# Librostoma > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Librostoma > Markdown URL: https://mediated.wiki/source/Librostoma.md > Source: https://en.wikipedia.org/wiki/Librostoma > Source revision: 1354675162 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Short description|Extinct subclass of trilobites}} {{Automatic taxobox | image = Asaphus.jpg | image_caption = ''[Asaphus lepidurus](/source/Asaphus_lepidurus)'' | fossil_range = {{Fossil range|Cambrian series 2|Lopingian}} | taxon = Librostoma | authority = [Fortey](/source/Richard_Fortey), 1990Ontogeny, hypostome attachment and trilobite classification. RA Fortey, Palaeontology, 1990 | subdivision_ranks = Orders | subdivision = * {{Extinct}}[Asaphida](/source/Asaphida) * {{Extinct}}[Harpetida](/source/Harpetida) *{{Extinct}}[Phacopida](/source/Phacopida)?{{Efn|Two primitive calymenines, ([Pharostomina](/source/Pharostomina) and [Bavarilla](/source/Bavarilla)), had natant hypostomes, suggesting that the Cambrian sister taxon is likely also natant, making them Librostomes.}} * {{Extinct}}[Proetida](/source/Proetida) * {{Extinct}}[Ptychopariida](/source/Ptychopariida) * {{Extinct}}[Trinucleida](/source/Trinucleida)?(proposed){{cite journal |last1=Bignon |first1=Arnaud |last2=Waisfield |first2=Beatriz G. |last3=Vaccari |first3=Emilio |last4=Chatterton |first4=Brian D. E. |title=Reassessment of the Order Trinucleida (Trilobita) |date=2020 |url=https://www.tandfonline.com/doi/abs/10.1080/14772019.2020.1720324 |journal=[Journal of Systematic Palaeontology](/source/Journal_of_Systematic_Palaeontology) |volume=18 |issue=13 |pages=1061–1077 |doi=10.1080/14772019.2020.1720324|bibcode=2020JSPal..18.1061B |s2cid=212995185 |url-access=subscription |hdl=11336/145642 |hdl-access=free }} }} '''Librostoma''' is a subclass of [trilobite](/source/trilobite)s defined by having a natant hypostome, which is a [hypostome](/source/Hypostome_(trilobite)) (mineralized trilobite mouthpart) that is free from the anterior doublure and aligned with the anterior of the glabella,{{cite web |title=The Hypostome |url=https://trilobites.info/hypoterms.htm}} this is unlike a conterminant hypostome, which is attached to the exoskeleton.{{cite web |last1=Whittington |first1=H. B. |title=Reflections on the Classification of the Trilobita |url=https://www.researchgate.net/publication/256082447 |publisher=[University of Cambridge](/source/University_of_Cambridge)}} They are a large and long lasting group, with some of the candidates for the first trilobites being librostomes in the [order](/source/Order_(biology)) [Ptychopariida](/source/Ptychopariida); and all post-[Devonian](/source/Devonian){{Efn|Arguably all Post-Frasnian triobites as phacopids are cladistically included}} trilobites being in the order [Proetida](/source/Proetida), who are librostomes. ==Taxonomy== File:Cummingella belisama dorsal light2 CRF.jpg|''[Cummingella](/source/Cummingella) belisama'', a [Phillipsiid](/source/Phillipsiidae) [Proetid](/source/Proetida) from the [Carboniferous](/source/Carboniferous). File:Harpes perradiatus fossil trilobite (Devonian, Morocco).jpg|''[Harpes](/source/Harpes) perridatus'', a [Harpetid](/source/Harpetida) from the [Devonian](/source/Devonian) of Morocco. File:ElrathiaKingi.jpg| [''Elrathia kingii''](/source/Elrathia_kingii), a ptychopariid from the [Middle cambrian](/source/Miaolingian) Librostomes make up a large component of the [Trilobita](/source/Trilobita). Traditionally, four orders are placed in the Librostoma; they are the: [Asaphida](/source/Asaphida), [Harpetida](/source/Harpetida), [Proetida](/source/Proetida), and [Ptychopariida](/source/Ptychopariida); however, two primitive [phacopids](/source/Phacopida) (''[Pharostomina](/source/Pharostomina)'' and ''[Bavarilla](/source/Bavarilla)'') have natant hypostomes, indicating that the phacopids are also librostomes.{{cite web |title=Phacopida fact sheet |url=https://trilobites.info/ordphacopida.htm |website=trilobites.info}} In more recent publications, the asaphid superfamily [Trinucleioidea](/source/Trinucleioidea) is placed in its own order, Trinucleida,{{cite journal |last1=Bignon |first1=Arnaud |last2=Waisfield |first2=Beatriz G. |last3=Vaccari |first3=Emilio |last4=Chatterton |first4=Brian D. E. |title=Reassessment of the Order Trinucleida (Trilobita) |date=2020 |url=https://www.tandfonline.com/doi/abs/10.1080/14772019.2020.1720324 |journal=[Journal of Systematic Palaeontology](/source/Journal_of_Systematic_Palaeontology) |volume=18 |issue=13 |pages=1061–1077 |doi=10.1080/14772019.2020.1720324|bibcode=2020JSPal..18.1061B |s2cid=212995185 |url-access=subscription |hdl=11336/145642 |hdl-access=free }}{{cite web |title=Trilobite order Trinucleioidea |url=https://trilobites.info/ordtrinucleida.htm |website=trilobites.info}} however, even some more recent studies recover them as asaphids.{{Cite journal |last1=Beech |first1=James D. |last2=Bottjer |first2=David J. |last3=Smith |first3=Nathan D. |date=2024-10-15 |title=Parallel evolution of unusual 'harpiform' morphologies in distantly related trilobites |journal=Journal of Paleontology |volume=98 |issue=4 |language=en |pages=732–743 |doi=10.1017/jpa.2024.47 |bibcode=2024JPal...98..732B |issn=0022-3360|doi-access=free }} Some librostomes [may not even be within the group](/source/Polyphyly), with [Whittington](/source/Harry_B._Whittington) (2003) placing some genera (''[Hemibarrandia](/source/Hemibarrandia)'', ''[Lakaspis](/source/Lakaspis)'', ''[Peraspis](/source/Peraspis)'' and ''[Symphysurina](/source/Symphysurina)'') of the asaphid family [Nileidae](/source/Nileidae) in the order [Corynexochida](/source/Corynexochida).{{cite journal |last1=Whittington |first1=Harry B. |date=2003 |title=The trilobite family Nileidae: morphology and classification |journal=[Palaeontology](/source/Palaeontology_(journal)) |volume=46 |issue=4 |pages=635–646 |bibcode=2003Palgy..46..635W |doi=10.1111/1475-4983.00313 |doi-access=free}} ==Evolution == ===Origins=== The first librostomes were [ellipsocephaloid](/source/Ellipsocephaloidea) [ptychopariids](/source/Ptychopariida) in the [family](/source/Family_(taxonomy)) [Bigotinidae](/source/Bigotinidae) from the early [Cambrian](/source/Cambrian).{{cite web |title=The earliest trilobites |url=https://www.trilobites.info/firsttrilos.htm}} This group was once thought to be in the order [Redlichiida](/source/Redlichiida), but are now considered primitive Ptychopariida. ===Evolutionary history=== File:Asaphus kowalewskii 3.jpg|[''Asaphus kowalewskii''](/source/Asaphus) from the [Ordovician](/source/Ordovician) of [Russia](/source/Russia). File:Opipeuterella swimming.png|[''Opipueterella''](/source/Opipueterella) is a genus of swimming trilobite in the family [Telephinidae](/source/Telephinidae); order [Proetida](/source/Proetida). File:Ampyx cetsarum - specimen number MGL 96718 - white (cropped).jpg|[''Ampyx''](/source/Ampyx_(trilobite)), An [Ordovician](/source/Ordovician) [trinucleioid](/source/Trinucleioidea). these trilobites may have gone in single-file lines from deeper water to shallow water at night, mirroring modern [Spiny lobster](/source/Spiny_lobster)s. During the Middle Cambrian, the Ptychopariida became the dominant trilobites. Around that time, the [Asaphida](/source/Asaphida) and [Trinucleida](/source/Trinucleioidea) would first appear. The first [Harpetida](/source/Harpetida) would appear in the [Late Cambrian](/source/Furongian) with the primitive genera ''[Baikadamaspis](/source/Baikadamaspis)'' and ''[Entomaspis](/source/Entomaspis)'' of the family [Entomaspididae](/source/Entomaspididae). The first [Proetida](/source/Proetida) appeared during the Cambrian-[Ordovician](/source/Ordovician) transition. Since the earliest [Phacopida](/source/Phacopida) (which are most likely librostomes) appeared during the early ordovician, it is assumed that a late cambrian sister taxon was present. During the [Ordovician](/source/Ordovician), the Ptychopariida declined. After the decline of the Ptychopariida, the order [Asaphida](/source/Asaphida) rose to prominence, becoming the dominant order of trilobites by the end of the mid-ordovician. [[File:Triarthrus eatoni ventral cropped.jpg|thumb|[Triarthrus eatoni](/source/Triarthrus_eatoni), one of the last ptychopariids.]] The [End-Ordovician extinction event](/source/End-Ordovician_extinction_event) would drastically reduce trilobite diversity, with librostomes included. The already endangered Ptychopariida would go extinct. All trilobites with [plankton](/source/plankton)ic or [nekton](/source/nekton)ic life stages would go extinct,{{Cite journal |last1=Chatterton |first1=Brian D. E. |last2=Speyer |first2=Stephen E. |date=April 1989 |title=Larval ecology, life history strategies, and patterns of extinction and survivorship among Ordovician trilobites |url=https://www.cambridge.org/core/journals/paleobiology/article/abs/larval-ecology-life-history-strategies-and-patterns-of-extinction-and-survivorship-among-ordovician-trilobites/ABD0735C7F5312639FE775B71FA7D087 |journal=Paleobiology |language=en |volume=15 |issue=2 |pages=118–132 |doi=10.1017/S0094837300009313 |bibcode=1989Pbio...15..118C |issn=0094-8373|url-access=subscription }} which included the swimming Proetida family [Telephinidae](/source/Telephinidae), and all asaphids & trinucleids except for the [raphiophorid](/source/Raphiophoridae) ''[Raphiophorus](/source/Raphiophorus)'', which would go extinct shortly after in the [Silurian](/source/Silurian). ==Diversity== Librostomes occupied many [niches](/source/Ecological_niche), sizes, and ecologies. Both some of the largest (Ordovician asaphids ''[Isotelus](/source/Isotelus) rex'', and ''[Hungioides](/source/Hungioides)'') and smallest trilobites (Ordovician ptychopariid ''[Acanthopleurella](/source/Acanthopleurella) stipulae'') are librostomes.{{Citation |last1=Forli |first1=Maurizio |title=Scorpions, Ants, and Other Stone Insects. The Understanding of Trilobites Over the Centuries |date=2022 |work=The History of Fossils Over Centuries: From Folklore to Science |pages=417–442 |editor-last=Forli |editor-first=Maurizio |url=https://link.springer.com/chapter/10.1007/978-3-031-04687-2_23 |access-date=2024-10-01 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-031-04687-2_23 |isbn=978-3-031-04687-2 |last2=Guerrini |first2=Andrea |editor2-last=Guerrini |editor2-first=Andrea|url-access=subscription }} Many trilobites in the group had some ability to stay above the sea floor, such as asaphids in the superfamilies [Cyclopygoidea](/source/Cyclopygoidea) and [Remopleuroidea](/source/Remopleuroidea),{{Cite journal |last1=Esteve |first1=Jorge |last2=López-Pachón |first2=Matheo |date=2023-09-01 |title=Swimming and feeding in the Ordovician trilobite Microparia speciosa shed light on the early history of nektonic life habits |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=625 |article-number=111691 |doi=10.1016/j.palaeo.2023.111691 |bibcode=2023PPP...62511691E |issn=0031-0182|doi-access=free }}{{Cite journal |last1=Shiino |first1=Yuta |last2=Kuwazuru |first2=Osamu |last3=Suzuki |first3=Yutaro |last4=Ono |first4=Satoshi |last5=Masuda |first5=Chihiro |date=2014-06-01 |title=Pelagic or benthic? Mode of life of the remopleuridid trilobite Hypodicranotus striatulus. {{!}} EBSCOhost |url=https://openurl.ebsco.com/EPDB:gcd:1:9925153/detailv2?sid=ebsco:plink:scholar&id=ebsco:gcd:96213802&crl=c |access-date=2024-10-01 |website=openurl.ebsco.com |volume=89 |issue=2 |page=207 |doi=10.3140/bull.geosci.1409 |language=en}} proetids in the family [Telephinidae](/source/Telephinidae), and perhaps some [Cheirurid](/source/Cheiruridae) phacopids such as [Deiphon](/source/Deiphon) and [Crotalocephalus](/source/Crotalocephalus). The Asaphida, Ptychopariida (and Phacopida if included) are some of the most morphologically and taxonomically diverse orders of Trilobites. Meanwhile, the Proetida and Harpetida had a more modest morphological diversity; the former, sometimes referred to as "garden variety trilobites",{{Cite journal |last1=Lieberman |first1=Bruce S. |last2=Karim |first2=Talia S. |date=2010-03-01 |title=Tracing the trilobite tree from the root to the tips: A model marriage of fossils and phylogeny |url=https://www.sciencedirect.com/science/article/abs/pii/S1467803909000565 |journal=Arthropod Structure & Development |series=Fossil Record and Phylogeny of the Arthropoda |volume=39 |issue=2 |pages=111–123 |doi=10.1016/j.asd.2009.10.004 |bibcode=2010ArtSD..39..111L |issn=1467-8039|url-access=subscription }} containing [the most diverse family of trilobites in terms of genera](/source/Proetidae), and the latter being more modest in both terms of diversity. == See also == * [Agnostida](/source/Agnostida) * [Artiopoda](/source/Artiopoda) * [Trilobita](/source/Trilobita) * [Triops](/source/Triops) * [Redlichiida](/source/Redlichiida) ==Notes== {{Notelist}} == References == {{Reflist}} ==External links== * https://trilobites.info/Trilobites.info A guide to the orders of trilobites {{Trilobites}} {{Taxonbar|from=Q15587047}} Category:Librostoma Category:Arthropod subclasses Category:Prehistoric arthropod taxa Category:Fossil taxa described in 1990 Category:Cambrian Series 2 first appearances Category:Lopingian extinctions --- Adapted from the Wikipedia article [Librostoma](https://en.wikipedia.org/wiki/Librostoma) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Librostoma?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.