Marine Trematosaurid Temnospondyls from the Early Triassic of Western Australia.

The Temnospondyls were an ancient group of Tetrapods, which are the sister group to the modern Lisamphibians (Frogs, Salamanders, and Caecilians), although they were in many ways more Reptile-like, with many apparently able to live completely away from water for much of their lives, while others colonised marine environments. The first Temnospondyls appeared in the Carboniferous, rapidly expanding to become one of the most diverse and abundant groups of terrestrial Vertebrates. The Temnospondyls remained a major group throughout the Permian and Triassic, but were badly affected by the End Triassic extinction from which they never recovered. A few Temnospondyl lineages persisted through the Jurassic and into the Early Cretaceous, when they finally disappeared.

The Trematosaurids were a group of Temnospondyls which migrated into marine environments in the Early Triassic, evolving to occupy a large marine predator role which had become vacant during the End Permian Extinction, and spreading throughout much of the world's environments. Trematosaurids have been described from Madagascar, Greenland, Australia, Pakistan, Spitsbergen, European Russia, the Russian Far East, Germany, and Jordan. 

To date, only a single species of Marine Trematosaurid (several others are known from clearly non-marine environments) has been described from Australia, Erythrobatrachus noonkanbahensis, which described in 1972 by John Cosgriff and Neil Garbutt on the basis of a composite of fragmentary cranial remains from the Early Triassic Blina Shale of the central-southern Kimberley region of far northwestern Western Australia, collected during a series of expeditions to the area in the 1960s.

The Blina Shale records a transgressive delta setting (setting where the land is extending into the sea over a delta system), which would have faced onto the East Gondwana interior rift seaway. These deposits record a mixture of saline, brackish, and freshwater environments, and have produced non-Trematosaurid Temnospondyls such as the Rhytidosteid, Deltasaurus kimberleyensis, the Capitosauroid, Warrenisuchus aliciae, and the Brachyopids, Batrachosuchus henwoodi, and Banksiops townrowi. A variety of other fossils have also been found within the Blida Shale, including the ubiquitous Triassic Saurichthyid Actinopterygian, Saurichthys, a variety of Ceolacanths, the Ptychoceratodontid Lungfish, Ptychoceratodus philippsi, the Sagenodontid Lungfish, Aphelodus anapes, the Ceratodontid Lungfish, Asiatoceratodus tiguidensis, several possible Sharks, Conodonts, Insects, Spinicaudatans and Lingulid Brachiopods, possible Pseudomonotid Bivalves, indeterminate Ammonoids, some possible Mollusc egg cases, burrow traces, palynomorphs (fossil pollen and spores), Achritarchs, Horsetails, and possible Lycopods. 

Temnospondyls from the Blina Shale are typically found in a disarticulated state, either as individual bones or accumulations, and show signs of having been transported before their final deposition, including weathering and sorting by size. This is consistent with deposition in beds with preserved ripple marks and thin cross-lamination, which is suggestive of a shallow, tidal environment. 

In a paper published in the Journal of Vertebrate Palaeontology on 22 February 2026, Benjamin Kear of the Department of Palaeobiology at the Swedish Museum of Natural History, Nicolás Campione of the Palaeoscience Research Centre at the University of New England, Mikael Siversson of the Western Australian Museum, and the School of Molecular and Life Sciences at Curtin University, Mohamad Bazzi of the Department of Earth and Planetary Sciences at Stanford University, and Lachlan Hart of the School of Education and Earth and Sustainability Science Research Centre at the University of New South Wales, as well as the Australian Museum Research Institute, reassess that material assigned to Erythrobatrachus noonkanbahensis from the Blinda Shale deposits, and draw new conclusions about the presents of Trematosaurid Temnospondyls in the Early Triassic of Western Australia.

The original material assigned to Erythrobatrachus noonkanbahensis included the holotype, WAM 62.1.46, two topotype specimens, WAM 71.6.22 and WAM 62.1.50, and a high-definition plaster caste of the holotype, WAM 62.1.59 (in taxonomy, a holotype is the specimen from which a species is described, any other specimen considered to belong to the same species as the holotype therefore belongs to that described species, but if the holotype is found to belong to the same species as the previously described holotype of another species, then the newer species is considered invalid; a topotype is a specimen asigned to a species which comes from the same location as the holotype). All of these specimens were placed in the collection of the Western Australian Museum, but when Kear et al. came to look for them, only WAM 62.1.50 and WAM 62.1.59 could be found, WAM 62.1.46 and WAM 71.6.22 having apparently been loaned to John Cosgriff in 1984, at which time he was working at Wayne State University in Detroit, Michigan. 

A search of the palaeontological collection of Wayne State University could not locate these specimens, although WAM 62.1.46 was subsequently found in a search for potentially related specimens in the collection of the University of California Museum of Paleontology, where it had been identified as cf. Tertrema sp., and given the identifier UCMP 65858. The collection of the University of California Museum of Paleontology was also found to contain a second high-definition plaster caste of this specimen, listed as UCMP 65850. The University of California Museum of Paleontology has subsequenty returned WAM 62.1.46 to the Western Australian Museum. 

Also found within the collection of the University of California Museum of Paleontology was a box labelled WAM 62.1.50, however, this was found to be empty, having been 'withdrawn for study' by John Cosgriff in August 1968.

Source locality for the Erythrobatrachus noonkanbahensis holotype (WAM 62.1.46) and referred material (WAM 62.1.50). Map of the Noonkanbah Station area with the Great Northern Highway (1) extending southeast of Derby towards Fitzroy Crossing in northwestern Western Australia. Outcrop areas of the Lower Triassic Blina Shale are shown with the overlying Erskine Sandstone, and Middle Triassic Munkayarra Shale. Kear et al. (2026).

Specimen WAM 62.1.46, the holotype of Erythrobatrachus noonkanbahensis is a steinkern internal cast from the naso-frontal region of the skull and vomero-palatine section of the palate. This, along with the plaster casts WAM 62.1.59 and UCMP 65850, show Erythrobatrachus noonkanbahensis to have had an elongate skull with a basally constricted rostrum, dorsolaterally facing orbits that are positioned close to the lateral jaw margin, broad nasals that contact the lacrimals posterolaterally, and possibly the septo-maxilla near the external bony nasal opening, anteriorly narrow interpterygoid vacuities that are bordered by transversely broad palatines, ctopterygoids apparently lacking large palatal tusks, at least at the ectopterygoid-palatine suture, and a narrow cultriform process of the parasphenoid that divides the interpterygoid vacuities along the palatal midline, and extends to a point level with the anterior edges of the choanae.

High-definition plaster cast (WAM 62.1.59) and holotype specimen (WAM 62.1.46/UCMP 69858) of Erythrobatrachus noonkanbahensis from the Blina Shale. (A) Cast, and (B) original internal steinkern of the naso-frontal section of the cranium in dorsal aspect. (C) Interpretation of the cranial sutures (solid/dashed lines), openings (black fills), and broken/plaster surfaces (hatching). (D) Skull reconstruction in dorsal aspect. (E) Cast and (F) original internal steinkern of the vomero-palatine section of the cranium in ventral aspect. (G) interpretation of the cranial sutures and openings. (H) Skull reconstruction in ventral aspect. Skull outlines based on Tertrema acuta and Hyperokynodon keuperinus. Abbreviations: ch, choana; cp, cultriform process of the parasphenoid; ec, ectopterygoid; fr, frontal; ju, jugal; la, lacrimal; mx, maxilla; na, nasal; nc, nerve channel cast; or, orbit; pf, postfrontal; pl, palatine; pr, prefrontal; pv, pterygoid vacuity; sm, septomaxilla; ?tb, possible palatal tusk base; vo, vomer. Scale bars equal 50 mm. Kear et al. (2026).

Specimen WAM 62.1.50 is an external impression of the vomerine palate showing multiple dental rows and anterior margins of the choanae. This is recorded as a paratype of Erythrobatrachus noonkanbahensis on its Western Australia Museum label (a paratype is a specimen other than the holotype of a species which is used in the formal description of that species), but as 'cf. Aphaneramma' (refer to Aphaneramma) on the label of the empty box at the University of California Museum of Paleontology, a label which Kear et al. assume reflects Cosgriff's original thoughts on the classification of the specimen. Aphaneramma is a cosmopolitan Trematosaurid Temnospondyl also known from the Early Triassic of Pakistan, Madagascar, Russia, and Svarlbard. 

WAM 62.1.50 appears to be similar in proportions to the skull of Aphaneramma gavialimimus, a large (skull-lenght about 400 mm) species of Aphaneramma described from Madagascar in 2017. It also has fine longitudinal bone ridges, which have previously been observed in members of the genera Aphaneramma, Wantzosaurus, and Cosgriffius. The choanae of WAM 62.1.50 are longitudinally offset, such that the left opening would have been displaced anteriorly relative to the right, something which has also been recorded in other specimens of Aphaneramma. In their 1972 description of Erythrobatrachus noonkanbahensis, Cosgriff and Garbutt identify this as being the result of displacement of the right choanae, which they believe was 'compressed and pushed forward from its original position', but which Kear et al. consider may be a diagnostic feature of the genus. Notably, WAM 62.1.50 shows several rows of vomerine teeth (teeth on the roof of the mouth), which are absent in WAM 62.1.46, suggesting the two do not belong to the same species. Vonerine teeth are found in Aphaneramma, as well as some other genera of Trematosaurid Temnospondyls, although the size and arrangement of those of WAM 62.1.50 do not appear to exactly match any previously described taxa. For this reason, Kear et al. return WAM 62.1.50 to the designation cf. Aphaneramma. 

Referred material (WAM 62.1.50) of cf Aphaneramma sp. from the Blina Shale. (A) Palate impression in ventral aspect (coated with ammonium chloride sublimate). (B) Interpretation of the palatal sutures, dentition (solid/dashed lines), and openings (black fills). Skull outline based on Aphaneramma gavialimimus. (C) Skull reconstruction in ventral aspect. Skull outline based on Aphaneramma gavialimimus. Abbreviations: ch, choana; mx, maxilla; tr, tooth row; vo, vomer. Scale bar equals 30 mm in (A) and (B); and 50 mm in (C). Kear et al. (2026).

Cosgriff and Garbutt apparently viewed the additional specimens assigned to Erythrobatrachus noonkanbahensis, WAM 71.6.22 and WAM 62.1.50, as developmental stages of the species, noting that they were smaller than the holotype, WAM 62.1.46. As WAM 71.6.22 could not be located, this assessment could not be evaluated for this specimen, but Kear et al.'s study clearly shows that the smaller size of WAM 62.1.50 only relates to its fragmentary nature, and that it was clearly derived from quite a large animal. Furthermore, it differs significantly in morphology to WAM 62.1.46, and cannot be assigned to the same species.

This expands the diversity of Temnospondyls known from the Blina Shale, and expands our knowledge of how that assemblage relates to wider Temnospondyl faunal distributions in the Early Triassic. This includes widespread Australian species such as Deltasaurus kimberleyensis, Warrenisuchus aliciae, and Banksiops townrowi, taxa also known from South Africa, such as the genus Batrachosuchus, species not found anywhere else, such as Erythrobatrachus noonkanbahensis, and now an example of the globally distributed genus Aphaneramma. This also increases the distribution of these marine Temnospondyls, raising the possibility that their distribution was not just due to expansion along the continuous coastal Tethyan periphery of the Pangean supercontinent, but may also have involved longer distance, ocean-crossing dispersals between Laurasia and Gondwana across the Tethys Ocean.

Early Triassic (about 250 million years ago) paleobiogeographic distributions of Erythrobatrachus noonkanbahensis (star) and Aphaneramma in Australia (star), Madagascar (circle), Pakistan (square), Svalbard (polygon); and Russia (triangle). Kear et al. (2026).

See also...

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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Arenaerpeton supinatus: A new species of Temnospondyl Amphibian from the Triassic of New South Wales.

Modern Amphibians all belong to a single group, the Lisamphibians, which are quite closely related to the Amniotes (Reptiles, Birds, and Mammals). However, in the Carboniferous other Amphibian groups, such as the Temnospondyls and Ichthyostegids, which were more distantly related to the Amniotes. Although considered to be 'primitive' compared to modern Tetrapods, some Temnospondyls independently acquired Reptile-like traits such as the scaley skin and the ability to live away from water. The majority of Temnospondyls perished in the End Permian Extinction, but a few groups survived into the Mesozoic, and persisted as long as the Cretaceous. One of these groups was the Chigutisauridae, an exclusively Gondwanan group of wide-headed predatory, aquatic Temnospondyls, which first appeared in the Early Triassic of Australia and persisted across the southern continents until the mid-Cretaceous. However, despite having originated in Australia, the Australian fossil record of Chigutisaurids is very sparse, with three known species from Queensland, one from the Early Triassic, one from the Early Jurassic, and one from the Early Cretaceous, plus a possible species from the Late Triassic of South Australia.

In a paper published in the Journal of Vertebrate Paleontology on 3 August 2023, Lachlan Hart of the Earth and Sustainability Science Research Centre at the University of New South Wales, and the Australian Museum Research Institute, Bryan Gee of the Burke Museum and Department of Biology at the University of Washington, Patrick Smith, also of the Australian Museum Research Institute, and of the Department of Biological Sciences at Macquarie University, and Matthew McCurry, also of the Earth and Sustainability Science Research Centre at the University of New South Wales, and the Australian Museum Research Institute, and of the Department of Paleobiology at the Smithsonian National Museum of Natural History, describe a new species of Chigutisaurid Temnospondyl from the Early–Middle Triassic Terrigal Formation of New South Wales.

The new species is described from a single specimen, AM F125866, which was found among rocks obtained from Kincumber Quarry, approximately 90 km to the north of Sydney on the Central Coast of New South Wales, for the purpose of building a wall on a private property, and donated to the Australian Museum in the mid 1990s. The specimen  is preserved in ventral aspect (belly-up) in a piece of sandstone, with the forward part of the skeleton and the articulated skull preserved, as well as a soft-tissue outline of the body. Only the part (body fossil) of the specimen is known, the counterpart (would of the fossil) was not found, and was apparently lost during the quarrying process. The fossil proved to be impossible to further separate from the matrix without damaging it, and an attempt to X-ray the specimen using a large cargo scanner used by the Australian Border Force proved unsuccessful, as there was to little contrast between the fossil and the matrix.

The new species is named Arenaerpeton supinatus, where 'Arenaerpeton' means 'thing that creeps in the sand' a reference to the sandstone matrix in which the fossil was found, and 'supinatus' means 'on its back' a reference to the position in which the fossil was found. The specimen from which it is described comprises elements of the pre-maxilla, maxilla, vomers, parasphenoid, exoccipital, pterygoid, quadrate, quadratojugal, mandible, and possible remnants of the ectopterygoid, the onterclavicle and clavicle, a possible scapula, a humerus, radius, ulna, and metacarpal, and a near complete precaudal vertebral series with associated ribs. A small piece of what might be the pelvis is present, but no other parts of the pelvic girdle, hindlimbs, or tail.

Arenaerpeton supinatus, AM F125866, articulated skeleton. (A) Full fossil in ventral view. (B) schematic interpretation. Abbreviations:cl, clavicle; cp, cultriform process of the parasphenoid; ect, ectopterygoid; eo, exoccipital; h, humerus; ic, interclavicle; m, mandible; mca, metacarpal; mx, maxilla; p, pelvis; pmx, premaxilla; psph, parasphenoid; pt, pterygoid; q, quadrate; qj, quadratojugal; ra, radius; s, scapula; ul, ulna; v, vomer, ve, vertebrae. Light gray elements represent exposed bone. Darker sections represent cavities in the matrix. Unfilled outlines indicate unexposed bones within the matrix. Thomas Peachey in Hart et al. (2023).

Despite a small number of known fossils, Chigutisaurids are the only group of Temnospondyls which are known to have survived the End Triassic Extinction in Australia. Arenaerpeton supinatus is the second known Triassic species from Australia, along with Keratobrachyops australis, from the Early Triassic of Queensland (another Late Triassic probable Chigutisaurid is known from the South Australia, but this is poorly preserved and has not formally been described). Also known from Queensland are the Early Jurassic Siderops kehli, and the Early Cretaceous Koolasuchus cleelandi. Both of the post-Triassic species were large for Temnospondyls, with Siderops kehli having a total estimated length of 2.6 m, while Koolasuchus cleelandi reached about 3 m, while the Early Triassic Keratobrachyops australis was much smaller; its length cannot be reconstructed from the available material, but the largest known specimen has a maximum skull width of 14.5 cm. Arenaerpeton supinatus appears to be intermediate in size, with a maximum skull width of 23.6 cm, and a bodylength of 94 cm excluding the tail (which was not preserved, comparable with Triassic Chigutisaurids from India and South America. 

Reconstruction of Arenaerpeton supinatus, preying on the Ray-finned Fish Cleithrolepis granulata, which is also known from the Triassic of New South Wales. José Vitor Silva in Hart et al. (2023).

Arenaerpeton supinatus is the second known Temnospondyl from the Terrigal Formation of the Sydney Basin, the other being the Brachyopid Platycepsion wilkinsoni. This is only the second known co-occurrence of Chigutisaurid and Brachyopid Temnospondyls (the only two Temnospondyl groups which survived the End Triassic Extinction), with the two groups otherwise tending to be found in different settings, possibly implying different ecological specializations.

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An immature Temnospondyl Amphibian from the Late Triassic of Brazil.

The Temnospondyls were an ancient group of Amphibians, thought to have been the first group of Vertebrates fully adapted to life on land. They flourished in the Carboniferous, Permian and Triassic, with a small number surviving as late as the Cretaceous. They were much larger than modern Amphibians, and were quite different in appearance, with boney armoured plates, scales and well developed claws. Nevertheless some experts have suggested that the Lisamphibians (modern Amphibians) are descended from the Temnospondyls.

In a paper published in the January 2012 edition of the journal Palaeontology, Sérgio Dias-da-Silva of the Laboratório de Paleobiologia at Campus de São Gabriel at the Universidade Federal do Pampa, Dhurjati Sengupta of the Geological Studies Unit at the Physics and Earth Science Division at the Indian Statistical Institute, and Sérgio Cabreira and Lúcio da Silva of the Laboratório de Paleontologia at the Universidade Luterana do Brasil, describe an immature Temnospondyl Amphibian from the upper levels of the Santa Maria Formation in the Municipality of São João do Polêsine in the State of Rio Grande do Sul, Brazil.

The new specimen closely resembles Compsocerops cosgriffi, a Late Triassic Temnospondyl from India, and assigned to the genus Compsocerops, though due to the fragmentary nature of the specimen, and the fact that it appears to be a juvenile, it is not given a specific name. The specimen comprises a partial skull, part of a jawbone, a fragment of the clavicle (collarbone), and part os a humerus (upper arm bone). The specimen is considered to be a juvenile because the bones appear thin with widely separated sutures, and the simple ornamentation of the bones; the ornamentation of a mature Temnospondyl being rather more elaborate.

Compsocerops sp., cranial fragment; (A) photograph in dorsal view, (B) photograph in lateral view, (C) interpretive drawing of (A), (D) interpretive drawing of (B). Abbreviations: aj, alar process of the jugal; f, frontal; is, infraorbital sulcus; j, jugal; po, postorbital; pof, postfrontal. Scale bars represent 10 mm. Dias-da-Silva et al. (2012).

Compsocerops sp., second cranial fragment; (A) photograph in dorsal view, (B) photograph in lateral view, (C) interpretive drawing of (A), (D) interpretive drawing of (B). Abbreviations: pp,

postparietal; ppp, postparietal process; ptf, posttemporal fenestra; st, supratemporal; t, tabular. Scale bars represent 10 mm. Dias-da-Silva et al. (2012).

Compsocerops sp., reconstruction of the skull, based on available material. Scale bar represents 10 mm. Dias-da-Silva et al. (2012).

Compsocerops sp.: (Top) part of the mandible in (A) dorsal view, (B) labial view, and (C) lingual view. (Bottom) partial clavicle in  (D)ventral view and (E) dorsal view. (F) Partial humerus in ventral view. Abbreviation: dg, deep groove. Scale bars represent 10 mm. Dias-da-Silva et al. (2012).

See also Two new species of Moss from the Permian of Brazil,  Three new species of Frog from the Peruvian Andes, New species of Robber Frog from Panama, A cryptic species of Ground Frog from southern Chile and A Salamander from the Late Jurassic of China.

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