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Restudy of Regalerpeton weichangensis (Amphibia: Urodela) from the Lower Cretaceous of Hebei, China

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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 eight new specimens and its diagnosis and phylogenetic position are reexamined. This work shows that R. weichangensis was a neotenic form with ossified carpals and tarsals. It has a series of unique combination of characteristics including the vomer with a transverse vomerine tooth row, anterior end of the cultriform process of the parasphenoid indented, basibranchial II triradiate, a long tail exceeded the snout-pelvis length and scapulocoracoid with a rectangular coracoid end. Phylogenetic analysis suggests Regalerpeton, Jeholotriton and Pangerpeton should be placed in the suborder Salamandroidea with three synapomorphies. Moreover, they also share unicapitate ribs with Cryptobranchoidea, which indicates that they represent an important stage of evolution in the Cryptobranchoidea-Salamandroidea split.
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古 脊 椎 动 物 学 报
VERTEBRATA PALASIATICA
DOI: 10.19615/j.cnki.1000-3118.170627
Restudy of Regalerpeton weichangensis (Amphibia:
Urodela) from the Lower Cretaceous of Hebei, China
RONG Yu-Fen1,2,3
(1 Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate
Paleontology and Paleoanthropology, Chinese Academy of Sciences Beijing 100044 rongyufen@ivpp. ac.cn)
(2 CAS Center for Excellence in Life and Paleoenvironment Beijing 100044)
(3 University of Chinese Academy of Sciences Beijing 100049)
Abstract 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 eight new
specimens and its diagnosis and phylogenetic position are re-examined. This work shows that
R. weichangensis was a neotenic form with ossied carpals and tarsals. It has a series of unique
combination of characteristics including the vomer with a transverse vomerine tooth row,
anterior end of the cultriform process of the parasphenoid indented, basibranchial II triradiate, a
long tail exceeded the snout-pelvis length and scapulocoracoid with a rectangular coracoid end.
Phylogenetic analysis suggests Regalerpeton, Jeholotriton and Pangerpeton should be placed in
the suborder Salamandroidea with three synapomorphies. Moreover, they also share unicapitate
ribs with Cryptobranchoidea, which indicates that they represent an important stage of evolution
in the Cryptobranchoidea-Salamandroidea split.
Key words Weichang, Hebei; Lower Cretaceous; Salamandroidea, Regalerpeton weichangensis;
morphology; phylogeny
Citation Rong Y F, 2018. Restudy of Regalerpeton weichangensis (Amphibia: Urodela) from the
Lower Cretaceous of Hebei, China. Vertebrata PalAsiatica, 56(2): 121–136
1 Introduction
Since the late 1990s, a large number of salamander fossils have successively been
unearthed from Jurassic and Cretaceous strata in northeastern China, and eleven taxa have
been established: Laccotriton subsolanus Gao et al., 1998, Liaoxitriton zhongjiani Dong
&Wang, 1998, Jeholotriton paradoxus Wang, 2000, Sinerpeton fengshanensis Gao & Shubin,
2001, Chunerpeton tianyiensis Gao & Shubin, 2003, Liaoxitriton daohugouensis Wang, 2004,
Pangerpeton sinensis Wang & Evans, 2006, Regalerpeton weichangensis Zhang et al., 2009,
Beiyanerpeton jianpingensis Gao & Shubin, 2012, and Qinglongtriton gangouensis Jia &
国家自然科学基金(批准号:41472018)和中国科学院战略性先导科技专项(编号:XDB18030503)资助。
收稿日期:2017-05-23
56卷 第2
20184
pp. 121–136
gs. 1–8
122 Vertebrata PalAsiatica, Vol. 56, No. 2
Gao, 2016a, Nuominerpeton aquilonaris Jia & Gao, 2016b. These taxa provide a rich source
of information on primitive salamanders, and are significant in understanding the origin of
modern salamander clades. Among these taxa, R. weichangensis was erected on an incomplete
skeleton preserved mainly as impression. This preservation limited our understanding of its
morphology and phylogeny. In the original paper, Regalerpeton was placed as the sister taxon
of Chunerpeton plus living cryptobranchids (Zhang et al., 2009), whereas Skutschas and Gubin
(2012) suggested it as a sister taxon of Hynobiidae.
In this paper, eight new specimens which can be referred to R. weichangensis are
described from northern Hebei Province of China. These better preserved materials permit
a revised diagnosis of the taxon and allow a new phylogenetic analysis to be conducted that
includes most of the fossil taxa from China.
Abbreviations ac, acetabulum; ad. f, anterodorsal fenestra; am. f, anteromedial
fenestra; at, atlas; bb I–II, basibranchial I–II; c, centrale; cb I–II, ceratobranchial I–II; cr vent,
crista ventralis; d, dentary; dc, distal carpal; dt 1–3, distal tarsal 1–3; d 1–5, digit 1–5; e+o,
exoccipital+opisthotic; fe, femur; , bula; b, bulare; fo. i. den, inferior dental foramen; fr,
frontal; gf, gill lament; gr, gill raker; hb I–II, hypobranchial I–II; hu, humerus; i, intermedium;
il, ilium; in. c. a, internal carotid artery; isc, ischium; lac, lacrimal; m, maxilla; n, nasal; os,
orbitosphenoid; p+c, prearticular+coronoid; pa, parietal; ph 2–5, phalanx 2–5; pm, premaxilla;
pm. apr, ascending process of the premaxilla; prf, prefrontal; pro, prootic; ps, parasphenoid; pt,
pterygoid; qua, quadrate; ra, radius; rad, radiale; sa, sacral; sca, scapulocoracoid; sq, squamosal;
st, stapes; ti, tibia; tib, tibiale; ul, ulna, uln; ulnare; vo, vomer; vot, vomerine tooth row.
IVPP, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of
Sciences, Beijing.
2 Systematic paleontology
Class Amphibia Linnaeus, 1758
Subclass Lissamphibia Haeckel, 1866
Superorder Caudate Scopoli, 1777
Order Urodela Duméril, 1806
Family Salamandroidea Dunn, 1922
Genus Regalerpeton Zhang et al., 2009
Type species Regalerpeton weichangensis Zhang et al., 2009.
Holotype IVPP V 14391A, B, an incomplete skeleton impression preserved as part and
counterpart on slabs of siltstone.
Referred specimens IVPP V 15677, an incomplete skeleton impression with a nearly
complete skull in dorsal view. V 16776A, B, an incomplete skeleton with a nearly complete
skull and partial postcranial skeleton that shows well-developed anterodorsal and anteromedial
fenestrae. V 16790A, B, an incomplete skeleton with disarticulated bones of the skull that
shows the morphology of the premaxilla, vomer, pterygoid, squamosal and dentary. V 16798A,
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B, an incomplete skeleton impression with impression of the external gills and ossified
carpals. V 17989, a nearly complete skeletal impression with a well-preserved skull in ventral
view. V 16802A, B, an incomplete skeletal impression with ossified carpals. V 23342A, B,
an incomplete skeletal impression lacking part of the tail, with some bones displaced from
their original positions due to lateral compression. V 23343A, B, an incomplete skeleton
with disarticulated bones of the skull that shows the morphology of the premaxilla, maxilla,
prearticular+coronoid, parasphenoid and ilium.
Revised diagnosis Regalerpeton weichangensis, a neotenic salamander, is diagnosed
by the following unique combination of characters: premaxilla with a distinct ascending
process and bearing approximately 25 teeth; slender maxilla without the facial process and
bearing approximately 28 teeth; dentary bearing approximately 40 teeth; nasals without
midline contact; anterodorsal and anteromedial fenestrae present; lacrimal and prefrontal
present; parietal-prefrontal contact absent; squamosal with two proximal expansions; quadrate
ossication present; roughly pentagonal vomer with transversely oriented vomerine tooth row;
parasphenoid inverted arrow-shaped with an indented anterior end of the cultriform process;
internal carotid foramina penetrating parasphenoid; pterygoid triradiate with a vimineous
dentate anterior ramus; paired hypobranchial I and II ossified; basibranchial II triradiate;
prearticular and coronoid fused with two processes; opisthotic and exoccipital fused; stapes
present; three pairs of external gills present with ossied or calcied gill rakers; 16 presacral
vertebrae; atlas with bifid interglenoid tuberosity; trunk vertebrae amphicoelous and ribs
unicapitate; three pairs of free postsacral ribs; a long tail exceeded the snout-pelvis length;
coracoid portion of scapulocoracoid rectangular; ilium spoon-shaped; humerus with crista
ventralis; carpals and tarsals ossified; digit 2 in manus and digit 1 in pes short; phalangeal
formulae 2-2-3-2 in manus and 2-2-3-3-2 in pes.
Locality and horizon The specimens of Regalerpeton weichangensis are from three
different localities: Daobaziliang, Weichang County, Hebei Province, China (the holotype);
Xishunjing village, Weichang County (V 15677, V 16776A, B, V 16790A, B, V 16798A, B,
V 16802A, B, V 17989, V 23342A, B), and Yulinzi village, Weichang County (V 23343A, B).
Dabeigou Formation, Lower Cretaceous (Gao et al., 2013).
Remarks Because of incomplete preservation and distortion of the holotype, several
morphological characteristics are absent and misinterpreted. Further, series of reliable
characteristics can be concluded as below: the pterygoid is triradiate, with a vimineous dentate
anterior ramus. Although the original article is described as two pairs of ceratobranchials due
to poor preservation, it is reinterpreted as two pairs of hypobranchials. The coracoid portion
of scapulocoracoid is rectangular. In the original article, a detailed discussion about the shape
of coracoid portion shows that scapulocoracoid is the identification of the characteristics
of Regalerpeton. The study of new specimens also agrees that conclusion is reliable.
The vomerine tooth row is transversely oriented and vomer is pentagonal. The primitive
interpretation of the orientation is parallel to the maxillary arcade because of distortion of the
124 Vertebrata PalAsiatica, Vol. 56, No. 2
parasphenoid. New study on the holotype indicates that vomer should be roughly pentagonal.
The parasphenoid has prominent cultriform process. The angular is absent in the mandible.
The tarsals are ossied. Based on the comparison of the above characteristics combination, the
new specimen are referred to R. weichangensis.
3 Description
Among the eight new specimens, V 23342 (Figs. 1, 2) is the best preserved. The
following description is based on it unless otherwise noted.
Skull roof The skull roof is composed of the paired nasals, lacrimals, prefrontals,
frontals and parietals, showing no dermal sculpture.
The 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, C).
The 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.
Fig. 1 Photograph (A) and line drawing (B) of Regalerpeton weichangensis (IVPP V 23342A) in dorsal view
125
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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 parietal.
The frontal (Figs. 1, 3A) is a longitudinal bone with a small anterolateral extension.
Its anterior border completely contacts nasal. Posteriorly, the frontal overlies the parietal
extensively.
The 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 ventrally.
Palate The oor of the skull consists of two completely separated vomers anteriorly and
one parasphenoid posteriorly.
The vomer (Figs. 3B, 4B) is roughly pen-tagonal with a prominent extension laterally.
Poster-olateral border of vomer has a slightly notch for the choana. There are about 20 teeth
Fig. 2 Photograph (A) and line drawing (B) of Regalerpeton weichangensis (IVPP V 23342B) in ventral view
126 Vertebrata PalAsiatica, Vol. 56, No. 2
(V 17989) in the vomer, they are monostichous
and nonpedicellate. The vomerine tooth row (Figs.
3B, 4B) is transversely oriented and runs from the
midline towards extension laterally.
The parasphenoid (Fig. 4D) is a large arrow-
shape bone. The anterior end of the parasphenoid
is serrated including four processes, the medial two
of which are cuspidal and the lateral two long and
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 ossied to form the
lateral side of the neurocranium.
Suspensorium The suspensorium consists of
the paired pterygoids, squamosals and quadrates.
The pterygoid (Figs. 2, 3) is triradiate, with a
vimineous anteromedial process which is free and
curving and has ten teeth. Its posterolateral process
articulates with squamosal and quadrate. It has a
shorter medial process that points to parasphenoid.
There is no contact between the pterygoid and the
parasphenoid.
The 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. 3B).
The quadrate (Fig. 3A, B) is a roughly
triangular bone that lies in the ventral surface of the
squamosal.
Fig. 3 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
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 of the
otic capsule respectively. The stapes (Fig. 2) is nail-shaped, with the head forming the round
127
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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 impression.
Upper and lower jaws The upper jaw is formed by two dermal bones on each side: the
paired dentate premaxillae medially and the paired dentate maxillae posteriorly.
The 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 nonpedicellate.
The maxilla (Fig. 3B) is a slender bone that articulates with the premaxilla anteriorly. A
Fig. 4 Skeletons and impressions of Regalerpeton weichangensis
Impressions of right premaxilla (A), left ilium (C), parasphenoid (D), left dentary showing articular surface for
prearticular+coronoid (F) and left prearticular+coronoid (G); skeletons of right vomer (B), right dentary (E)
A, C, D from IVPP V 23343A; B, E, F from V 16790B; G from V 23343B
128 Vertebrata PalAsiatica, Vol. 56, No. 2
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
comprising the prearticular and the coronoid. They surround Meckel’s cartilage.
The dentary (Fig. 4E) bears approximately 40 teeth on the lingual surface of the lower
jaw. The teeth are small, closely packed and nonpedicellate.
The compound of prearticular+coronoid possesses two processes (Figs. 1, 2, 4G). It has
a slender extension that runs along the lingual surface of the lower jaw (Fig. 4G). The inferior
dental foramen (Fig. 4G) is a conspicuous feature near the posterior of the compound bone
and it carried the ramus alveolaris of facial nerve and the alveolar artery (Francis, 1934). The
articular and the angular are not visible.
Hyobranchium The hyobranchium consists of three ossied elements: hypobranchial
I, hypobranchial II and basibranchial II (os thyroideum) (Figs. 2, 3B). Hypobranchials I and
II are paired, parallel to each other, and each of them is a slightly curved strip. The azygous
midline basibranchial II is positioned posterior to other hyobranchial elements and it is
triradiate.
Axial skeleton The vertebral column consists of 16 presacrals including the atlas and
15 trunk vertebrae, one sacral, and about 40 caudal vertebrae.
The atlas lacks free ribs and is shorter than the trunk vertebrae. It has two relatively
elongated transverse processes (Fig. 3A) and a bid 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 rst three caudosacrals bear free ribs. The remaining caudal vertebrae lack free
ribs, but bear elongate transverse processes, and distinct neural and haemal arches.
Appendicular skeleton The pectoral girdle lies roughly at the level of the 3rd to 4th
trunk
vertebrae. It consists of only one ossied bone: the scapulocoracoid. The coracoid portion is
almost rectangular, and the scapular portion is cuneate.
The humerus is claviform, with expanded proximal and distal portions. In V 23342, the
epiphysis of the humerus is wholly ossied and a crista ventralis is present (Figs. 1, 2, 5). The
radius is a slender and claviform bone, although the distal portion is inated. The ulna, which
is parallel to the radius, is a slightly curved bone that is longer than the radius (Figs. 1, 2, 5).
The carpals are ossied and consist of a radiale, ulnare, intermedium, one centrale, three distal
carpals (Fig. 6). There are four digits in the manus and phalanx 2 is very short (V 16776A, B;
V 17989). The phalangeal formula is 2-2-3-2.
The pelvic girdle has two ossied elements: a pair of ischia ventrally and a pair of ilia
laterally. Each ischium is approximately blade-shaped and the anterior portion is wider than
the posterior one. The ischium joins the cartilagious pubis anteriorly and the ilium laterally to
form the acetabulum for the articulation of the femur. The ilium is a spoon-shaped bone (Fig.
129
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Fig. 5 Reconstruction of the skeleton of Regalerpeton weichangensis
A. skeleton in dorsal view; B. skull in ventral view; C. mandible in lingual view. Not to scale
4C). Its proximal portion is expanded and forms part of the acetabulum, while the posterior
dorsal portion is slightly curved, and articulates with the sacral rib to attach the pelvic girdle.
The femur (Figs. 1, 2) is a long, straight claviform bone, with the proximal end narrower
than the distal one. The tibia and bula are relative short and straight (Figs. 1, 2). The proximal
portion of the tibia is more expanded than the distal end, whereas the bula is slight curved
and its distal portion is relatively inflated. There are seven ossified elements in the ankle
(Fig. 2). These consist of the tibiale and bulare proximally, intermedium, two centralia, and
130 Vertebrata PalAsiatica, Vol. 56, No. 2
three distal tarsals. There are ve digits in the pes. Digit 1 is relatively short (Fig. 1) and the
phalangeal formula is 2-2-3-3-2. (Fig. 1, 2)
Fig. 6 Regalerpeton weichangensis (IVPP V 16802B)
A. photograph of an incomplete skeletal impression; B. the details of gill rakers;
C. the details of ossied carpals
4 Comparison and discussion
4.1 Vomer and vomerine tooth row
The vomer is one of the important dentate elements on the palate for salamanders. The
vomerine teeth has played important role in the systematics of salamanders (Regal, 1966;
Rose, 2003; Fei and Ye, 2017). In the Cryptobranchidae the vomerine teeth is parallel to
the maxillary arcade (Qiu and Yang, 1986; Rose, 2003). In the Hynobiidae the vomerine
teeth varies in length, shape, location and orientation in different genus-species (Fei and
Ye, 2017). In the Salamandroidea the vomerine teeth have more complex types such as
transverse row along posterior border of the vomer in the Ambystomatidae, teeth covered the
posterior extension of the vomer in the Salamandridae and Plethodontidae, vomerine teeth
row paralleled to the maxillary arcade in the Proteidae and Amphiumidae (Regal, 1966; Rose,
2003; Darda and Wake, 2015; Gregory et al., 2016).
The vomer of the Regalerpeton is roughly pentagonal and the vomerine tooth row is
transversely oriented. Compared with other fossil salamanders (Fig. 7), the vomers do not meet
each other in the midline, as in Pangerpeton, Seminobatrachus, Chunerpeton, Jeholotriton
and Qinglongtriton. In contrast, a midline contact of the vomers is present in Liaoxitriton,
Valdotriton and Beiyanerpeton. Moreover, the pentagonal shape of the vomers is unique in
Regalerpeton.
In Chunerpeton, Beiyanerpeton, Qinglongtriton, Seminobatrachus, and Valdotriton, the
vomerine tooth row is parallel to the maxillary arcade. In Jeholotriton paradoxus, the vomer
overgrows the vomerine teeth and has a gracile posterior palatal extension. In Liaoxitriton
131
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daohugouensis, like Regalerpeton, the vomerine teeth row is transverse and medially placed
in the palate, but the vomers are larger and of a different shape (Fig. 7). The Nuominerpeton
aquilonaris (Jia and Gao, 2016b) from the Lower Cretaceous Guanghua Formation of Nei
Mongol, China, differs from Regalerpeton in having a Liaoxitriton-like vomer with short
multiple rows of vomerine teeth.
4.2 Parasphenoid
In most salamanders, the shape of anterior border of the parasphenoid cannot be well
displayed because it is covered with vomers (Regal, 1966; Rose, 2003; Darda and Wake, 2015;
Gregory et al., 2016; Fei and Ye, 2017). In Regalerpeton, parasphenoid is fully exposed in the
palate of the skull on account of separated vomer. It is clearly shown that Regalerpeton has
an arrow-shaped parasphenoid with an indented anterior end. Other than this taxon, this type
is only known in Liaoxitriton daohugouensis (Fig. 7), which has a relatively shorter anterior
process. Besides, it is unique that parasphenoid has an indented anterior end of the cultriform
process. The special morphology of the parasphenoid can be used as the identication feature
of Regalerpeton.
4.3 Hyobranchium
The hyobranchium lies in the oor of the mouth and supports the tongue. It varies in its
conguration in different species (Table 1). In Chunerpeton, Beiyanerpeton, Qinglongtriton,
and Regalerpeton, the hyobranchium consists of ossified hypobranchial I, hypobranchial II
Fig. 7 Comparison of vomer and vomerine tooth row of the fossil salamanders
A. Liaoxitriton zhongjiani (Dong and Wang, 1998); B. Seminobatrachus boltyschkensis (Skutschas and Gubin,
2012); C. Chunerpeton tianyiensis (Gao and Shubin, 2003); D. Pangerpeton sinensis (Wang and Evans, 2006);
E. Liaoxitriton daohugouensis (Wang, 2004); F. Regalerpeton weichangensis (IVPP V 17989);
G. Valdotriton (reconstruction) (Evans and Milner, 1996); H. Jeholotriton paradoxus (Wang, 2000);
I. Qinglongtriton gangouensis (Jia and Gao, 2016a); J. Beiyanerpeton jianpingensis (Gao and Shubin, 2012)
Not to scale
132 Vertebrata PalAsiatica, Vol. 56, No. 2
and basibranchial II, but the shape of basibranchial II differs among these taxa (Fig. 7). It is
triradiate in Regalerpeton. However, in Beiyanerpeton, basibranchial I and II are co-ossied
to form a trident-shaped element with slender arms extending anteriorly and anterolaterally
(Gao and Shubin, 2012). In Chunerpeton, basibranchial II is trident-shaped (Gao and Shubin,
2003), whereas in Qinglongtriton, it is more complex in shape, with paired anterolateral and
posterolateral processes fused to a median rod (Jia and Gao, 2016a). In modern salamanders,
the paired ossified hypobranchial I and hypobranchial II and paralleled to each other,
this occurs in the larval and neotenic salamanders like Siren intermedia, Pachyhynobius
shangchengensis, Batrachuperus mustersi, Pseudobranchus striatus, Proteus anguinus,
Amphiuma means, Desmognathus aeneus (Deban and Wake, 2000; Rose, 2003; Xiong et al.,
2013). Accordingly, pairs of hypobranchial I and hypobranchial II present in fossil taxon are
considered larval hyobranchium.
Table 1 The ossied elements of the hyobranchium in different fossil taxa
Taxa Ceratobranchial Hypobranchial Basibranchial
Kokartus honorarius1) 0 hb I, hb II 0
Laccotriton subsolanus2) ? ? bb II
Liaoxitriton zhongjiani3) cb I ? ?
Jeholotriton paradoxus4) 0 ? 0? 0?
Sinerpeton fengshanensis5) cb II ? ?
Chunerpeton tianyiensis6) 0 hb I, hb II bb II
Liaoxitriton daohugouensis7) cb I hb I bb II
Pangerpeton sinensis8) cb I, cb II 0 0
Regalerpeton weichangensis 0 hb I, hb II bb II
Beiyanerpeton jianpingensis9) 0 hb I, hb II bb I + bb II
Qinglongtriton gangouensis10) 0 hb I, hb II bb II
Nuominerpeton aquilonaris11) cb II hb II bb II
Based on: 1) Skutschas and Martin, 2011; 2) Gao et al., 1998; 3) Dong and Wang, 1998; 4) Wang, 2000; 5) Gao and
Shubin, 2001; 6) Gao and Shubin, 2003; 7) Wang, 2004; 8) Wang and Evans, 2006; 9) Gao and Shubin, 2012; 10) Jia and
Gao, 2016a; 11) Jia and Gao, 2016b.
4.4 Neoteny
In salamanders, neoteny is a phenomenon in which an animal retains the larval
conguration 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 laments 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. Regalerpeton therefore resembles Chunerpeton (Gao and Shubin, 2003),
Beiyanerpeton (Gao and Shubin, 2012) and Qinglongtriton (Jia and Gao, 2016a). However,
Regalerpeton differs from the other three taxa in having the carpals and tarsals fully ossied in
the adult stage. It is implied that Regalerpeton has the ability to support the body.
133
Rong - Restudy of Regalerpeton weichangensis
Fig. 8 50% majority rule consensus tree of the most
parsimonious trees obtained in TNT (Goloboff and
Catalano, 2016) for caudate phylogeny
Clade A. Cryptobranchoidea; B. Salamandroidea;
C. Cryptobranchidae; D. Hynobiidae
5 Phylogenetic analysis
In order to determine the phy-
logenetic position of Regalerpeton,
it is added into the latest data matrix
of caudates as show in Jia and Gao
(2016a). The character states of Jehol-
otriton were also added based on
descriptions in Wang (2000), Wang and
Rose (2005) and Carroll et al. (2012).
Some character states of Pangerpeton
were modied by reexamination of the
holotype (see Appendix 1). Karaurus
was the designated outgroup taxon, and
all the characters were unordered and
unweighted as in Jia and Gao (2016a).
The implicit enumeration search
algorithm using TNT (Goloboff and
Catalano, 2016) resulted in fifteen
most parsimonious trees (tree length =
263 steps, consistency index = 0.464,
retention index = 0.702). 50% majority
rule consensus of
15 most parsimonious
trees (Fig. 8) suggests that Jeholotriton
and Pangerpeton
are sister taxa with
three synapomorphies: vomer with
greatly elongated process extending
along lateral border of parasphenoid
[character state 13(2)]; ossified hypo-
branchial I absent [character state
33(1)]; pterygoid without teeth [cha-
racter state 39(0)]. Regalerpeton
forms a sister taxon to the “Jeholotriton + Pangerpeton” clade. The analysis also reveals that
Regalerpeton, Jeholotriton, Pangerpeton, Qinglongtriton and Beiyanerpeton together form a
clade that is sister-taxon to the rest of Salamandroidea. This sister clade is supported by three
synapomorphies: ossied nasal without midline contact [character state 8(1)]; angular fused
to prearticular [character state 26(1)]; articular absent or by fusion with prearticular [character
state 29(1)]. Besides, Regalerpeton, Jeholotriton and Pangerpeton (from the Early Cretaceous
of Hebei, Middle/Late Jurassic of Nei Mongol and Liaoning, respectively) share unicapitate
ribs with the suborder Cryptobranchoidea. This is in accordance with their transitional position
134 Vertebrata PalAsiatica, Vol. 56, No. 2
between Cryptobranchoidea and Salamandroidea, which indicates that the two groups may
have started to split in the Middle to Late Jurassic. There is also mitochondrial genomes
evidence showing the Cryptobranchoidea-Salamandroidea split in the Mid-Jurassic (~171 Ma)
(Zhang and Wake, 2009). Therefore, Regalerpeton, Jeholotriton and Pangerpeton represent an
important stage of evolution in the history of salamanders.
6 Conclusions
The following conclusions can be drawn from this study:
(1) R. weichangensis differs from other salamanders mainly in the following charac-
teristics: it is a neotenic salamander with ossified carpals and tarsals; roughly pentagonal
vomer with transversely oriented vomerine tooth row; presence of triradiate basibranchial II;
parasphenoid inverted arrow-shaped with an indented anterior end of the cultriform process;
a long tail exceeded the snout-pelvis length coracoid portion of scapulocoracoid rectangular.
These features support the generic distinction of Regalerpeton.
(2) New phylogenetic analysis places Regalerpeton, Jeholotriton and Pangerpeton into
the suborder Salamandroidea. They also share unicapitate ribs with Cryptobranchoidea, so
the three taxa Regalerpeton, Jeholotriton and Pangerpeton represent an important transitional
stage in the evolution of salamanders.
Acknowledgments Thanks to Dr. Dong Liping for discussions on the phylogenetic analysis
and Mr. Zhang Shaoguang for taking photographs. I am grateful for my MSc advisor Prof.
Wang Yuan for his support and revisions of early versions of this manuscript. Thanks also
to reviewers Profs. Susan Evans (UCL), Liu Jun (IVPP) and Dr. Chen Jianye (AMNH)
for their constructive revisions on the paper. This work was supported by grants from the
NNSF of China (Grant NO. 41472018) and the Chinese Academy of Sciences (Grant NO.
XDB18030503).
河北围场下白垩统围场皇家螈(Regalerpeton weichangensis)
(两栖类:有尾类)的再研究
戎钰芬1,2,3
(1 中国科学院古脊椎动物与古人类研究所,中国科学院脊椎动物演化与人类起源重点实验室 北京 100044)
(2 中国科学院生物演化与环境卓越创新中心 北京 100044)
(3 中国科学院大学 北京 100049)
摘要:围场皇家螈(Regalerpeton weichangensis)2009年基于一件产自河北围场下白垩统不
完整的骨骼印痕标本命名。然而由于标本变形导致皇家螈的部分解剖学特征被曲解,系统
135
Rong - Restudy of Regalerpeton weichangensis
发育位置也存在争论。本文基于8件新标本对该蝾螈的鉴定特征和系统发育位置进行了修
订。研究显示,皇家螈是一种腕骨和跗骨骨化的幼态持续型蝾螈,具有独特的特征组合,
包括犁骨齿列横向排列、副蝶骨前端呈齿状、基鳃骨II呈三射型,尾长超过吻臀距以及肩
胛乌喙骨的乌喙端呈矩形。新的系统发育分析根据三个近裔共性将围场皇家螈、热河螈和
胖螈归入蝾螈亚目。此外,它们还与隐鳃鲵亚目共有“肋骨单关节头”这一特征,显示这
三种蝾螈可能代表了隐鳃鲵亚目与蝾螈亚目分离时期这一重要演化阶段。
关键词:河北围场,下白垩统,蝾螈亚目,围场皇家螈,形态学,系统发育学
中图法分类号Q915.863 文献标识码A 文章编号1000–3118(2018)02–0121–16
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Appendix 1 Additions and changes to the date matrix (Jia and Gao, 2016a) used in the phylogenetic analysis
Regalerpeton weichangensis 0000100100 1201000010 0001?11?10 000?001?10 0002?0110? ?01??0?101
000100??10 0??100???? ?????????? 1111????0? 000??
Jeholotriton paradoxus 0000100000 1320000010 ?111??1??0 0?1??01?00 0012?0?10? ?01???0100
000100??10 0??100???? ?????????? 1111????0? 000??
Pangerpeton sinensis 0000??1??? 1020000010 0????11??? 0010001000 ?00?00110? ???????1??
????1???00 0????????? ?????????? ?111????0? ?00??
... 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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Ecological preferences and life history strategies have enormous impacts on the evolution and phenotypic diversity of salamanders, but the yet established reliable ecological indicators from bony skeletons hinder investigations into the paleobiology of early salamanders. Here we statistically demonstrate, by using time-calibrated cladograms and geometric morphometric analysis on 71 specimens in 36 species, that both the shape of the palate and many non-shape covariates particularly associated with vomerine teeth are ecologically informative in early stem- and basal crown-group salamanders. Disparity patterns within the morphospace of the palate in ecological preferences, life history strategies and taxonomic affiliations were analyzed in detail, and evolutionary rates and ancestral states of the palate were reconstructed. Our results show that the palate is heavily impacted by convergence constrained by feeding mechanisms and also exhibits clear stepwise evolutionary patterns with alternative phenotypic configurations to cope with similar functional demand. Salamanders are diversified ecologically before the Middle Jurassic and achieved all their present ecological preferences in the Early Cretaceous. Our results reveal that the last common ancestor of all salamanders shares with other modern amphibians a unified biphasic ecological preference, and metamorphosis is significant in the expansion of ecomorphospace of the palate in early salamanders.
... 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 (in addition to using scattered primary sources and copying from each other). Using a recent example of a large node-dated timetree inferred from molecular data, I reevaluate all 30 calibrations in detail, present the current state of knowledge on them with its various uncertainties, rerun the dating analysis, and conclude that calibration dates cannot be taken from published compendia or other secondary or tertiary sources without risking strong distortions to the results, because all such sources become outdated faster than they are published: 50 of the (primary) sources I cite to constrain calibrations were published in 2019, half of the total of 280 after mid-2016, and 90% after mid-2005. It follows that 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, and that literature is not optimized for that task, but largely has other objectives.
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Over the past 10 years, there has been a wealth of discoveries of fossil salamanders from the Jehol Biota in northern China. These specimens have revealed many new species in addition to establishing probable divergence times and relationships among modern salamander families. Among these are numerous specimens of a neotenic species Jeholotriton paradoxus. In this study, we focused on this particular salamander species because its classification still remains enigmatic. The aim of this research was to determine the relationship of Jeholotriton with respect to other Jehol salamanders as well as modern salamander families. Although Jeholotriton has been described in previous studies, the discovery of new specimens and increasing knowledge of other Mesozoic salamanders has allowed for a more through description of the genus. Jeholotriton is known only from the Daohugou locality in Ningchen, south-eastern Inner Mongolia. It may be close to the base of the modern Urodele radiation, and might provide evidence of their transition from putative ancestors in the Permo-Triassic. We discovered that the fossil Kokartus (family Karauridae) and the living hynobiids (the most primitive group of modern salamanders) Ranodon sibiricus and Hynobius maculosus, as well as Dicamptodontidae tenebrosus all share some similarities with Jeholotriton. However, conclusive relationships could not be confidently established because of the unique combination of mature and larval characteristics in Jeholotriton. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 164, 659–668.