograph of Sheep Mountain anticline (view from the NNW); (c) Geological cross-section through of Sheep Mountain anticline perpendicular to the strike of the average fold axis, and (d) Geological map of the Sheep Mountain anticline area. Amrouch et al. (2010).

Wagonhound Ridge is a similar, and associated, structure to the south of Sheep Mountain, showing slightly less uplift. The Mule Creek, Fetterman Ridge, Fetterman Road, and Palmer Canyon Road exposures are found on the southwestern slope of the basement uplift of the Laramie Mountains in transition to the Shirley Basin, where the Casper Formation has largely been eroded away, but is exposed on several remaining buttes.

The largest cluster of impact-related structures is found on the northeastern flank of the Sheep Mountain, where a series of circular, irregular-shaped, and ellipsoidal have been confirmed as impact craters. These vary in their preservation quality from pristine to heavily eroded, with erosion apparently linked to the recent exposure of structures which were rapidly buried after their formation; i.e. the most eroded structures are located higher on the flanks of the mountain. The most pristine structures show steep crater walls, raised rims with overturned ejecta flaps, and remains of proximal ejecta blankets. These craters have floors are covered by soil and filled with muds derived from the overlying Opeche shales, making it hard to establish their depth-to-diameter ratio. Many of these craters are elliptical-to-ovoid in shape, with their long axes having fairly consistent orientations of 315–328°. The distribution of ejecta around the craters is uneven, with well-developed overturned flaps on their northwestern sides, suggesting they were caused by debris thrown from a primary impact to the southeast. Four of the craters form a chain, with a similar orientation. The more eroded structures further upslope tend also to be more rounded, with an internal ring structures. These often stand proud of the eroded surface, being more resilient to erosion due to the shock-fusion of the sandstone.

Ten possible craters have been found on the exposed surface of the Casper Formation at Wagonhound Ridge. Two of these have been confirmed as definite craters due to elevated rims. These are again filled with soil, and slightly elliptical. 

At Mule Creek a large elliptical crater measuring 56 m by 44 m has an orientation of 284±5°. A second structure, measuring 30 by 27 m is adjacent to this. Neither of these are elevated above the surrounding rock surface, and neither preserves any rim structure or surrounding breccia. It is thought that these represent the lower portions of larger craters that have been mostly eroded away; the larger of them appears to be surrounded by a larger ring at a distance of about 100 m, possibly representing underlying rocks that were consolidated by the impact. This area is cut through by a north-south and northwest-southeast–trending tectonic joint system visible in remote sensing images, which would have served to hasten erosion in this area. This joint system extends about 300 m to the northwest of the main crater, and contains at least nine irregular, soil-filled depressions which might represent further impacts. Another cluster of possible craters, one of which has been confirmed as an impact structure, is found about 2.5 km to the southeast of the main crater at Mule Creek. These structures have crater rims composed of sandstone breccia sealed with chert matrix.

At Fetterman Ridge a series of erosional buttes have exposures of the upper surface of the Casper Formation which have been eroded away from much of the surrounding landscape. One of these, a hill measuring roughly 200 m by 100 m, hosts three impact craters, measuring 30 m by 22 m, 28 m by 17 m, and 10 m by 10 m. The long axes of the two elliptical craters trend west-north-west to east-south-east, although their southern rims are more eroded. The 28 m by 17 m is distinctly elevated on its northwestern rim, with a visible ejecta flap on its western side. Again, the brecciated and fragmented rocks are sealed by microcrystalline silica, making them resistant to erosion. Other buttes to the northwest and southeast show possible additional impact craters, although these are more heavily eroded.

The Fetterman Road cluster comprises six possible craters 7–30 m in diameter, some of which are distinctly eliptical. The most distinct of these is 25 m by 15 m and has an orientation of 296°. The rim of this crater is elevated about a metre above its interior.

Eight possible craters are present at Palmer Canyon Road, about 10 km to the southeast of the Fetterman Road cluster. The two most conspicuous of these measure 42 m by 40 m, and 28 m by 19 m. Again, elevated rims are composed of quartzitic breccia with microcrystalline chert fill.

 

Outcrop-scale observations at the Wyoming crater field. (A) Panoramic view of crater WR-5 that shows very little relief. Note the outcrops along the rim. Persons for scale. (B) Brecciated ejecta. Fragments are partly angular and partly subrounded (SM-34). (C) The wind-scoured crater walls composed of quartzitic sandstone show abundant ventifacts (PCR-001). (D) Chert with flow textures and vesicles is very abundant at most of the craters (SM-36). (E) Breccia with quartzitic matrix (PCR-001). (F) The variegated contact of Casper sandstone and the Opeche Member of the Goose Egg Formation contains a few shocked quartz grains. Kenkman et al. (2022).

All of the discovered craters are on the upper surface of the Casper Formation, and all are in sandstones, but the nature of these sandstones varies slightly from site-to-site, reflecting an environment which was fully sub-aerial in the southwest, passing through a braided-river system into a shallow marine environment with some carbonate deposition in the northeast. The presence of water in the sands in some environments does not appear to have led to degradation of the crater rims. In all cases the craters were buried beneath Opeche Shale Member red beds of the Goose Egg Formation rapidly after their formation.

Brittle deformation, indicative of sudden physical shocks, can be seen on both large and small scales. The crater rims and ejecta all show brecciation (breaking into angular fragments) and brittle deformation, while individual grains are often intensely fractured.

Microstructures related to impact. (A) Crosscutting {1013} and (0001) PDF lamellae in sample from crater SM-19 are decorated by fluid inclusions. (B) {1013} PDF lamellae in sample from crater MC-1. A + B show that shock effects are restricted to the detrital grains while the overgrowth is undeformed. (C) Relatively wide-spaced planar fracture lamellae in sample from crater WR-4. (D) Concussion fractures in adjacent quartz grains emanate from initial grain contacts. (E) Crater SM-28 contains abundant chert layers and chert lumps that are embedded in the sandstone. Some of the chert lumps contain spherical lapilli. For interpretation, see text. (F) Close-up of a spherical lapillus that is interpreted as an accretionary lapillus. The concentric rings are composed of microcrystalline quartz around a dark-colored center. All photomicrographs were taken with crossed polarizers. Kenkman et al. (2022).

However, shocked grains are somewhat rare in the crater sediments, with slides made up from samples taken in the field typically showing only two-or-three shocked grains, and these usually being surrounded by unshocked grains rather than clustered together. Shocked grains were found in all parts of the crater structures, and at a much lower fequency level, outside the craters in undeformed sands, probably indicating their having been blown from craters by winds shortly after their formation. The degree of fracturing implies that these grains were subjected to pressures in excess of 10 gigapascals. 

Cherty (amorphous) silica is present at all sites, often forming the matrix which binds the sand grains together. Investigation of one of the craters at Sheep Mountain found a variety of structures within this chert, including elongated shapes and wavy layers. Within the chert were spherical structures resembling accretionary lapilli; glassy grains which are typically associated with violent volcanic eruptions, formed by the accretion of glassy siliica layers onto grains suspended in hot, turbulent air. 

The Wyoming Crater Field shows a number of features that help the reconstruction of the direction being travelled by impactors. The most obvious of these are oval or elliptical shaped craters, and craters arranged into chains, which gives the orientation of the direction of travel, but not the actual direction. However, direction of travel can be determined by using the following lines of evidence: (1) a steeper crater wall uprange; (2) a preserved overturned ejecta flap downrange, with a preferred deposition of ejecta downrange; (3) an ovoid crater shape with the strongest curvature downrange, and (4) V-shaped herringbone patterns of ejecta pointing up-range. 

The area has been subjected to some deformation since the impact craters formed, but none appears to have had its orientation changed by more than about 5%, enabling the use of craters from different sites to attempt to relocate the site of the original impact. Based upon this, Kenkman et al. suggest that the original impact happened at a site with map co-ordinates close to 41°28′N, 103°59′W; all of the craters lie between 150 km and 200 km from this site.

Modelling of possible trajectories of objects thrown from a primary impact crater suggest that boulders with a diameter of 2 m would need an initial velocity of 3-4 km per second to reach 150-200 km from the initial impact, while 4 m objects could reach this distance with an initial speed of 2 km per second would also fall within this zone. Such objects would deliver energy in the range of 12 to 400 gigajoules when they impacted, arriving at angles of between 45° and 60°.

Kenkman et al. calculate that an object with a density of 2500 kg per cubic meter (typical for many rock types), with a 4 m radius impacting at 1 km per second would create an impact crater about 45 m in diameter. A similar object 2 m in radius would create a crater 25-30 m in diameter, depending on its angle of approach. A range of objects between 1 and 4 m in diameter, travelling at between 500 and 1500 m per second, would generate craters between 8 and 55 m in diameter, with larger impacts releasing more energy and creating more shocked material as a proportion of the impactors mass.

Kenkman et al.'s findings reveal a series of clusters of craters across a wide area of southeast Wyoming, all of which appear to have formed simultaneously about 280 million years ago. These are best explained as secondary craters caused by material thrown from a large primary impact crater. No obviously foreign material was found in any of the craters, making it likely that the impacting material was similar in composition to the rocks of the areas impacted, and reconstructions of the direction of travel suggest the primary impact was between 150 and 200 km from the discovered craters.

Based upon the reconstructed size and impact speeds of the ejecta material, Kenkman et al. predict that the original impactor would have been 2.0-2.7 km in diameter, and to have hit the ground at about 20 km per second, creating a crater 50-65 km in diameter. 

This would place the location of the original impact in Goshen or Laramie counties in Wyoming, or Kimball, Banner, or Cheyenne counties in Nebraska. These areas fall within the Denver Basin, and Permian strata are deeply buried beneath subsequent Mesozoic and Cainozoic deposits. Despite this apparent lack of accessibility, these deposits have been heavily boreholed by hydrocarbons exploration companies, which may enable reconstruction of the original impact site. To date, Kenkman et al. have not found evidence of distorted or missing sedimentary strata which might be associated with such an impact in any well log data examined, but one drill core, 1–35 Hawk Fee, does show a breccia layer at 3023–3066 m below the surface, and Kenkman et al. are hoping to visually inspect this core in the near future. 

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New Chroniosuchian materials from the Permian and Triassic of Xinjiang Province, China

The Chroniosuchians were an enigmatic clade of non-Amniotic Tetrapods with uncertain phylogenetic position. This group can be divided into two families, Bystrowianidae and Chroniosuchidae. The earliest representatives of both families are known from the middle Permian Dashankou Fauna of Gansu Province, China. The latest representative of Chroniosuchidae is known only from a single Triassic taxon, Madygenerpeton pustulatus, from the Ladinian or Carnian of Kyrgyzstan; while those of Bystrowianidae are known from Middle Triassic of Russia and Germany.

This group was first reported from the late Permian Jiyuan fauna in China, i.e. Bystrowiana sinica; later, two more species were named and referred to Bystrowianidae for this fauna (Jiyuanitectum flatum and Dromotectum largum). Some postcranial bones were identified as Bystrowianid from the Permo-Triassic Guodikeng Formation of Jimusar in Xinjiang Province, China, but no definite Triassic Chroniosuchian is known from China up to now. Recent fieldwork has shown that Chroniosuchians were a diverse and persistent group in Xinjiang: they survived from the late Permian to at least the Early Triassic here.

In a paper published in the journal Vertebrata PalAsiatica in October 2020, 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 the Chinese Academy of Sciences, reports three new Chroniosuchian specimens from Xinjiang, including the first definite Triassic Chroniosuchian from the Jiucaiyuan Formation.

 

Permian to Triassic stratigraphic sequence within Turpan-Hami Basin, Xinjiang, showing the horizons of studying specimens. Liu (2020).

The first specimen described, IVPP V 26539, is a left femur from the upper part of the middle Permian Quanzijie Formation at the Dalongkou section in Santai in Jimusar, Xinjiang. 

This femur is slightly dorsoventrally compressed, and is not so curved as the femur of IVPP V 23295. It is slender and waisted as other Chroniosuchians. The anterior margin is more concave than the posterior margin. The length of the bone is 40 mm, and the width is 13, 15 mm respectively for the proximal and distal ends. Both expanded ends are incompletely ossified. The unfinished proximal articular surface is convex in outline dorsally and slightly concave ventrally when viewed mesially. It extends anteroventrally, forms a continuous surface with the unfinished internal trochanter. The proximal articular surface decreases in dorsoventral height backwards and forms a pointed angle posteriorly.

 

Chroniosuchian left femur (IVPP V 26539) from the Quanzijie Formation in Jimusar, Xinjiang in extensor (A), anterior (B), flexor (C), proximal (D), and distal (E) views Abbreviations: ab. adductor blade; ac. anterior (tibial) condyle; adc. adductor crest; ff. fibula fossa; icg. intercondylar groove; it. internal trochanter; itf. intertrochanteric fossa; pa. popliteal area; pc. posterior (fibular) condyle. Liu (2020).

The dorsal surface of the femur bears striations on the proximal side. The dorsal surface of the distal end of the femur is divided by a relatively broad intercondylar groove. The anterior condyle extends slightly wider than the posterior one. Due to the incomplete ossification, the anterior condyle projects distally similar to the posterior condyle. The anterodorsal surface of the anterior condyle, near the middle, bears distinct longitudinal ridges for ligaments.

The adductor blade is low, directed posteroventrally, forming the anterior margin of the large intertrochanteric fossa. The anterior surface of the adductor blade is rugose. Distal to the adductor blade, a low but distinct adductor crest is slightly curved, runs distally near the posterior margin of the shaft on the ventral surface, and ends by a crack. Distal to the crest, there is a low ridge to a point close to the triangular popliteal area. However, it is likely separated from the adductor crest. Posterior to it, another crest runs on the posterior side of the shaft ending on the distal posterior corner. Two crests frame the small fibula fossa on the posteroventral corner of the distal end.

The shape of this femur is primitive among Tetrapods. However, it is slender, similar to that of Temnospondyls like Trimerorhachis or Chroniosuchians, rather than robust as in many other basal Tetrapod groups. As in IVPP V 23295 and Bystrowiella schumanni, the adductor crest follows a diagonal course, ending distally close to the posterior margin of the shaft. In most Permian Tetrapods, adductor crest generally runs towards, not posterior to the popliteal area. This could be a diagnostic character of Chroniosuchians.

IVPP V 26539 also shares the following features with other chroniosuchian femurs (V 23295 and SMNS 96948): the adductor blade is directed posteroventrally, and the posterior end of the proximal articular surface is pointed. So this specimen can be referred to Chroniosuchia.

This specimen has unfinished ends, as in the much longer femur of SMNS 96948, may indicated juvenile state of both specimens. Meanwhile, a medium sized femur of V 23295 is well-ossified, indicated that species has a smaller adult size.

The second specimen described, IVPP V 26540, comprises four vertebrae, one rib, and several scutes, from the base of the upper Permian Guodikeng Formation at the Taoshuyuan (Taoxigou) section,  at Turpan in Xinjiang. 

There are four articulated and one isolated vertebrae, two of them are nearly complete. They are identified as the vertebrae around sacral region. The vertebrae have a basic shape of Bystrowianidae. 

 

Bystrowianid specimen (IVPP V 26540) from the Guodikeng Formation in Turpan, Xinjiang (A)–(B) Four continuous vertebrae in ventral (A) and right lateral (B) views; (C)–(D) Isolated vertebra in anterior (C) and posterior (D) views; (E) An incomplete rib; (F)–(G) The impression of dorsal surface of three osteoderms (F) and two osteoderms (G) Abbreviations: dp. diapophysis; ic. intercentrum; ns. neural spine; pc. pleurocentrum; pnc. paraneural canal; poz. postzygapophysis; pp. parapophysis; prz. prezygapophysis; tp. transverse process; vp. ventral process of osteoderm; vr. ventral ridge. Lui (2020).

Only two articulated intercentra are exposed. The anterior one shows smooth periosteal bone on ventral and lateral surfaces. Its lateral surface bears part of the parapophyses for articulation with the capitulum near the posterior margin, and ventral surface has no haemal arch. In lateral view, its length relative to the pleurocentrum is similar to IVPP V 23295, much narrower than in Chroniosaurus dongusensis.

The lengths of the pleurocentra are approximately 10 mm, while the heights are about 9 mm. The pleurocentra are massive with a round cross-section, and they are not perforated by the notochord. The ventral surface is relatively flat (slightly convex on the anterior one, slightly concave on the posterior one) with faint ventral ridges on three articulated larger pleurocentra. Two longitudinally aligned, low ridges are clear on the narrow ventral face of the smaller pleurocentrum of the isolated vertebra. This feature has been proposed as a Bystrowianid characteristic. The neural arches are fused to the pleurocentra, but their suture is clear; so this specimen looks like in a younger stage than V 23295, in which the suture is absent. This suture runs across the diapophysis in three articulated vertebrae, indicating the pleurocentrum participates in formation of the diapophysis. On two posterior pleurocentra, the anterior half of the ventrolateral surface participates in formation of the parapophysis, which is separated from the diapophysis by a narrow groove. So they are identified as the sacral and the first caudal vertebrae, as in Kotlassia and Proterogyrinus.

The transverse processes are very short and massive, directed ventrolaterally. The facets of the diapophyses are strongly enlarged in the sacral and first caudal. In the isolated vertebra, the transverse processes are completely formed by the neural arch. It is probably derived from the anterior tail region.

The neural spines are only nearly complete in the sacral vertebra and one isolated caudal vertebra. The neural spines are anteroposteriorly slightly shorter than the pleurocentrum. In the sacral, its anterior and posterior margins are nearly parallel. Its height is less than twice the height of the pleurocentrum. Its dorsal tip is connected with the osteoderm by interdigitating sutures. In the isolated caudal, the neural spine widens dorsally near the tip then narrows. Its dorsal tip does not carry an osteoderm.

A curved incomplete rib measures more than 5 cm in original length. The proximal side is not preserved.

There are two pieces of impression of the dermal surface of the osteoderms, one with three osteoderms, and the other with two osteoderms. Neither of the osteoderms is complete, so it is unsure on the width of the osteoderms. The distinct dermal sculpturing is composed of ridges and depressions. A mid-ridge is preserved. The pits have different sizes on two sides of the ridge, and they likely arrange in posterolaterally radiated line. No prominent parasagittal ridge is observed.

This specimen is diagnosed as a Bystrowianid chroniosuchian for the presence of the sculptured dorsal osteoderms which are sutured with the neural spine, paired deep paraneural canals on anterior and posterior surfaces of the neural arch. It cannot be further diagnosed for the poor preservation of the osteoderms.

The final specimen described, IVPP V 26541, is an incomplete dorsal osteoderm from the Lower Triassic Jiucaiyuan Formation, at a location 4 km east to the Dalongkou section at Santai in Jimusar, Xinjiang. 

This single osteoderm is slightly convex dorsally. Most of the margins are broken other than right anterolateral margin The complete width should be approximately 3 cm. The dermal sculpture is not symmetric, and it is dominated by different-sized polygonal pits formed mainly by longitudinally oriented and oblique ridges. Transversely elongated sculptural depressions are only present near the posterior area. The sculpture has no axial crest or any parasagittal ridge, as in Synesuchus muravjevi or Dromotectum spinosum. The right anterior wing is preserved its posterior portion, with a smooth dorsal facet for the facies alaris (ventral facets) of the preceding osteoderm. The right accessory process is also partially preserved. The maximum width of one anterior wing is estimated as 9 mm, slightly smaller than the width of accessory processes.

 

Bystrowianid osteoderm (IVPP V 26541) from the Jiucaiyuan Formation in Jimusar, Xinjiang in dorsal (A), ventral (B), and posterior (C) views Abbreviations: am. area marginalis; ap. accessory process; aw. anterior wing; cl. lateral crista; cm. medial crista; co. crista obliqua; df. dorsal facet; dv. ventral depression; fa. facies alaris; pv. ventral process; sa. sulcus articularis. Liu (2020).

The incomplete median articular plate measures 10 mm in width. It lies posteriorly and slightly ventral to the sculptured dorsal plate. The median crista decreases in width backwards and is triangular in shape in dorsal view. The broad lateral cristae are longer than and located at the same level as the median crista. Most parts of these cristae are formed by tapered extensions of the posterior margin of the sculptured dorsal plate. As most Bystrowianids, two deep longitudinal grooves (sulci articulares) lies between the median and lateral crests, for accommodation of the accessory processes and associated ligaments of the successive osteoderm. The area marginalis (marginal zone) is incompletely preserved on the right side. It extends anteriorly ventral to the dorsal plate as in Bystrowiana and Jiyuanitectum.

On the ventral surface, the shallow median depression, between the anterior wings back to the base of the ventral process, is preserved for most of the right side and nearly posterior half of the left side. The ridge extends from the right accessory process is distinct. The sulcus medius (median groove) should be narrow. A broad, low but distinct crista obliqua (oblique crest) extends along the ventral surface of the osteoderm posteromedially from the anterior wings toward the region of the ventral process, and continuous to the margin zone of the median articular plate. Lateral to the ventral margin, a shallow depression on the posterior part of the ventral surface is the ventral facet that overlapped the dorsal facet of the anterior wing of the succeeding osteoderm.

The base of the ventral process is located in the posterior half of the osteoderm, and its posterior margin extends posteriorly beyond the boundary of the sculptured surface of the osteoderm. The process is ovate in transverse section and lacks anterior and posterior extensions.

IVPP V 26541 can be referred to Bystrowianidae based on the unpaired posterior articular plate and weakly expanded plate bearing broadly separated anterior facets. IVPP V 26541 represents a new taxon closely related to Dromotectum. However, it is not named by Liu, who feels it should be named from more complete material. Its close relationship with Dromotectum is not surprise, because Dromotectum existed in the upper Permian of Henan, China.

The new specimens described here increase the diversity of Permo-Triassic Tetrapods. Previously, only one Tetrapod species, Kunpania scopulusa, was reported from the top of the Quanzijie Formation. Also, only one Chroniosuchian specimen was reported from the Guodikeng Formation. Although Chroniosuchian should have existed from middle Permian in Xinjiang based on their known distributions, this is the first evidence which confirmed its existence from the Quanzijie Formation. The bystrowianian Chroniosuchian specimens from the base and the top of the Guodikeng Formation and the Jiucaiyuan Formation demonstrated that this group survived in the end-Permian mass extinction here in Xinjiang, together with Lystrosaurus.

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