Sturgeons (Acipenseridae) from the Late Miocene of Ukraine, with a discussion of materials associated with Widhalm’s (1886) nomen nudum, †Acipenser euhuso

The fossil record of the family Acipenseridae (sturgeons) extends to the Late Cretaceous (c. 85 MY), with a ghost lineage extending to approximately 120 MY when the first members of the family Polyodontidae are known. Much of the fossil record of Acipenseridae is formed by isolated and fragmentary dermal bones, which bear characteristic surface ornamentation. In this paper, we report on a collection of fossil sturgeons from the Upper Miocene deposits of southern Ukraine. These specimens include those used by Widhalm to establish †Acipenser euhuso, which is a nomen nudum. While we do not establish a new taxon for these specimens, the morphological variation of those elements that are preserved does suggest the presence of several species represented in this fauna.

Mandible histology in Metoposaurus krasiejowensis (Temnospondyli, Stereospondyli) from the Upper Triassic of Poland

Recent studies that have systematically augmented our knowledge of dermal bones of the Late Triassic temnospondyl amphibian Metoposaurus krasiejowensis have mostly focused on shoulder girdle elements and the skull. So far, histological data on the mandible are still scant. For the present study, two mandibles have been examined, using 50 standard thin sections. Dermal bones of the mandible reveal a uniform diploë structure, with the external cortex consisting of moderately vascularised, parallel-fibred bone, as well as a distinct alternation of thick zones and thinner annuli. Dense bundles of well-mineralised Sharpey’s fibres are seen in the external cortex over the entire length of the mandible. The trabecular middle region is highly porous and well vascularised, showing small primary vascular canals and more numerous secondary osteons; irregular erosion spaces occur in large numbers as well. The thin and poorly vascular internal cortex consists of parallel-fibred bone. The articular is not a dermal bone in origin, having been formed of a thin layer of avascular cortex and a very extensive, trabecular middle region. In contrast to the dermal bones of the mandible, the articular developed from a cartilaginous precursor, as evidenced by numerous remains of calcified cartilage in the central parts of the bone. Histological variability is extremely high along the mandible, its anterior part being characterised by high compactness and biomechanically good resistance in contrast to the highly porous posterior parts. Distinct variations of bone thickness and degree of bone porosity in specific areas of the mandible, may be due to local differences in biomechanics during feeding. The microstructure of the mandible corroborates a previous study of the active and ambush predation strategy in metoposaurids.

Osteology, relationships and functional morphology of Weigeltisaurus jaekeli (Diapsida, Weigeltisauridae) based on a complete skeleton from the Upper Permian Kupferschiefer of Germany

Background Weigeltisauridae is a clade of small-bodied diapsids characterized by a horned cranial frill, slender trunk and limbs, and a patagium supported by elongated bony rods. Partial skeletons and fragments are definitively known only from upper Permian (Lopingian) rocks in England, Germany, Madagascar and Russia. Despite these discoveries, there have been few detailed descriptions of weigeltisaurid skeletons, and the homologies of many skeletal elements—especially the rods supporting the patagium—remain the subject of controversy. Materials & Methods Here, we provide a detailed description of a nearly complete skeleton of Weigeltisaurus jaekeli from the upper Permian (Lopingian: Wuchiapingian) Kupferschiefer of Lower Saxony, Germany. Briefly addressed by past authors, the skeleton preserves a nearly complete skull, postcranial axial skeleton, appendicular skeleton, and patagial supports. Through comparisons with extant and fossil diapsids, we examine the hypotheses for the homologies of the patagial rods. To examine the phylogenetic position of Weigeltisauridae and characterize the morphology of the clade, we integrate the material and other weigeltisaurids into a parsimony-based phylogenetic analysis focused on Permo-Triassic non-saurian Diapsida and early Sauria (61 taxa, 339 characters). Results We recognize a number of intriguing anatomical features in the weigeltisaurid skeleton described here, including hollow horns on the post-temporal arch, lanceolate teeth in the posterior portion of the maxilla, the absence of a bony arch connecting the postorbital and squamosal bones, elongate and slender phalanges that resemble those of extant arboreal squamates, and patagial rods that are positioned superficial to the lateral one third of the gastral basket. Our phylogenetic study recovers a monophyletic Weigeltisauridae including Coelurosauravus elivensis, Weigeltisaurus jaekeli, and Rautiania spp. The clade is recovered as the sister taxon to Drepanosauromorpha outside of Sauria (=Lepidosauria + Archosauria). Conclusions Our anatomical observations and phylogenetic analysis show variety of plesiomorphic diapsid characters and apomorphies of Weigeltisauridae in the specimen described here. We corroborate the hypothesis that the patagial ossifications are dermal bones unrelated to the axial skeleton. The gliding apparatus of weigeltisaurids was constructed from dermal elements unknown in other known gliding diapsids. SMNK-PAL 2882 and other weigeltisaurid specimens highlight the high morphological disparity of Paleozoic diapsids already prior to their radiation in the early Mesozoic.

Mandibular musculature constrains brain–endocast disparity between sarcopterygians

The transition from water to land by the earliest tetrapods in the Devonian Period is seen as one of the greatest steps in evolution. However, little is understood concerning changes in brain morphology over this transition. Here, we determine the brain–braincase relationship in fishes and basal lissamphibians as a proxy to elucidate the changes that occurred over the fish–tetrapod transition. We investigate six basal extant sarcopterygians spanning coelacanths to salamanders ( Latimeria chalumnae, Neoceratodus, Protopterus aethiopicus, P. dolloi, Cynops, Ambystoma mexicanum ) using micro-CT and MRI and quantify the brain–braincase relationship in these extant taxa. Our results show that regions of lowest brain–endocast disparity are associated with regions of bony reinforcement directly adjacent to masticatory musculature for the mandible except in Neoceratodus and Latimeria . In Latimeria this deviation from the trend can be accounted for by the possession of an intracranial joint and basicranial muscles, whereas in Neoceratodus difference is attributed to dermal bones contributing to the overall neurocranial reinforcement. Besides Neoceratodus and Latimeria, regions of low brain–endocast disparity occur where there is less reinforcement away from high mandibular muscle mass, where the trigeminal nerve complex exits the braincase and where endolymphatic sacs occupy space between the brain and braincase wall. Despite basal tetrapods possessing reduced adductor muscle mass and a different biting mechanism to piscine sarcopterygians, regions of the neurocranium lacking osteological reinforcement in the basal tetrapods Lethiscus and Brachydectes broadly correspond to regions of high brain–endocast disparity seen in extant taxa.

Marginal dentition and multiple dermal jawbones as the ancestral condition of jawed vertebrates

The dentitions of extant fishes and land vertebrates vary in both pattern and type of tooth replacement. It has been argued that the common ancestral condition likely resembles the nonmarginal, radially arranged tooth files of arthrodires, an early group of armoured fishes. We used synchrotron microtomography to describe the fossil dentitions of so-called acanthothoracids, the most phylogenetically basal jawed vertebrates with teeth, belonging to the genera Radotina, Kosoraspis, and Tlamaspis (from the Early Devonian of the Czech Republic). Their dentitions differ fundamentally from those of arthrodires; they are marginal, carried by a cheekbone or a series of short dermal bones along the jaw edges, and teeth are added lingually as is the case in many chondrichthyans (cartilaginous fishes) and osteichthyans (bony fishes and tetrapods). We propose these characteristics as ancestral for all jawed vertebrates.

Retention of fish-like odontode overgrowth in Permian tetrapod dentition supports outside-in theory of tooth origins

Teeth are often thought of as structures that line the margins of the mouth; however, tooth-like structures called odontodes are commonly found on the dermal bones of many Palaeozoic vertebrates including early jawless fishes. ‘Odontode’ is a generalized term for all tooth-like dentine structures that have homologous tissues and development. This definition includes true teeth and the odontodes of early ‘fishes’, which have been recently examined to gain new insights into the still unresolved origin of teeth. Two leading hypotheses are frequently referenced in this debate: the ‘outside-in’ hypothesis, which posits that dermal odontodes evolutionarily migrate into the oral cavity, and the ‘inside-out’ hypothesis, which posits that teeth originated in the oropharyngeal cavity and then moved outwards into the oral cavity. Here, we show that, unlike the well-known one-to-one replacement patterns of marginal dentition, the palatal dentition of the early Permian tetrapods, including the dissorophoid amphibian Cacops and the early reptile Captorhinus , is overgrown by a new layer of bone to which the newest teeth are then attached. This same overgrowth pattern has been well documented in dermal and oral odontodes (i.e. teeth) of early fishes . We propose that this pattern represents the primitive condition for vertebrates and may even predate the origin of jaws. Therefore, this pattern crosses the fish–tetrapod transition, and the retention of this ancestral pattern in the palatal dentition of early terrestrial tetrapods provides strong support for the ‘outside-in’ hypothesis of tooth origins.

Actinopterygians of The Permian Locality Buxières-Les-Mines (Bourbonl’archambault Basin, France) and Their Relationship to Other Early Actinopterygians

Actinopterygians from the large opencast coal mine in the vicinity of the village of Buxières-les-Mines (Bourbonl’Archambault Basin, Allier, France) are revisited and redescribed based on newly studied specimens. The understanding of the anatomy of Progyrolepis heyleri POPLIN, 1999, originally described by Poplin (1999) on the basis of the upper and lower jaws only, is greatly enhanced and is relatively complete. The anatomy of the palatoquadrate, dermal bones of the skull roof, hyoid arch, operculum, suboperculum, shoulder girdle, cheek bones and branchiostegal rays is described. In addition, new observations have been made on changes in the shape of the maxilla during ontogenesis and microstructure of the teeth. Details of Progyrolepis heyleri scales, including their microstructure and morphology of the ridge scales are provided. The collection of whole individuals, body fragments and numerous isolated bones provide confirmation of the presence of Aeduella blainvillei which is the main component of the actinopterygian fauna in Buxières-les-Mines. Additional new knowledge was obtained regarding the great variability in bones of the opercular apparatus and maxilla, presence of the supraorbital, branchiostegal ray with a conspicuous hyoid process and the direction of mutual overlapping of the suboperculum and branchiostegal ray in Aeduella blainvillei (AGASSIZ, 1833). Microsculpture on the scales is redescribed in this species. Paramblypterus cf. duvernoy is the third member of the actinopterygians in the locality Buxières-les-Mines. Fragments of Paramblypterus are very rare and the bones of the skull roof are presented here. Anatomical features of Progyrolepis heyleri, Aeduella blainvillei and Paramblypterus cf. duvernoy were studied and compared with those of other Devonian and Permo-Carboniferous actinopterygians.