Rainer R. Schoch

Two temnospondyl specimens from the Ruthweiler deposit (M8) in the early Permian Meisenheim Formation of the Saar-Nahe Basin are identified as pertaining to a new branchiosaurid taxon, Schoenfelderpeton brevifrons . They are distinct from all other temnospondyls in the region by the delta-shaped skull, small orbits, and short frontals. The maxilla fails to contact the cheek and has tiny, pin-shaped teeth, a feature that persists in the mature specimen. Schoenfelderpeton brevifrons is found to nest with Leptorophus and “ Melanerpeton ” humbergense and forms the sister taxon to Schoenfelderpeton prescheri , with which it shares the short gape, open cheek, and an emarginated squamosal embayment.

Neoteny is widespread in extant Caudata and has also been inferred in extinct temnospondyls. Here, we compare osteohistology, microanatomy, and life history traits of the Permian branchiosaurid Apateon spp. with those of modern obligate and facultative neotenic and not neotenic caudates to possibly identify common patterns separating groups. The osteohistology of these modern caudates is studied for the first time based on petrographic ground sections, which yield a better comparability between modern and fossilized bones than microtomized thin sections. We found in all adult individuals’ avascular lamellar matrix, except for Necturus maculosus , which grew with avascular parallel-fibered bone. The presence of osteoblasts indicates prolonged bone mineralization process in caudates. Medullary cavity size varies widely in humeri of Ambystoma mexicanum and in humeri and femora of Apateon spp., whereas in all other taxa it is more uniform and tendentially compacter which, however, might be the result of lower sample sizes. Apateon spp. had numerous lines of arrested growth indicating strong seasonal growth as was described in detail before and which is in accordance with the inferred environmental conditions. The markedness of growth marks is well pronounced in Necturus maculosus , Amphiuma means , Triturus cristatus , Lissotriton vulgaris and Salamandra salamandra but not in others. Poor expression of growth marks might be related to constant climatic conditions (e.g., Ambystoma mexicanum , Proteus anguinus ) or due to an early ontogenetic stage and a yet low mineralized matrix of some individuals in our sample ( Ichthyosaura alpestris , Calotriton asper ). Growth mark counts of captive A. mexicanum of known age considerably underestimated their actual age. The analysis of adult body mass, age at maturation and maximum longevity of a large dataset on obligate neotenic and non-obligate neotenic caudates indicated a high variability in the two latter traits and associations among each other and to adult body mass. Due to this large variability, we did not find any pattern that can be used to unequivocally infer whether a taxon is obligate neotenic or not. Overall, our results suggest that no shared pattern in osteohistology, microanatomy or life history traits exists among extant obligate neotenic, non-obligate neotenic and extinct neotenic Apateon .

The Devonian fish‐to‐tetrapod transition and the subsequent conquest of land involved multiple amphibious stem and early tetrapod lineages, yet how these animals reduced their dependence on aquatic environments remains uncertain. Feeding is central to this transition, as early tetrapods likely moved from predominantly aquatic suction feeding to jaw‐based prey prehension and processing. Although recent functional approaches—including morphometrics, functional morphology and computational modelling—offer new perspectives, their interpretive strength depends on realistic soft‐tissue inputs, particularly cranial musculature. Here, we reconstruct the principal cranio‐mandibular (skull) musculature of the Middle Triassic capitosaur temnospondyl Mastodonsaurus giganteus to provide an explicit anatomical foundation for future functional and modelling studies of stem and early tetrapods and to refine ecological interpretations for this species. We formulate alternative muscle hypotheses within an extant phylogenetic bracket (EPB) framework that explicitly reflects uncertainty in temnospondyl placement (temnospondyl versus lepospondyl origin of lissamphibians). We developed hypotheses from a literature review and digital dissections of contrast‐enhanced soft‐tissue μCT datasets from selected extant bracket taxa and outgroups and assessed them against osteological correlates in M. giganteus . Our reconstruction indicates a more differentiated adductor system than commonly assumed, with subdivision of the adductor mandibulae externus and internus complexes and an inferred intramandibular component consistent with a cartilaginous sesamoid (‘ cartilago transiliens ’) functioning as a force‐transmitting pulley. We further provide osteological evidence for previously unrecognised pterygoideus components, suggesting additional jaw‐closing capacity and a potential contribution to rapid gape formation. The ‘tongue’ in M. giganteus was likely comparatively weak and less flexibly movable, while as a stereospondyl, it possessed a comparatively strong neck and specialised anterior ribs. Collectively, these traits are consistent with a mainly crocodile‐like bite‐and‐hold prehension ecology and likely indicate kinetic‐inertial feeding. Our muscle reconstruction further suggests a more balanced jaw‐opening/closing system that may have enabled compensatory suction during gape formation.

An articulated temnospondyl skeleton from Middle Triassic deposits of Bjørnøya (Bear Island) in the western Barents Sea is described as a new plagiosaurid genus and species, Arctobatrachus urdensis . With a body length well exceeding 2 m, it represents by far the largest known member of the Plagiosauridae. Large parts of the heavily weathered skull could be reconstructed on the basis of photos taken when the specimen was first discovered in 1948. The skull outline forms a near‐perfect semicircle, with the jaw articulation located well behind the occipital condyles. The palatal and dentary tooth rows consist of large, closely set teeth and intercalated fangs, whereas the maxilla and coronoids bear numerous tiny teeth. The mandible is low but massive, with a prominent, posterodorsally curved retroarticular process. Plesiomorphic character states consist of a rhomboidal interclavicle, a tall and slender cleithrum, short disc‐shaped vertebral centra, and the total absence of gastral scales and osteoderms. Some anterior vertebral centra closely resemble those of large capitosaurs and metoposaurs. A cladistic analysis finds A. urdensis to nest at the base of the plagiosaurids, sharing the extensive pectoral girdle and derived skull features with other taxa of that clade. With its huge size and enlarged gape, A. urdensis represents the first plagiosaurid top predator known so far, and its occurrence in marine deposits is consistent with the euryhaline habits of some other taxa in the clade.

A new species of dissorophoid temnospondyl, Melanerpeton kuselense new species, is reported from the Remigiusberg Formation (Carboniferous-Permian boundary) of southwestern Germany. The type and only known specimen is a skull belonging to a moderately advanced larva with distinctive features: (1) a very slender postorbital skull table, (2) large nasal, (3) short squamosal giving a short gape, and (4) a gracile and extremely small pterygoid. Phylogenetic analysis finds it to fall well within the branchiosaurids, above the Pennsylvanian Branchiosaurinae, and sister taxon to Melanerpeton pusillum Fritsch, 1878 from lower Permian deposits of the Czech Republic. It is not closely related to any of the branchiosaurids from the Saar-Nahe Basin, adding to the distinctive Remigiusberg tetrapod faunal assemblage. UUID: http://zoobank.org/52c398e1-78be-45db-b2e0-988fc3c1af77

The small, gill-bearing branchiosaurids were the most abundant tetrapods in the Late Palaeozoic of Europe. Other than its mostly microvorous relatives, the 12-cm-long Apateon caducus (v. Ammon 1889) was a small predator in some of the nutrient-rich lakes of the Saar-Nahe Basin in Western Germany. This is the first survey of the entire material which accumulated in the last 130 years. The sample includes 221 specimens from nine different black shale deposits, and it covers a size range from 2 to 33 mm skull length. Unlike often co-occurring Apateon pedestris, A. caducus developed stronger, conical teeth and a firmly sutured upper jaw at smaller size. Gut contents evidence that it fed on small branchiosaurid larvae, most often plankton-feeding Apateon pedestris. In the studied rock sequence, slight morphological differences are recognized from oldest to youngest, and as far as they are consistent, suggest minor evolutionary changes.

Plagiosaurids form a small but highly disparate clade of Triassic temnospondyls that are characterized by extremely flattened and wide skulls, large orbits and a knobby to pustular ornamentation. The largest European taxon is Plagiosternum granulosum from the Middle Triassic of Germany. Originally known from fragmentary bonebed material only, recent finds add well-preserved specimens that reveal the structure of the skull, mandible and pectoral girdle in great detail. The humerus and atlas of P. granulosum are described for the first time, and a putative cleithrum is identified. Ontogenetic changes include a proportional extension of the orbit, a more convex occipital margin, elongation of the parietal, proportional increase of the occipital condyles and formation of pustular ornament at nodal points of reticulate ridges. The presence of gastral scales can be inferred from the structure of the interclavicle, but there is no evidence of osteoderms. Plagiosternum granulosum was the most salt-tolerant temnospondyl in the Ladinian palaeoenvironments, where it dwelled brackish lagoons and lakes and formed a community with nothosaurids and other euhaline taxa.

Complex integumentary appendages such as avian feathers and mammalian hair play a principal role in tetrapod evolution, with critical functions in insulation, sensation, display and flight. Although feathers and hair originated in the stem-lineages of birds and mammals, respectively^1,2, their underlying gene regulatory network has much deeper amniote roots³. The early evolution of amniote integumentary appendages, however, remains poorly understood because of the absence of fossil evidence. Here we present Mirasaura grauvogeli, a small-sized diapsid from the Middle Triassic epoch (about 247 million years ago) with a distinctive crest formed by elongate integumentary appendages extending serially along its back, similar to those of the poorly understood Triassic reptile Longisquama^4,5,6,7. Despite its superficially bird-like skull, Mirasaura is not closely related to avemetatarsalians but instead belongs to the exclusively Triassic reptilian clade Drepanosauromorpha⁸. Melanosomes preserved in its integumentary appendages are consistent in geometry with melanosomes of feathers but not those of reptilian skin or mammalian hair. Nevertheless, the morphology of the integumentary appendages and phylogenetic placement of Mirasaura indicate that they are not structurally homologous to feathers or other integumentary appendages in living amniotes. Our findings show that complex integumentary appendages are not restricted to avemetatarsalians and mammaliaforms among amniotes and evolved in a lineage basal to all extant reptiles, challenging our understanding of the evolution of the reptilian integument.