''Hyloplesion'' is an extinct

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 microbrachomorph

microsaur Microsauria ("small lizards") is an extinct, possibly polyphyletic order of tetrapods from the late Carboniferous and early Permian periods. It is the most diverse and species-rich group of lepospondyls. Recently, Microsauria has been considere ...

. It is the type and only genus within the family Hyloplesiontidae. Fossils have been found from the

Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...

near the towns of

Plzeň Plzeň (; German and English: Pilsen, in German ) is a city in the Czech Republic. About west of Prague in western Bohemia, it is the Statutory city (Czech Republic), fourth most populous city in the Czech Republic with about 169,000 inhabita ...

Nýřany Nýřany (; german: Nürschan) is a town in Plzeň-North District in the Plzeň Region of the Czech Republic. It has about 6,900 inhabitants. Administrative parts Villages of Doubrava and Kamenný Újezd are administrative parts of Nýřany. Geo ...

, and

Třemošná Třemošná (; german: Tschemoschna) is a town in Plzeň-North District in the Plzeň Region of the Czech Republic. It has about 5,100 inhabitants. Administrative parts Village of Záluží is an administrative part of Třemošná. Geography Tře ...

, and date back to the

Middle Pennsylvanian The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, in the ICS geologic timescale, the younger of two subperiods (or upper of two subsystems) of the Carboniferous Period. It lasted from roughly . As with most o ...

. The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

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 Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...

, 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 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 tooth is enlarged and resembles a canine. The skull of ''Hyloplesion'' superficially resembles that of the unrelated romeriid

reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...

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

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 ...

. However, the skull differs from that of ''Romeria'' in dorsal view, as the parietals are much wider in ''Hyloplesion''. The

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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 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'' is an extinct genus of lepospondyl amphibian from the Carboniferous Kladno Formation of the Czech Republic. Description ''Microbrachis'' was an elongated, salamander-like creature, about long, with over 40 vertebrae ins ...

'', ''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 The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial ...

canals in the skull, although they were most likely present, separated from the skull by a layer of connective tissue.

References

External links

''Hyloplesion''
in the

Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database (PBDB) originated in the NCEAS-funded Phanerozoic Marine Pale ...

Microsauria Carboniferous amphibians of Europe Prehistoric amphibian genera Taxa named by Antonin Fritsch {{carboniferous-animal-stub