''Liaobatrachus'' (meaning "Liaoning frog") is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of prehistoric

frog A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...

, the first fossil specimen of which was recovered from the

Yixian Formation The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its ex ...

Liaoning Province Liaoning () is a coastal provinces of China, province in Northeast China that is the smallest, southernmost, and most populous province in the region. With its capital at Shenyang, it is located on the northern shore of the Yellow Sea, and i ...

, China. It was the first

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

era frog ever found in China.Ji, S. and Ji, Q. (1998). "The first Mesozoic frog from China (Amphibia: Anura), ''Liaobatrachus grabaui'' gen. et sp. nov." ''Chinese Geology'', March 1998: 39-49
English translation
/ref> The species '' Callobatrachus sanyanensis,'' '' Mesophryne beipiaoensis'' and ''Yizhoubatrachus'' ''macilentus'' were classified as species of ''Liaobatrachus'' in one study, but this has been rejected by other authors. The genus has been considered a ''

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium'' it may be impossible to determine whether a s ...

'' by some authors due to the poor preservation of the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

specimen. Fossils were found in the Sihetun locality of the western part of Liaoning province, in the lower part of the Yixian Formation, and date to approximately 124.6 Ma. Another specimen was collected near Heitizigou, south of

Beipiao Beipiao () is a city in Chaoyang prefecture, Liaoning province, in Northeast China. It has a population of 202,807. The main industry in the area is coal mining. With vertical shafts of almost 1000m, these are some of the deepest coal mines in C ...

. The specimen has a snout–vent length of . ''Liaobatrachus'' is considered to be the most basal member of Discoglossidae based on phylogenetic analysis. As frogs are rarely found as articulated skeletons in the fossil record, the discovery of this new

taxon In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

has provided important insight into anuran evolution. The

, IVPP V11525, is known from a nearly complete skeleton exposed in a

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...

view on a

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

slab. Its total body length (from snout to vent) is estimated at approximately 94 mm. It differs morphologically in many respects from all other discoglossoids, including the number of presacral

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

(9 instead of the usual 8) and other primitive characters. Although it had a mosaic of primitive and

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

characters, it can be unequivocally placed as the most basal taxon of the

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

. This shows that the taxon diverged early from the stem and evolved separately as a distinct lineage by the Early Cretaceous in East Asia. The skull is described as being short and wide and is well preserved. The

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

ry region is less well-preserved but it can be determined that each

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

bears 18-20 slender and conical teeth, and the maxilla bears approximately 40-50 fine

pedicellate teeth Pedicellate teeth are a tooth morphology today unique to modern amphibians, but also seen in a variety of extinct labyrinthodonts. Pedicellate teeth consist of a tooth crown and a base (both composed of dentine) separated by a layer of uncalcifie ...

. The vertebral column consists of nine presacral vertebrae, a single sacral vertebra, and a free

urostyle The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

. Three pairs of ribs were found associated with presacrals II-IV. The hind limbs are remarkably well-preserved and are slenderly built, with an approximate total length of 116 mm. Its hind feet have the phalangeal formula 2-2-3-4-3, with its fourth digit being the longest at 27 mm.

References

External links

"Chinese frog discovery sheds light on amphibians' evolution"
from ABC News Online {{Taxonbar, from1=Q6540131, from2=Q2122942, from3=Q6821563 Early Cretaceous frogs Cretaceous amphibians of Asia Prehistoric animals of China Fossil taxa described in 1999 Yixian fauna