Holostei

{{Short description|Group of bony fish}} {{Automatic taxobox | fossil_range = {{Fossil range|Roadian|recent|Middle Permian to present<ref name="Broughton2013"/><ref name="PBDB"/>}} | image = Lepisosteus oculatus.jpg | image_caption = Spotted gar, ''Lepisosteus oculatus'' | image2 = Amia calva1.jpg | image2_caption = Bowfin, ''Amia calva'' | taxon = Holostei | authority = Müller, 1846 | subdivision_ranks = Clades (with orders) | subdivision = * Halecomorphi ** Amiiformes ** {{extinct}}Ionoscopiformes ** {{extinct}}Parasemionotiformes ** {{extinct}}Panxianichthyiformes * Ginglymodi ** {{extinct}}Kyphosichthyiformes ** Lepisosteiformes ** {{extinct}}Semionotiformes *{{extinct}} Dapediidae (''incertae sedis'') }} {{Portal|Fish}} '''Holostei''' is a group of ray-finned bony fish. It is divided into two major clades, the Halecomorphi, represented by the single living genus, ''Amia'' with two species, the bowfins (''Amia calva'' and ''Amia ocellicauda''), as well as the Ginglymodi, the sole living representatives being the gars (Lepisosteidae), represented by seven living species in two genera (''Atractosteus'', ''Lepisosteus'').<ref name="Neopterygian phylogeny: the merger">{{cite journal |last1=López-Arbarello |first1=Adriana |last2=Sferco |first2=Emilia |title=Neopterygian phylogeny: the merger assay. |journal=Royal Society Open Science |date=March 2018 |volume=5 |issue=3 |article-number=172337 |doi=10.1098/rsos.172337|pmid=29657820 |pmc=5882744 |bibcode=2018RSOS....572337L |doi-access=free }}</ref> The earliest members of the clade, which are putative "semionotiforms" such as ''Acentrophorus'' and ''Archaeolepidotus'', are known from the Middle to Late Permian and are among the earliest known neopterygians.<ref>{{Cite journal|last=Romano|first=Carlo|date=2021|title=A Hiatus Obscures the Early Evolution of Modern Lineages of Bony Fishes|journal=Frontiers in Earth Science|volume=8|page=672|doi=10.3389/feart.2020.618853|issn=2296-6463|doi-access=free|bibcode=2021FrEaS...8.8853R |url=https://www.zora.uzh.ch/id/eprint/198125/1/feart-08-618853-2.pdf}}</ref><ref>{{Cite journal |last1=Brinkmann |first1=W. |last2=Romano |first2=C. |last3=Bucher |first3=H. |last4=Ware |first4=D. |last5=Jenks |first5=J. |date=2010 |title=Palaeobiogeography and stratigraphy of advanced Gnathostomian fishes (Chondrichthyes and Osteichthyes) in the Early Triassic and from selected Anisian localities (report 1863-2009): Literaturbericht |url=http://www.schweizerbart.de/series/zgp2 |journal=Zentralblatt für Geologie und Paläontologie, Teil II |volume=2009 |issue=5/6 |pages=765–812 |doi=10.5167/uzh-34071 |issn=0044-4189}}</ref><ref name="Broughton2013">{{Cite journal |last1=Broughton |first1=Richard E. |last2=Betancur-R. |first2=Ricardo |last3=Li |first3=Chenhong |last4=Arratia |first4=Gloria |last5=Ortí |first5=Guillermo |date=2013-04-16 |title=Multi-locus phylogenetic analysis reveals the pattern and tempo of bony fish evolution |journal=PLOS Currents |volume=5 |article-number=ecurrents.tol.2ca8041495ffafd0c92756e75247483e |doi=10.1371/currents.tol.2ca8041495ffafd0c92756e75247483e |doi-broken-date=12 July 2025 |doi-access=free |issn=2157-3999 |pmc=3682800 |pmid=23788273}}</ref><ref name="PBDB">{{Cite web |title=PBDB |url=https://paleobiodb.org/classic/basicTaxonInfo?taxon_no=99748 |access-date=2024-02-26 |website=paleobiodb.org}}</ref>

Holostei was thought to be regarded as paraphyletic. However, a recent study provided evidence that the Holostei are the closest living relatives of the Teleostei, both within the Neopterygii. This was found from the morphology of the Holostei, for example presence of a paired vomer.<ref>{{Cite book|last=Hastings, Walker Jr., Galland|title=FISHES, A GUIDE TO THEIR DIVERSITY|publisher=University of California Press|year=2014|location=Oakland, California|pages=60–62}}</ref> Holosteans are closer to teleosts than are the chondrosteans, the other group intermediate between teleosts and cartilaginous fish, which are regarded as (at the nearest{{efn|Depending who you ask, the Chondrostei may be paraphyletic, or the Polypteridae may be considered not part of them.}}) a sister group to the Neopterygii.

The spiracles of holosteans are reduced to vestigial remnants and the bones are lightly ossified. The thick ganoid scales of the gars are more primitive than those of the bowfin.

==Characteristics== Holosteans share with other non-teleost ray-finned fish a mixture of characteristics of teleosts and sharks. In comparison with the other group of non-teleost ray-finned fish, the chondrosteans, the holosteans are closer to the teleosts and further from sharks: the pair of spiracles found in sharks and chondrosteans is reduced in holosteans to a remnant structure: in gars, the spiracles do not even open to the outside;<ref>[http://www.ebooksread.com/authors-eng/ontario-game-and-fish-commission/commissioners-report-hci/page-37-commissioners-report-hci.shtml Ontario. Game and fish commission]</ref> the skeleton is lightly ossified: a thin layer of bone covers a mostly cartilaginous skeleton in the bowfins. In gars, the tail is still heterocercal but less so than in the chondrosteans. Bowfins have many-rayed dorsal fins and can breathe air like the bichirs.

In the holosteans a primary pulmonoid (respiratory) swim bladder is still present, a trait that was independently lost in both chondrostei and teleostei, the only other two lineages of fish with a swim bladder (in some teleosts the swim bladder have since evolved to become secondarily respiratory again).<ref>[https://books.google.com/books?id=H5OwDwAAQBAJ&dq=Chondrostei+non-respiratory+swim+bladder+non-teleost&pg=PA178 Respiratory Biology of Animals: evolutionary and functional morphology]</ref>

The gars have thick ganoid scales typical of sturgeons whereas the bowfin has thin bony scales like the teleosts. The gars are therefore in this regard considered more primitive than the bowfin.<ref name="holo">{{cite web | url =http://www.liv.ac.uk/~rickl/Fisheries_Web/ichthyology/holostei.htm| title=Holostei| author=Rick Leah |publisher=University of Liverpool}}</ref>

The name ''Holostei'' derives from the Greek words ''holos'', meaning whole, and ''osteon'', meaning bone: a reference to their bony skeletons.

==Systematics of Neopterygii== The evolutionary relationships of gars, bowfin and teleosts were a matter of debate. There are two competing hypotheses on the systematics of neopterygians:

===Halecostomi hypothesis=== The Halecostomi hypothesis proposes Halecomorphi (bowfin and its fossil relatives) as the sister group of Teleostei, the major group of living neopterygians, rendering the Holostei paraphyletic.<ref>Patterson C. Interrelationships of holosteans. In: Greenwood P H, Miles R S, Patterson C, eds. ''Interrelationships of Fishes''. Zool J Linn Soc, 1973, 53(Suppl): 233–305</ref>

{{clade| style=font-size:100%;line-height:100%; | label1=Neopterygii | 1={{clade |label1='''Halecostomi''' |1={{clade |1=Teleostei 120px |2=Halecomorphi 120px }} |2=Ginglymodi 130px }} }}

===Holostei hypothesis=== The Holostei hypothesis, where the gars and bowfin form the clade Holostei as the sister group to Teleostei, is better supported than the Halecostomi hypothesis, rendering the latter paraphyletic.<ref>{{cite web | author = Betancur-R | title = Phylogenetic Classification of Bony Fishes Version 4 | url = https://sites.google.com/site/guilleorti/classification-v-4 | date = 2016 | access-date = 2021-06-07 | archive-date = 2017-07-11 | archive-url = https://web.archive.org/web/20170711171156/https://sites.google.com/site/guilleorti/classification-v-4 }}</ref><ref>{{cite book| last = Nelson| first = Joseph, S.| title = Fishes of the World| year = 2016| publisher = John Wiley & Sons, Inc| isbn = 978-1-118-34233-6 }}</ref><ref>{{ITIS |id=161061 |taxon=Actinopterygii |access-date=3 April 2006}}</ref><ref>{{cite web | editor = R. Froese and D. Pauly| title = FishBase | url = http://www.fishbase.org |date=February 2006}}</ref> It proposes Halecomorphi as the sister group of Ginglymodi, the group which includes living gars (Lepisosteiformes) and their fossil relatives.<ref>{{cite journal|author=Olsen P. E.|title= The skull and pectoral girdle of the parasemionotid fish ''Watsonulus eugnathoides'' from the Early Triassic Sakemena Group of Madagascar with comments on the relationships of the holostean fishes|journal= J Vertebr Paleontol|year= 1984|volume= 4|issue= 3|pages= 481–499|doi= 10.1080/02724634.1984.10012024|bibcode= 1984JVPal...4..481O|citeseerx= 10.1.1.384.2050}}</ref><ref>{{cite journal|last=Grande|first=Lance|author2=Bemis, William E.|title=A Comprehensive Phylogenetic Study of Amiid Fishes (Amiidae) Based on Comparative Skeletal Anatomy. an Empirical Search for Interconnected Patterns of Natural History|journal=Journal of Vertebrate Paleontology |year=1998 |volume=18 |issue=sup001 |pages=1–696 |doi=10.1080/02724634.1998.10011114|bibcode=1998JVPal..18S...1G }}</ref><ref name="Neopterygian phylogeny: the merger"/> It is estimated that the last common ancestor of gars and bowfin lived at least 250 million years ago.<ref>{{Cite journal |last1=Thompson |first1=Andrew W. |last2=Hawkins |first2=M. Brent |last3=Parey |first3=Elise |last4=Wcisel |first4=Dustin J. |last5=Ota |first5=Tatsuya |last6=Kawasaki |first6=Kazuhiko |last7=Funk |first7=Emily |last8=Losilla |first8=Mauricio |last9=Fitch |first9=Olivia E. |last10=Pan |first10=Qiaowei |last11=Feron |first11=Romain |last12=Louis |first12=Alexandra |last13=Montfort |first13=Jérôme |last14=Milhes |first14=Marine |last15=Racicot |first15=Brett L. |date=2021 |title=The bowfin genome illuminates the developmental evolution of ray-finned fishes |journal=Nature Genetics |language=en |volume=53 |issue=9 |pages=1373–1384 |doi=10.1038/s41588-021-00914-y |pmid=34462605 |pmc=8423624 |issn=1546-1718}}</ref>

{{clade| style=font-size:100%;line-height:100%; | label1=Neopterygii | 1={{clade |1=Teleostei 120px |label2='''Holostei''' |2={{clade |1=Halecomorphi 120px |2=Ginglymodi 130px }} }} }}

Ginglymodi comprises three orders: Lepisosteiformes, Semionotiformes and Kyphosichthyiformes. Lepisosteiformes includes 1 family, 2 genera, and 7 species that are commonly referred to as gars. Semionotiformes and Kyphosichthyiformes are extinct orders.

Halecomorphi contains the orders Parasemionotiformes, Panxianichthyiformes, Ionoscopiformes, and Amiiformes. In addition to many extinct species, Amiiformes includes only 1 extant species that is commonly referred to as the bowfin. Parasemionotiformes, Panxianichthyiformes, and Ionoscopiformes have no living members.

Gars and bowfins are found in North America and in freshwater ecosystems. The differences in each can be spotted very easily from just looking at the fishes. The gars have elongated jaws with fanlike teeth, only 3 branchiostegal rays, and a small dorsal fin. Meanwhile the bowfins have a terminal mouth, 10–13 flattened branchiostegal rays, and a long dorsal fin.

==Phylogeny of bony fishes== [[File:Cipactlichthys scutatus holotype.png|thumb|''Cipactlichthys scutatus'' holotype fossil, from the Lower Cretaceous Tlayua Formation of Mexico<ref>{{cite journal |author1=Brito, Paulo M. |author2=Alvarado-Ortega, Jesus |journal=PLOS ONE |volume=8 |issue=9 |article-number=e73551 |doi=10.1371/journal.pone.0073551 |pmid=24023885 |pmc=3762789 |title=Cipactlichthys scutatus, gen. nov., sp. nov. a New Halecomorph (Neopterygii, Holostei) from the Lower Cretaceous Tlayua Formation of Mexico |year=2013|bibcode=2013PLoSO...873551B |doi-access=free }}</ref>]]

The cladogram shows the relationships of holosteans to other living groups of bony fish (Osteichthyes), the great majority of which are teleosts,<ref name=PNAS>{{cite journal |title=Resolution of ray-finned fish phylogeny and timing of diversification |author=Thomas J. Near |journal=PNAS |doi=10.1073/pnas.1206625109 |date=2012 |volume=109 |issue=34 |pages=13698–13703|display-authors=etal |pmid=22869754 |pmc=3427055|bibcode=2012PNAS..10913698N |doi-access=free }}</ref> and to the terrestrial vertebrates (tetrapods) that evolved from a related group of lobe-finned fish.<ref name=TOL>{{cite journal|author=Betancur-R, Ricardo |display-authors=etal |year=2013 |title=The Tree of Life and a New Classification of Bony Fishes |journal=PLOS Currents Tree of Life |issue=Edition 1 |doi=10.1371/currents.tol.53ba26640df0ccaee75bb165c8c26288 |pmc=3644299 |pmid=23653398 |volume=5 |hdl=2027.42/150563 |doi-access=free }}</ref><ref name=laurin&reisz1995>{{cite journal|author1=Laurin, M. |author2=Reisz, R.R. |year=1995 |title=A reevaluation of early amniote phylogeny |journal=Zoological Journal of the Linnean Society |volume=113 |pages=165–223 |doi=10.1111/j.1096-3642.1995.tb00932.x |issue=2}}</ref> Approximate dates are from Near et al. (2012).<ref name=PNAS/>

{{clade |label1=Euteleostomi/ |sublabel1=Osteichthyes |1={{clade |label1=Sarcopterygii |1={{clade |1=Actinistia (Coelacanths) 70px |2={{clade |1=Dipnoi (Lungfish) <span style="{{MirrorH}}">70 px</span> |2={{clade |label1=Tetrapods |1={{clade |1=Amphibians 70px |label2=Amniota |2={{clade |1=Mammals 70px |2=Sauropsids (reptiles, birds) 70px }} }} }} }} }} |label2=Actinopterygii 400 mya |2={{clade |1={{clade |1=part of "Chondrostei"{{efn|Thus the former "Chondrostei" is not a clade, but is broken up. See Actinopteri for a possible reclassification.}} Polypteridae (bichirs) 80px |2={{clade |label1=part of "Chondrostei" |1=Acipenseriformes (sturgeons, paddlefish) 70px |label2=Neopterygii 360 mya |2={{clade |1=Teleostei 310 mya 70px |2='''Holostei''' (bowfins, gars) 275 mya 70px }} }} }} }} }} }}

==Notes== {{notelist}}

==References== {{Reflist}}

==External links== *[https://web.archive.org/web/20040814230926/http://www.liv.ac.uk/~rickl/Fisheries_Web/ichthyology/holostei.htm Holostei on The University of Liverpool website]

Category:Holostei Category:Neopterygii Category:Extant Jurassic first appearances