''Callobatrachus'' is an extinct genus of

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 ...

from the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

-age

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 Liaoning () is a coastal 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 is the northernmost ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

. It was described in 1999 by K. Gao of the

American Museum of Natural History The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...

and Y. Wang of the Chinese Academy of Sciences. It was discovered in the Sihetun locality of the western part of Liaoning province. 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

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 ...

, 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. Before its description, ''Callobatrachus'' was announced in Chinese media as "sanyanlichan". While some authors have suggested ''Callobatrachus'' is a synonym of ''

Liaobatrachus ''Liaobatrachus'' (meaning "Liaoning frog") is a genus of prehistoric frog, the first fossil specimen of which was recovered from the Yixian Formation of Liaoning Province, China. It was the first Mesozoic era frog ever found in China.Ji, S. and ...

'', this has been rejected by other authors. While originally suggested to be a "

discoglossid The Alytidae are a family of primitive frogs. Their common name is painted frogs or midwife toads. Most are endemic to Europe, but three species occur in northwest Africa, and a species formerly thought to be extinct is found in Israel. This fam ...

", in a 2017 phylogenetic analysis it was found to be a crown group frog which was more derived than ''

Ascaphus The tailed frogs are two species of frogs in the genus ''Ascaphus'', the only taxon in the family Ascaphidae . The "tail" in the name is actually an extension of the male cloaca. The tail is one of two distinctive anatomical features adapting the ...

'' and ''

Leiopelma __NOTOC__ ''Leiopelma'' is a genus of New Zealand primitive frogs, belonging to the suborder Archaeobatrachia. It is the only genus in the monotypic family Leiopelmatidae. The leiopelmatids' relatively basal form indicates they have an ancient li ...

,'' but less so than alytids and more advanced frogs.

References

External links

"Chinese frog discovery sheds light on amphibians' evolution"
from ABC News Online {{Taxonbar, from=Q2122942 Early Cretaceous frogs Mesozoic amphibians of Asia Fossil taxa described in 1999 Painted frogs Prehistoric amphibian genera Prehistoric animals of China