# Hyloplesion

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***Hyloplesion*** is an extinct [genus](/source/Genus) of [microbrachomorph](/source/Microbrachomorpha) [microsaur](/source/Microsaur). It is the [type](/source/Type_genus) and only genus within the family **Hyloplesiontidae**.[1] Fossils have been found from the [Czech Republic](/source/Czech_Republic) near the towns of [Plzeň](/source/Plze%C5%88), [Nýřany](/source/N%C3%BD%C5%99any), and [Třemošná](/source/T%C5%99emo%C5%A1n%C3%A1), and date back to the [Middle Pennsylvanian](/source/Middle_Pennsylvanian). The [type species](/source/Type_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.[1]

## Description

*Hyloplesion* was about as large as a medium-sized [salamander](/source/Salamander), with the length of known specimens ranging from 17-77mm.[2]

The skull is triangular in shape. Unlike many other microsaurs, the palate of *Hyloplesion* contains large vacuities, or openings.[3] The fifth [maxillary](/source/Maxilla) tooth is enlarged and resembles a canine. The skull of *Hyloplesion* superficially resembles that of the unrelated [romeriid](/source/Romeriidae) [reptile](/source/Reptile) *[Romeria](/source/Romeria_(genus))* in lateral view due to similarities in the pattern of the dermal bones and the hooked shape of the [premaxilla](/source/Premaxilla). However, the skull differs from that of *Romeria* in dorsal view, as the [parietals](/source/Parietal_bone) are much wider in *Hyloplesion*.[1]

The [atlas](/source/Atlas_bone) 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](/source/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](/source/Microbrachis)*, *Hyloplesion* has only three digits in the [manus](/source/Manus_(anatomy)), a condition known as [tridactyly](/source/Tridactyly).[1]

## Paleobiology

A range of morphological characteristics makes it difficult to determine whether *Hyloplesion* was primarily terrestrial or aquatic.[1] 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](/source/Lateral-line) canals in the skull, although they were most likely present, separated from the skull by a layer of connective tissue.

## References

1. Carroll, R. L. & Gaskill, P. (1978). "The Order Microsauria". *Memoirs of the American Philosophical Society*. **126**: 1–211.

1. Carroll, R. L. (1991). "*Batropetes* from the Lower Permian of Europe-a microsur, not reptile". *Journal of Vertebrate Paleontology*. **11** (2): 229–242. [Bibcode:1991JVPal..11..229C](https://ui.adsabs.harvard.edu/abs/1991JVPal..11..229C). [doi:10.1080/02724634.1991.10011390](https://doi.org/10.1080/02724634.1991.10011390)

1. Baird, D. (1965). "Paleozoic lepospondyl amphibians". *American Zoologist*. **5** (2): 287–294. [doi:10.1093/icb/5.2.287](https://doi.org/10.1093/icb/5.2.287)

## External links

- [*Hyloplesion*](https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=37313) in the [Paleobiology Database](/source/Paleobiology_Database)

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Adapted from the Wikipedia article [Hyloplesion](https://en.wikipedia.org/wiki/Hyloplesion) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Hyloplesion?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.