◄ Carnets Geol. 25 (3)
Outline:
[1. Introduction]
[2. Material and methods]
[3. Description of the sections]
[4. Litho- and biostratigraphy]
[5. Systematic palaeontology]
[6. Phyletic discussion]
[7. Conclusions]
and ... [Bibliographic references]
Musée
cantonal des sciences naturelles, Department of Geology, Anthropole, 1015
Lausanne (Switzerland)
389 rue centrale, 01110 Hauteville-Lompnes (France)
160 rue Pierre Valdo, 69005 Lyon (France)
Published online in final form (pdf) on January 15, 2025
DOI: 10.2110/carnets.2025.2503
[Editor: Bruno
R.C. Granier; language editor: Stephen Carey]
Several ammonoid specimens from the upper Valanginian (Lower Cretaceous) sedimentary succession of Hauteville-Lompnes, Department of Ain, eastern France, are assigned to the new genera and species Itierella melognensis n.gen., n.sp., and Paradicostella hautevillelompnesensis n.gen., n.sp. Specimens collected in the past were misidentified as Acanthodiscus Uhlig, 1905, and erroneously assigned to the lowermost part of the Hauterivian stage. The revision of the Marnes de Mélogne, along with the collection of a rich associated ammonite fauna, allows Itierella to be recognized as a latest Valanginian homeomorphic form of the genus Acanthodiscus, and Paradicostella as closely related to the genus Dicostella Busnardo, 1966. The Marnes de Mélogne are revised as mostly belonging to the upper Saynoceras verrucosum to Criosarasinella furcillata ammonite zones (uppermost Valanginian), while their uppermost metre is assigned to the Acanthodiscus radiatus Zone (lowermost Hauterivian).
• Lower
Cretaceous;
• ammonite
systematics;
• biostratigraphy;
• homeomorphism;
• lithostratigraphy
Pictet A., Hugon B. & Pierangelini G. (2025).- Itierella melognensis n.gen., n.sp., and Paradicostella hautevillelompnesensis n.gen., n.sp. (Ammonoidea, Neocomitidae, Neocomitinae), two new upper Valanginian trituberculated ammonoids from the Jura Mountains, eastern France.- Carnets Geol., Madrid, vol. 25, no. 3, p. 73-87. DOI: 10.2110/carnets.2025.2503
Itierella melognensis n.gen., n.sp., et Paradicostella hautevillelompnesensis n.gen., n.sp. (Ammonoidea, Neocomitidae, Neocomitinae), deux nouveaux ammonoïdes trituberculés du Valanginien des montagnes du Jura, Est de la France.- Plusieurs spécimens d'ammonoïdes de la succession sédimentaire du Valanginien supérieur (Crétacé inférieur) de Hauteville-Lompnes, Département de l'Ain, Est de la France, sont attribués aux nouveaux genres et espèces Itierella melognensis n.gen., n.sp., et Paradicostella hautevillelompnesensis n.gen., n.sp. Des spécimens collectés dans le passé avaient été identifiés à tort comme Acanthodiscus Uhlig, 1905 et attribués à l'Hauterivien basal. La révision des Marnes de Mélogne et la récolte d'une riche faune d'ammonites associée permettent d'attribuer Itierella à une forme du Valanginien supérieur, homéomorphe au genre Acanthodiscus, et Paradicostella très proche du genre Dicostella Busnardo, 1966. L'âge des Marnes de Mélogne est révisé comme appartenant à l'intervalle compris entre la partie supérieure de la Zone à Saynoceras verrucosum et la Zone à Criosarasinella furcillata du Valanginien supérieur, tandis que le dernier mètre peut être attribué à la Zone à Acanthodiscus radiatus de l'Hauterivien inférieur.
• Crétacé
inférieur ;
• systématique
des ammonites ;
• biostratigraphie ;
• homéomorphisme ;
• lithostratigraphie
A large number of trituberculate ammonite species from the Berriasian to the Hauterivian stages have been historically assigned to the genus Acanthodiscus Uhlig, 1905, which soon became highly polyphyletic. A great deal of effort has later been invested in disentangling numerous homeomorphic forms, with the introduction of the genera Neocosmoceras Blanchet, 1922, Octagoniceras Spath, 1924, Transcaspiites Luppov & Mikhailova, 1985, and Kilianites Énay et al., 1998; for Berriasian forms, and Luppovella Nikolov, 1966, and Pseudacanthodiscus Baraboshkin, 1997, for lower Valanginian forms. Similarly, Rawson (1971) excluded certain northern European forms of the genus Acanthodiscus, which he presented in inverted commas, namely 'Acanthodiscus' ebergensis (Weerth, 1884), 'A.' bivirgatus (Weerth, 1884), 'A.' confusus Spath, 1924, 'A' n.sp. a and 'A' n.sp. b, which are probably related to the genus Endemoceras Thiermann, 1964. Consequently, Acanthodiscus is currently regarded as a natural group of forms that is up to now exclusively confined to the basal Hauterivian sedimentary series from Tethys and Boreal-Atlantic Subrealm (Mutterlose et al., 1996, 2021). Busnardo and Thieuloy (1989) have provided a comprehensive list of its specific composition.
A set
of ammonites with polygonal whorl section and trituberculated ribbing has been
collected over the past few decades by several collectors from natural outcrops
and from building sites in the vicinity of Hauteville-Lompnes, in the Bugey
area, of the meridional Jura Mountains (Ain Department, France; Fig. 1 
). In
general appearance, these ammonites resemble either the Hauterivian genus Acanthodiscus
or Dicostella Busnardo, 1966.
The first occurrence (FO) of the ammonite genus Acanthodiscus defines the base of the Hauterivian stage (Mutterlose et al., 1996, 2021), while the faunal association of the Marnes de Mélogne is mostly that of the upper Valanginian Neocomites peregrinus and Criosarasinella furcillata zones. A detailed examination of the collected specimens reveals significant differences compared to the genus Acanthodiscus. These homeomorphic morphotypes are here described as a new genus and a new species Itierella melognensis n.gen., n.sp.
Furthermore, an isolated specimen, similar to Dicostella but with strong ventro-lateral tubercles, is presently described as a new genus and species Paradicostella hautevillelompnesensis n.gen., n.sp.
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Figure 1: A.
Map
showing of the city of Hauteville-Lompnes in the Bugey, Ain Department, eastern
France. B. Location of the four sections (red stars) studied around
Hauteville-Lompnes. |
The
ammonites described in this contribution were collected by Mr Bruno Hugon
(B.H.), who spent several decades investigating the Lower Cretaceous marlstones
of the Hauteville-Lompnes area for its fossils. Mr Gustavo Pierangelini
(G.P.) contributes to this study with a high-quality specimen used as the
holotype of one of the two new genera described. These marlstones, designated
here as the Marnes de Mélogne,
are situated in the lowermost part of the Grand Essert Formation (Fig. 2 )
defined by Strasser et al. (2016,
2018). A partial lithological
log of the Marnes de Mélogne is
provided by Busnardo et al.
(1966) at the type locality on the Mélogne stream.
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Figure 2:
Comparison of the Valanginian and Hauterivian lithological series between the
Bugey and central Jura. Lithological log of the central Jura modified after
Godet et al. (2010). |
In this
study, four natural sections and earthworks (Fig. 3 ) have been investigated in
recent decades by the second author (B.H.): Chomarasse quarry (geographical WGS
84 coordinate system: 46°00'50"N,
5°34'43"E, altitude 805 m), Le Crêt (45°58'42"N,
5°36'02"E, altitude 801 m), Pré Frais (45°59'14"N,
5°35'21"E, altitude
784 m) and Mélogne (45°58'03"N,
5°36'39"E, altitude 830 m). The four
sections permit a comprehensive overview of the lithological succession of the
Marnes de Mélogne.
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Figure 3:
NW to SE correlation of the four sections across the Hauteville-Lompnes
syncline. |
The specimens illustrated and measured here are held in the private collections of the second (B.H.) and the third (G.P.) authors. However, plaster casts are deposited in the 'Muséum cantonal des sciences naturelles' at Lausanne, Geology department (MGL), Switzerland.
The photographed specimens were previously whitened with ammonium chloride and photographed using the High Dynamic Range (HDR) method at three different light intensities (underexposed, normal, overexposed).
Morphometric measurements were taken with a caliper and expressed in millimetres, with values assessed to tenths of a millimetre. The estimated values are presented in brackets. All the dimensions of the specimens are given in millimetres. Abbreviations: D = diameter, Wb = whorl breadth, Wh = whorl height, U = umbilical diameter.
3.1 Chomarasse quarry
The
Chomarasse quarry (Fig. 4.A-C ) is exploited for the extraction of building stone.
The lithostratigraphic sequence is composed from bottom to top by:
Unit
1: Choin d'Hauteville (CH, Fig. 4.A ) - about ten to fifteen metres of light
pinkish-white to slightly yellow limestone in thick, massive and compact beds
forming a bar. The upper surface is commonly karstified where it crops out. The
Choin d'Hauteville is the exploited limestone (e.g., Énay,
1989).
It contains a fauna of nerineids gastropods, echinoids, and corals. The top is
marked by a bored hardground coated with an iron crust;
Unit
2: Calcaire roux (CR, Fig. 4.A ) - 1.8 metres of cross-bedded, yellow-brown,
coarse-bioclastic limestone containing abundant crinoid, bryozoan, and
brachiopod remains. The top is
marked by a bored hardground coated with an iron crust (Fig.
4.B );
Unit
3: Marne jaune de Morteau (MJM, Fig. 4.C ) - 10 centimetres of yellow, plastic
marlstone, extremely fossiliferous, delivering some Olcostephanus sp. and
Valanginites nucleus (Roemer, 1841);
Unit
4: Marnes de Mélogne (Fig. 4.A ) -
about 7 metres of marlstones divided into three subunits: a lower, 2.5 metres
thick sandy marlstone (Lower sandy marlstones), a middle, 2.5 metres thick and
less indurated sandy marlstone (Upper sandy marlstones), and an upper, two
metres thick marlstone with extremely fossiliferous nodular marly-limestone
intercalations (Coquina-rich marlstones), which delivered Karakaschiceras cf.
companyi Reboulet, 1996, and Dicostella sp.
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Figure 4: A. Overview of the Chomarasse quarry and the lithostratigraphic units
composing it. CH = Choin d'Hauteville. CR = Calcaire roux. B. Detail of
the bored hardground on top of the Calcaire roux. C. Detail of the Marne
jaune de Morteau (MJM) sandwiched between the Calcaire roux and the Lower sandy
marlstones (LSM) of the lower Marnes de
Mélogne. D. Section through the upper Marnes
de Mélogne consisting of the Upper sandy marlstones and the Coquina-rich
marlstones, and overlain by the first Pierre jaune de Neuchâtel (PJN) unit. |
3.2 Pré Frais
The Pré Frais section is a natural hillside outcrop, strongly vegetated, which displays the same lithological succession of the Marnes de Mélogne as in the Chomarasse Quarry. The base of the lower sandy marlstones delivered Karakaschiceras biassalense (Karakasch, 1889). The exact source location in the section of a specimen assigned to K. pronecostatum ? (Felix, 1891) is unknown but may also derive from this unit. The Coquina-rich marlstones are characterised by yellow marls, just below the soil, which provided ex situ K. cf. companyi, Neocomites sp., Olcostephanus sp., Oosterella sp. cf. ondulata (Reboulet, 1996), and Himantoceras gigas (Thieuloy & Bulot, 1993).
3.3 Le Crêt
The Le Crêt section was an ephemeral section excavated during the construction of a building (Carrefour supermarket). This section allowed the observation of the upper half of the Marnes de Mélogne and their transition to a first crinoidal limestone bundle, belonging to the "Pierre jaune de Neuchâtel" facies (yellow bioclastic and oolithic limestone). What appears to be the base of this section was excavated in several places in the village and produced Karakaschiceras cf. companyi, Neolissoceras desmoceratoides (Wiedmann, 1966), Itierella melognensis n.gen., n.sp., Olcostephanus densicostatus (Wegner, 1909), and an unidentified ammonite. A specimen of Tescheniceras sp. was collected ex situ. It is likely that this ammonite originated from a higher level within the section, when compared to the nearby Mélogne section. The original stratigraphic position of these ammonites within the coquina-rich marlstone remains uncertain.
3.4 Mélogne
The
Mélogne stream section is located between Hauteville and Cormaranche, upstream
of the Cascade bridge. The stream is incised into marlstones, which can be
observed on the left bank in a succession of small cliffs topped with limestone
(Fig. 4.D ). Going upstream, the following succession – previously described in
detail by Busnardo et al. (1966) – can be observed:
Massive limestones of the Choin d'Hauteville cropping out downstream of the road, at the waterfall;
The Marnes de Mélogne with around 6 metres of sandy, alternating marlstones and marly limestones. The lower two metres are devoid of fossils, while the 3-metre interval, above a 1-metre-thick crinoidal bed, is very fossiliferous and contains a rich in situ ammonite fauna. The fauna, from bottom to top, includes Dicostella sp., Stoicoceras teutoburgense (Weeth, 1884), Dicostella pitrei Busnardo, 1966, Neocomites sp., Karakaschiceras companyi, Eleniceras tchechitevi Breskovski, 1967, Lytoceras sp., Himantoceras gigas, Olcostephanus sp., Oosterella cultrata (Orbigny, 1841), Itierella melognensis n.gen., n.sp., Sarasinella n.sp., Neolissoceras sp., Breistrofferella cf. varappensis (Baumberger, 1906), Acanthodiscus sp., A. bernensis (Baumberger, 1906), A. vaceki (Neumayr & Uhlig, 1881), A. aff. wallrathi Baumberger, 1906, Olcostephanus sp. juv., Tescheniceras cf. callidiscus Thieuloy, 1971, T. muretensis Breistroffer, 1936, and T. spp. Beds 6 to 10 display indications of condensation. Partial phosphatisation of the fossils was observed in bed 6 and especially in bed 10 (P in Fig. 3). A considerable number of ferruginous ooids and bioclasts were observed at the base of bed 7.
5 metres of a yellow, crinoidal limestone bundle of "Pierre jaune de Neuchâtel" (PJN) facies, with at its base Acanthodiscus ? sp. and Tescheniceras sp.
3.5 Hauteville-Lompnes
In various earthworks in the city of Hauteville-Lompnes, a number of ammonites were discovered. These included Criosarasinella cf. subheterocostata Reboulet, 1996, Dicostella pitrei, D. cf. houdardi (Roman, 1933), Karakaschiceras cf. companyi, Neocomites sp., Olcostephanus densicostatus, Eleniceras tchechitevi, Itierella melognensis n.gen., n.sp., Paradicostella hautevillelompnesensis n.gen., n.sp., and other enigmatic neocomitids that remain undetermined.
The upper Valanginian record begins on top of the Calcaire roux with yellow marlstones, which are frequently observed along the Jura Mountain range. These typically comprise coquina-rich marlstones with episodic marly-limestone intercalations and can attain thicknesses of several metres in the Central Jura. In most cases, these deposits are reduced to a few decimetres in thickness and contain a rich fossil content, indicative of sedimentary condensation (Donze & Thieuloy, 1975). In the literature, these marls are frequently designated as "Marnes jaunes à Ammonites Astierianus" (Desor & Gressly, 1859) or "Marne jaune de Morteau" (Renevier, 1874). These open-marine marlstone deposits are characterised in particular by the presence of Saynoceras verrucosum (Orbigny, 1841) (Sayn, 1889, p. 684), which indicates the lower part of the S. verrucosum Zone (Bulot, 1990). This age is confirmed in the Hauteville syncline by the presence of Valanginites nucleus, which has the same stratigraphic range as Saynoceras verrucosum (see Thieuloy, 1977a; Bulot, 1990).
The above Marnes de Mélogne can be considered as lateral equivalents of the eastern Couches de Censeau (French Jura Department; Marcou, 1859, p. 123) and the Marnes à Bryozoaires / Marnes à Spongiaires (Swiss Vaudois Jura; Pictet & Campiche, 1858 -1860; Jaccard, 1869; Schardt, 1895) due to their lithostratigraphic position between the Marnes jaune de Morteau and the Hauterivian series, and also because of their ammonite faunas. Both eastern facies are typically present below the Marne d'Hauterive stricto sensu and show a very reduced thickness, ranging from a few decimetres to a few metres, indicative of condensation in the Central Jura. In the Hauteville syncline, the Marnes de Mélogne are fully developed and show no signs of condensation except at their top. The ammonites present in the Marnes de Mélogne are mostly restricted to the upper part of the formation. Ammonites are typically well preserved, with internal limestone moulds lying horizontally in the strata. Body chambers are not always preserved. This is generally attributed to a bias in the fossilisation process, whereby the phragmocone is more mineralised than the body chamber, which is filled with marlstones. No evidence of reworking or lateral winnowing of the fossils was observed; nor were bioencrusted. The ammonites in beds 8 to 10 from the Mélogne section are less well preserved than those on other beds due to the presence of more bioclastic sediment. From the perspective of biostratigraphy, the most ancient age indices are derived from the Pré Frais section. Karakaschiceras pronecostatum ?, collected ex situ, indicates the presence of the K. pronecostatum Subzone, probably from the Lower sandy marlstones. This age attribution is corroborated by Karakaschiceras biassalense, which was collected near the base of the Lower sandy marlstones of the Pré Frais section. Younger age indices are obtained from the Coquina-rich marlstones on the Mélogne section. Dicostella pitrei, found in bed 5, is reported by Bulot in Mojon et al. (2013) from the upper part of the Saynoceras verrucosum Zone (Karakaschiceras pronecostatum Subzone) and the lower part of the Neocomites peregrinus Zone (N. peregrinus Subzone). The associated Stoicoceras teutoburgense is reported from the Dichotomites bidichotomoides and lowermost Stoicoceras tuberculata zones of north-west European Province (= upper Neocomites peregrinus Zone, Olcostephanus nicklesi Subzone and the extreme base of the Criosarasinella furcillata Zone; see Reboulet et al., 2014). According to Reboulet (1996), the sudden appearance of Eleniceras tchechitevi, Himantoceras gigas, Oosterella cultrata, and Karakaschiceras companyi at the base of bed 7, followed by abundant Tescheniceras Vašíček, 2020, in bed 10, indicates the Criosarasinella furcillata Zone. Bed 10 shows a slight overlap of uppermost Valanginian and lowermost Hauterivian faunas. This faunal overlap, together with the slight phosphatisation of the fossils, suggests subtle condensation around the Valanginian - Hauterivian boundary. However, no evidence of reworking was observed. According to Reboulet et al. (1992) and Reboulet (1996), an ammonoid turnover occurred at the boundary of the Valanginian and Hauterivian, and has been interpreted as the response of nektonic organisms to eustatic and climatic changes, probably towards warmer sea-water temperatures. Thieuloy (1977b) defined the base of the Hauterivian stage and the base of the Acanthodiscus radiatus Zone by the first occurrence of the ammonite genus Acanthodiscus, essentially following the opinion of Paquier (1900).
The almost exclusively latest Valanginian age of the Marnes de Mélogne below the first crinoidal limestone bundle of the "Pierre jaune de Neuchâtel" facies contrasts strongly with the Swiss Jura, further east, where the marlstones (Marnes d'Hauterive) below the first crinoidal limestone bundle of "Pierre jaune de Neuchâtel" facies are almost entirely of early Hauterivian age, up to the Lyticoceras nodosoplicatum ammonite Zone in the eastern areas (Mojon et al., 2013).
Superfamily Perisphinctoidea Steinmann, 1890
Family Neocomitidae Salfeld, 1921
Subfamily Neocomitinae ? Salfeld, 1921
Genus Itierella n.gen.
Type species. Itierella melognensis n.gen., n.sp.
Derivatio nominis. A tribute to Jules Itier (1802-1877), customs inspector for the Ain department and geologist. Itier is renowned for his pioneering contributions to the study of the Lower Cretaceous of the Bugey region.
Locus typicus. Mélogne section, Hauteville-Lompnes, Ain Department, eastern France.
Stratum typicum. Beds 8 to 10, Coquina-rich marlstones of the Marnes de Mélogne, Hauterive Member, Grand Essert Formation, Criosarasinella furcillata to lowermost? A. radiatus zones.
Diagnosis. Ammonite morphologically very close to the genus Acanthodiscus. Hexagonal whorl section higher than wide. Main ribs bearing prominent tubercles at the umbilical shoulder, lateral at mid-flank, and on the ventro-lateral border. Main ribs regularly bifurcated from the lateral tubercle. Few single intercalated ribs on the outer whorl, starting on the umbilical edge, bearing strong lateral and ventro-lateral tubercles. Flat, smooth, and narrow venter, progressively becoming concave between ventro-lateral tubercles.
Content. The genus is currently monospecific.
Stratigraphic and geographic distribution. Coquina-rich marlstones of the Marnes de Mélogne, Grand Essert Formation, Jura Mountains.
Affinities
and differences.
The genus Itierella is distinguished by its hexagonal whorl section and
robust trituberculate ribbing, which closely resemble those of the genera Distoloceras
Hyatt, 1900, Acanthodiscus and to a lesser extent to the
immature Dicostella (Fig. 6 ).
According to Hyatt (1900), the type-species of the genus Distoloceras is Hoplites hystrix (Phillips), based on the specimens of Neumayr and Uhlig (1881, Pl. XLII, fig. 3; Pl. XLVI, fig. 4), and not that of Phillips. However, the two illustrated specimens do not show bifurcations of the lateral tubercles. Conversely, the lectotype of of Neumayr and Uhlig's specimens (Neumayr & Uhlig, 1881, Pl. XLVI, fig. 4) exhibits ribs branching from the umbilical tubercle into the ephebetic whorls, whereas at the same diameter Itierella displays single ribs at the umbilical border. In Distoloceras only the main ribs are tuberculated on the siphonal rim, whereas in Itierella the ribs are uniformly tuberculated on the siphonal border. In Distoloceras, the lateral tuberculation appears after the shell reaches a diameter of 30 mm, whereas it is already present at a diameter of less than 10 mm in Itierella.
Itierella
can be distinguished from Acanthodiscus by its distinctive ornamentation
style, which resembles to the internal whorls of the genus Sarasinella Uhlig,
1905. This ornamentation is characterised by trituberculate ribs, which
bifurcate from an umbilical and/or mid-flank tubercle and alternate in outer
whorls with weaker and less strongly tuberculated single ribs. Acanthodiscus,
also present in the Mélogne section (bed 10), appears later, at the base of the
Hauterivian. In our species, perisiphonal tubercles are twice as numerous as the
median tubercles and in some ribs the ratio is even 1:1 (Fig.
6 ). In contrast,
the number of perisiphonal tubercles in Acanthodiscus is usually triple
that of median tubercles (Busnardo et al., 1966). This lower number and decreasing ratio of lateral/umbilical
tubercles is found only in Acanthodiscus vaceki (Neumayr & Uhlig,
1881). In Acanthodiscus, the
ventrolateral tubercles are tight and small, sometimes clavate, whereas in Itierella
they are prominent, round to clavate on the body chamber, and widely spaced
(Fig. 6). The intercalated ribs in Acanthodiscus are relatively short,
beginning in the upper third of the flank. In contrast, the ribs in Itierella
are considerably longer, beginning at or near the umbilical shoulder. The
species Acanthodiscus wallrathi shows similarities with Itierella,
in particular, in the rounded and widely spaced tubercles, the presence of
intercalated ribs which may extend up to the umbilical shoulder, and the
dominance of well-spaced simple ribs on the external whorls. It should be noted
that the single-rib stage of the holotype is teratological and may result from
damage during shell development. Acanthodiscus wallrathi differs in
having an isometric whorl section, whereas in Itierella it clearly
becomes higher than wide. Furthermore, the venter is large in Acanthodiscus
wallrathi, whereas it is narrow in Itierella. Finally, Acanthodiscus
wallrathi was collected in the Marnes d'Hauterive of the Neuchâtel area (Swiss
Jura Mountains) and is likely to belong to the lowermost Hauterivian stage. In contrast, Itierella is
actually restricted to the uppermost Valanginian stage. The poor preservation of
the suture line in Itierella specimens does not allow a comparison with
that of Acanthodiscus.
Itierella n.gen. melognensis n.sp.
(Fig. 5.A-E )
Synonymy.
? 1908 Acanthodiscus Euthymi.- Baumberger, p. 10, Fig. 102, Pl. 21, fig. 2a, 2b
Holotype. Specimen MGL.110474 (Fig. 5.D-E ), collected in the Coquina-rich marlstones of the Marnes de
Mélogne,
Coll. G. Pierangelini.
Derivatio nominis. Species named after the Mélogne stream, where the holotype was collected.
Material. Four calcareous internal moulds from the Coquina-rich marlstones. The holotype MGL.110474 and three paratypes, MGL.110471 from Le Crêt section, MGL.110472 from Mélogne section, and MGL.110473 from Hauteville-Lompnes.
Diagnosis. As for the genus.
Description.
Specimen MGL.110471 (Fig. 5.A ) is
a small-sized calcareous mould (D = 27.24
mm) of grey colour. The umbilicus is narrow (U/D = 0.22). The whorl section
is subhexagonal in shape, higher than wide (Wb/Wh = 0.73). The flanks are parallel in the lower half and converge in
the upper half. The venter is flat and smooth. The umbilical wall is vertical
and joins the flanks at a blunt right angle. Up to a diameter of 20 mm, the
ornamentation consists of prorsiradiate, falcoid ribs bifurcating from the
umbilical tubercle. All ribs bifurcate from the lateral tubercle, which is
located on the upper third of the flank. The secondary ribs are projected
forward and terminate in a ventro-lateral tubercle that is slightly stretched
towards the siphon. From 20 mm in diameter, all ribs originate singly from the
umbilical tubercle and become more radially arranged, resulting in a perfectly
homogeneous ornamentation. The ventro-lateral tubercles gradually lie down on
the edge of the ventral band with an oblique orientation. The suture line is not
visible due to the small size of the specimen and the nature of the sediment.
Specimen MGL.110472 (Fig. 5.B ) is a
moderately large calcareous mould (D = 52.00
mm) of grey colour. The umbilicus is narrow to moderately evolute (U/D = 0.30).
The whorl section is subhexagonal, higher than wide (Wb/Wh = 0.72).
The flanks are slightly divergent in the lower half and then convergent in the
upper half. The venter is slightly rounded and smooth. The umbilical wall is
convex and moderately high with a rounded umbilical shoulder. From a diameter of
45 mm, simple intercalated ribs
are observed with weaker umbilical and lateral tubercles. The ventro-lateral
tubercles spread out on the edge of the ventral band with an oblique
orientation. The suture line is indistinguishable due to bioclastic nature of
the internal mould.
Specimen MGL.110473 (Fig. 5.C ) is a
moderately large calcareous mould (D = 57.87
mm) of grey colour. The umbilicus is moderately evolute (U/D = 0.32).
The whorl section is subhexagonal, and higher than wide (Wb/Wh = 0.69).
The flanks are slightly divergent in the lower half and then convergent in the
upper half. The venter is slightly rounded and smooth. The umbilical wall is
vertical, with a rounded umbilical shoulder. From a diameter of 30 mm, two
simple intercalated ribs are visible, with vestigial umbilical and lateral
tubercles. All ribs are clearly forward-projecting on the upper third of the
flanks and bear a ventro-lateral tubercle. All tubercles are prominent. The
ventro-lateral tubercles are somewhat obliquely elongated. From a diameter of 50
mm, the venter becomes concave between the ventro-lateral tubercles. The suture
line is partially visible but not amenable to study.
Specimen
MGL.110474 (Fig. 5.D-E ) is a
moderately large calcareous mould (D = 81.20
mm) of grey colour. The umbilicus is moderately evolute (U/D = 0.35).
The whorl section is subhexagonal, and higher than wide (Wb/Wh = 0.73).
The flanks are slightly divergent in the lower half and then convergent in the
upper half. The venter is slightly rounded and smooth. The umbilical wall is
vertical with a rounded umbilical shoulder. Internal whorls are poorly preserved
but we observe rigid prorsiradiate ribs bearing umbilical and lateral tubercles.
Some ribs are more robust than others and more strongly tuberculated. On the
outer whorl, we observe that the more robust ribs (main ribs) bifurcate from the
lateral tubercle and alternate with one to exceptionally two weaker single ribs
with less prominent umbilical and lateral tubercles. The ventro-lateral
tubercles are somewhat obliquely elongated and the venter becomes concave
between the ventro-lateral tubercles. The suture line is indistinguishable due
to bioclastic nature of the internal mould.
Measurements (in mm).
| Cat. num. | D | U | Wb | Wh | U/D | Wb/Wh |
| MGL.110471 | 27.24 | 6.10 | 9.45 | 13.00 | 0.22 | 0.73 |
| MGL.110472 | 52.00 | 15.67 | 15.64 | 21.81 | 0.30 | 0.72 |
| MGL.110473 | 57.87 | 18.73 | 17.48 | 25.24 | 0.32 | 0.69 |
| MGL.110474 | 81.20 | 28.27 | 23.71 | 32.38 | 0.35 | 0.73 |
Discussion. Specimens show a gradually increasing umbilical width index (U/D) from 0.22 to 0.35, due to an increasing rate of evolution of the coiling. The whorl width index is stable between 0.69 and 0.73.
Stratigraphic and geographic distribution. As for the genus.
|
|
Figure 5:
A-C:
Itierella melognensis n.gen., n.sp., paratypes, coll. B.
Hugon, from the Coquina-rich marlstones subunit. A MGL.110471 from Le Crêt section, B. MGL.110472 from Mélogne section, C. MGL.110473 from
Hauteville-Lompnes.
D-E. Itierella melognensis
n.gen., n.sp., holotype, coll. G. Pierangelini, MGL.110474,
Coquina-rich marlstones subunit from Mélogne section, unknown position within
beds 8 to 10. F-G. Paradicostella
hautevillelompnesensis n.gen., n.sp., holotype, coll. B. Hugon,
MGL.110475, Coquina-rich
marlstones subunit from Hauteville-Lompnes. |
Genus Paradicostella n.gen.
Type-species. Paradicostella hautevillelompnesensis n.gen., n.sp.
Derivatio nominis. Genus close (marginally) to the genus Dicostella Busnardo, 1966.
Locus typicus. Hauteville-Lompnes, Ain Department, eastern France.
Stratum typicum. Coquina-rich marlstones of the Marnes de Mélogne, Hauterive Member, Grand Essert Formation. Found in earthworks in association with ammonites from the Neocomites peregrinus and/or Criosarasinella furcillata zones.
Diagnosis. Hexagonal whorl section higher than wide. Main ribs trituberculated, umbilical, lateral at midflank, and ventro-lateral. Ribs regularly bifurcated from the lateral tubercle. Flat, smooth and narrow venter. Two single, sigmoidal, intercalated ribs between each pair of strong ribs on the phragmocone, starting on the umbilical edge and ending on the ventro-lateral edge with a round tubercle. One or no intercalated rib on the outer whorls.
Content. The genus is currently monospecific.
Stratigraphic and geographic distribution. Neocomites peregrinus and/or Criosarasinella furcillata zones from the Coquina-rich marlstones of the Marnes de Mélogne, Grand Essert Formation, of the Jura Mountains. Olcostephanus nicklesi Subzone from bed Be 103, Formation 12, boundary between V5-V6 units, La Bégude, Alpes de Haute-Provence in SE France (Thieuloy et al., 1990). Unknown level in the Troyes region, Paris Basin (Goguel, 1940).
Affinities
and differences. The
genus Paradicostella exhibits strong similarities to the genus Dicostella
(Fig. 6 ) and more particularly with D. tuberculatum (Roman, 1933)
and D. pitrei, with which the similarities in the rate of
involution, the shape of the section, and the ornamental style are striking.
However, the genus Paradicostella differs
from Dicostella essentially in that it exhibits strong ventro-lateral
protuberances (Fig. 6 ). In contrast, Dicostella always has obliquely
oriented ribs on the ventro-lateral border, which may be somewhat angular as in
the inner whorls of D. tuberculate and D. pitrei, but never
clearly tuberculated. In Paradicostella,
the venter can become markedly concave between the tubercles, whereas it is flat
to convex in Dicostella (Fig. 6 ). In Paradicostella,
one or two secondary ribs extend from the lateral tubercle, whereas in Dicostella
they are usually double or triple.
Goguel (1940, Pl. III, fig. 4) illustrated an ammonite from the Pietresson de Saint-Aubin collection from near Troyes (Aube, France), which he attributed to Acanthodiscus radiatus. This specimen shows very clearly, in the inner whorls, ribs bifurcating in the lower third of the flanks. The last half-whorl exhibits a significant spacing of the main ribs, which bear a pronounced median tubercle that is more developed than the umbilical tubercle. Additionally, there are two intercalated ribs, which are visible towards the umbilical edge and exhibit a pronounced strengthening towards the venter. There is little doubt that this specimen belongs to the new genus and species Paradicostella hautevillelompnesensis.
Thieuloy et al. (1990) described and illustrated (op. cit., Pl. IV, figs. 5-6) a morphotype, left in open nomenclature, which is distinguished by its well individualised margino-ventral clavi, and coming from their Olcostephanus nicklesi Horizon (= current subzone).
Paradicostella n.gen. hautevillelompnesensis n.sp.
(Fig. 5.F-G )
Synonymy.
1940 Acanthodiscus radiatus (Bruguière).- Goguel, Pl. III, fig. 4.
1990 Dicostella sp. inc. – Thieuloy et al., Pl. IV, figs. 5-6.
Holotype. Specimen MGL.110475, collected in the Coquina-rich marlstones of the Marnes de Mélogne, Coll. B. Hugon.
Derivatio nominis. Species named after the city of Hauteville-Lompnes, Ain Department, eastern France, where the holotype was collected.
Material. One calcareous internal mould.
Diagnosis. As for the genus.
Description.
Specimen MGL.110475 (Fig. 5.F-G )
is a moderately large calcareous mould (D = 82.43
mm) of grey colour. The umbilicus is moderately evolute (U/D = 0.30).
The whorl section is subhexagonal, and higher than wide (Wb/Wh = 0.66).
The flanks are slightly divergent in the lower half and then convergent in the
upper half. The venter is slightly rounded and smooth, and progressively becomes
concave between the ventro-lateral tubercles. The umbilical wall is vertical to
convex, with a well-rounded umbilical shoulder. Up to a diameter of 65 mm, two
to three simple, sigmoidal, intercalated
ribs are visible, with no umbilical or lateral tubercles. All ribs are clearly
forward projected on the upper third of the flanks and bear a ventro-lateral
tubercle. At a diameter larger than 65 mm, all tubercles are very prominent. The
ventro-lateral tubercles are somewhat obliquely elongated. In this specimen, the
bifurcation of the primary ribs persists until the end of the shell. The suture
line is not visible.
Measurements (in mm).
| Cat. num. | D | U | Wb | Wh | U/D | Wb/Wh |
| MGL.110475 | 82.43 | 24.84 | 23.50 | 35.76 | 0.30 | 0.66 |
Discussion. A single specimen was collected ex situ during earthworks in the city of Hauteville-Lompnes together with other upper Valanginian ammonites usually observed in the Coquina-rich marlstones.
Stratigraphic and geographic distribution. As for the genus.
|
|
Figure 6: Comparative table of the trituberculated genera
present in the Hauteville-Lompnes syncline with Acanthodiscus Uhlig,
1905, Itierella
n.gen., Dicostella Busnardo, 1966, and Paradicostella
n.gen. The morphology, ornamentation and suture line are
compared. |
The morphology of the ammonite shells is favoured trough natural selection, through its environmental and intra- and/or interspecific competitive factors (adaptive selection). It is generally accepted that homeomorphy between two taxa could be the result of a morphofunctional adaptation linked to a similar way of life like the occupation of the same ecological niche. Because of its mode of development and of growth, the ammonites shell has great potential to develop homeomorphies between different taxa that may or may not belong to different lineages and/or at very different times (Bert et al., 2020). Furthermore, some of the homeomorphs discussed here may share a very close genetic heritage as members of a possible evolutionary lineage, as well as homeomorphy by parallel evolution.
6.1. About the phyletic position of Itierella n.gen.
Itierella
has internal whorls strikingly similar to those of Sarasinella, with
trituberculate ribs that bifurcate from an umbilical and/or mid-flank tubercle
and alternate in outer whorls with much weaker and less strongly tuberculated
single ribs. Itierella n.gen. is moreover found alongside forms
attributed to Sarasinella, a genus which is present throughout the Valanginian according to Reboulet (1996).
However, Reboulet points out that the upper Valanginian forms are characterised
by an acceleration of ontogenetic development, with a shorter trituberculate
pattern, less development of the external bullae and a lower frequency of
bifurcated ribs on the median tubercle. Indeed, the specimens found at
Hauterville-Lompnes closely reflect this phyletic trend. In contrast, Itierella
n.gen. shows a completely opposite phyletic trend with the conservation and
reinforcement of the initial trituberculate stage throughout the shell, as far
as is known from the rare specimens discovered. Furthermore, according to Company
(1987), the genus Sarasinella forms a well-characterised and
morphologically homogeneous group that develops along the lower Valanginian "Thurmanniceras"
pertransiens and Neocomites neocomiensiformis zones. On the contrary,
the upper Valanginian and lower Hauterivian forms attributed to Sarasinella
appear sporadically and without stratigraphic continuity and probably do not
belong to Sarasinella. At the present time, establishing a phyletic link
between Itierella and Sarasinella is challenging. However, an
origin in upper Valanginian genera with strongly trituberculate inner whorls
appears to be the most plausible hypothesis (Fig. 7 ). Itierella n.gen., shows a homeomorphy by convergence with
Paradicostella n.gen. and Acanthodiscus.
|
|
Figure 7: Presumed phylogeny of Itierella n.gen. and Paradicostella
n.gen. in the upper Valanginian to basal Hauterivian interval. |
6.2. The Neohoploceras - Dicostella - Acanthodiscus plexus
The genus Dicostella was introduced by Busnardo et al. (1966) to accommodate a fairly heterogeneous group of Neocomitidae from the upper Valanginian of the Tethys and Boreal realms (Kemper et al., 1981; Thieuloy et al., 1990), characterised by strong, most often tuberculated, primary ribs, somehow homeomorphic to the early late Valanginian Neohoploceras Spath, 1939, and early Hauterivian Acanthodiscus.
Company (1987) had considered a possible phylogenetic relationship between the genera Karakaschiceras Thieuloy, 1971, and Dicostella. Bulot (1990) proposed an origin of Dicostella from the genus Neohoploceras, due to the importance of the peri-umbilical fasciculations preceding the establishment of the thickened primary ribs with medio-lateral bulges.
Busnardo
et al. (1966) suggested that Dicostella could lead to Acanthodiscus
because of their similar ornamentation. Thieuloy (1977b) expressed
reservations about the proposed emergence of the genus Acanthodiscus from
Dicostella because of the absence of latero-ventral clavi and the suture
line, which is more endemoceratid than leopoldiid. Neohoploceras, the
parent genus of Dicostella strains, has ventro-lateral tubercles, a
feature that is clearly present in primitive forms, and that tends to disappear
in more evolved Dicostella species. However, in the internal whorls of
evolved Dicostella the ribs clearly form an angulation on the
ventro-lateral margin and it is therefore not difficult to imagine that they
could return to tubercles. In such case, it would be an example of iterative
evolution, which leads to the reappearance of the ancestral phenotype under
environmental pressure (selection pressure; Bert et al.,
2020). In this sense, the phyletic link between Dicostella
and Acanthodiscus is provided by the reappearance of latero-ventral
tubercles as in the new genus Paradicostella (Fig. 7 ). Several tabular representations of the phyletic
relationships between elements of the neocomitid fauna of the late Valanginian
and early Hauterivian have been proposed for the relationships of Dicostella
with related genera (Busnardo et
al., 1966; Thieuloy, 1971,
1977b).
A significant number of trituberculate species from the Berriasian to the Hauterivian have been historically attributed to the genus Acanthodiscus, which has subsequently become highly polyphyletic. Extensive research has been conducted to elucidate the relationships between these homeomorphic forms. The individualisation of the latest Valanginian genera Itierella n.gen. and Paradicostella n.gen. represents a further step in the understanding of Early Cretaceous 'Acanthodiscid-like' morphologies. The 'Acanthodiscid-like' phenotype is regularly observed in species with no phyletic relationship, indicating that the process is iterative and could be the result of a morphofunctional adaptation related to similar living conditions on platform-border environments.
Furthermore, the revision of the faunas of the Marnes de Mélogne, including the specimens collected by Busnardo et al. (1966), allows for the positioning of the Valanginian-Hauterivian boundary in the Hauteville-Lompnes sector, 1 m below the first units of the Pierre jaune de Neuchâtel, which is consistent with the proposal of Strasser et al. (2018, Fig. 10).
The authors would like to express their gratitude to the Carrière Blanc for granting them access to the Chaumarasse quarry. This paper has benefited from constructive comments by Dr. Josep Anton Moreno-Bedmar (Universidad Nacional Autónoma de México), Dr. Miguel Company (Universidad de Granada), and Dr. Michel Grenon (Editor of the Archives des Sciences). The authors are grateful to Dr. Emmanuel Robert (University of Lyon, France) for supplying information and access to the material under his care. The authors express their gratitude to the 'Muséum cantonal des sciences naturelles' in Lausanne for providing essential equipment and laboratories for casting and photographing specimens, as well as to Ms Régine Monnin and Ms Vanessa Terrapon for tinting the casts.
Baumberger E. (1908).- Fauna der unter Kreide im westschweizerischen Jura, part IV.- Abhandlungen des schweizerischen paläontologischen Gesellschaft, Zürich, t. XXXIV (1907), p. 1-45.
Bert D., Bersac S. & Canut L. (2020).- Implications of the 'hemihoplitid-like' ammonites iterative morphology in the context of the late Tethyan Barremian (Early Cretaceous).- Cretaceous Research, vol. 106, article 104239, 22 p.
Bulot L.G. (1990, unpublished).- Évolution des Olcostephaninae (Ammonitina, Cephalopoda) dans le contexte paléo-biogéographique du Crétacé inférieur (Valanginien-Hauterivien) du Sud-Est de la France.- D.S.E.R. Université de Dijon, 177 p.
Busnardo R., Énay R. & Pitre B. (1966).- L'Hauterivien inférieur et ses ammonites près d'Hauteville (Ain).- Travaux du Laboratoire de Géologie de la Faculté des Sciences de Lyon, Villeurbanne, vol. 13, p. 229-241.
Busnardo R. & Thieuloy J.-P. (1989).- Les ammonites de l'Hauterivien jurassien : Révision des faunes de la région du stratotype historique de l'étage Hauterivien.- Mémoires de la Société Neuchâteloise des Sciences Naturelle, vol. 11, p. 101-147.
Company M. (1987).- Los ammonites del Valanginiense del sector oriental de las Cordilleras Béticas (SE de España).- PhD thesis, Universidad de Granada, 294 p.
Desor E. & Gressly A. (1859).- Études géologiques sur le Jura neuchâtelois.- Mémoires de la Société des Sciences Naturelles de Neuchâtel, vol. 4, p. 1-153.
Donze P. & Thieuloy J.-P. (1975).- Sur l'extrême condensation du Valanginien supérieur dans le Jura neuchâtelois, en particulier dans le stratotype de Valangin, et sa signification dans l'ensemble des formations valanginiennes du Sud-Est de la France.- Comptes Rendus de l'Académie des Sciences, Paris, vol. 280 (Série D), p. 1661-1664.
Énay R. (1989).- Saint-Rambert-en-Bugey (3230).- Notice explicative, Carte géologique à 1/50 000, Orléans, no. 676, 84 p. URL: http://ficheinfoterre.brgm.fr/Notices/0676N.pdf
Goguel J. (1940).- Contribution à l'étude du groupe de Acanthodiscus radiatus.- Annales de Paléontologie, Paris, vol. 28 (1939-1940), p. 43-67.
Hyatt A. (1900).- Class 5. Cephalopoda. In: Zittel K.A. von (ed.), Text-book of palaeontology, vol. I.- Macmillan, London & New York, p. 502-592. URL: https://www.biodiversitylibrary.org/page/17392244
Jaccard A. (1869).- Description géologique du Jura vaudois et neuchâtelois et de quelques districts adjacents du Jura français et de la plaine suisse, compris dans les feuilles XI et XVI de l'Atlas fédéral.- Matériaux pour la Carte géologique de la Suisse, Berne, vol. 6, p. 1-340. URL: https://gallica.bnf.fr/ark:/12148/bpt6k6215563r
Kemper E., Rawson P. F. & Thieuloy J.-P. (1981).- Ammonites of Tethyan ancestry in the early Lower Cretaceous of north-west Europe.- Palaeontology, vol. 24, p. 251-311.
Marcou J. (1859).- Sur le Néocomien dans le Jura et son rôle dans la série stratigraphique.- Archives des Sciences physiques et naturelles (n. pér. 2), Genève, vol. 4, p. 42-66, 113-154.
Mojon P.-O., Musolino A., Bucher S. & Claude B. (2013).- Nouvelles données sur les ammonites du Valanginien - Hauterivien de la région stratotypique de Neuchâtel (Jura suisse) : Implications biostratigraphiques.- Carnets Geol., Madrid, vol. 13, no. A06 (CG2013_ A06), p. 237-254. DOI: 10.4267/2042/51216
Mutterlose J. (reporter), Autran G., Baraboschkin E.-J., Cecca F., Erba E., Gardin S., Herngreen W., Hoedemaeker P., Kakabadze M., Klein J., Leereveld H., Rawson P. F., Ropolo P., Vašíček Z. & Salis K. von (1996).- The Hauterivian Stage. In: Rawson P.F., Dhondt A.V., Hancock J.M. & Kennedy W.J. (eds.), Proceedings Second International Symposium on Cretaceous Stage Boundaries, Brussels 8-16 September 1995.- Bulletin de l'Institut Royal des Sciences Naturelles de Belgique, Sciences de la Terre, Bruxelles, vol. 66, p. 19-24.
Mutterlose J., Rawson P. F., Reboulet S., Baudin F., Bulot L., Emmanuel L., Gardin S., Martinez M. & Renard M. (2021).- The Global Boundary Stratotype Section and Point (GSSP) for the base of the Hauterivian Stage (Lower Cretaceous), La Charce, southeast France.- Episodes, Seoul, vol. 44, p. 129-150.
Neumayr M. & Uhlig V. (1881).- Ueber Ammonitiden aus der Hilsbildungen Nordeutsclands.- Palaeontographica, vol. 27, p. 129-203.
Paquier V. (1900).- Recherches géologiques dans le Diois et les Baronnies orientales.- Allier, Grenoble, 410 p.
Pictet F.-J. & Campiche G. (eds., 1858-1860).- Description des fossiles du terrain Crétacé des environs de Sainte-Croix.- Matériaux pour la Paléontologie Suisse, Genève, séries 2, vol. 1 Stratigraphie, Céphalopodes. 1858-1860: p. 1-380; 1858: p. 1-96; 1859: p. 97-208; 1860: p. 209-380. URL: https://gallica.bnf.fr/ark:/12148/bpt6k65397362
Rawson P. F. (1971).- The Hauterivian (Lower Cretaceous) biostratigraphy of the Speeton Clay of Yorkshire, England.- Newsletters on Stratigraphy, vol. 1, no. 4, p. 61-76.
Reboulet S. (1996).- L'évolution des ammonites du Valanginien-Hauterivien inférieur du bassin vocontien et de la plate-forme provençale (sud-est de la France) : Relations avec la stratigraphie séquentielle et implications biostratigraphiques.- Documents des Laboratoires de Géologie de la Faculté des Sciences de Lyon, Villeurbanne, vol. 137, 371 p.
Reboulet S., Atrops F., Ferry S. & Schaaf A. (1992).- Renouvellement des ammonites en fosse vocontienne à la limite Valanginien-Hauterivien.- Geobios, Villeurbanne, vol. 25, p. 469-476.
Reboulet S. & Szives O. (reporters), Aguirre-Urreta B., Barragán R., Company M., Idakieva V., Ivanov M., Kakabadze M.V., Moreno-Bedmar J.A., Sandoval J., Baraboshkin E.J., Çağlar M.K., Főzy I., González-Arreola C., Kenjo S., Lukeneder A., Raisossadat S.N., Rawson P.F. & Tavera J.M. (2014).- Report of the 5th International Meeting of the IUGS Lower Cretaceous Ammonite Working Group, the Kilian Group (Ankara, Turkey, 31st August 2013).- Cretaceous Research, vol. 50, p. 126-137.
Renevier E. (1874).- Tableau des terrains sédimentaires qui représentent les époques de la phase organique.- Bulletin de la Société Vaudoise des Sciences Naturelles, Lausanne, vol. 13, no. 72, p. 218-252.
Sayn G. (1889).- Note sur quelques Ammonites nouvelles ou peu connues du Néocomien inférieur.- Bulletin de la Société Géologique de France (3ème série), Paris, vol. 17, p. 679-688.
Schardt H. (1895).- Sur l'âge de la marne à Bryozoaires.- Actes de la Société helvétique des Sciences naturelles, Aarau, vol. 78, p. 41.
Strasser A., Charollais J., Conrad M. A., Clavel B., Pictet A. & Mastrangelo B. (2016).- The Cretaceous of the Swiss Jura Mountains: An improved lithostratigraphic scheme.- Swiss Journal of Geosciences, vol. 109, p. 201-220.
Strasser A., Clavel B., Monteil E., Charollais J., Piuz A. & Mastrangelo B. (2018).- La Formation du Grand Essert (Jura franco-suisse ; Valanginien supérieur p.p. à Hauterivien supérieur basal.- Archives des Sciences, Genève, vol. 70, p. 205-282.
Thieuloy J.-P. (1971).- Réflexions sur le genre Lyticoceras Hyatt, 1900 (Ammonoidea).- Comptes Rendus de l'Académie des Sciences (série D), Paris, vol. 272, p. 2297-2300.
Thieuloy J.-P. (1977a).- Les ammonites boréales des formations néocomiennes du Sud-Est français (province subméditerranéenne).- Geobios, Villeurbanne, vol. 10, p. 395-461.
Thieuloy J.-P. (1977b).- La zone à callidiscus du Valanginien supérieur vocontien (Sud-Est de la France). Lithostratigraphie, ammonitofaune, limite Valanginien-Hauterivien, corrélations.- Géologie Alpine, Grenoble, vol. 53, p. 83-143.
Thieuloy J.-P., Fuhr M. & Bulot L.G. (1990).- Biostratigraphie du Crétacé inférieur de l'Arc de Castellane (S.E. de la France). 1 : Faunes d'ammonites du Valanginien supérieur et âge de l'horizon dit de "La Grande Lumachelle".- Géologie Méditerranéenne, Marseille, t. XVII, no. 1, p. 55-99.
| Nomenclatural note: Life Sciences Identifier (LSID) https://zoobank.org/References/6A05A2C2-2C1A-42CD-8C53-FB104DE2ECC7 Genus Group Species Group |
