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Albanerpetontids are an extinct clade of salamander-like lissamphibians characterised by features such as fused frontals and sculptured skull roof bones. Here we provide a histological analysis of ...

The Lowerverse local fauna of West Texas, USA, preserves a rare, early Campanian assemblage of microvertebrates from Laramidia. The recovery of 137 fragmentary specimens reveals that albanerpetontids were locally abundant here and also widespread throughout much of the Western Interior of North America by early Campanian time. Both gracile- and robust-snouted species are represented within the assemblage. Among these, the occurrence of Albanerpeton nexuosum is consistent with its occurrence in paracontemporaneous deposits elsewhere in the Western Interior. The referral of two specimens to Albanerpeton sp., cf. Albanerpeton galaktion, strongly suggests that this long-lived taxon was far more widespread during the early Campanian than previously known and its likely occurrence in West Texas represents a significant geotemporal range extension for the species. However, Albanerpeton gracile is seemingly restricted to Judithian “age” deposits in North America and was not identified at Lowerverse. The Lowerverse assemblage supports the current paradigm involving the occurrence of these three named albanerpetontids during middle Campanian – Maastrichtian time in the Western Interior of North America.

Albanerpeton pannonicum Venczel & Gardner, 2005 (Figs 3; 4) MATERIAL. — Fifty-five isolated bones: Italy. MoncuccoTorinese, Layer M3 (n = 3): Premaxilla (n = 1): MGPT-PU 132112. Dentaries (n = 2): MGPT-PU 132630, 132631. — Layer M3/4 (n = 10): Maxilla (n = 1): MGPT-PU 132274. Dentaries (n = 9): MGPT-PU 132640-132647, 132652. — Layer M4 (n = 1): Sacral vertebra (n = 1): MGPT-PU 132017.— Layer M4/5(n = 20): Premaxillae(n = 3): MGPT-PU 132001, 132002, 132232.Maxillae (n = 4): MGPT-PU 132011, 132012, 132632, 132633.Dentaries (n= 11): MGPT-PU132005-132009,132634-132639. Trunk vertebrae (n = 2): MGPT-PU 132015, 132016. — Layer M5 (n = 2): Dentaries (n = 2): MGPT-PU 132003, 132004. — Layer M7+25 (n = 6): Premaxillae (n = 4): MGPT-PU 132648-132651.Dentaries (n = 2): MGPT-PU 132653, 132654. Collected in situ, from unrecorded layer(s) (n = 4): Premaxilla (n = 1): MGPT-PU 132165. Maxilla (n = 1): MGPT-PU 132307. Dentaries (n = 2): MGPT-PU 132318, 132319. Surface collected, from unknown layer(s) (n = 9): Maxillae (n = 2): MGPT-PU 132013, 132014. Dentaries (n = 7): MGPT-PU 132010, 132655-132660. DESCRIPTION OF MONCUCCO TORINESE ALBANERPETONTID SPECIMENS Premaxillae (Fig. 3 A-L) Nine isolated premaxillae are available. The best-preserved specimen is MGPT-PU 132112 (Fig. 3 A-C), an intact left premaxilla. Most other specimens (e.g., Fig. 3 D-L) preserve an intact dorsally directed pars dorsalis, at least some portion of the lingually directed pars palatinum, and much of the ventrally directed pars dentalis and its tooth row. All premaxillae are relatively small (total intact heights range from 1.5-1.7 mm), yet are comparatively robust in build when compared to similar sized premaxillae of other albanerpetontids (e.g., Gardner 1999b: text-fig. 2A-E). The medial edge is straight and bears prominent, vertical grooves and flanges for strong sutural contact or, perhaps, weak fusion (although no examples of fused premaxillae are present in our sample) in life between the paired premaxillae. In the eight specimens preserving an intact pars dorsalis, the process is moderately tall and broad, with the ratio of maximum height vs width across the suprapalatal pit ranging from 1.30-1.55 (i.e., relative height is “low” sensu Gardner 2002; Venczel & Gardner 2005). The dorsal edge of the pars dorsalis is slightly swollen labiolingually and is roughened for abutting or weak sutural contact with the nasal. As seen in the five figured premaxillae, considerable variation is evident in the outline of the dorsal end of the pars dorsalis, the relative depth and width of the lateral dorsal notch along the upper portion of the pars dorsalis, and the outline of the laterally directed swelling immediately below the lateral dorsal notch (Fig. 3A, D, G, I, K). The uppermost portion of the pars dorsalis labially bears a low bony boss that is weakly ornamented with irregular-shaped, small pits and low ridges. The remainder of the premaxillary labial surface is relatively smooth, aside from small and scattered nutritive foramina. Midway across its lower half, the lingual surface of the pars dorsalis bears a suprapalatal pit that faces lingually, is moderately large and undivided, has an asymmetrically ovoid to subtriangular outline, and is bounded laterally by an obliquely oriented bony strut (Fig. 3C, F, H, J, L). Preserved intact on just one specimen, MGPT-PU 132112 (Fig. 3B, C), the pars palatinum is a shallow, bony shelf that medially bears a lingually projecting, triangular vomerine process and laterally is expanded into a maxillary process for contact with the maxilla. The central portion of the pars palatinum is pierced by a prominent palatal foramen that opens into the floor of the suprapalatal pit. The palatal foramen is subcircular and varies in size, with its diameter ranging from approximately the same as the diameter of shafts of medial teeth on the same specimen to twice the diameter of those shafts. The pars dentalis is relatively deep. Five premaxillae preserve an intact tooth row, consisting of either seven or eight tooth positions (two and three specimens, respectively). Teeth are typical for albanerpetontids in being highly pleurodont, non-pedicellate, and closely spaced in a comb-like arrangement, in having shafts that are deep, straight, cylindrical, and slightly mesiodistally compressed, and in bearing chisel-shaped crowns that are labiolingually compressed and mesiodistally tricuspid, with the median cusp most prominent. Some premaxillae have fully functional teeth occupying all loci (e.g., Fig. 3C, J), whereas others have one or several empty tooth slots (e.g., Fig. 3F). One of the figured examples (Fig. 3L) exhibits a nearly functional replacement tooth in its fifth locus from the mesial (= medial) end. Maxillae (Fig. 3 M-S) The most nearly complete and informative of the eight maxillary specimens is MGPT-PU 132307 (Fig. 3 M-O), a right maxilla missing only a small piece from the anteroventral portion of its premaxillary lateral process and the distal ends of five teeth. Considering the minor amount of breakage at its anterior end, the specimen’s preserved maximum length of 2.7 mm likely reflects the true size of that maxilla. Although the other two figured specimens are less nearly complete, when intact those maxillae would have been slightly smaller (MGPT-PU 132012: Fig. 3P, Q) and larger (MGPT-PU 132014: Fig. 3R, S) in their maximum lengths compared to MGPT-PU 132307. As best shown by MGPT-PU 132307 and, to a lesser extent by MGPT-PU 132012, in overall form the maxilla is moderately elongate, low, and triangular in labial or lingual outline. The pars dorsalis increases in height anteriorly, culminating in the dorsally projecting, triangular nasal process having a leading edge that is either nearly vertical or shallowly concave in labial or lingual outline (cf., Fig. 3M vs Fig. 3P, R). The pars dorsalis extends forward below and past the level of the nasal process as a moderately elongate premaxillary lateral process that, in life, labially (= laterally) overlapped with a corresponding facet on the premaxilla (see Venczel & Gardner 2005: text-fig. 1A). The intact premaxillary lateral process preserved on MGPT-PU 132014 (Fig. 3R, S) is bluntly pointed in labial or lingual outline. From the posterior base of the nasal process backwards to the posterior end of the bone, the dorsal surface of the pars facialis is slightly flattened where, in life, it was overlain by the jugal and lacrimal (see Venczel & Gardner 2005: text-fig. 4). The labial surface of the maxilla is smooth, aside from a few small external nutritive foramina arranged in a loose row along about the anterior one-half of the bone. The lingual surface of the maxilla bears a lingually directed, shelf-like pars palatinum that is broadest anteriorly and narrows posteriorly (Fig. 3O). The anterior end of the pars palatinum is expanded into the premaxillary dorsal process that, in life, dorsally overlapped onto the similarly expanded lateral portion (= maxillary process) of the pars palatinum on the premaxilla. More posteriorly, the medial edge of the pars palatinum is indented by a shallow concavity forming the lateral margin of the internal narial opening and the dorsal surface of the shelf bears short ridges and a trough for contact, in life, with palatal bones. The pars dentalis is deepest anteriorly, becomes shallower posteriorly, and its ventral margin is essentially straight in labial or lingual outline. Starting at a point approximately below the leading edge of the nasal process (Fig. 3N, S), the maxillary tooth row extends backwards to the posterior end of the bone (Fig. 3N). The only maxilla with an intact tooth row, MGPT-PU 132307 (Fig. 3N), has 19 tooth positions comprised of 13 intact teeth, five broken tooth shafts, and one empty tooth slot. Teeth are similar in form, attachment, and arrangement to the premaxillary teeth. Maxillary teeth are weakly heterodont in size, being longest about one-third of the distance along the tooth row. MGPT-PU 132012 (Fig. 3Q) preserves a misshaped, slightly procurved replacement tooth in the fifth preserved locus from the mesial (= anterior) end, whereas MGPT-PU 132014 (Fig. 3S) preserves a similarly misshaped functional tooth in the second locus from the mesial end. Dentaries (Fig. 4 A-M) None of the 35 dentaries is complete, but collectively they document much of the structure of this element. The most nearly complete specimen is MGPT-PU 132003 (Fig. 4 A-C), a right dentary preserving about the anterior four-fifths of the bone, including the entire tooth-bearing region and the anterior part of the area for attachment of the post-dentary bones. As best shown by MGPT-PU 132003, the dentary is elongate and moderately deep along its length in labial or lingual view, and is broadly curved in dorsal or ventral view. In labial view (Fig. 4A, D, G, J, L), the dorsal edge of the tooth-bearing region is essentially horizontal. Behind the tooth row, the dorsal edge bears a low, almost indistinct, dorsally directed swelling and, more posteriorly, the dorsal edge descends shallowly above the area for attachment of the post-dentary bones. The labial surface of the bone is unornamented, although it is slightly roughened and, along the tooth-bearing portion, is perforated by a half dozen or more, moderate sized external nutritive foramina loosely arranged in either one or two horizontal rows (cf., Fig. 4G vs Fig. 4A, D). As seen in lingual and dorsal views (Fig. 4B, E, H and C, F. I, respectively), the symphyseal end of the dentary consists of an anteriorly swollen, flat, vertical face and, more posteriorly, bears either one or two short, medioposteriorly directed prongs that, in life, formed a mortise-in-tenon style inter-symphyseal joint. The toothbearing portion consists of a relatively tall dental parapet that becomes shallower posteriorly and a well-developed subdental shelf with a gutter-like dorsal surface. The subdental shelf becomes narrower and deeper posteriorly. Near the end of the tooth row, the subdental shelf is perforated by the large posterior opening for the Meckelian canal and, more posteriorly, in the area lingually (= medially) overlain in life by the post-dentary bones (see Venczel & Gardner 2005: text-fig. 5A, D), the lingual surface of the dentary is shallowly concave and bears thin, posteriorly extending bony ridges. The few specimens preserving a complete or nearly complete tooth row (e.g., MGPT-PU 132003: Fig. 4 A-C) indicate that 20-25 tooth positions were present. Teeth are similar in form, attachment, and arrangement to those on the upper jaws and, like on the maxilla, dentary teeth are weakly heterodont in size, with the longest teeth occurring about one-third of the distance along the tooth row. The anterior portion of a right dentary, MGPT-PU 132010 (Fig. 4G, H), is notable for having an anomalous, plate-like patch of bone developed on the underside of its symphyseal region. Vertebrae (Fig. 4 N-U) Although incomplete and less distinctive than the abovedescribed jaws, albanerpetontid post-atlantal vertebrae can be recognized by a suite of features (Estes & Hoffstetter 1976; Estes 1981; McGowan 1996; Wiechmann 2003; Venczel & Gardner 2005; Sweetman & Gardner 2013; Matsumoto & Evans 2018), including: small size; centra amphicoelous, notochordal, external surfaces relatively smooth, and bearing donut-like ring of calcification around cotylar rims; no spinal foramina; and unicipital rib-bearers. Two trunk vertebrae and one sacral vertebra are available from Moncucco Torinese; here we figure the better preserved trunk vertebra (MGPT-PU 132015: Fig. 4 N-P) and the sole sacral vertebra (MGPT-PU 132017: Fig. 4 Q-U). All three specimens are tiny (maximum centra lengths = 1.2-1.4 mm). Each consists of an intact centrum, the broken bases of the neural arch walls, and varying amounts of the transverse processes. Judging from the broken bases of the neural arch walls, the neural arches and rcc canals were broad. In each specimen, the centrum is deeply amphicoelous and perforated by a persistent or open notochord, the anterior and posterior cotyles are rimmed with a donut-like ring of calcified cartilage, and no spinal foramina or ventromedian keel are present. In both trunk vertebrae, the centrum is relatively elongate and somewhat hourglass-shaped (i.e., moderately constricted midway along its length), the anterior and posterior cotyles are subcircular in outline, and a faint ridge extends posteriorly and slightly laterally along either side of the ventral midline. On both trunk vertebrae, the broken bases of the transverse processes are positioned low on the broken neural arch wall, slightly forward of the anteroposterior midpoint of the centrum. Judging by their broken bases, the transverse processes were rod-shaped. Trunk vertebra MGPT-PU 132015 bears weakly-developed anterior basapophyses in the form of low, anteroposteriorly short knobs that barely extend forward beyond the anterior cotylar rim (Fig. 4 N-P); the other trunk vertebra (MGPT- PU 132016: unfigured) lacks anterior basapophyses. We identify MGPT-PU 132017 (Fig. 4 Q-U) as a sacral vertebra because its centrum is relatively broad and anteroposteriorly short, not constricted, and slightly flattened dorsoventrally, it lacks basapophyses, and it bears deep and stout transverse processes that arise lower on the neural arch wall. Although the form of the transverse processes on MGPT-PU 132017 resembles those on anteriormost trunk vertebrae figured by Estes & Hoffstetter (1976: fig. 2A, B, pl. VI, 12, 13) for Albanerpeton inexpectatum, the latter specimens differ from MGPT-PU 132017 in bearing both anterior and posterior basapophyses.

Albanerpetontids are an extinct clade of superficially salamander-like lissamphibians that range from the Middle Jurassic (Bathonian)-Early Pleistocene and have a primarily Laurasian distribution. The best Cenozoic record for the clade is in Europe, where two species in the type genus Albanerpeton Estes & Hoffstetter, 1976 occur in over 40 localities of early Oligocene-Early Pleistocene age in Austria, Czech Republic, France, Germany, Hungary, Italy, and Serbia. From the post-evaporitic Messinian (5.41-5.33 Ma or latest Miocene) succession at Moncucco Torinese, in the Piedmont Basin, northwestern Italy, here we describe isolated albanerpetontid jaws and vertebrae referable to A. pannonicum Venczel & Gardner, 2005. This Italian occurrence extends the temporal record for A. pannonicum from the Early Pleistocene and Pliocene back into the latest Miocene and it narrows the temporal gap between that species and its European congener, A. inexpectatum Estes & Hoffstetter, 1976 (early Oligocene-late Miocene). Les albanerpetontidés représentent un clade éteint de lissamphibiens ressemblant superficiellement à des salamandres, dont l'aire de répartition s'étend du Jurassique moyen (Bathonien) au Pléistocène inférieur, et dont la distribution est principalement laurasiatique. Le meilleur registre cénozoïque pour ce clade se trouve en Europe, où deux espèces du genre-type Albanerpeton Estes & Hoffstetter, 1976 sont présentes dans plus de 40 localités de l'Oligocène inférieur-Pléistocène inférieur d'Autriche, Tchéquie, France, Allemagne, Hongrie, Italie et Serbie. Nous décrivons ici des mâchoires et des vertèbres isolées d'albanerpetontidés pouvant être attribuées à A. pannonicum Venczel & Gardner, 2005, provenant de la succession post-évaporitique du Messinien (5,41-5,33 Ma ou Miocène terminal) à Moncucco Torinese, dans le bassin du Piémont, au nord-ouest de l'Italie. Cette occurrence italienne étend l'enregistrement stratigraphique d'A. pannonicum du Pléistocène inférieur et du Pliocène jusqu'au Miocène supérieur, et réduit l'écart temporel entre cette espèce et son congénère européen, A. inexpectatum Estes & Hoffstetter, 1976 (Oligocène inférieur-Miocène supérieur).

Altres ajuts: Generalitat de Catalunya/CERCA Programme Among the Early Pleistocene Italian fossil herpetofaunas, Rivoli Veronese is remarkable in having yielded the youngest known allocaudates, represented by Albanerpeton pannonicum, together with remains of other amphibians and reptiles. The assemblage includes at least 15 other taxa, including two caudates (Speleomantes sp., Ichthyosaura alpestris), four anurans (Bombina sp., Bufo bufo, Hyla gr. H. arborea, Rana sp.), five lizards (Lacerta gr. L. viridis, cf. Zootoca vivipara, a third, small-sized lacertid, Anguis gr. A. fragilis, cf. Pseudopus sp.) and four snakes (Coronella sp., Zamenis longissimus, Natrix sp., Vipera gr. V. aspis). The finding of Speleomantes is particularly interesting as it is one of only a handful of fossil occurrences of this genus, being only the second one outside of its extant range. Excluding the extinct Albanerpeton and Speleomantes, which has a very narrow environmental range, the remainder of the assemblage suggests a Mean Annual Temperature rather similar or slightly colder than the present one in Rivoli Veronese (11.6 °C versus 12.4 °C), with much higher Mean Annual Precipitation (1322 mm versus 834 mm). The palaeoenvironment would have included either permanent or temporary water bodies, located in a forested area. More open landscapes might have also been present in the local vicinity. The palaeoherpetofauna of Rivoli Veronese supports the hypothesis of Albanerpeton favouring a moist environment, and confirms the presence of a humid forested landscape on the northern side of the Po Plain during the cold phases of the Gelasian, as already suggested by the pollen record for its southern margin.

The Mesozoic and Palaeocene record of lissamphibians (i.e. anurans, caudates, gymnophionans and albanerpetontids) in North America is reviewed on the basis of over 400 published and unpublished occurrences from 61 geological formations. The record is heavily biased towards isolated bones, although some associated and articulated skeletons and rare tracks and trackways are known. Most of the localities are in the Western Interior: in central and southern Alberta and southern Saskatchewan, Canada, extending southwards through the USA and into northern Mexico. Outside of that region, records are limited to one Late Cretaceous age formation in Baja California and several Late Triassic and Cretaceous age formations in the eastern USA. Putative lissamphibians have been reported from the Late Triassic (middle Carnian and early Norian). Unambiguous lissamphibians are known from the Early Jurassic (Sinemurian–Pliensbachian), the Late Jurassic (Kimmeridgian–earliest Tithonian), the basal Cretaceous (late Berriasian–Valanginian) and a nearly continuous sequence extending from the Aptian through to the terminal Palaeocene. The Early Jurassic (Sinemurian–Pliensbachian) of Arizona documents the oldest global occurrences of an anuran (i.e. crown frog) and a stem caecilian; the latter also is the only North American fossil occurrence for Gymnophiona prior to the Quaternary. Late Jurassic (Kimmeridgian–earliest Tithonian) age deposits in Colorado, Utah and Wyoming contain a moderate diversity of anurans, urodeles (i.e. crown salamanders) and possibly stem salamanders. A basal Cretaceous locality (late Berriasian–Valanginian) in South Dakota contains a urodele and the first North American occurrence for Albanerpetontidae. Aptian/Albian age localities in Montana, Wyoming, Texas and Oklahoma contain a mixture of anurans, urodeles and albanerpetontids—that tripartite lissamphibian composition persists in North America through the remainder of the Cretaceous and intermittently through the Palaeocene. Most of the anurans are of uncertain familial affinities. The urodeles contain a mixture of extinct families (Scapherpetontidae and Batrachosauroididae) that were prominent through the Cretaceous into the early Palaeogene, along with the earliest appearances of several extant families, specifically sirenids in the Santonian, amphiumids and proteids in the late Maastrichtian and dicamptodontids and unequivocal cryptobranchids in the late Palaeocene. The albanerpetontid genus Albanerpeton was moderately diverse during the Cretaceous and Palaeocene, before vanishing from the North American record near the end of the Palaeocene. Temporal richness estimates of North American lissamphibians were calculated based on taxic and minimum lineage level occurrence data per 5 million year time interval beginning in the Early Jurassic and though to the end of the Palaeocene. The resulting richness curves demonstrate a general pattern of increasing richness leading up to the Cretaceous-Palaeogene (K-Pg) boundary, with peak values during the Campanian and Maastrichtian and a decline thereafter. The latter part of that pattern suggests higher extinction rates for lissamphibians across the K-Pg boundary compared to previous estimates, which we attribute to our coarser temporal binning, taxonomic additions and changes to some earlier taxonomic identifications. Although the overall richness pattern may at least partially reflect a true signal, it is heavily influenced by factors such as taphonomy, temporal gaps, fossil sampling and publication biases towards particular intervals and taxonomic groups; more detailed studies of all major lissamphibian clades are needed to corroborate these findings. This review highlights the strengths and weaknesses of the Mesozoic and Palaeocene portion of the North American lissamphibian record and provides a framework for future work.

The Albanerpetontidae, small salamander-like tetrapods from the Middle Jurassic-Neogene of Laurasia and northern Africa, are widely considered to be lissamphibians; however, relationships among major lissamphibian clades are unresolved. A recently identified, isolated, and three-dimensionally preserved neurocranium (early Pliocene, Hungary) referred to Albanerpeton pannonicum is described, incorporating information gained from the application of micro-computed tomography. It is revealed that the neurocranium is a robust, box-like structure composed of the coossification of the parasphenoid, otic capsules, and occipital elements. The otic capsule endocast reveals the morphology of the endosseous labyrinth, complete with well-defined endosseous semicircular canals and a modestly developed ventral endosseous auditory region; however, details of the individual auditory organs are not discernable from the endocast. Features of the neurocranium and endosseous labyrinth are consistent with the hypothesis that A. pannonicum, and albanerpetontids in general, were somewhat fossorial. The neurocranium and endosseous labyrinth exhibit a mosaic of anuran, urodele, and apodan traits, thus precluding refinement of the phylogenetic position of albanerpetontids. In general, the neurocranium and endosseous labyrinth appear most similar to urodeles, and similarities with apodans and anurans may be due to convergent evolution resulting from similar habits and responses to inner ear stimulation. This new neurocranium represents the best-known specimen of its kind for albanerpetontids, and the data presented here combined with future comparative studies will contribute to a better understanding of the biology and evolution of this group.

An assemblage of amphibians and squamates from the Upper Maastrichtian of the Iberian Peninsula is described here for the first time. The material is disarticulated and comes from the Blasi 2 site of Huesca, Spain). The site is made up of grey marls belonging to the lower part of the Tremp Formation, and contains dinosaurs, crocodilians, testudines and Osteichthyes. The amphibians from Blasi 2 include one albanerpetontid ( Albanerpeton aff. nexuosum ) and two different anuran taxa: a discoglossid and a palaeobatrachid. The squamates comprise three lizards (two indeterminate lizards and one anguid) as well as an indeterminate snake (Alethinophidia). The vertebrate assemblage may be interpreted as pertaining to an aquatic environment and its terrestrial surroundings. The presence of estuarine fishes, freshwater amphibians and marine invertebrates together suggests that Blasi 2 may correspond to a coastal, mangrove-like swamp. The amphibians and squamates of Blasi 2 are typically Laurasiatic taxa. This contrasts with the older (Campanian-Maastrichtian) sites of the Iberian Peninsula, where typical Gondwanan taxa have been identified. Blasi 2 provides important information on the biodiversity of amphibians and squamate reptiles in the north of the Iberian Peninsula during the late Maastrichtian, from a point just a few hundred thousand years before the K-T boundary event. These taxa have representatives in the Cenozoic, so as a group they do not appear to have been affected by the boundary event.

The Albanerpetontidae are salamander-like, Middle Jurassic to Neogene lissamphibians from Laurasia and North Africa. Extensive series of albanerpetontid bones recently identified in collections from the Csarnota 2 locality, south-central Hungary, extend the temporal range of the clade forward about seven million years from the middle Miocene to the early Pliocene. The Hungarian material is diagnostic for the Euramerican type genus Albanerpeton and pertains to a new species, A. pannonicus sp. nov., which differs from the seven previously reported congeners (Early Cretaceous–Miocene) in a distinctive combination of primitive and derived character states of the jaws and frontals, including a unique ventromedian keel on the azygous frontals. Some of the Hungarian specimens are articulated sets of skull bones, including ones containing the first three-dimensional examples of a nasal and jugals known for albanerpetontids, that help clarify some details of cranial osteology in these amphibians. Cladistic analysis nests A. pannonicus within the robust-snouted clade, as the sister taxon to an unnamed late Palaeocene species from Canada and A. inexpectatum from early–middle Miocene deposits in France, Austria and Germany. This phylogeny and recent reports of diagnostic Albanerpeton material from the Campanian of France and Maastrichtian of Romania suggest the evolutionary history of Albanerpeton was more complex than previously hypothesized, with Europe having played a larger role. The 25 fossiliferous layers at Csarnota 2 record a shift from forest to grassland palaeoenvironments. Fossils of A. pannonicus are present in all layers, implying that this species was not adversely affected by the change in palaeoenvironments.

Data sets of Central European temporal distributions of thermophilic ectothermic vertebrates (Channidae, Varanidae, Chamaeleonidae, Cordylidae, Tomistomidae, Alligatoridae, giant turtles) and of North Alpine Foreland Basin (NAFB) distributions of ectothermic vertebrates adapted to dryer habitats (Albanerpeton inexpectatum, Salamandra sansaniensis, Bufo cf. viridis, Chamaeleo caroliquarti, Gekkonidae, Varanus hofmanni, Bransateryx sp.) are analysed. Two main migration events of thermophilic ectotherms at 20 Ma and 18 Ma in the Lower Miocene are discerned. They indicate the beginning of the Miocene Climatic Optimum in Central Europe (42–45°N palaeolatitude) with a lower limit of the mean annual temperature (MAT) of 17.4°C derived from the minimal MAT of their extant relatives. Furthermore, additional palaeobotanical data and records of bauxite point to a MAT of 22°C. This warm and humid optimum peaked at 18–16.5 Ma (Ottnangian, Karpatian), and is confirmed by the coexistence of all investigated thermophilic taxa. The following period (Early Badenian) is characterised by probably unchanged temperatures but a seasonality in precipitation with dry periods up to six months. Two major seasonal phases between 16.3 and ∼15.7 Ma (earliest Early Badenian) and between 14.7 and ∼14.5 Ma (Early/Middle Badenian transition) are indicated by an immigration of dry adapted taxa from the surrounding karst plateau to the NAFB. It is presumed that the tectonical reorganisation of the Central Paratethys realm had considerable influence on this regional humidity pattern. The warm period ended abruptly between 14.0 and 13.5 Ma (Middle/Late Badenian transition) with major regional extinction events of most of the thermophilic groups in Central Europe and a drop of the MAT of probably more than 7°C to temperatures around 14.8–15.7°C. This drop can be attributed predominantly to a decrease of more than 11°C of the minimum cold months temperature. This temperature decrease marked the beginning of a climatic zonation of the European continent and is also evidenced by a progressively southward disappearance of the crocodile Diplocynodon from 38–45°N palaeolatitude to 30–37°N during the Middle and earliest Late Miocene. The results correlate well with palaeobotanical data from the mid-latitudes of Europe and North America, and the deep-sea temperature curve generated from oxygen isotope ratios.

The first phylogenetic analysis of the Euramerican Early Cretaceous–Miocene genus Albanerpeton is presented based on 16 characters of the jaws, frontals, and inferred body size scored for the seven recognized species in the genus and three other albanerpetontid taxa. Monophyly of Albanerpeton is corroborated and nested sets of synapomorphies yield the following hypothesized relationships: A. arthridion ((A. cifellii + A. galaktion + A. gracilis) (A. nexuosus (unnamed late Paleocene species + A. inexpectatum))). Osteological modifications identified in Albanerpeton initially involve the frontals, then shift largely to the jaws. Many of these changes are interpreted to be associated with broadening the head and strengthening the snout and jaws, presumably for feeding and burrowing. The first half or more (latest Aptian/earliest Albian to late Paleocene) of the known record for Albanerpeton and six of the seven species are restricted to the North American Western Interior. These occurrences and the ...

The Albanerpetontidae are Middle Jurassic–Miocene amphibians that have variously been regarded as caudates (salamanders), a clade distinct from caudates, or incertae sedis lissamphibians. Here I test for monophyly of the Albanerpetontidae and examine the affinities of the group, within the framework of a more inclusive Temnospondyli, by performing a cladistic analysis using 59 informative characters scored for four non-lissamphibian temnospondyl genera, stem- and crown-clade caudates, salientians (frogs), gymnophionans (caecilians), and the two recognized albanerpetontid genera Albanerpeton andCeltedens . Monophyly of the Albanerpetontidae is corroborated. I interpret synapomorphies of the marginal teeth (non-pedicellate; crowns chisel like, labiolingually compressed, with three mesiodistally aligned cuspules) in albanerpetontids as being associated with a shearing bite. Other synapomorphies evidently strengthened and increased the mobility of the skull, mandible, and cervical region for burrowing, feeding, or both. Nested sets of synapomorphies place the Albanerpetontidae within the Lissamphibia, as the sister-taxon of Caudata plus Salientia. None of the 17 characters previously advanced as albanerpetontid–caudate synapomorphies convincingly places the Albanerpetontidae within the Caudata or allies the two groups as sister-taxa. Albanerpetontids are better interpreted not as aberrant caudates, but as a distinct clade of lissamphibians in which numerous apomorphies are superimposed upon an otherwise primitive lissamphibian body plan.

Newly discovered fossils described herein from Utah, USA, help fill a sizeable gap in the Cretaceous record of the Albanerpetontidae and provide information on the evolution of the family during th...

Albanerpeton inexpectatum Estes and Hoffstetter, 1976 , the type species of Albanerpeton and the geologically youngest albanerpetontid, is rediagnosed and redescribed based on a large collection of jaws and frontals from Miocene fissure fills near La Grive-Saint-Alban, southeastern France. Intraspecific variation is documented in these elements, and is attributed to growth and individual differences. Synapomorphies of the upper jaws indicate that A. inexpectatum a) belongs in a clade whose members are otherwise known from the Upper Cretaceous-Paleocene of North America and b) is the sister species of an undescribed North American Paleocene species. The presence of A. inexpectatum in the Miocene of France is postulated to be the result of an Early or Middle Tertiary dispersal of an unknown ancestral species from North America into Europe. Cranial apomorphies of A. inexpectatum are interpreted as having strengthened the skull for burrowing in rocky soil and feeding.

A new albanerpetontid, Wesserpeton evansae gen. et sp. nov., from the Early Cretaceous (Barremian) Wessex Formation of the Isle of Wight, southern England, is described. Wesserpeton is established on the basis of a unique combination of primitive and derived characters relating to the frontals and jaws which render it distinct from currently recognized albanerpetontid genera: Albanerpeton (Late Cretaceous to Pliocene of Europe, Early Cretaceous to Paleocene of North America and Late Cretaceous of Asia); Celtedens (Late Jurassic to Early Cretaceous of Europe); and Anoualerpeton (Middle Jurassic of Europe and Early Cretaceous of North Africa). Although Wesserpeton exhibits considerable intraspecific variation in characters pertaining to the jaws and, to a lesser extent, frontals, the new taxon differs from Celtedens in the shape of the internasal process and gross morphology of the frontals in dorsal or ventral view. It differs from Anoualerpeton in the lack of pronounced heterodonty of dentary and maxillary teeth; and in the more medial location and direction of opening of the suprapalatal pit. The new taxon cannot be referred to Albanerpeton on the basis of the morphology of the frontals. Wesserpeton currently represents the youngest record of Albanerpetontidae in Britain.

ALBANERPETONTIDS are a group of enigmatic salamander-like fossil amphibians known from deposits of middle Jurassic to Miocene age across Euramerica and Central Asia. Throughout a long history they remained remarkably conservative but can be diagnosed by a suite of unique derived character states, including an anterior peg-and-socket joint between the mandibles, non-pedicellate tricuspate teeth, a distinctive polygonal dermal sculpture pattern, and a two-part craniovertebral joint analogous to that of amniotes. Previous interpretations have placed albanerpetontids within salamanders1, 2 or as a separate amphibian group3, 4. We report here on the recovery of the first complete albanerpetontid specimens (including traces of skin and possible male courtship glands) from the early Cretaceous of Spain. The new material supports the interpretation of albanerpetontids as predominantly terrestrial animals. Albanerpetontids resemble salamanders only in retaining an unspecialized tailed body form; cladistic analysis suggests they represent a distinct lissamphibian lineage.

Previously thought to be a salamander (Prosirenidae), Albanerpeton Estes and Hoffstetter (Jurassic to Miocene) possesses no known features otherwise restricted to salamanders. Its salamander-like features are only those held in common with small, limbed, non-saltatorial amphibians in general. In still other aspects (including feeding apparatus, dermal bones of the skull, and anterior cervical vertebrae), Albanerpeton appears unique. Already well isolated from salamanders, Albanerpeton seems no nearer phyletically to any other known amphibians, from Devonian to Recent. The relationships of Albanerpeton are most consistently indicated by classification in its own family (Albanerpetontidae, new) and order (Allocaudata, new), perhaps referrable to the Lissamphibia.

Albanerpetontids are an enigmatic fossil amphibian group known from deposits of Middle Jurassic to Pliocene age. The oldest and youngest records are from Europe, but the group appeared in North America in the late Early Cretaceous and radiated there during the Late Cretaceous. Until now, the Asian record has been limited to fragmentary specimens from the Late Cretaceous of Uzbekistan. This led to speculation that albanerpetontids migrated into eastern Asia from North America in the Albian to Cenomanian interval via the Beringian land bridge. However, here we describe albanerpetontid specimens from the Lower Cretaceous Kuwajima Formation of Japan, a record that predates their first known occurrence in North America. One specimen, an association of skull and postcranial bones from a single small individual, permits the diagnosis of a new taxon. High Resolution X-ray Computed Microtomography has revealed previously unrecorded features of albanerpetontid skull morphology in three dimensions, including the presence of a supraoccipital and epipterygoids, neither of which occurs in any known lissamphibian. The placement of this new taxon within the current phylogenetic framework for Albanerpetontidae is complicated by a limited overlap of comparable elements, most notably the non-preservation of the premaxillae in the Japanese taxon. Nonetheless, phylogenetic analysis places the new taxon closer to Albanerpeton than to Anoualerpeton, Celtedens, or Wesserpeton, although Bootstrap support values are weak. The results also question the monophyly of Albanerpeton as currently defined.