except for one taxon, Chunerpeton, which is referred to the Cryptobranchidae.
Laccotriton subsolanus (Fig. 109) is the first Mesozoic salamander reported from China. It is a small-sized metamorphosed salamander, represented by a large number of articulated skeletons from a small quarry in Fengshan Basin of northern Hebei Province. Laccotriton subsolanus is characterized by having 16 presacrals and unicapitate ribs with a broadened base (most living salamanders have bicapitate ribs, except for hynobiids and cryptobranchids). It primitively retains lacrimal and prefrontal bones on the skull, and has five separate bones in the lower jaw. The phalangeal formula (number of phalanges in hand and foot) is 2-2-3-2 in the hands, and 2-2-3-4-2 in the feet.
Sinerpeton fengshanensis (Fig. 110) is another salamander from the Fengshan
1113 Holotype of Chunerpcton tianyiensis Ipart and counterpart of a slab of shale, body length about ISO mm), a basal cryptobranchid salamander and the only Mesozoic member of the group found to date, from Daohugou locality in Ningcheng, Inner Mongolia. Il'hoto; Mick Ellison/ AMNH)
1114 Andrias davidianus |Upper| and Balrachupems pinclionii I Lower), a living representative of the Cryptobranchidae and Hynobiidae. respectively; the two families are widely accepted as the most basal groups of living salamanders, (Courtesy: Er-mi Zhao/CIR)
site, and the fossils were collected from the same quarry as that of Laccotriton. Different from the metamorphosed Laccotriton, this salamander has ossified ceratobranchials (as bony support for external gill filaments in life) and ossified carpals and tarsals (ossification of these bones only seen in adulthood). The combination of these features suggests a mature individual with larval external gills, a condition called neoteny in modern biology. Sinerpeton also differs from Laccotriton in having the phalangeal formula of 1-2-3-2 in the hands and
Jeholotritonparadoxus (Figs. Ill, 112) is reported from the Daohugou locality, Ningcheng County, Inner Mongolia. This apparently is an aquatic salamander as indicated by its external gills, laterally compressed tail, presence of well-developed haemal arches on caudal vertebrae, and the lack of ossified carpal and tarsal dements. Jeholotriton is a special Mesozoic salamander showing a combination of larval and adult features that indicate neoteny. The larval features include the presence of external gills, a tooth-bearing coronoid bone on the lower jaw, the larval shaped pterygoids and a short maxillary arcade with underdeveloped maxilla in the cranial part. The adult features include extensive medial contact of the two nasals and the presence of a posteriorly directed tooth row in the palate. Jeholotriton is characterized by having 17 presacrals, the vertebrae with short transverse processes, and a prominent dorsal process on the premaxillae. Its ribs are like those of Fengshan salamanders as unicapitate and proximally expanded. The phalangeal formula is 2-2-3-2 for the hands and
Chunerpeton tianyiensis (Fig. 113) is another salamander from the Daohugou site. This salamander represents a basal member of the Cryptobranchidae, the family including the endangered Asian giant salamander Andrias (Fig. 114, Upper) and the North American hellbender Cryptobranchus. Morphologically, Chunerpeton shares with extant cryptobranchids several derived characters, such as the nasals being much narrower than the interorbital width; nasal-prefrontal contact absent; and the anterolateral process of parietal extending along the lateral border of the frontal. It primarily differs from extant cryptobranchids, however, in lacking the frontal-maxillary contact; retention of a palatal fenestra between vomers; presence of a distinct medial process of pterygoid; and ossification of basibranchial II as a trident-shaped structure. Because no pre-Paleocene fossils were known for the family, the Chunerpeton fossils from the Daohugou site document the first Mesozoic and the earliest known record of the Cryptobranchidae. The fossils also provide evidence supporting the hypothesis that the divergence of the Cryptobranchidae irom the Hynobiidae had taken place during the Jurassic in Asia.
Liaoxitriton zbongjiani (Fig. 1 15) is the only salamander taxon of the Jehu! Biota that is known from the Jiufotang Formation. Fossils of this salamander were recovered from a site near Huludao City of western Liaoning. As the formation is dated as about 110 million years BP, Liaoxitriton documents so far the youngest stratigraphie occurrence of salamander fossils in the Jehol Group. The species is represented by dozens of articulated skeletons in various preservation conditions, and was the first Chinese Mesozoic lissamphibian to be reported with well-preserved soft tissue impressions (e.g., the skin & eye impressions). The diagnostic features of this animal include the presence of 16 presacral vertebrae and transverse processes of vertebra about half-length of the centrum. It also has the cryptobranchoid type unicapitate ribs with an expanded proximal end. The phalangeal formula is 2-2-3-2 in the hands and 1-2-3-4-3 in the feet. This salamander is similar to some living hynobiids (Fig. 114, Lower) in several osteologtcal features. It is noted that the species is represented by a series of fossils showing different developmental stages, which allows a possible ontogenetic study of the animal in the near future.
In general, the amphibian fossils (especially those of salamanders) from the Mesozoic beds in northern China are important for their superb preservation, large quantity, and considerable taxonomic diversity. The discoveries of these wonderful fossils provide solid paleontological evidence to answer some major questions on the evolution of amphibians; and the studies of these fossils have opened a new window to view the evolutionary history, including the origins, taxonomic diversification and geographic radiation, of modern amphibians.
115 Holorype of Liaoxitriton zhongjiani (Slab A, ventral view, body length about 120 mm), a primitive salamander similar to living hynobiids in some skeletal structures, from Shuikotizi locality (Jiufotang Formation) in Huludao. Liaoning. (Photo: IVPP)
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