This article is about the trilobite structure. For other organisms, see Hypostome.
The hypostome is the hard mouthpart of trilobites found on the ventral side of the cephalon (head). The hypostome can be classified into three types based on whether they are permanently attached to the rostrum or not and whether they are aligned to the anterior dorsal tip of the glabella.
A partially complete, forked, conterminant hypostome of the trilobiteIsotelus (Ordovician of southern Ohio).
The center of the hypostome is an ovoid, typically convex part called the median body, often divided into an anterior lobe and a posterior lobe. Either side of the median body is a border with various extensions, including anterior and posterior wings, sometimes bearing knob-like processes. The hypostome is hollow, and encloses the mouthparts, the anterior digestive tract, and the bases of the antennae. Trilobite antennae pass through notches between the anterior and posterior wings, then forward. The anterior wings are designed to rest firmly against internal structures (ventral apodemes) on the glabella.[1]
Variation in trilobite hypostome morphology is crucial in modern discussions of trilobite phylogeny.[2][3] Functional interpretations of hypostome shape also allow for reasonable speculation on the feeding habits of trilobite species.[4]
Typesedit
Although hypostome morphology is highly variable, three broad types are generally recognized:
Trilobite hypostome types (in blue)
Natantedit
A natant hypostome is not attached to the anterior doublure, with support assumed to be provided by a non-mineralised membrane. Natant hypostomes appear to have been conservative over the course of the evolution of trilobites[2] with overall form and shape of a simple ovoid without posterior extensions or ornamentation.[1] Natant hypostomes are thought to be ancestral to other hypostome forms[2] and thought to belong to trilobites with generalized particle feeding habits (i.e. little need to modify mouth-parts to deal with specialized food items).[4]
Conterminantedit
A conterminant hypostome is attached to the anterior doublure, aligned with the front edge of the glabella and found on trilobites thought of as predators. Anchoring the hypostome against the anterior doublure and cephalon provides structural bracing against which to tear apart prey. Different specializations of hypostome form might reflect different kinds of prey, or different feeding behaviors.[4]
Impendentedit
An impendent hypostome is attached to the anterior doublure but not aligned with the front edge of the glabella. Many impendent hypostomes have prongs, grooves and other adaptations thought to relate to feeding on complex food sources.[4]
^ abWhittington, H.B. (1997a), "Morphology of the Exoskeleton.", in Kaesler, R.L. (ed.), Treatise on Invertebrate Paleontology, Part O, Arthropoda 1, Trilobita, revised. Volume 1: Introduction, Order Agnostida, Order Redlichiida., Boulder, CO & Lawrence, KA: The Geological Society of America, Inc. & The University of Kansas, pp. 1–85, ISBN0-8137-3115-1
^ abcFortey, R.A. (1990), (PDF), Palaeontology, 33 (3): 529–576, archived from the original (PDF) on 2009-03-26
^Fortey, RA (2001), "Trilobite systematics: The last 75 years", Journal of Paleontology, 75 (6): 1141–51, doi:10.1666/0022-3360(2001)075<1141:TSTLY>2.0.CO;2, S2CID 86291472
^ abcdFortey, R. A.; Owens, R. M. (1999), "Feeding habits in trilobites", Palaeontology, 42 (3): 429–65, Bibcode:1999Palgy..42..429F, doi:10.1111/1475-4983.00080, S2CID 129576413
January 01, 1970
hypostome, trilobite, this, article, about, trilobite, structure, other, organisms, hypostome, hypostome, hard, mouthpart, trilobites, found, ventral, side, cephalon, head, hypostome, classified, into, three, types, based, whether, they, permanently, attached,. This article is about the trilobite structure For other organisms see Hypostome The hypostome is the hard mouthpart of trilobites found on the ventral side of the cephalon head The hypostome can be classified into three types based on whether they are permanently attached to the rostrum or not and whether they are aligned to the anterior dorsal tip of the glabella A partially complete forked conterminant hypostome of the trilobite Isotelus Ordovician of southern Ohio Contents 1 Morphology 1 1 Types 1 1 1 Natant 1 1 2 Conterminant 1 1 3 Impendent 2 See also 3 ReferencesMorphology editThe center of the hypostome is an ovoid typically convex part called the median body often divided into an anterior lobe and a posterior lobe Either side of the median body is a border with various extensions including anterior and posterior wings sometimes bearing knob like processes The hypostome is hollow and encloses the mouthparts the anterior digestive tract and the bases of the antennae Trilobite antennae pass through notches between the anterior and posterior wings then forward The anterior wings are designed to rest firmly against internal structures ventral apodemes on the glabella 1 Variation in trilobite hypostome morphology is crucial in modern discussions of trilobite phylogeny 2 3 Functional interpretations of hypostome shape also allow for reasonable speculation on the feeding habits of trilobite species 4 Types edit Although hypostome morphology is highly variable three broad types are generally recognized nbsp Trilobite hypostome types in blue Natant edit A natant hypostome is not attached to the anterior doublure with support assumed to be provided by a non mineralised membrane Natant hypostomes appear to have been conservative over the course of the evolution of trilobites 2 with overall form and shape of a simple ovoid without posterior extensions or ornamentation 1 Natant hypostomes are thought to be ancestral to other hypostome forms 2 and thought to belong to trilobites with generalized particle feeding habits i e little need to modify mouth parts to deal with specialized food items 4 Conterminant edit A conterminant hypostome is attached to the anterior doublure aligned with the front edge of the glabella and found on trilobites thought of as predators Anchoring the hypostome against the anterior doublure and cephalon provides structural bracing against which to tear apart prey Different specializations of hypostome form might reflect different kinds of prey or different feeding behaviors 4 Impendent edit An impendent hypostome is attached to the anterior doublure but not aligned with the front edge of the glabella Many impendent hypostomes have prongs grooves and other adaptations thought to relate to feeding on complex food sources 4 See also editMandible arthropod References edit a b Whittington H B 1997a Morphology of the Exoskeleton in Kaesler R L ed Treatise on Invertebrate Paleontology Part O Arthropoda 1 Trilobita revised Volume 1 Introduction Order Agnostida Order Redlichiida Boulder CO amp Lawrence KA The Geological Society of America Inc amp The University of Kansas pp 1 85 ISBN 0 8137 3115 1 a b c Fortey R A 1990 Ontogeny Hypostome attachment and Trilobite classification PDF Palaeontology 33 3 529 576 archived from the original PDF on 2009 03 26 Fortey RA 2001 Trilobite systematics The last 75 years Journal of Paleontology 75 6 1141 51 doi 10 1666 0022 3360 2001 075 lt 1141 TSTLY gt 2 0 CO 2 S2CID 86291472 a b c d Fortey R A Owens R M 1999 Feeding habits in trilobites Palaeontology 42 3 429 65 Bibcode 1999Palgy 42 429F doi 10 1111 1475 4983 00080 S2CID 129576413 Retrieved from https en wikipedia org w index php title Hypostome trilobite amp oldid 1186441191, wikipedia, wiki, book, books, library,
