# Halosaur

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Family of eel-like deep-sea fishes

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Halosaurs Temporal range: Late Campanian to present PreꞒ Ꞓ O S D C P T J K Pg N Scientific classification Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Division: Teleostei Superorder: Elopomorpha Order: Notacanthiformes Family: Halosauridae Günther 1868[1] Genera see text Synonyms Halosauropsinae McDowall 1973

**Halosaurs** are [eel](/source/Eel)-shaped [fishes](/source/Fish) found only at great ocean depths. As the family **Halosauridae**, halosaurs are one of two families within the order [Notacanthiformes](/source/Notacanthiformes); the other being the deep-sea spiny eels, [Notacanthidae](/source/Notacanthidae). Halosaurs are thought to have a worldwide distribution, with some 17 species in three genera represented. Only a handful of specimens have been observed alive, all in chance encounters with [remotely operated underwater vehicles](/source/Remotely_operated_underwater_vehicle).

The term "halosaur" refers to the type genus, *[Halosaurus](/source/Halosaurus)*, which is a [Greek](/source/Greek_language) [compound word](/source/Compound_word), *hals* meaning "sea" and *sauros* meaning "[lizard](/source/Lizard)". Halosaurs have a spotty fossil record, the oldest known genus being *[Echidnocephalus](/source/Echidnocephalus)* from the [Late Cretaceous](/source/Late_Cretaceous) ([Campanian](/source/Campanian)) strata of [Westphalia](/source/Westphalia), [Germany](/source/Germany),[2] and the second-oldest known genus, *[Laytonia](/source/Laytonia)*, from [Miocene](/source/Miocene) strata of [California](/source/California) and [Oregon](/source/Oregon). The fossil specimens already bear strong resemblance to the modern genera. The halosaurs' greatly elongated bodies end in whip-like tails; their scales are large. One small dorsal fin is close to the sharply pointed, mostly scaleless head. The tail fin is greatly reduced, with the anal fin being the largest fin. Their pectoral fins are slender and greatly elongated. Their mouths are somewhat large, with the lower jaw shorter than the upper jaw. The [swim bladder](/source/Swim_bladder) is absent in all known species, except for *Aldrovandia oleosa*, which has a very small bladder.[3]

The largest species, the 90-cm (3-ft) long [abyssal halosaur](/source/Abyssal_halosaur) (*Halosauropsis macrochir*) is also one of the most deep-living fish, recorded at depths of 3,300 m (11,000 ft). Halosaurs have developed certain adaptations to life at these extreme depths, where no light penetrates. Their [lateral line](/source/Lateral_line) system enabling the detection of vibrations in the water is highly developed; the pores run the length of the fish's body. Some species are also known to hold their elongated pectorals erect and forward, possibly providing a further means of detection.

Halosaurs are [benthic](/source/Benthic) fish, spending their time cruising over or resting on the sea floor, where temperatures may be just 2–4 °C. They propel themselves with rhythmic, lateral undulations of their bodies, not unlike [sea snakes](/source/Sea_snake). Halosaurs are thought to prey mainly on benthic [invertebrates](/source/Invertebrate), such as [polychaete](/source/Polychaete) worms, [echinoderms](/source/Echinoderm), and [crustaceans](/source/Crustacea) such as [copepods](/source/Copepod), but they may also consume small [fishes](/source/Fish) and [cephalopods](/source/Cephalopod).

In life, most halosaurs are grey to bluish-black in colour. Like other notacanthiform fish, halosaurs are able to regenerate their tails easily if lost. This adaptation can be likened to certain terrestrial [reptiles](/source/Reptile), such as the [glass lizard](/source/Glass_lizard), which sacrifices its tail to evade predators.

## Genera

Halosaurs are classified into the following genera:[4][5]

- *[Aldrovandia](/source/Aldrovandia)* [Goode](/source/George_Brown_Goode) & [Bean](/source/Tarleton_Hoffman_Bean), 1896
- *[Halosauropsis](/source/Halosauropsis)* [Collett](/source/Robert_Collett), 1896
- *[Halosaurus](/source/Halosaurus)* [J. Y. Johnson](/source/James_Yate_Johnson), 1864
- †*[Laytonia](/source/Laytonia)* [David](https://en.wikipedia.org/w/index.php?title=Lore_Rose_David&action=edit&redlink=1), 1943
- †*[Echidnocephalus](/source/Echidnocephalus)* [von der Marck](https://en.wikipedia.org/w/index.php?title=Wilhelm_von_der_Marck&action=edit&redlink=1), 1858[6]

The genus *[Enchelurus](/source/Enchelurus)* is sometimes considered a halosaur, but has more recently been found to either be [sister](/source/Sister_group) to the [Anguilliformes](/source/Anguilliformes) and [Notacanthiformes](/source/Notacanthiformes)[6] as a whole, or a stem-member of the Anguilliformes.[2]

## References

1. **[^](#cite_ref-1)** ["Part 7- Vertebrates"](https://web.archive.org/web/20161005114629/http://mave.tweakdsl.nl/tn/genera7.html). *Collection of genus-group names in a systematic arrangement*. Archived from [the original](http://mave.tweakdsl.nl/tn/genera7.html) on 5 October 2016. Retrieved 30 June 2016.

1. ^ [***a***](#cite_ref-:1_2-0) [***b***](#cite_ref-:1_2-1) Dornburg, Alex; Friedman, Matt; Near, Thomas J. (2015-08-01). ["Phylogenetic analysis of molecular and morphological data highlights uncertainty in the relationships of fossil and living species of Elopomorpha (Actinopterygii: Teleostei)"](https://doi.org/10.1016%2Fj.ympev.2015.04.004). *Molecular Phylogenetics and Evolution*. **89**: 205–218. [Bibcode](/source/Bibcode_(identifier)):[2015MolPE..89..205D](https://ui.adsabs.harvard.edu/abs/2015MolPE..89..205D). [doi](/source/Doi_(identifier)):[10.1016/j.ympev.2015.04.004](https://doi.org/10.1016%2Fj.ympev.2015.04.004). [ISSN](/source/ISSN_(identifier)) [1055-7903](https://search.worldcat.org/issn/1055-7903). [PMID](/source/PMID_(identifier)) [25899306](https://pubmed.ncbi.nlm.nih.gov/25899306).

1. **[^](#cite_ref-3)** [Aldrovandia oleosa, a New Species of the Halosauridae, with Observations on Several Other Species of the Family](https://www.jstor.org/stable/1443498)

1. **[^](#cite_ref-CofF_4-0)** Fricke, Ron; [Eschmeyer, William N.](/source/William_N._Eschmeyer) & van der Laan, Richard (eds.). ["Genera in the family Halosauridae"](http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatget.asp?tbl=genus&family=Halosauridae). *[Catalog of Fishes](/source/Catalog_of_Fishes)*. [California Academy of Sciences](/source/California_Academy_of_Sciences). Retrieved 5 November 2024.

1. **[^](#cite_ref-pdbd_5-0)** ["Halosauridae"](https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=265727&is_real_user=1). *Palebiology Database*. Retrieved 5 November 2024.

1. ^ [***a***](#cite_ref-:0_6-0) [***b***](#cite_ref-:0_6-1) Near, Thomas J.; Thacker, Christine E. (2024-04-18). ["Phylogenetic Classification of Living and Fossil Ray-Finned Fishes (Actinopterygii)"](https://bioone.org/journals/bulletin-of-the-peabody-museum-of-natural-history/volume-65/issue-1/014.065.0101/Phylogenetic-Classification-of-Living-and-Fossil-Ray-Finned-Fishes-Actinopterygii/10.3374/014.065.0101.full). *Bulletin of the Peabody Museum of Natural History*. **65** (1). [Bibcode](/source/Bibcode_(identifier)):[2024BPMNH..65..101N](https://ui.adsabs.harvard.edu/abs/2024BPMNH..65..101N). [doi](/source/Doi_(identifier)):[10.3374/014.065.0101](https://doi.org/10.3374%2F014.065.0101). [ISSN](/source/ISSN_(identifier)) [0079-032X](https://search.worldcat.org/issn/0079-032X).

- [Froese, Rainer](/source/Rainer_Froese); [Pauly, Daniel](/source/Daniel_Pauly) (eds.). ["Family Halosauridae"](https://www.fishbase.org/summary/FamilySummary.php?family=Halosauridae). *[FishBase](/source/FishBase)*. February 2006 version.

## External links

- [Video footage of a halosaur from NOAA's Ocean Explorer](http://oceanexplorer.noaa.gov/explorations/02davidson/logs/may21/media/eels_video.html)

v t e Elopomorph genera Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Subclass: Neopterygii Infraclass: Teleostei Actinopterygii see Actinopterygii Neopterygii see Neopterygii Teleostei see Teleostei Elopomorpha see below↓ Elopomorpha Elopiformes †Anaethalion †Aulothrissus †Daitingichthys †Davichthys †Echinelops †Eichstaettia †Elopsomolos †Eoprotelops †Epaelops †Flindersichthys †Ichthyemidion †Leptoelops †Naiathaelon †Protelops †Phyllodontidae? Egertonia Eodiaphyodus Paralbula Phyllodus Pseudoegertonia Elopidae †Ctenodentelops Elops †Kipalelops †Lyrolepis †Protoelops Megalopidae †Arratiaelops †Brouweria †Elopoides †Ikawaihere Megalops †Paratarpon †Promegalops †Protarpon †Sedenhorstia Albuliformes †Baugeichthys †Brannerion †Bullichthys †Euroka †Farinichthys †Holcolepis †Lebonichthys †Marathonichthys †Osmeroides †Palealbula †Paraelops †Protalbula †Stewartichthys Albulidae Albula †Casierius †Deltaichthys †Elopothrissus †Hajulia †Istieus †Italoalbula Nemoossis †Nunaneichthys †Phosphonatator †Pteralbula Pterothrissus Notacanthiformes Notacanthidae Lipogenys Notacanthus Polyacanthonotus Halosauridae Aldrovandia †Echidnocephalus Halosauropsis Halosaurus †Laytonia Anguilliformes see Eels Category Commons

Taxon identifiers Halosauridae Wikidata: Q1193126 Wikispecies: Halosauridae ADW: Halosauridae AFD: Halosauridae BOLD: 941 CoL: 625JN EoL: 5416 GBIF: 9666 iNaturalist: 85807 IRMNG: 113533 ITIS: 161657 NBN: NHMSYS0000335541 NCBI: 143897 NZOR: dd64350b-b26a-499b-9f90-99e07ae56255 Open Tree of Life: 925747 Paleobiology Database: 265727 Plazi: AC642D14-3A43-FFC1-34F2-FD7ADF862CD7 WoRMS: 125500

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