Hyloplesion is an extinct genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of microbrachomorph microsaur. It is the type

Type genus

In biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...

 and only genus within the family Hyloplesiontidae. Fossils have been found from the Czech Republic

Czech Republic

The Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....

 near the towns of Plzeň, Nýřany

Nýrany

Nýřany is a town in the Plzeň Region of the Czech Republic. It lies to the West from the region capital of Plzeň.Nýřany is also the seat of the Municipality with Extended Competence....

, and Třemošná

Tremošná

Třemošná is a town in the Plzeň Region of the Czech Republic. It lies some to the north from the region capital of Plzeň.Třemošná is also the seat of the Municipality with Commissioned Local Authority within the Nýřany Municipality with Extended Competence....

, and date back to the Middle Pennsylvanian. The type species

Type species

In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...

 is H. longicostatum, named in 1883. Two species belonging to different genera, Seeleya pusilla and Orthocosta microscopica, have been synonymized with H. longicostatum and are thought to represent very immature individuals.

Description

Hyloplesion was about as large as a medium-sized salamander

Salamander

Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...

, with the length of known specimens ranging from 17-77mm.

The skull is triangular in shape. Unlike many other microsaurs, the palate of Hyloplesion contains large vacuities, or openings. The fifth 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 tooth is enlarged and resembles a canine. The skull of Hyloplesion superficially resembles that of the unrelated romeriid reptile

Reptile

Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

 Romeria

Romeria (genus)

Romeria is an extinct genus of Early Permian captorinid known from Texas of the United States. It was first named by Llewellyn Ivor Price in 1937 and the type species is Romeria texana. R. texana is known from the holotype MCZ 1480, a three-dimensionally preserved skull...

in lateral view due to similarities in the pattern of the dermal bones and the hooked shape of the 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....

. However, the skull differs from that of Romeria in dorsal view, as the parietal

Parietal bone

The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....

s are much wider in Hyloplesion.

The atlas arch also resembles those of romeriids and, unlike other microsaurs, is unswollen. The trunk is elongate, with thin ribs extending from each vertebra. The presence of a large scapulocoracoid

Scapulocoracoid

The Scapulocoracoid is the unit of the pectoral girdle that contains the coracoid and scapula.The coracoid itself is a beak-shaped bone that is commonly found in most vertebrates with a few exceptions.The scapula is commonly known as the shoulder blade...

 in Hyloplesion distinguishes it from Microbrachis. The limb bones are small and robust, with the hindlimbs being quite larger than the forelimbs . Like other microbrachomorphs such as Microbrachis

Microbrachis

Microbrachis is an extinct genus of lepospondyl amphibian from the Carboniferous period of what is now the Czech Republic....

, Hyloplesion has only three digits in the manus, a condition known as tridactyly.

Paleobiology

A range of morphological characteristics makes it difficult to determine whether Hyloplesion was primarily terrestrial or aquatic. Although the digits are well ossified, the reduced number of toes in Hyloplesion is seen as an adaptation for an aquatic lifestyle. There is no evidence for lateral-line canals in the skull, although they were most likely present, separated from the skull by a layer of connective tissue.

External links

• Hyloplesion in the Paleobiology Database
  Paleobiology Database
  ' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...