The osteostracans reconstructed here belong to the major clade Cornuata, whose generalised morphology is exemplified by the zenaspididZenaspis (bottom left). Some highly derived head-shield morphologies are exemplified by the benneviaspididsHoelaspis (top right) and Tauraspis (top left), or the thyestiidTremataspis (bottom right). The latter has lost the paired fins, possibly as a consequence of an adaptation to burrowing habits.[2]
Anatomically speaking, the osteostracans, especially the Devonian species, were among the most advanced of all known agnathans. This is due to the development of paired fins, and their complicated cranial anatomy. The osteostracans were more similar to lampreys than to jawed vertebrates in possessing two pairs of semicircular canals in the inner ear, as opposed to the three pairs found in the inner ears of jawed vertebrates. They are thought to be the sister-group to pituriaspids, and together, these two taxa of jawless vertebrates are the sister-group of gnathostomes. Several synapomorphies support this hypothesis, such as the presence of: sclerotic ossicles, paired pectoral fins, a dermal skeleton with three layers (a basal layer of isopedin, a middle layer of spongy bone, and a superficial layer of dentin), and perichondral bone.[3]
Most osteostracans had a massive cephalothorac shield, but all Middle and Late Devonian species appear to have had a reduced, thinner, and often micromeric dermal skeleton. This reduction may have occurred at least three times independently because the pattern of reduction is different in each taxon.[4] The largest known osteostracan is Parameteoraspis, its crescent-shaped headshield was 35 to 40 cm wide.[5]
They were probably relatively good swimmers, possessing dorsal fins, paired pectoral fins, and a strong tail. The shield of bone covering the head formed a single piece, and so presumably did not grow during adult life. However, the way in which the bone was laid down makes it possible to examine the imprints of nerves and other soft tissues. This reveals the presence of complex sensory organs and the sides and upper surface of the head, which may have been used to sense vibrations.[6]
^Sansom, Robert S.; Randle, Emma; Donoghue, Philip C. J. (February 7, 2015). "Discriminating signal from noise in the fossil record of early vertebrates reveals cryptic evolutionary history". Proceedings of the Royal Society B. 282 (1800): 20142245. doi:10.1098/rspb.2014.2245. PMC4298210. PMID 25520359.
^ abSansom, R. S. (2009). "Phylogeny, classification and character polarity of the Osteostraci (Vertebrata)". Journal of Systematic Palaeontology. 7: 95–115. doi:10.1017/S1477201908002551.
^Otto, M.; Laurin, M. (2001). "Microanatomy of the dermal skeleton of Balticaspis latvica (Osteostraci, Middle Devonian)". Journal of Vertebrate Paleontology. 21 (1): 186–189. doi:10.1671/0272-4634(2001)021[0186:motdso]2.0.co;2.
^"Cephalaspidomorphi: Cornuata". palaeos.com. from the original on April 7, 2023.
^Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 24. ISBN978-1-84028-152-1.
Referencesedit
Janvier, Philippe. Early Vertebrates Oxford, New York: Oxford University Press, 1998. ISBN0-19-854047-7
Long, John A. The Rise of Fishes: 500 Million Years of Evolution Baltimore: The Johns Hopkins University Press, 1996. ISBN0-8018-5438-5
External linksedit
March 15, 2024
osteostraci, class, meaning, bony, shells, extinct, taxon, bony, armored, jawless, fish, termed, ostracoderms, that, lived, what, north, america, europe, russia, from, middle, silurian, late, devonian, temporal, range, wenlock, late, devonian, preꞒ, ncephalasp. The class Osteostraci meaning bony shells is an extinct taxon of bony armored jawless fish termed ostracoderms that lived in what is now North America Europe and Russia from the Middle Silurian to Late Devonian OsteostraciTemporal range Wenlock 1 Late Devonian 433 359 Ma PreꞒ Ꞓ O S D C P T J K Pg NCephalaspis speciesScientific classificationDomain EukaryotaKingdom AnimaliaPhylum ChordataSubphylum VertebrataClass OsteostraciLankester 1868OrdersZenaspidaBenneviaspididaThyestiidaSynonymsOsteostracida CephalaspidiformesThe osteostracans reconstructed here belong to the major clade Cornuata whose generalised morphology is exemplified by the zenaspidid Zenaspis bottom left Some highly derived head shield morphologies are exemplified by the benneviaspidids Hoelaspis top right and Tauraspis top left or the thyestiid Tremataspis bottom right The latter has lost the paired fins possibly as a consequence of an adaptation to burrowing habits 2 Anatomically speaking the osteostracans especially the Devonian species were among the most advanced of all known agnathans This is due to the development of paired fins and their complicated cranial anatomy The osteostracans were more similar to lampreys than to jawed vertebrates in possessing two pairs of semicircular canals in the inner ear as opposed to the three pairs found in the inner ears of jawed vertebrates They are thought to be the sister group to pituriaspids and together these two taxa of jawless vertebrates are the sister group of gnathostomes Several synapomorphies support this hypothesis such as the presence of sclerotic ossicles paired pectoral fins a dermal skeleton with three layers a basal layer of isopedin a middle layer of spongy bone and a superficial layer of dentin and perichondral bone 3 Most osteostracans had a massive cephalothorac shield but all Middle and Late Devonian species appear to have had a reduced thinner and often micromeric dermal skeleton This reduction may have occurred at least three times independently because the pattern of reduction is different in each taxon 4 The largest known osteostracan is Parameteoraspis its crescent shaped headshield was 35 to 40 cm wide 5 They were probably relatively good swimmers possessing dorsal fins paired pectoral fins and a strong tail The shield of bone covering the head formed a single piece and so presumably did not grow during adult life However the way in which the bone was laid down makes it possible to examine the imprints of nerves and other soft tissues This reveals the presence of complex sensory organs and the sides and upper surface of the head which may have been used to sense vibrations 6 Contents 1 Phylogeny 2 Notes 3 References 4 External linksPhylogeny edit nbsp Parameteoraspis fossilized headshieldBelow is a cladogram showing the phylogenetic relationships of osteostracans from Sansom 2009 3 Osteostraci Ateleaspididae HirellaAceraspisAteleaspisHemicyclaspisCephalaspisZenaspida SpangenhelmaspisWladysagittaParameteoraspididae ParameteoraspisBalticaspisTrewiniaEscuminaspisLevesquaspisZenaspididae TegaspisStensiopeltaDiademaspisZenaspisScolenaspisUkrainaspisMachairaspisSuperciliaspisPattenaspisZychaspisHildenaspisMimetaspisWaengsjoeaspisCamptaspisYvonaspisBenneviaspidida EctinaspisSecuriaspis Benneviaspis longicornis Benneviaspis anglica Benneviaspis lankesteriBenneviaspisBoreaspidoidei HoelaspisSeveraspis Boreaspis ceratops Boreaspis intermediaBoreaspisDicranaspisSpatulaspisBelonaspisHapilaspisTauraspisThyestiida IlemoraspisProcephalaspisAuchenaspisThyestesWitaaspisTremataspidoidea SaaremaspisTyriaspisAestiaspisDartmuthiaTimanaspisOeselaspisTremataspisDobraspisSclerodusTannuaspisKiaeraspidoidea DidymaspisKiaeraspisNorselaspisNectaspisAxinaspisAcrotomaspisGustavaspisNotes edit Sansom Robert S Randle Emma Donoghue Philip C J February 7 2015 Discriminating signal from noise in the fossil record of early vertebrates reveals cryptic evolutionary history Proceedings of the Royal Society B 282 1800 20142245 doi 10 1098 rspb 2014 2245 PMC 4298210 PMID 25520359 Janvier Philippe 1997 Osteostraci The Tree of Life Web Project a b Sansom R S 2009 Phylogeny classification and character polarity of the Osteostraci Vertebrata Journal of Systematic Palaeontology 7 95 115 doi 10 1017 S1477201908002551 Otto M Laurin M 2001 Microanatomy of the dermal skeleton of Balticaspis latvica Osteostraci Middle Devonian Journal of Vertebrate Paleontology 21 1 186 189 doi 10 1671 0272 4634 2001 021 0186 motdso 2 0 co 2 Cephalaspidomorphi Cornuata palaeos com Archived from the original on April 7 2023 Palmer D ed 1999 The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals London Marshall Editions p 24 ISBN 978 1 84028 152 1 References editJanvier Philippe Early Vertebrates Oxford New York Oxford University Press 1998 ISBN 0 19 854047 7 Long John A The Rise of Fishes 500 Million Years of Evolution Baltimore The Johns Hopkins University Press 1996 ISBN 0 8018 5438 5External links editNatural History of Vertebrates Lecture Notes Chapter 3 Jawless Vertebrates and the Origin of Jawed Vertebrates Retrieved from https en wikipedia org w index php title Osteostraci amp oldid 1199088290, wikipedia, wiki, book, books, library,
