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Photograph of the impression of the skull roof of Regalerpeton weichangensis A. IVPP V 15677; B. V 16776 A; C. V 16776B. Scale bars equal 5 mm 

Photograph of the impression of the skull roof of Regalerpeton weichangensis A. IVPP V 15677; B. V 16776 A; C. V 16776B. Scale bars equal 5 mm 

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Regalerpeton weichangensis was established in 2009 on an incomplete skeleton preserved mainly as an impression from the Lower Cretaceous of Hebei, China. However, several anatomical characters were misinterpreted due to distortion of the holotype, and its taxonomic position has been in debate. In this paper, R. weichangensis is redescribed based on...

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Context 1
... nasal (Fig. 3A) is a large triangular bone. It contacts the ascending process of the maxilla anteriorly, frontal posteriorly and prefrontal laterally. It is not connected to the lacrimal. The nasals are separated by a large anterodorsal fenestra (Fig. 3A, ...
Context 2
... nasal (Fig. 3A) is a large triangular bone. It contacts the ascending process of the maxilla anteriorly, frontal posteriorly and prefrontal laterally. It is not connected to the lacrimal. The nasals are separated by a large anterodorsal fenestra (Fig. 3A, ...
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... lacrimal is a small quadrilateral bone (V 16798) that forms the posterior edge of the narial fenestra and the anterior edge of the orbit. The nasolacrimal ducts are not observed due to poor preservation. The prefrontal (Fig. 3) is a cuneate bone. Its anterior border has inverted V-shape, with the anteromedial side suturing with the nasal and the posterolateral side with the lacrimal. Medially, it contacts the frontal, but not the ...
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... parietal (Figs. 1, 3A) is also a longitudinal bone. It is slightly shorter than frontal and lies posterior to the frontal. The parietal is sutured along the posterior midline, but separated anteriorly by an anteromedial fenestra (Fig. 3A, C). The parietal has a well-developed anterolateral extension along the posterolateral margin of the frontal, but it fails to extent to the prefrontal. Posteriorly, parietal has an obvious lateral extension that articulates with squamosal ( Fig. 3A). In lateral view, the parietal is seen to articulate with the orbitosphenoid ...
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... is sutured along the posterior midline, but separated anteriorly by an anteromedial fenestra (Fig. 3A, C). The parietal has a well-developed anterolateral extension along the posterolateral margin of the frontal, but it fails to extent to the prefrontal. Posteriorly, parietal has an obvious lateral extension that articulates with squamosal ( Fig. 3A). In lateral view, the parietal is seen to articulate with the orbitosphenoid ...
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... obtuse. The lateral margins of the serrated part have facets for the vomers. Posteriorly, the parasphenoid broadens obviously and has a recognized conule of the both side, for articulating with orbitosphenoids. There is a groove on each side of the parasphenoid wing, along which the internal carotid artery runs. The orbitosphenoid (sphenethmoid) (Fig. 3B) is approximately cuboid and they ossified to form the lateral side of the ...
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... squamosal (Fig. 3) is a slightly curving lamellate of bone and presents as a transverse bar in the posterior skull. It has two proximal ex- pansions, anterior one smaller than the posterior one. Ventrally, the squamosal articulates with the pterygoid and the quadrate (Fig. ...
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... squamosal (Fig. 3) is a slightly curving lamellate of bone and presents as a transverse bar in the posterior skull. It has two proximal ex- pansions, anterior one smaller than the posterior one. Ventrally, the squamosal articulates with the pterygoid and the quadrate (Fig. ...
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... quadrate (Fig. 3A, B) is a roughly triangular bone that lies in the ventral surface of the squamosal. Otico-occipital region The otico-occipital region of Regalerpeton consists of three endochondral bones: the prootic, a compound containing opisthotic and exoccipital, and stapes (columella). Both prootic and opisthotic form the anterior and posterior walls ...
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... the anterior and posterior walls of the otic capsule respectively. The stapes (Fig. 2) is nail-shaped, with the head forming the round footplate and its shaft forming a short stylus. Its footplate covers the lateral wall of the otic capsule. In Regalerpeton, opisthotic and exoccipital form a compound which expose completely in the parietal end (Fig. 3A). The opisthotic portion seems to have an obvious expansion on account of deep impression preserved in V 15677 (Fig. 3A). However, more information from otico-occipital region is not observed because most specimens are preserved as ...
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... forming the round footplate and its shaft forming a short stylus. Its footplate covers the lateral wall of the otic capsule. In Regalerpeton, opisthotic and exoccipital form a compound which expose completely in the parietal end (Fig. 3A). The opisthotic portion seems to have an obvious expansion on account of deep impression preserved in V 15677 (Fig. 3A). However, more information from otico-occipital region is not observed because most specimens are preserved as ...
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... premaxilla (Figs. 1, 2, 4A) has a distinct ascending process extending along about one-third of the premaxilla near the midline, which contacts the anterior part of the nasal (Fig. 3A). The premaxilla bears approximately 25 teeth that are gracile, pointed and ...
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... maxilla (Fig. 3B) is a slender bone that articulates with the premaxilla anteriorly. A distinct facial process is easily observable. The maxilla is slightly longer than the premaxilla and bears approximately 28 teeth which are similar to the premaxillary teeth. The mandible consists of two distinct dermal bones: the dentary and a compound bone ...
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... atlas lacks free ribs and is shorter than the trunk vertebrae. It has two relatively elongated transverse processes (Fig. 3A) and a bifid interglenoid tuberosity (Figs. 3B, C) that articulate with the exoccipitals. All the trunk vertebrae are amphicoelous and all the ribs are unicapitate. The sacral vertebra is larger than the trunk vertebrae, and its ribs are long, thick and expanded proximally. Regalerpeton has a very long tail that exceeds the snout-pelvis ...
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... atlas lacks free ribs and is shorter than the trunk vertebrae. It has two relatively elongated transverse processes (Fig. 3A) and a bifid interglenoid tuberosity (Figs. 3B, C) that articulate with the exoccipitals. All the trunk vertebrae are amphicoelous and all the ribs are unicapitate. The sacral vertebra is larger than the trunk vertebrae, and its ribs are long, thick and expanded proximally. Regalerpeton has a very long tail that exceeds the snout-pelvis length. The first three caudosacrals bear free ...
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... salamanders, neoteny is a phenomenon in which an animal retains the larval configuration while attaining reproductive maturity (Pierce and Smith, 1979;Shaffer, 2013). There are gill filament impressions (three pairs) (Fig. 3B, C) and ossified or calcified gill rakers (Figs. 1, 2, 6) present in our newly discovered specimens. As in modern relatives, the gill filaments or rakers are indicative of external gills. Regalerpeton must therefore have been neotenic, as the adult individuals have 1) external gills; 2) larval-shaped pterygoids; 3) a larval hyobranchium. ...

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... The Asian record is rich in the Early Cretaceous. Chinese taxa are represented by the proposed stemhynobiids Nuominerpeton aquilonaris and Liaoxitriton zhongjiani [42,61], the possible salamandroid Regalerpeton weichangensis [62,63], as well as Jeholotriton paradoxus [64] (figures 1 and 3). However, the phylogenetic positions of all of these Chinese species are uncertain [43], with cryptobranchoid [65], salamandroid [63] and stem caudate [30] affinities proposed. ...
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... However, inadequate knowledge of the osteology of the extant relatives of these extinct hynobiids hampers our understanding of the character evolution within the Hynobiidae (e.g. Dong & Wang, 1998;Gao et al., 1998;Gao & Shubin, 2001;Wang, 2004;Wang & Evans, 2006;Zhang et al., 2009;Rong, 2018;, and further obstructs our understanding of the paleobiology of these early salamanders (e.g. life history, ecological preferences). ...
... All stem hynobiids known to date (e.g. Nuominerpeton aquilonaris, Linglongtriton daxishanensis) have cartilaginous ceratohyals, including the neotenic Regalerpeton (Rong, 2018); indicating that the ossification of the ceratohyal represents a derived character that may convergently evolved in aquatic hynobiid lineages, a hypothesis awaits to be tested in future studies. ...
... Formation of northern Hebei, China (Rong, 2018) and Linglongtriton from the Upper Jurassic Tiaojishan Formation of Liaoning Province, ...
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... Chinese cryptobranchoids or even some of the more crownward stem-urodeles toward them, even if some 824 (Rong, 2018) or most (Jia and Gao, 2019) end up in the hynobiid total group rather than in 825 ...
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Molecular divergence dating has the potential to overcome the incompleteness of the fossil record in inferring when cladogenetic events (splits, divergences) happened, but needs to be calibrated by the fossil record. Ideally but unrealistically, this would require practitioners to be specialists in molecular evolution, in the phylogeny and the fossil record of all sampled taxa, and in the chronostratigraphy of the sites the fossils were found in. Paleontologists have therefore tried to help by publishing compendia of recommended calibrations, and molecular biologists unfamiliar with the fossil record have made heavy use of such works. Using a recent example of a large timetree inferred from molecular data, I demonstrate that calibration dates cannot be taken from published compendia without risking strong distortions to the results, because compendia become outdated faster than they are published. The present work cannot serve as such a compendium either; in the slightly longer term, it can only highlight known and overlooked problems. Future authors will need to solve each of these problems anew through a thorough search of the primary paleobiological and chronostratigraphic literature on each calibration date every time they infer a new timetree; over 40% of the sources I cite were published after mid-2016. Treating all calibrations as soft bounds results in younger nodes than treating all calibrations as hard bounds. The unexpected exception are nodes calibrated with both minimum and maximum ages, further demonstrating the widely underestimated importance of maximum ages in divergence dating.
... Chinese cryptobranchoids or even some of the more crownward stem-urodeles toward them, even if some 824 (Rong, 2018) or most (Jia and Gao, 2019) end up in the hynobiid total group rather than in 825 ...
Preprint
Full-text available
Molecular divergence dating has the potential to overcome the incompleteness of the fossil record in inferring when cladogenetic events (splits, divergences) happened, but needs to be calibrated by the fossil record. Ideally but unrealistically, this would require practitioners to be specialists in molecular evolution, in the phylogeny and the fossil record of all sampled taxa, and in the chronostratigraphy of the sites the fossils were found in. Paleontologists have therefore tried to help by publishing compendia of recommended calibrations, and molecular biologists unfamiliar with the fossil record have made heavy use of such works. Using a recent example of a large timetree inferred from molecular data, I demonstrate that calibration dates cannot be taken from published compendia without risking strong distortions to the results, because compendia become outdated faster than they are published. The present work cannot serve as such a compendium either; in the slightly longer term, it can only highlight known and overlooked problems. Future authors will need to solve each of these problems anew through a thorough search of the primary paleobiological and chronostratigraphic literature on each calibration date every time they infer a new timetree; over 40% of the sources I cite were published after mid-2016. Treating all calibrations as soft bounds results in younger nodes than treating all calibrations as hard bounds. The unexpected exception are nodes calibrated with both minimum and maximum ages, further demonstrating the widely underestimated importance of maximum ages in divergence dating.
... The axial skeleton consists of 16 presacrals including the atlas, one sacral, five caudosacrals, and 28 caudals (Figs. 2, 6). Among other hynobiid-like fossil taxa, the same presacral count is found in Laccotriton, Liaoxitriton, and Regalerpeton (Gao et al., 1998;Dong and Wang, 1998;Gao and Shubin, 2001;Wang, 2004;Rong, 2018), whereas it is 16 or 17 in Sinerpeton (Gao and Shubin, 2001) and 15 in Nuominerpeton (Jia and Gao, 2016a). The vertebral centrum is amphicoelous as commonly seen in urodeles (Reese, 1906;Tihen, 1958;Gilbert, 1973;Zhang, 1985;Wake, 2001;Gardner, 2003aGardner, , 2003bAmphibiaTree, 2007) and stem caudates (e.g., Evans et al., 1988;Skutschas and Krasnolutskii, 2011;Skutschas, 2016b). ...
... Digit 3 is slightly longer than digit 5, which in turn is longer than digit 2. The phalangeal formula is 2-2-3-4-2. A similar phalangeal formula was reported in the hynobiid-like fossil taxa Laccotriton and Liaoxitriton daohugouensis, whereas it is 1-2-3-4-2 in Sinerpeton, 1-2-3-4-3 in Liaoxitriton zhongjiani, and 2-2-3-3-2 in Nuominerpeton and Regalerpeton (Dong and Wang, 1998;Gao et al., 1998;Gao and Shubin, 2001;Wang, 2004;Zhang et al., 2009a;Jia and Gao, 2016a;Rong, 2018). ...
... Whether shifts of position regarding the openings of CNs II and III on the orbitosphenoid bone have occurred in the early evolutionary history of hynobiids awaits detailed morphological investigation on Pangerpeton, which obviously goes beyond the scope of this study. Second, the problematic Regalerpeton was originally described by Zhang et al. (2009a) as a putative cryptobranchid but was recently argued to be a basal member of Salamandroidea (Rong, 2018). However, our current study found that Regalerpeton is a stem hynobiid with a sister-group relationship with Liaoxitriton zhongjiani, on the basis that both of these taxa have an ossified hypobranchial I (33-0). ...
Article
Hynobiids are a group of small- to moderate-sized salamanders living primarily in Asia. They are a primitive crown-group clade, with a poor fossil record. Several hynobiid-like taxa have been discovered from the Lower Cretaceous strata of northern China during the last 20 years, with Liaoxitriton zhongjiani and Nuominerpeton aquilonaris identified as the oldest known stem hynobiids. However, the record of pre-Cretaceous hynobiid-like taxa is only known by Liaoxitriton daohugouensis, of which both the morphology and the congeneric status with L. zhongjiani remain problematic. Here, we report on a new hynobiid-like salamander, Linglongtriton daxishanensis, gen. et sp. nov., on the basis of two specimens from the Upper Jurassic Lanqi/Tiaojishan Formation (∼160 Ma) of Liaoning Province, China. Linglongtriton is diagnosed by a unique combination of features revealed by both observation under microscope and micro-computed tomography (μCT) scan of the holotype, including nasals separated from each other at the midline; prootic, opisthotic, and exoccipital retained as discrete elements; dentary with a lateral groove; articular not ossified; metacarpal III enlarged; a single centrale; and distal tarsals 4 and 5 fused into a single element. Phylogenetic analysis identified Linglongtriton and several other hynobiid-like taxa, including Liaoxitriton daohugouensis, as stem hynobiids, thereby extending the temporal range of the stem by at least 40 Ma—from the Early Cretaceous (Aptian–Barremian) to the Middle Jurassic (Bathonian). Comparative study of Linglongtriton with living and fossil hynobiids sheds new lights on the evolution and developmental mechanisms of several characters, including nasal separation and tarsal elements.