Euhoplites

Last updated

Euhoplites
Temporal range: Albian [1]
Euhoplites subcrenatus (2).jpg
E. subcrenatus
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass:† Ammonoidea
Order:† Ammonitida
Family:† Hoplitidae
Genus:† Euhoplites
Spath, 1925
Type species
Euhoplites truncatus
Spath, 1925
Species
  • E. loricatusSpath, 1925
  • E. lautus(J. Sowerby, 1821)
  • E. ochetonotus(Seeley, 1865)
  • E. subcrenatusSpath, 1925
  • E. alphalautusSpath, 1926
  • E. barroisiAmédro, 2013
Synonyms
  • EuhoplitoidesCooper & Owen, 2011
  • ProeuhoplitesCooper & Owen, 2011

Euhoplites is an extinct ammonoid cephalopod from the Lower Cretaceous, characterized by strongly ribbed, more or less evolute, compressed to inflated shells with flat or concave ribs, typically with a deep narrow groove running down the middle. In some, ribs seem to zigzag between umbilical tubercles and parallel ventrolateral clavi. In others the ribs are flexuous and curve forward from the umbilical shoulder and lap onto either side of the venter.

Contents

Fossils of this animal are commonly found in Lower Cretaceous, middle to upper Albian age strata. [1]

Its shell was covered with lumps and bumps. The function of these adornments are unknown, although they may have been a source of hydrodynamic drag, preventing Euhoplites from swimming at high speeds. Studying them, therefore, may give some insight into the lifestyle of this ancient marine predator. Euhoplites was a small ammonite with shells of diameters of at most a few centimetres in diameter, depending on the age, species and possibly gender of the individual.

Distribution

Euhoplites has been found in Middle and Upper Albian beds in France where it is associated respectively with Hoplites and Anahoplites , and with Pleurohoplites , Puzosia , and Desmoceras ; in the Middle Albian of Brazil with Anahoplites and Turrilites; and in the Cenomanian of Texas. It is the most common ammonite fossil of the Folkstone (sometimes spelt "Folkestone") fossil beds in southeastern England where a variety of species are found.

Classification

Taxonomic relations

Euhoplites is closely related to Hoplites and to other hoplitid genera such as Epihopites and Protohoplites included in the subfamily, Hopliitinae. Other subfamilies in the Hoplitidae, with more distantly related genera are the Cleoniceratinae and Gastrohoplitinae.

Species

In the past, big number of species have been attributed to this genus. In later research it has been found that species of Euhoplites have big intraspecific variability and most of the species are just synonyms. This is even the case of the type species E. truncatus, which is synonym of E. lautus. [1]

E. loricatus

Synonyms: [1] [2]

  • E. priceiSpath, 1925
  • E. aspasiaSpath, 1925
  • E. microcerasSpath, 1925
  • E. subtuberculatusSpath, 1927
  • E. meandrinusSpath, 1930
  • E. neglectusMilbourne, 1963

Lateral ends of lautiform ribs that are strongly bent forward forms blades around concave furrow on the venter. Excavated siphonal line, which is characteristic for most of its descendants is missing in the case of this species. Due to intraspecific variability, many species have been erected that are now considered to be synonyms. These can be ordered from most compressed to thickest as E. aspasia, E. microceras, E. loricatus, E. pricei and E. subtuberculatus. E. loricatus var. meandrina has been formerly promoted to separate species, as its ribs do not start in the groups of 2, or 3, but in groups of 3, or 4. It is the youngest variation of E. loricatus, but now, this separation of it is not considered to be necessary. E. neglectus is considered to be a synonym of E. meandrinus. [1] [3]

Euhoplites lautus (J. Sowerby, 1821), Cretaceous, Albian, Gault Clay, Folkestone, Kent, UK. Size of Ammonite = 25mm Euhoplites lautus.jpg
Euhoplites lautus (J. Sowerby, 1821), Cretaceous, Albian, Gault Clay, Folkestone, Kent, UK. Size of Ammonite = 25mm

E. lautus

Synonyms: [1]

  • E. truncatusSpath, 1925
  • E. opalinusSpath, 1930
  • E. nitidusSpath, 1925
  • E. proboscideusJ. Sowerby, 1921

Ammonite with strong lautiform ribs that are curved forward in the last third of the flank. It differs from its predecessor, E. loricatus by having excavated siphonal line with subrectangular section. There is big variability in the case of shell thickness. Old synonyms can be ordered by thickness from most compressed to thickest as E. lautus, E. truncatus, E. opalinus, E. nitidus and E. proboscideus. It has lived during middle and early part of upper Albian and gave rise to E. ochetonotus. [4]

E. ochetonotus

Synonyms: [1]

  • E. sublautusSpath, 1928
  • E. solenotusSeeley, 1865
  • E. serotinusSpath, 1930
  • E. trapezoidalisSpath, 1930
  • E. armatusSpath, 1925

Ribs are subradial to flexuous and became attenuated on the living chamber. Venter is flat with siphonal canal and ventro-lateral clavi are slightly oblique to it. Forms of this species, which has been formerly considered to be valid species can be ordered from slimmest to thickest as E. ochetonotus, E. sublautus, E. solenotus, E. serotinus, E. trapezoidalis and E. armatus. It has been living during the base of upper Albian. [1] [4]

E. subcrenatus

Synonyms: [1]

  • E. inornatusSpath, 1930

Micromorph with very weakened ornamentation. Sigmoid ribs ends at the venter, where they create crenulations by both sides of siphonal canal. Its form, that has been named as formerly separate species E. inornatus is almost smooth. It lived during the early part of upper Albian. [4]

E. alphalautus

Synonyms: [1]

  • E. vulgarisSpath, 1928
  • E. bolonienseSpath, 1926

Species with sigmoid ribs that tends to form crenulations on the ventro-lateral shoulder. Siphonal canal is tending to form shape of V and is less hollow than in the case of other species. Species that are now considered to be synonyms were based on the difference in their thickness. E. alphalautus is the thinnest one, while E. boloniense is the thickest one. This species lived during upper Albian. [4]

E. barroisi

These ammonites had moderately evolute whorls, where umbilicus makes 29% of diameter. Whorld section is subhexagonal and biggest thickness is at the level of umbilical tubercules. Umbilical wall is rounded and flanks are slightly convex. Lautiform ribs begins at spiny umbilical tubercules and are tending strongly forward. They are joining at the strongly developed ventro-lateral clavi, which are pinched obliquely to siphonal line and are alternating on both sides. Some other ribs are zigzagging from umblical tubercules to ventro-lateral clavi. On the venter, there is deep concave groove. This is very well visible difference from its predecessor, E. lautus which had siphonal channel. Very similar is E. loricatus, shich also has only ventral groove and is missing siphonal channel. Difference is, that in the case of E. loricatus, ventro-lateral clavi are not oblique to siphonal line, while they are oblique to it in the case of E. barroisi. Important difference is also in stratigraphy, as E. loricatus is middle albian species, while E. barroisi lived during upper Albian zone of Dipoloceras cristatum. There is a gap between their occurrence during the zone of Dimorphoplites biplicatus ammonite zone, during which, the only member of this genus was E. lautus. [1]

Evolution

Euhoplites has evolved during Lower Albian from Hoplites (Hoplites) canavarii . Among early species belonging to this genus were Euhoplites loricatus, E. aspasia, or E. meandrinus. These early species were added to genus Proeuhoplites, but this genus is by some authors considered to be synonym of Euhoplites. Later species have evolved channelled venter by which they differ from these early species. To these later species belongs for example Euhoplites truncatus, E. lautus, or E. elenae. In the Upper Albian, during Hysteroceras varicosum zone, Euhoplites inornatus has evolved. This differs greatly from contemporaneous members of this genus by not having channelled venter and it looked much more similar to genus Anahoplites . For this species a monotypic genus Euhoplitoides was proposed, but it is also considered to be just a synonym of Euhoplites. Latest members of this genus gave rise to genus Hyphoplites (Discohoplites) . [2] [5] [6]

Related Research Articles

<i>Acanthohoplites</i> Extinct genus of Cretaceous ammonites

Acanthohoplites is an extinct genus of ammonites in the family Parahoplitidae that lived in the Aptian and Early Albian stages of the Early Cretaceous.

<i>Anahoplites</i> Genus of molluscs (fossil)

Anahoplites is a genus of rather involute, compressed hoplitid ammonites with flat sides, narrow flat or grooved venters, and flexious ribs or striae arising from weak umbilicle tubercles that end in fine dense ventrolateral nodes. The elements of their sutures are short, wide and jaggedy. Specimens of Annahoplites have diameters typically in the range of 4–6 centimetres (1.6–2.4 in) although some with diameters of as much as 19 centimetres (7.5 in) have been reported. The genus lived during the Cretaceous, from the Middle to the late Albian.

<i>Aulacostephanus</i> Genus of molluscs (fossil)

Aulacostephanus is an extinct ammonoid cephalopod genus from the Upper Jurassic Tithonian belonging to the perisphinctacean family Aulacostephanidae.

<i>Schloenbachia</i> Genus of molluscs (fossil)

Schloenbachia is a genus of ammonoid cephalopods from the Cenomanian stage of the Upper Cretaceous, and type for the Schloenbachiidae, a family within the ammonitid Hoplitoidea.

<i>Placenticeras</i> Genus of molluscs (fossil)

Placenticeras is a genus of ammonites from the Late Cretaceous. Its fossils have been found in Asia, Europe, North and South America.

<i>Douvilleiceras</i> Genus of ammonite cephalopod

Douvilleiceras is a genus of ammonites from the Middle to Late Cretaceous. Its fossils have been found worldwide, in Africa, Asia, Europe, and North and South America.

<i>Hoplites</i> (ammonite) Genus of molluscs (fossil)

Hoplites is a genus of ammonite that lived from the Early Albian to the beginning of the Middle Albian. Its fossils have been found in Europe, Transcaspia and Mexico. Shell has compressed, rectangular till depressed and trapezoidal whorl section. There are strong umbilical bullae from which, prominent ribs are branching and these are interrupted on venter. Ends of ribs on the venter are prominent and can be both alternate or opposite. Some species have zigzagging ribs and these ribs ends usually thickened, or they can be raised into ventrolateral tubercles. These tubercles are mostly oblique clavi.

<i>Pachydiscus</i> Genus of molluscs (fossil)

Pachydiscus is an extinct genus of ammonite from the Late Cretaceous with a worldwide distribution, and type for the desmoceratacean family Pachydiscidae. The genus' type species is P. neubergicus. Altogether some 28 species have been described.

Hoplitidae Family of molluscs (fossil)

The Hoplitidae is a family of Cretaceous ammonites that lived during the middle of the period from the late Aptian to the Cenomanian. They are part of the superfamily Hoplitoidea.

Callihoplites is a genus of rather evolute ammonites from the Lower Cretaceous, Late Albian. Its whorl section squarish or compressed, inner whorls bearing umbilical bullae and ventrolateral clavi, with or without looped ribs between. The body chamber is smooth with a rounded venter.

Leymeriellidae is a family of Lower Cretaceous ammonites comprising rather small forms distinguished from Hoplitidae by their flattened and grooved ribs and virtual absence of umbilical tubercles. The family is derived from the Desmoceratidae. Leymeriella schrammeni anterior has evolved from Desmoceras keilhacki keilhacki.

Holcodiscidae Extinct family of ammonites

Holcodiscidae is an ammonite family placed in the Ammonite superfamily Desmoceratoidea.

Proplacenticeras is a discoidal ammonite from the lower part of the Upper Cretaceous and precursor of the overall similar Placenticeras.

<i>Watinoceras</i> Genus of molluscs (fossil)

Watinoceras is a genus of acanthoceratid ammonite that lived during the early Turonian stage of the Late Cretaceous.

Cunningtoniceras is a stocky acanthoceratid ammonite from the upper Cenomanian stage of the late Cretaceous of the western U.S., found e.g. in Arizona and New Mexico.

Neocardioceras is a genus of evolute acanthoceratid ammonites from the uppermost Cenomanian, Upper Cretaceous, of Europe, western U.S. and Brazil.

Flickiidae is a family of dwarf ammonites with little ornament and very simples sutures known from small pyritic specimens found in middle Cretaceous deposits. Inclusion in the Acanthoceratoidea is tentative.

<i>Cleviceras</i> Genus of molluscs (fossil)

Cleviceras is an extinct genus of cephalopod belonging to the family Hildoceratidae. These cephalopods existed in the Jurassic period, during Toarcian and possibly even uppermost Pliensbachian age. Sometimes, it is considered to be a synonym of Eleganticeras.

Otohoplites is a genus of ammonite that lived in the Early Albian age and whose fossils were found in Svalbard, Denmark, England, France, Austria, Poland, Russia and Kazakhstan. It has evolved from Hemisonneratia and gave rise to the genus Hoplites. Shells belonging to this genera are rather inflated to compressed and have zigzagging, or looped ribs that end in oblique ventrolateral clavi. Usually, ribs are zigzagging through venter. Macroconchs have a smooth body chamber and rounded venter.

Antarcticoceras is a genus of crioconic ammonites in the family Shasticrioceratidae. It lived during the Early Cretaceous Period. Antarcticioceras fossils can be found in the Cretaceous rocks of Antarctica and South America.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 AMÉDRO, Francis (2013). "Euhoplites Barroisi sp. nov.: Une Nouvelle Ammonite de L'Albien Supérieur de Wissant (Pas-de-Calais, France)." Société Géologique du Nord.
  2. 1 2 Amédro, F., Matrion, B., Magniez-Jannin, F., & Touch, R. (2014). La limite Albien inférieur-Albien moyen dans l’Albien type de l’Aube (France): ammonites, foraminifères, séquences. Revue de Paléobiologie, 33(1), 159-279.
  3. ↑ HANCOCK, J. M., et al. The Gault of the Weald. In: A symposium held. 1963. p. 243-260.
  4. 1 2 3 4 AMEDRO, Francis. L'Albien du Bassin Anglo-Parisien: ammonites, zonation phylétique, séquences. The Albian in the Anglo-Paris Basin: ammonites, phyletic zonation, sequences. Bulletin des Centres de Recherches Exploration-Production Elf-Aquitaine, 1992, 16: 187-233.
  5. ↑ Cooper, M. R., & Owen, H. G. (2011). Evolutionary relationships within Hoplitidae (Cretaceous Ammonoidea). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 261(3), 337-351.
  6. ↑ Cooper, M. R., & Owen, H. G. (2011). The phylogeny and classification of primitive Placenticeratidae (Cretaceous Hoplitina, Hoplitoidea). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 260(3), 331-342.

for pictures of Euhoplites:

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.