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{{Short description|Infraphylum of jawless fish}}{{Distinguish|Agnathia}}{{Paraphyletic group! colspan=2 | Subgroup! Example! Comments! rowspan=2 | Cyclostomes! Myxini! Hyperoartia! rowspan 4 | Myllokunmingiida!†Myllokunmingiidae(extinct)! rowspan 5 | Conodonta! †Conodont(extinct)! rowspan=6 | Ostracoderms! †Pteraspidomorphi(extinct)! †Thelodonti(extinct)! †Anaspida(extinct)! †Cephalaspido-morphi(extinct)

Cambrian Stage 3–Holocene>Present{{fossil range

0

ref=YANG>FIRST1=CHUAN

FIRST2=XIAN-HUA

FIRST3=MAOYAN

FIRST4=DANIEL J.

FIRST5=JUNYUAN

TITLE=GEOCHRONOLOGICAL CONSTRAINT ON THE CAMBRIAN CHENGJIANG BIOTA, SOUTH CHINA

LANGUAGE=EN

ISSUE=4

DOI=10.1144/JGS2017-103

S2CID=135091168

URL=HTTP://NORA.NERC.AC.UK/ID/EPRINT/521412/1/2018-JGS-CHUAN%20YANG%20ET%20AL.PDF, }}| image = Одинока мінога.JPG| image_caption = One of the surviving agnatan familiy, Geotria| auto = yes| taxon = Agnatha

Edward Drinker Cope>Cope, 1889| includes = *†Anaspidomorphi Cephalaspidomorphi (including Gnathostomata) †Conodonta Cyclostomi †Myllokunmingiida? †Metaspriggina? †Palaeospondylus? †Pteraspidomorphi †ThelodontomorphiJOURNAL, Märss, T., Miller, C.G., 2004, Thelodonts and distribution of associated conodonts from the Llandovery-lowermost Lochkovian of the Welsh Borderland, Palaeontology, 47, 5, 1211–1265, 10.1111/j.0031-0239.2004.00409.x, 2004Palgy..47.1211M, [W. Kiessling/M. Krause/E. Ito] †Yunnanozoonidae?| image2 = Pteraspis Wiki2.png| image2_caption = Life reconstruction of extinct agnatan genus, Pteraspis }}Agnatha ({{IPAc-en|’|æ|g|n|É™|θ|É™|,_|æ|g|’|n|eɪ|θ|É™}};Shorter Oxford English Dictionary {{etymology|grc|{{wikt-lang|grc|á¼€-}} ({{grc-transl|á¼€-}})|without||{{wikt-lang|grc|γνάθος}} ({{grc-transl|γνάθος}})|jaws}}) is an infraphylumJOURNAL, PLOS One, April 2015, A Higher Level Classification of All Living Organisms, 10.1371/journal.pone.0119248, 4418965, Michael, Ruggiero, Dennis P., Gordon, Thomas M., Orrell, Nicolas, Bailly, 10, 4, e0119248, 25923521, 2015PLoSO..1019248R, free, of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both living (cyclostomes) and extinct (conodonts, anaspids, and ostracoderms) species. Among recent animals, cyclostomes are sister to all vertebrates with jaws, known as gnathostomes.JOURNAL, Heimberg, Alysha M., Cowper-Sal·lari, Richard, Sémon, Marie, Donoghue, Philip C.J., Peterson, Kevin J., 2010-11-09, microRNAs reveal the interrelationships of hagfish, lampreys, and gnathostomes and the nature of the ancestral vertebrate, Proceedings of the National Academy of Sciences, 107, 45, 19379–19383, 10.1073/pnas.1010350107, 2984222, 20959416, free, Molecular data, both from rRNAJOURNAL, Mallatt, J., Sullivan, J., December 1998, 28S and 18S rDNA sequences support the monophyly of lampreys and hagfishes, Molecular Biology and Evolution, 15, 12, 1706–1718, 9866205, 10.1093/oxfordjournals.molbev.a025897, and from mtDNAJOURNAL, Delarbre C, Gallut C, Barriel V, Janvier P, Gachelin G, Complete mitochondrial DNA of the hagfish, Eptatretus burgeri: The comparative analysis of mitochondrial DNA sequences strongly supports the cyclostome monophyly, Molecular Phylogenetics and Evolution, 22, 2, 184–92, February 2002, 11820840, 10.1006/mpev.2001.1045, as well as embryological data,JOURNAL, Oisi Y, Ota KG, Kuraku S, Fujimoto S, Kuratani S, Craniofacial development of hagfishes and the evolution of vertebrates, Nature, 493, 7431, 175–80, January 2013, 23254938, 10.1038/nature11794, 2013Natur.493..175O, 4403344, 20.500.14094/D1005717, free, strongly supports the hypothesis that both groups of living agnathans, hagfishes and lampreys, are more closely related to each other than to jawed fish, forming the clade Cyclostomi.JOURNAL, Janvier, P., MicroRNAs revive old views about jawless vertebrate divergence and evolution, Proceedings of the National Academy of Sciences of the United States of America, 107, 45, 19137–19138, November 2010, 21041649, 2984170, 10.1073/pnas.1014583107, 2010PNAS..10719137J, Although I was among the early supporters of vertebrate paraphyly, I am impressed by the evidence provided by Heimberg et al. and prepared to admit that cyclostomes are, in fact, monophyletic. The consequence is that they may tell us little, if anything, about the dawn of vertebrate evolution, except that the intuitions of 19th century zoologists were correct in assuming that these odd vertebrates (notably, hagfishes) are strongly degenerate and have lost many characters over time., free, The oldest fossil agnathans appeared in the Cambrian, and two groups still survive today: the lampreys and the hagfish, comprising about 120 species in total. Hagfish are considered members of the subphylum Vertebrata, because they secondarily lost vertebrae; before this event was inferred from molecularJOURNAL, Stock, D.W., Whitt, G.S., Evidence from 18S ribosomal RNA sequences that lampreys and hagfishes form a natural group, Science, 257, 5071, 787–9, August 1992, 1496398, 10.1126/science.1496398, 1992Sci...257..787S, and developmentalJOURNAL, Ota KG, Fujimoto S, Oisi Y, Kuratani S, June 2011, Identification of vertebra-like elements and their possible differentiation from sclerotomes in the hagfish, Nature Communications, 2, 6, 373, 21712821, 3157150, 10.1038/ncomms1355, 2011NatCo...2..373O, data, the group Craniata was created by Linnaeus (and is still sometimes used as a strictly morphological descriptor) to reference hagfish plus vertebrates.While a few scientists still regard the living agnathans as only superficially similar, and argue that many of these similarities are probably shared basal characteristics of ancient vertebrates, newer taxonomic studies clearly place hagfish (the Myxini or Hyperotreti) with the lampreys (Hyperoartii) as being more closely related to each other than either is to the jawed fishes.JOURNAL, Stock, D.W., Whitt, G.S., Evidence from 18S ribosomal RNA sequences that lampreys and hagfishes form a natural group, Science, 257, 5071, 787–789, August 1992, 1496398, 10.1126/science.1496398, 1992Sci...257..787S, Metabolism Agnathans are ectothermic, meaning they do not regulate their own body temperature. Agnathan metabolism is slow in cold water, and therefore they do not have to eat very much. They have no distinct stomach, but rather a long gut, more or less homogeneous throughout its length. Lampreys feed on other fish and mammals. Anticoagulant fluids preventing blood clotting are injected into the host, causing the host to yield more blood. Hagfish are scavengers, eating mostly dead animals. They use a row of sharp teeth to break down the animal. The fact that Agnathan teeth are unable to move up and down limits their possible food types. Morphology In addition to the absence of jaws, modern agnathans are characterised by absence of paired fins; the presence of a notochord both in larvae and adults; and seven or more paired gill pouches. Lampreys have a light sensitive pineal eye (homologous to the pineal gland in mammals). All living and most extinct Agnatha do not have an identifiable stomach or any appendages. Fertilization and development are both external. There is no parental care in the Agnatha class. The Agnatha are ectothermic or cold, with a cartilaginous skeleton, and the heart contains 2 chambers. Body covering In modern agnathans, the body is covered in skin, with neither dermal or epidermal scales. The skin of hagfish has copious slime glands, the slime constituting their defense mechanism. The slime can sometimes clog up enemy fishes’ gills, causing them to die. In direct contrast, many extinct agnathans sported extensive exoskeletons composed of either massive, heavy dermal armour or small mineralized scales. Appendages Almost all agnathans, including all extant agnathans, have no paired appendages, although most do have a dorsal or a caudal fin. Some fossil agnathans, such as osteostracans and pituriaspids, did have paired fins, a trait inherited in their jawed descendants.Romer, A.S. & Parsons, T.S. (1985): The Vertebrate Body. (6th ed.) Saunders, Philadelphia. Reproduction Fertilization in lampreys is external. Mode of fertilization in hagfishes is not known. Development in both groups probably is external. There is no known parental care. Not much is known about the hagfish reproductive process. It is believed that hagfish only have 30 eggs over a lifetime.WEB,www.aquaticcommunity.com/mix/hagfish.php, Hagfish, Aquaticcommunity.com, 2013-06-30, There is very little of the larval stage that characterizes the lamprey. Lamprey are only able to reproduce once. After external fertilization, the lamprey’s cloacas remain open, allowing a fungus to enter their intestines, killing them. Lampreys reproduce in freshwater riverbeds, working in pairs to build a nest and burying their eggs about an inch beneath the sediment. The resulting hatchlings go through four years of larval development before becoming adults. Evolution File:Evolution of jawless fish.png|thumb|260px|right|Evolution of jawless fishes. The diagram is based on Michael Benton, 2005.Benton, M. J. (2005) Vertebrate PalaeontologyVertebrate Palaeontology{{See also|Evolution of fish}}Although a minor element of modern marine fauna, agnathans were prominent among the early fish in the early Paleozoic. Two types of Early Cambrian animal apparently having fins, vertebrate musculature, and gills are known from the early Cambrian Maotianshan shales of China: Haikouichthys and Myllokunmingia. They have been tentatively assigned to Agnatha by Janvier. A third possible agnathid from the same region is Haikouella. A possible agnathid that has not been formally described was reported by Simonetti from the Middle Cambrian Burgess Shale of British Columbia. Conodonts, a class of agnathans which arose in the early Cambrian,BOOK, Earth System History, 4th, Macmillan Publishers, Macmillan Education, 2015, 311, Conodonts arose late in the Early Cambrian and diversified into the Ordovician. ... Similar small teeth in very early Cambrian faunas ... may represent conodont ancestors., Steven M., Stanley, John A., Luczaj, remained common enough until their extinction in the Triassic that their teeth (the only parts of them that were usually fossilized) are often used as index fossils from the late Cambrian to the Triassic.JOURNAL, 10.1666/0022-3360(2001)0752.0.CO;2, Sweet, W. C., Donoghue, P. C. J., 2001, Conodonts: past, present and future, Journal of Paleontology, 75, 6, 1174–1184, 53395896, 0022-3360,donoghue.blogs.bristol.ac.uk/files/2019/08/Sweet_Donoghue_2001.pdf, live,web.archive.org/web/20221030162538/https://cpb-eu-w2.wpmucdn.com/blogs.bristol.ac.uk/dist/3/589/files/2019/08/Sweet_Donoghue_2001.pdf, 2022-10-30, Many Ordovician, Silurian, and Devonian agnathans were armored with heavy bony-spiky plates. The first armored agnathans—the Ostracoderms, precursors to the bony fish and hence to the tetrapods (including humans)—are known from the middle Ordovician, and by the Late Silurian the agnathans had reached the high point of their evolution. Most of the ostracoderms, such as thelodonts, osteostracans, and galeaspids, were more closely related to the gnathostomes than to the surviving agnathans, known as cyclostomes. Cyclostomes apparently split from other agnathans before the evolution of dentine and bone, which are present in many fossil agnathans, including conodonts.JOURNAL, Baker CV, The evolution and elaboration of vertebrate neural crest cells, Current Opinion in Genetics & Development, 18, 6, 536–543, December 2008, 19121930, 10.1016/j.gde.2008.11.006, Agnathans declined in the Devonian and never recovered.Approximately 500 million years ago, two types of recombinatorial adaptive immune systems (AISs) arose in vertebrates. The jawed vertebrates diversify their repertoire of immunoglobulin domain-based T and B cell antigen receptors mainly through the rearrangement of V(D)J gene segments and somatic hypermutation, but none of the fundamental AIS recognition elements in jawed vertebrates have been found in jawless vertebrates. Instead, the AIS of jawless vertebrates is based on variable lymphocyte receptors (VLRs) that are generated through recombinatorial usage of a large panel of highly diverse leucine-rich-repeat (LRR) sequences.BOOK, Hirano, Masayuki, Das, Sabyasachi, Guo, Peng, Cooper, Max D., 2011-01-01, Chapter 4 – The Evolution of Adaptive Immunity in Vertebrates, Advances in Immunology, 109, 125–157, Alt, Frederick W., Academic Press, 10.1016/b978-0-12-387664-5.00004-2, 21569914, 9780123876645,www.sciencedirect.com/science/article/pii/B9780123876645000042, 2019-12-03, Three VLR genes (VLRA, VLRB, and VLRC) have been identified in lampreys and hagfish, and are expressed on three distinct lymphocytes lineages. VLRA+ cells and VLRC+ cells are T-cell-like and develop in a thymus-like lympho-epithelial structure, termed thymoids. VLRB+ cells are B-cell-like, develop in hematopoietic organs, and differentiate into “VLRB antibody“-secreting plasma cells.JOURNAL, Wu, Fenfang, Chen, Liyong, Ren, Yong, Yang, Xiaojing, Yu, Tongzhou, Feng, Bo, Chen, Shangwu, Xu, Anlong, October 2016, An inhibitory receptor of VLRB in the agnathan lamprey, Scientific Reports, 6, 1, 33760, 10.1038/srep33760, 27762335, 5071834, 2045-2322, 2016NatSR...633760W, {{clear}} Classification {| class“wikitable“|+ Subgroups of jawless fish

170x170px){{center|hagfish}}

Myxini (hagfish) are eel-shaped slime-producing marine animals (occasionally called slime eels). They are the only known living animals that have a skull but not a vertebral column. The group has gone through the most extensive gene loss of all vertebrates, with 1,386 missing gene families.The hagfish genome and the evolution of vertebrates Along with lampreys, hagfish are jawless and are living fossils; hagfish are Basal (phylogenetics)>basal to vertebrates, and living hagfish remain similar to hagfish 300 million years ago.SPEER >FIRST = BRIAN R.

TITLE = INTRODUCTION TO THE MYXINI

PUBLISHER = UNIVERSITY OF CALIFORNIA, BERKELEY

ACCESS-DATE = 2013-02-21

ARCHIVE-URL = HTTPS://WEB.ARCHIVE.ORG/WEB/20171215173214/HTTP://WWW.UCMP.BERKELEY.EDU/VERTEBRATES/BASALFISH/MYXINI.HTML

lancelets). The original scheme groups hagfish and lampreys together as cyclostomata>cyclostomes (or historically, Agnatha), as the oldest surviving clade of vertebrates alongside gnathostomes (the now-ubiquitous jawed-vertebrates). An alternative scheme proposed that jawed-vertebrates are more closely related to lampreys than to hagfish (i.e., that vertebrates include lampreys but exclude hagfish), and introduces the category craniata to group vertebrates near hagfish. Recent DNA evidence has supported the original scheme.

170x170px){{center|lamprey}}

Hyperoartia is a disputed group of vertebrates that includes the modern lampreys and their fossil relatives. Examples of hyperoartians from early in their fossil record are Endeiolepis and Euphanerops, fish-like animals with hypocercal tails that lived during the Late Devonian Period. Some paleontology>paleontologists still place these forms among the “ostracoderms” (jawless armored “fishes“) of the class (biology)

Anaspida, but this is increasingly considered an artificial arrangement based on plesiomorph>ancestral traits. Placement of this group among the jawless vertebrates is a matter of dispute. While today enough fossil diversity is known to make a close relationship among the “ostracoderms” unlikely, this has muddied the issue of the Hyperoartia’s closest relatives. Traditionally the group was placed in a superclass Cyclostomata together with the Myxini (hagfishes). More recently, it has been proposed that the Myxini are more basal (evolution)

among the Craniata>skull-bearing chordates, while the Hyperoartia are retained among vertebrates. But even though this may be correct, the lampreys represent one of the oldest divergences of the vertebrate lineage, and whether they are better united with some “ostracoderms” in the Cephalaspidomorphi, or not closer to these than to e.g. to other “ostracoderms” of the Pteraspidomorphi, or even the long-extinct conodonts, is still to be resolved. Even the very existence of the Hyperoartia is disputed, with some analyses favoring a treatment of the “basal Hyperoartia” as a monophyletic lineage Jamoytiiformes that may in fact be very close to the ancestral jawed vertebrates.

140px){{center|Haikouichthys}}

Myllokunmingiidae>myllokunmingiids were a primitive order of agnathans that were endemic to the Cambrian aged Maotianshan Shales lagerstätte in China. These creatures are the earliest known group of craniates (chordates with a skull of Bone

or cartilage). Currently the group includes 3 known genera, Haikouichthys, Myllokunmingia, and Zhongjianichthys rostratus>Zhongjianichthys.SHU >FIRST=DEGAN

TITLE=A PALEONTOLOGICAL PERSPECTIVE OF VERTEBRATE ORIGIN

VOLUME=48

PAGES=725–735

DOI=10.1007/BF03187041

YEAR=2016

FAMILY-GROUP NAMES OF FOSSIL FISHES >DOI=10.5852/EJT.2018.466, European Journal of Taxonomy,

154x154px){{center|Panderodus}}

Conodonts were eel like agnathans that lived from the Cambrian up until the beginning of the Jurassic period. They were very diverse in terms of lifestyles, with some species being filter feeders and others being macropredators. For over a century, these animals were only known because of their microscopic, Phosphate>phosphatic tooth structures called “Conodont elements”. It wasn’t until the mid-1980s that body fossils of conodonts were found in Scotland and Wisconsin, showing these animals true appearance. Their teeth make great index fossils, as many species lived and died out in a relatively short period of time. These fish reached their peak in diversity during the middle of the Ordovician, but were hit hard by the Late Ordovician mass extinction

event. They then reached another spike in diversity in the Devonian>mid-late Devonian before again declining in the Carboniferous. They were relatively rare in the Permian, but dramatically increased in numbers in the early Triassic. Despite this, they went extinct during the lower Jurassic period, with some of the last surviving populations being in Japan. They possibly survived longer there due to the relative remoteness of the area. Originally, it was thought that they were wiped out by the Triassic–Jurassic extinction event

at the end of the Triassic. Instead, it is now thought that they were out competed by newer Mesozoic taxa.SWEET, WALTER C.

DATE=DECEMBER 2008

URL=HTTPS://WWW.RESEARCHGATE.NET/PUBLICATION/286568271

DOI=10.18814/EPIIUGS/2008/V31I4/009, GABBOTT >FIRST=S.E.

AUTHOR3=J. N. THERON

TITLE=A GIANT CONODONT WITH PRESERVED MUSCLE TISSUE FROM THE UPPER ORDOVICIAN OF SOUTH AFRICA

VOLUME=374

PAGES=800–803

DOI=10.1038/374800A0

YEAR=2016

JOURNAL=CHEMICAL GEOLOGY

PAGES=36–43

DOI=10.1016/J.CHEMGEO.2016.03.023, BERGSTRöM >FIRST1=S. M.

FIRST2=J. B.

FIRST3=R. L.

FIRST4=R. B.

FIRST5=P. B.

TITLE=APPALACHIGNATHUS, A NEW MULTIELEMENT CONODONT GENUS FROM THE MIDDLE ORDOVICIAN OF NORTH AMERICA

VOLUME=48

PAGES=227–235

JSTOR=1303249

LAST2=GOUDEMAND

DATE=DECEMBER 2020

JOURNAL=GLOBAL AND PLANETARY CHANGE

VOLUME=195

BIBCODE=2020GPC...19503325G

S2CID=225005180

URL=HTTPS://UNIV-LYON1.HAL.SCIENCE/HAL-02996040/FILE/S0921818120302162.PDF, DU >FIRST1=YIXING

FIRST2=TETSUJI

FIRST3=YUKI

FIRST4=QIANGWANG

FIRST5=MANUEL

TITLE=LOWER JURASSIC CONODONTS FROM THE INUYAMA AREA OF JAPAN: IMPLICATIONS FOR CONODONT EXTINCTION

VOLUME=11

ISSN=2296-701X

HDL=11577/3479836, free,

170x170px){{center|Astraspis}}| †Pteraspidomorphi is an extinct group of early jawless fish. The fossils show extensive shielding of the head. Many had hypocercal tails in order to generate lift to increase ease of movement through the water for their armoured bodies, which were covered in dermal bone. They also had sucking mouth parts and some species may have lived in fresh water.The taxon contains the subgroups Heterostraci, Astraspida, Arandaspida.

140px)

Thelodonti (nipple teeth) are a group of small, extinct jawless fishes with distinctive scales instead of large plates of armour. There is much debate over whether the group of Palaeozoic fish known as the Thelodonti (formerly coelolepidsTURNER S, TARLING DH

TITLE=THELODONT AND OTHER AGNATHAN DISTRIBUTIONS AS TESTS OF LOWER PALEOZOIC CONTINENTAL RECONSTRUCTIONS

PALAEOGEOGRAPHY, PALAEOCLIMATOLOGY, PALAEOECOLOGY >VOLUME=39

DOI=10.1016/0031-0182(82)90027-X

BIBCODE=1982PPP....39..295T, ) represent a Monophyly

, or disparate stem groups to the major lines of jawless and Gnathostome>jawed fish. Thelodonts are united in possession of “thelodont scales”. This defining character is not necessarily a result of shared ancestry, as it may have been Convergent evolution

. Thus the thelodonts are generally thought to represent a polyphyletic group,VERTEBRATE FOSSILS AND THE EVOLUTION OF SCIENTIFIC CONCEPTS: WRITINGS IN TRIBUTE TO BEVERLY HALSTEAD

VAUTHORS = SARJEANT WA, HALSTEAD LB

PUBLISHER = GORDON AND BREACH

JOURNAL = BIOLOGICAL REVIEWS OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY

ISSUE = 2

DATE = MAY 2000

DOI = 10.1111/J.1469-185X.1999.TB00045.X

206}} “Thelodonts” were morphologically very similar, and probably closely related, to fish of the classes Heterostraci and Anaspida, differing mainly in their covering of distinctive, small, spiny scales. These scales were easily dispersed after death; their small size and resilience makes them the most common vertebrate fossil of their time.TURNER S >YEAR=1999

EDITOR1=A. J. BOUCOT

TITLE=PALAEOCOMMUNITIES – PROJECT ECOSTRATIGRAPHY, FINAL REPORT

VOLUME=53

CAMBRIDGE UNIVERSITY PRESS >PAGES=42–78, The early and mid Silurian. See KAZLEV MA, WHITE T >TITLE=THELODONTI

DATE=MARCH 6, 2001

URL-STATUS=DEAD

ARCHIVE-URL=HTTPS://WEB.ARCHIVE.ORG/WEB/20071028153634/HTTP://WWW.PALAEOS.COM/VERTEBRATES/UNITS/050THELODONTI/050.100.HTML#THELODONTI

Ordovician, and perishing during the Late Devonian extinction>Frasnian–Famennian extinction event of the Late Devonian. They occupied a large variety of ecological niches, with a large amount of species preferring reef ecosystems, where their flexible bodies were more at ease than the heavily armoured bulks of other jawless fish.FERRóN HG, BOTELLA H > TITLE = SQUAMATION AND ECOLOGY OF THELODONTS

VOLUME = 12

PAGE = E0172781

PMID = 28241029

DOI = 10.1371/JOURNAL.PONE.0172781

DOI-ACCESS = FREE,

140px)

Anaspida (without shield) is an extinct group of primitive jawless vertebrates that lived during the Silurian and Devonian periods.AHLBERG

NAME-LIST-STYLE = VANC

PUBLISHER=TAYLOR & FRANCIS

YEAR=2001

URL=HTTPS://BOOKS.GOOGLE.COM/BOOKS?ID=ZEYRZNZL-74C&PG=PA188

TITLE=MOLECULES AND MORPHOLOGY IN EVOLUTION: CONFLICT OR COMPROMISE?

LOCATION=CAMBRIDGE, UK

ISBN=978-0-521-32271-3

PAGE= 142, Anaspids were small marine agnathans that lacked heavy bony shield and paired fins, but have a striking highly hypocercal tail. They first appeared in the Llandovery epoch

, and flourished until the Late Devonian extinction,HALL

LAST2 = HANKEN

AUTHOR2-LINK=JAMES HANKEN

PUBLISHER=UNIVERSITY OF CHICAGO PRESS

YEAR=1993

URL= HTTPS://BOOKS.GOOGLE.COM/BOOKS?ID=FB-HO7I50ESC&PG=PA131, 131, where most species, save for lampreys, became extinct due to the environmental upheaval during that time.

226x226px){{center

Thyestes (fish)>Thyestes}}

Cephalaspidomorphi is a broad group of extinct armored agnathans found in Silurian and Devonian strata of North America, Europe, and China, and is named in reference to the osteostraci>osteostracan genus Cephalaspis. Most biologists regard this taxon as extinct, but the name is sometimes used in the classification of lampreys, as lampreys are sometimes thought to be related to cephalaspids. If lampreys are included, they would extend the known range of the group from the early Silurian period through the Mesozoic, and into the present day. Cephalaspidomorphi were, like most contemporary fish, very well armoured. Particularly the head shield was well developed, protecting the head, gills and the anterior section of the innards. The body was in most forms well armoured as well. The head shield had a series of grooves over the whole surface forming an extensive lateral line organ. The eyes were rather small and placed on the top of the head. There was no proper jaw. The mouth opening was surrounded by small plates making the lips flexible, but without any ability to bite.COLBERT >FIRST1=MICHAEL

FIRST2=EDWIN H.

TITLE=EVOLUTION OF THE VERTEBRATES : A HISTORY OF THE BACKBONED ANIMALS THROUGH TIME

PUBLISHER=WILEY-LISS

ISBN=978-0-471-85074-8, Undisputed subgroups traditionally contained with Cephaloaspidomorphi, also called “Monorhina”, include the classes Osteostraci, Galeaspida, and Pituriaspida

Groups

{{See also|Placodermi#Cladogram}}Phylogeny based on the work of Mikko Haaramo and Delsuc et al.WEB, Haaramo, Mikko, 2007, Chordata – lancets, tunicates, and vertebrates, Mikko’s Phylogeny Archive,www.helsinki.fi/~mhaaramo/metazoa/deuterostoma/chordata/chordata.html#Vertebrata, 30 December 2016, JOURNAL, Delsuc F, Philippe H, Tsagkogeorga G, Simion P, Tilak MK, Turon X, López-Legentil S, Piette J, Lemaire P, Douzery EJ, April 2018, A phylogenomic framework and timescale for comparative studies of tunicates, BMC Biology, 16, 1, 39, 29653534, 5899321, 10.1186/s12915-018-0499-2, free, {hide}clade|{{clade|label1=Cyclostomata|1={{clade {edih} While the “agnatha” Conodonta was indeed jawless, if it would have continued to live, its descendants would still be closer related to e.g. humans than to lampreys, and also contempory it was closer related to the ancestor of humans. Due to such considerations, Agnatha can not be consolidated into a coherent grouping without either removing any non-cyclostomata, or by including all vertebrata thus rendering it into a junior synonym of vertebrata.The new phylogeny from Miyashita et al. (2019) is considered compatible with both morphological and molecular evidence.JOURNAL, Tetsuto, Miyashita, Michael I., Coates, Robert, Farrar, Peter, Larson, Phillip L., Manning, Roy A., Wogelius, Nicholas P., Edwards, Jennifer, Anné, Uwe, Bergmann, A. Richard, Palmer, Philip J., Currie, 6, 2019, Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological–molecular conflict in early vertebrate phylogeny, Proceedings of the National Academy of Sciences of the United States of America, 116, 6, 2146–2151, 10.1073/pnas.1814794116, 30670644, 6369785, 2019PNAS..116.2146M, free, {{cladelabel1=Agnatha |top1=45%}}|1={{clade }} }} }} }} }} }} }}|style=font-size:85%;line-height:85%;|label1=Vertebrata/|sublabel1=Craniata|subcladeA={{clade hidden |id=1 |mode=left }}|targetA={Anaspidomorphi}|targetB={Conodonta}|subcladeB={hide}clade hidden |id=2 |mode=left }}|targetC={Pteraspidomorphi}|subcladeC={{clade hidden |id=3 |mode=left }}}}

See also

• Gnathostomata
• Amphirhina, an alternate name for the above parallel, or sister, classification
• Cyclostomata

References

{{Wikispecies|position=left|Agnatha}}{{Reflist|25em}}{{Chordata}}{{Evolution of fish}}{{Taxonbar|from=Q161095}}{{Authority control}}