Callobatrachus
Encyclopedia
Callobatrachus is an extinct genus of discoglossid
anuran
amphibian
from the Early Cretaceous
-age Yixian Formation
of Liaoning, China. It was described in 1999 by K. Gao of the American Museum of Natural History
and Y. Wang of the Chinese Academy of Sciences
. Discovered in the Sihetun locality of the western Liaoning province, in the lower part of the Yixian Formation, the fossil dates to approximately 124.6 Ma. The discovery is notable for documenting the earliest and sole definite discoglossid fossil from the Mesozoic
. Callobatrachus 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
has provided important insight into anuran evolution. For the past 50 years the primitive discoglossid genus Eodiscoglossus
of early Cretaceous
Spain represented the most primitive discoglossid, but Callobatrachus is now shown to precede it phylogenetically.
The holotype
, IVPP V11525, is known from a nearly complete skeleton exposed in a dorsal
view on a shale
slab. Its total body length (from snout to vent) is estimated at approximately 94 mm. It differs morphologically in many respects from all other members of its family, including in number of presacral vertebrae
and other primitive characters. Although it had a mosaic of primitive and derived characters, it can be unequivocally placed as the most basal taxon of the clade
. 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
ry region is less well-preserved but it can be determined that each premaxilla
bears 18-20 slender and conical teeth, and the maxilla bears approximately 40-50 fine pedicellate teeth
. The vertebral column consists of nine presacral vertebrae, a single sacral vertebra, and a free urostyle
. 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.
Discoglossidae
Discoglossidae is a family of primitive frogs, with the common name Disc-Tongued Frogs. Most are endemic to Europe, but there are also three species in North-West Africa, and an extinct species formerly occurred in Israel....
anuran
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
from the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
-age Yixian Formation
Yixian Formation
The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans 11 million years during the early Cretaceous period...
of Liaoning, China. It was described in 1999 by K. Gao of the American Museum of Natural History
American Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
and Y. Wang of the Chinese Academy of Sciences
Chinese Academy of Sciences
The Chinese Academy of Sciences , formerly known as Academia Sinica, is the national academy for the natural sciences of the People's Republic of China. It is an institution of the State Council of China. It is headquartered in Beijing, with institutes all over the People's Republic of China...
. Discovered in the Sihetun locality of the western Liaoning province, in the lower part of the Yixian Formation, the fossil dates to approximately 124.6 Ma. The discovery is notable for documenting the earliest and sole definite discoglossid fossil from the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
. Callobatrachus 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
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
has provided important insight into anuran evolution. For the past 50 years the primitive discoglossid genus Eodiscoglossus
Eodiscoglossus
Eodiscoglossus is an extinct genus of prehistoric amphibian.-See also:* Prehistoric amphibian* List of prehistoric amphibians...
of early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Spain represented the most primitive discoglossid, but Callobatrachus is now shown to precede it phylogenetically.
The holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
, IVPP V11525, is known from a nearly complete skeleton exposed in a dorsal
Dorsum (anatomy)
In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
view on a shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
slab. Its total body length (from snout to vent) is estimated at approximately 94 mm. It differs morphologically in many respects from all other members of its family, including in number of presacral vertebrae
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...
and other primitive characters. Although it had a mosaic of primitive and derived characters, it can be unequivocally placed as the most basal taxon of the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
. 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
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
ry region is less well-preserved but it can be determined that each premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
bears 18-20 slender and conical teeth, and the maxilla bears approximately 40-50 fine pedicellate teeth
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 separated by a layer of uncalcified dentine....
. The vertebral column consists of nine presacral vertebrae, a single sacral vertebra, and a free urostyle
Coccyx
The coccyx , commonly referred to as the tailbone, is the final segment of the vertebral column. Comprising three to five separate or fused vertebrae below the sacrum, it is attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between...
. 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.
See also
- Prehistoric amphibian
- List of prehistoric amphibians