A detailed description is given of the cranial anatomy of the Lower Permian tetrapod Discosauriscus . This material is three–dimensionally preserved and represents one of the best know seymouriamorph tetrapods. Two species, D. austriacus and D. pulcherrimus , are distinguished in the material from the Boskovice Furrow. D. austriacus is abundant, D. pulcherrimus is rare. The two species differ in the following features: (1) the shape of the postorbital and the jugal and the nature of their junction; (2) the shape of the prefrontal and the postfrontal and the position of their contact; and (3) the morphology of the ventral surfaces fo the palatal bones and the arrangement of the denticles on them. The genus Discosauriscus represents larval, metamorphic and early juvenile individuals. Comparison of the cranial structures of Discosauriscus with those of Seymouria baylorensis , Seymouria sanjuanensis , and Seymouria cf. S. sanjuanensis (which is of similar size to the largest individuals of Discosauriscus ) shows that (i) Discosauriscus and Seymouria are structurally similar but different genera, (ii) Discosauriscus is a member of the taxon Seymouriamorpha, (iii) Discosauriscus and Ariekanerpeton comprise the family Discosauriscidae and (iv) Seymouria is not a reptile (an amniote animal). Ariekanerpeton , Utegenia , Urumquia , kotlassiids , leptorophids and Enosuchus require revision.

The description of the postcranial skeleton of larval, metamorphic and early juvenile specimens of the genusDiscosauriscusis based on three-dimensional material and includes a description of the ontogeny of the swollen neural arches and the central elements of the vertebrae.Discosauriscushas 24 (or 23) presacral vertebrae. The morphology of the atlas–axis complex is similar to that inSeymouria sanjuanensis. The neural arches start to swell slightly in specimens of late larval stage; they are completely swollen immediately after metamorphosis. There are about 40 caudal vertebrae and one sacral vertebra. The atlantal pleurocentrum is paired in metamorphic individuals. In postmetamorphic individuals, the pleurocentra 2–5 are not completely closed dorsally; the pleurocentra 6–30 form complete discs. The first haemal arch is situated on the sixth caudal vertebra. The atlantal rib is present. There are six caudal ribs.Discosauriscushas an anocleithrum which is the first record of this dermal pectoral element within seymouriamorphs and Lower Permian tetrapods. The scapula and the coracoid are separate elements. The phalangeal formula of the manus is 2, 3, 4, 5, 3. The iliac blade has a massive, almost horizontally oriented posterior process; the anterior process is absent. The phalangeal formula of the pes is 2, 3, 4, 5, 3. Rounded ventral scales are present. The comparison and evaluation of the available postcranial elements ofDiscosauriscus, Utegenia, AriekanerpetonandSeymouriasupport the view thatDiscosauriscusandAriekanerpeton, forming the family Discosauriscidae, are immediately related genera.

The morphology of the lower jaw and teeth of the legless lizard Pseudopus apodus (Anguimorpha, Anguidae, Anguinae) from Eurasia are described in detail and compared with those of other species of the subfamily Anguinae. The lower jaw anatomy of Pseudopus, especially the dentary and teeth, clearly differs from the genera Ophisaurus and Anguis. Even so, Ophisaurus is largely uniform in its lower jaw morphology across species. The teeth of North American Ophisaurus are slender cylinders, the shafts are mesiodistally compressed and bulge lingually; the apices are curved lingually and posteriorly and have weakly developed cutting edges. Southeast Asian and North African Ophisaurus present conical teeth, with broadened bases, apices more distinctly curved lingually and posteriorly, and cutting edges that are distinctly developed. The lingual surfaces of the tooth apices are striated in Ophisaurus and Pseudopus. The lower jaw of Ophisaurus is in many respects similar to that in Anguis, however, the teeth of Anguis are longer and markedly curved posteriorly. The result of the phylogenetic analysis rendered six equally parsimonious trees. Anguis appears in three alternative positions, as the sister taxon to a clade formed by Ophisaurus and Pseudopus, as the sister taxon of Ophisaurus, or as forming a clade with Ophisaurus which is the sister group to Pseudopus. Anat Rec,

The origin of amniotes was a key event in vertebrate evolution, enabling tetrapods to break their ties with water and invade terrestrial environments. Two pivotal clades of early tetrapods, the diadectomorphs and the seymouriamorphs, have played an unsurpassed role in debates about the ancestry of amniotes for over a century, but their skeletal morphology has provided conflicting evidence for their affinities. Using high-resolution X-ray microcomputed tomography, we reveal the three-dimensional architecture of the well preserved endosseous labyrinth of the inner ear in representative species belonging to both groups. Data from the inner ear are coded in a new cladistic matrix of stem and primitive crown amniotes. Both maximum parsimony and Bayesian inference analyses retrieve seymouriamorphs as derived non-crown amniotes and diadectomorphs as sister group to synapsids. If confirmed, this sister group relationship invites re-examination of character polarity near the roots of the crown amniote radiation. Major changes in the endosseous labyrinth and adjacent braincase regions are mapped across the transition from non-amniote to amniote tetrapods and include: a ventral shift of the cochlear recess relative to the vestibule and the semicircular canals; cochlear recess (primitively housed exclusively within the opisthotic) accommodated within both the prootic and the opisthotic; development of a distinct fossa subarcuata. The inner ear of seymouriamorphs foreshadows conditions of more derived groups, whereas that of diadectomorphs shows a mosaic of plesiomorphic and apomorphic traits, some of which are unambiguously amniotelike, including a distinct and pyramid-like cochlear recess.

A revision of the Early-Middle Miocene anguine, Pseudopus laurillardi (Lartet, 1851), is presented based on a detailed anatomical analysis of one newly discovered articulated specimen and numerous disarticulated cranial and postcranial elements from several localities in Germany, as well as on the restudy of the original skeletal material of Lartet. the articulated specimen represents the first record of an articulated anguine from the Neogene. We demonstrate that the contemporaneous anguine Propseudopus fraasii (= Pseudopus fraasi, Pseudopus moguntinus or Ophisaurus moguntinus) from Germany and elsewhere in Europe represents a junior synonym of P. laurillardi. Three species of Pseudopus can by discriminated in the Cenozoic of Eurasia: P. laurillardi (Early-Middle Miocene of Europe), P. pannonicus (Late Miocene-Middle Pleistocene of central and eastern Europe) and P. apodus (Late Pleistocene-Recent, from Eastern Europe to central Asia). Eleven morphological characters of the skull have been identified that distinguish Pseudopus laurillardi from P. pannonicus and P. apodus. Four of these characters regard the frontal and parietal bones, whereas all other characters regard the dentary and dentition. the genus Pseudopus represents the largest and most robust taxon in the subfamily Anguinae and first occurs in central Europe at the beginning of MN 4 (~18.5 Ma). in contrast to the extant species, P. apodus, the fossils P. laurillardi and P. pannonicus had a greater ecological plasticity and lived in various types of environments. the fossil remains of these taxa are most frequently found in localities characterized by sub-humid to humid climate, which may indicate that their preferential habitats include forested environments.

The amniotes generally lay eggs on land and are thereby differentiated from lissamphibians (salamanders, frogs and caecilians) by their developmental pattern. Although a number of 330–300-Myr old fossils are regarded as early tetrapods placed close to amniotes on the basis of anatomical data, we still do not know whether their developmental pattern was more similar to those of lissamphibians or amniotes. Here we report palaeohistological and skeletochronological evidence supporting a salamander-like development in the seymouriamorph Discosauriscus . Its long-bone growth pattern, slow diaphyseal growth rate and delayed sexual maturity (at more than 10 years old) are more comparable with growth features of extant salamanders rather than extant amniotes, even though they are mostly hypothesized to be phylogenetically closer to living amniotes than salamanders.

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