Search

Amphibamiform temnospondyls are at the forefront of discourse surrounding modern amphibian evolutionary origins. Here we present a new amphibamiform, Kermitops gratus gen. et sp. nov. from the Lower Clear Fork Formation of the Early Permian of Texas. Kermitops reveals a mosaic of features shared with other amphibamiforms and possesses unique characteristics, including an internarial fontanelle formed by the premaxillae without contribution of the nasals. It possibly possesses a basioccipital that contributes to the occipital condyle, which has significant implications for recent hypotheses of the evolution of the modern amphibian neurocranium. Parsimony analyses recover non-traditional amphibamiform relationships but place Kermitops within Amphibamiformes. Bayesian inference analysis captures a more traditional hypothesis of amphibamiform relationships; however, the time-calibrated analysis under the fossilized birth–death model recovers a topology that mirrors the parsimony topologies. The low robusticity of topologies across different permutations employing traditional and modern methods suggest a need for improvement of current morphological datasets of lissamphibian origins. A morphometric analysis of the crania of terrestrial amphibamiforms reveals the evolution of disparate cranial morphologies among coeval taxa from the Early Permian of Texas. [ABSTRACT FROM AUTHOR]

Western North America preserves iconic dinosaur faunas from the Upper Jurassic and Upper Cretaceous, but this record is interrupted by an approximately 20 Myr gap with essentially no terrestrial vertebrate fossil localities. This poorly sampled interval is nonetheless important because it is thought to include a possible mass extinction, the origin of orogenic controls on dinosaur spatial distribution, and the origin of important Upper Cretaceous dinosaur taxa. Therefore, dinosaurbearing rocks from this interval are of particular interest to vertebrate palaeontologists. In this study, we report on one such locality from Highwood Pass, Alberta. This locality has yielded a multitaxic assemblage, with the most diagnostic material identified so far including ankylosaurian osteoderms and a turtle plastron element. The fossil horizon lies within the upper part of the Pocaterra Creek Member of the Cadomin Formation (Blairmore Group). The fossils are assigned as Berriasian (earliest Cretaceous) in age, based on previous palynomorph analyses of the Pocaterra Creek Member and underlying and overlying strata. The fossils lie within numerous cross-bedded sandstone beds separated by pebble lenses. These sediments are indicative of a relatively high-energy depositional environment, and the distribution of these fossils over multiple beds indicates that they accumulated over multiple events, possibly flash floods. The fossils exhibit a range of surface weathering, having intact to heavily weathered cortices. The presence of definitive dinosaur material from near the Jurassic--Cretaceous boundary of Alberta establishes the oldest record of dinosaur body fossils in western Canada and provides a unique opportunity to study the Early Cretaceous dinosaur faunas of western North America. Key words: Ankylosauria, Berriasian, Blairmore Group, Cadomin Formation, Early Cretaceous, Kananaskis, osteoderm, Pocaterra Creek Member, Rocky Mountains, Testudines. Des assemblages de dinosaures emblematiques du Jurassique superieur au Cretace superieur sont preserves dans l'ouest de l'Amerique du Nord, mais ce registre est interrompu par une pause d'environ 20 millions d'annees caracterisee par l'absence presque totale de localites a fossiles de vertebres terrestres. Cet intervalle mal represente n'en est pas moins important parce qu'il comprendrait une possible extinction massive, l'origine de controles orogeniques de la repartition spatiale de dinosaures et l'origine d'importants taxons de dinosaures du Cretace superieur. Les roches renfermant des dinosaures de cet intervalle sont donc particulierement interessantes pour les paleontologues s'interessant aux vertebres. Nous faisons etat d'une telle localite a Highwood Pass (Alberta), qui a produit un assemblage multitaxons duquel le materiau le plus diagnostic obtenu a ce jour comprend des osteodermes ankylosauriens et un element de plastron de tortue. L'horizon fossilifere se trouve dans la partie superieure du membre de Pocaterra Creek de la Formation de Cadomin (Groupe de Blairmore). Un age berriasien (debut du Cretace) est attribue aux fossiles a la lumiere d'analyses anterieures de palynomorphes dans le membre de Pocaterra Creek et des strates sous-jacentes et sus-jacentes. Les fossiles sont presents dans de nombreux lits de gres a stratification croisee separes par des lentilles de galets. Ces sediments indiquent un milieu de depot assez dynamique, et la repartition des fossiles dans plusieurs lits indique qu'ils se sont accumules au fil de plusieurs evenements, possiblement des crues eclairs. Les fossiles presentent un eventail de types de meteorisation, montrant des cortex intacts a fortement meteorises. La presence de materiau definitivement dinosaurien a proximite de la limite Jurassique--Cretace de l'Alberta etablit la presence la plus ancienne de fossiles de corps de dinosaure dans l'Ouest canadien et offre une occasion unique d'etudier les assemblages de dinosaures du Cretace precoce de l'ouest de l'Amerique du Nord. [Traduit par la Redaction] Mots-cles : ankylosaures, Berriasien, Groupe de Blairmore, Formation de Cadomin, Cretace precoce, Kananaskis, osteoderme, membre de Pocaterra Creek, montagnes Rocheuses, testudines., Introduction The fossil record of dinosaurs is best sampled in North America, due to extensive deposits and ease of access. This is particularly the case in western North America, where [...]

Embolomeres have been considered candidate stem-amniotes by many authors, but recent work has shown that anatomical and phylogenetic support for this hypothesis may be ambiguous. Newer phylogenetic approaches focus on the anatomy of the endochondral bones surrounding the brain (neurocranium) and associated dermal investing bones, so accurate description of the neurocranium of tetrapods, and particularly embolomeres, is critical to assess the phylogenetic context of amniote origins. I here amend prior descriptions of the neurocranium of the abundant Early Permian embolomere, Archeria crassidisca , with a description of a previously unreported partial braincase. This specimen reveals features broadly associated with stem-tetrapods of the fin-to-limb transition and recently described in aïstopod stem-tetrapods, including a cranial notochordal remnant, a possible buccohypophyseal canal, and anteroventrally projecting saccular fossae that extend deep into the basioccipital. I present an amended description and reconstruction of the neurocranium and a phylogenetic analysis integrating these codings, which recovers embolomeres more robustly within the tetrapod stem. I review characters previously used to assign embolomeres to the amniote stem and find this evidence is ambiguous or incorrect. I then outline strong character support for a stem-tetrapod position of embolomeres, and implications for the ancestral body plan of crown-group tetrapods. [ABSTRACT FROM AUTHOR]

The group of Permo-Carboniferous tetrapods known as Recumbirostra have recently been hypothesized to represent the earliest radiation of fossorial reptiles. Therefore, understanding the anatomy and diversity of this clade is essential to understanding the origin and early evolution of amniotes. Here, we redescribe the diminutive 'microsaur' Odonterpeton triangulare from the Moscovian-age deposit of Linton, Ohio, revealing new details on the structure of the cranium and palate, including the presence of a conspicuous transverse flange of the pterygoid, which is a feature traditionally associated with early amniotes. Phylogenetic analysis supports the placement of Odonterpeton triangulare within Recumbirostra as sister taxon to the recently described Joermungandr bolti from the slightly older Mazon Creek, Illinois, Lagerstätte. Together, these two diminutive recumbirostrans are placed in an Odonterpetidae clade. Furthermore, we provide a discussion of newly recognized anatomical features in recumbirostrans and discuss major features of recumbirostran phylogeny. We designate a new recumbirostran clade, Chthonosauria (Brachystelechidae + Molgophidae), which is supported by a number of shared derived cranial features. [ABSTRACT FROM AUTHOR]

Author(s): Jason D. Pardo [1]; Matt Szostakiwskyj [2]; Per E. Ahlberg [3]; Jason S. Anderson (corresponding author) [1] Phylogenetic analysis of early tetrapod evolution has resulted in a consensus across [...]

The dissorophid genus Conjunctio (Temnospondyli) is poorly characterized, known only from two incomplete specimens from the upper El Cobre Canyon Formation (lower Permian), Cutler Group, New Mexico, U.S.A. Nonetheless, the taxon's conserved morphology and stratigraphic occurrence near the Carboniferous–Permian boundary (ca. 299 million years ago) make it an important datum to resolve the early diversification of dissorophids. We report the first occurrence of Conjunctio cf. C. multidens in the adjacent undivided Cutler Formation of San Miguel County, Colorado, which also represents only the second dissorophid from southwestern Colorado's historic Placerville assemblage. The new specimen highlights the plesiomorphic anatomy of Conjunctio, with newly described mandibular and postcranial data, and provides further evidence for a relationship to the Eucacopinae. We performed a phylogenetic analysis of 34 temnospondyl taxa by modifying a previously published matrix of 102 craniodental and postcranial characters, scoring Conjunctio at the specimen-level, and found a monophyletic Conjunctio at the base of Eucacopinae. The clade also included the earliest Permian Reiszerpeton and Scapanops in relatively basal positions, and an unresolved polytomy among the later Permian Cacops, Kamacops, Zygosaurus, and Anakamacops. Geographically, the discovery of Conjunctio among the Placerville assemblage is consistent with a broader southwestern U.S. Wolfcampian fauna, correlative to that of the upper El Cobre Canyon Formation in northern New Mexico, and may underscore previously proposed regional provincialism among early Permian tetrapod assemblages. [ABSTRACT FROM AUTHOR]

We describe a new specimen of the aïstopod Oestocephalus from Five Points, Ohio, which preserves much of the posterior braincase. The specimen, the largest aïstopod skull described, preserves the postorbital region to the occiput. The posterior braincase has coossified the basioccipital, exoccipitals, and opisthotic. The parasphenoid is rostrally restricted, toothless, and highly vaulted along the cultriform process. The lateral walls of the cultriform process are further reinforced by large longitudinally running, ventral flanges from the parietals. Two large endochondral ventral projections from the basioccipital, previously interpreted as basal tuberosities for hypaxial muscle insertion, are here instead interpreted as articulations for the branchial skeleton. This interpretation is further supported by traces of vasculature that is consistent with what is seen in gill-bearing species. A model for the reorganisation of the basicranial region on the transition from hyomandibula to stapes is proposed, which suggests that gills, or gill-support skeletal elements, might be further distributed along the tetrapod stem than previously thought. These data further support the placement of aïstopods in the tetrapod stem group and require a reconsideration of our understanding of early tetrapod evolution. [ABSTRACT FROM AUTHOR]

The severe greenhouse climate and seasonality of the early to mid-Late Triassic are thought to have limited terrestrial diversity at lower latitudes, but direct adaptations to these harsh conditions remain limited in vertebrates at the palaeoequator. Here, we present Ninumbeehan dookoodukah gen. et sp. nov., an early amphibian with specialized adaptations for seasonal estivation from the upper Jelm Formation of the Late Triassic of Wyoming, USA. Ninumbeehan are found in an association of vertebrate estivation burrows across a locally dense horizon, offering insights into the evolution and ecology of vertebrates amid the challenging conditions of low-latitude Late Triassic ecosystems. Estivation chambers were excavated within point bar deposits of an ephemeral river system, recording the cyclical signature of Triassic megamonsoons and documenting a vertebrate response to annual climate extremes across tens to hundreds of seasons. Phylogenetic analysis recovers Ninumbeehan within a group of temnospondyls characterized by fossorial adaptation, underscoring the widespread adoption of burrowing and estivation in total group Lissamphibia. Ninumbeehan hints at the pivotal role seasonal dynamics played in shaping amphibian evolution.