Amaltheus Montfort, 1808

Bardin, Jérémie, Rouget, Isabelle & Cecca, Fabrizio, 2013, Late Pliensbachian (Early Jurassic) ammonites from Lac de Charmes (Haute-Marne, France): Systematic, biostratigraphy and palaeobiogeography, Geodiversitas 35 (2), pp. 309-334 : 319-322

Genus Amaltheus Montfort, 1808

Nordamaltheus Repin in Efimova et al., 1968: 111. — Type species: Amaltheus (Nordamaltheus) viligaensis (Tuchkov, 1954) .

TYPE SPECIES. — Amaltheus margaritatus Monfort, 1808 (by original designation).

STRATIGRAPHIC DISTRIBUTION. — Late Pliensbachian, Margaritatus chronozone, base of Stockesi subchronozone up to middle Spinatum zone, top of Apyrenum subchronozone. Haute-Marne: bed 3 to 13.

DIAGNOSIS. — Ľe more distinctive character is the crenulated keel made by more or less inclined chevrons. Ľe shell is involute to moderately involute. Whorl section is subtriangular, often compressed (subovate to subcircular in some forms and at small diameter). Ľe ribs are bifurcated, trifurcated or quadrifurcated. Between the point of branching and the beginning of the chevrons (ventral) the coarseness of the ribs is often reduced. Chevrons are two to four times more numerous than the ribs. Ornamentation is highly variable and covaries with the curvature of the flanks: evolute forms develop strong ribs and spines, while compressed and involute forms are almost smooth. Ľerefore, lateral tubercles are common in the young specimens with low and rounded whorls. At the end of the growth all Amaltheus species show the compression of the whorls and a reduction of the radial ornamentation (including crenulation strength of the keel). A trifid first lateral saddle and a first, deep trifid lateral lobe characterize the suture. Auxiliary saddle is well developed in the ventral lobe.

DISCUSSION

Ľe combination of crenulated keel and triangular whorl section allows the distinction of the genus

Amaltheus from the genus Pleuroceras , which develops some quadrilateral whorls.

Amaltheus margaritatus Montfort, 1808 ( Figs 4A, B ; 5A, B ; 6F, G ; Table 3)

Amaltheus margaritatus Montfort, 1808: 90 . — d’Orbigny 1844: 246, pl. 67, figs 1-3; non pl. 68, figs 1-8. — Wright 1882: 397, pl. 53, fig.1, pl. 54, figs 1-3, text-fig. 8. — Howarth 1958: 15, 16, text-figs 8, 9. — Fischer 1994: 63, pl. 27, fig. 1a-c.

Ammonites acutus Sowerby, 1813: 51 , pl. 17, fig. 1.

Ammonites amaltheus Schlotheim, 1813: 101 .

Ammonites depressus Simpson, 1843; figured in Buckman S. S. 1911: pl. 25, figs 1, 2.

Ammonites Sedgwickii Buckman J., 1845: 40; figured in Buckman S. S. 1918: pl. 125 (nomen nudum).

Ammonites amaltheus nudus Quenstedt, 1849: 94, pl. 5, figs 11, 12 (refigured in Frentzen 1937: pl. I, fig. 28).

Ammonites foliaceus Giebel, 1852: 540 .

Ammonites amaltheus compressus Quenstedt, 1885: 327, pl. 41, fig. 17; pl. 42, fig. 8.

Amaltheus (Amaltheus) margaritatus – Tintant et al. 1961: pl. I, figs 6, 7.

TYPE MATERIAL. — Ľe specimen figured by Monfort (1808) is presumed to be lost. Howarth designated the specimen BM 37039 as neotype (1958: 15, text-fig. 8).

SPECIMENS AVAILABLE. — UPMC-101, 102, 104,105, 108-110, 112, 118, 120, 127, 129-131, 133, 136, 137, 143-145, 147, 149, 151, 155, 158, 159, 222-224.

STRATIGRAPHIC DISTRIBUTION. — Late Pliensbachian, Margaritatus chronozone, base of Subnodosus subchronozone up to the middle of the Spinatum chronozone , top of Apyrenum Subzone. Haute-Marne: bed 3 to bed 13.

GEOGRAPHIC DISTRIBUTION. — South-East France, Causses ( Monestier 1913, 1916, 1928; Mattéi 1985; Meister 1989; Morard 2004); eastern France, Burgundy ( Tintant et al. 1961; Lablanche et al. 1997) and Haute-Marne (this work); North-West France, Paris Basin, Normandy ( Dommergues et al. 2008); North-West Germany ( Jordan 1971); South- West Germany ( Frentzen 1934; Urlichs 1977); England ( Howarth 1958); Scotland ( Howarth 1958); Bulgaria ( Stephanov 1960); Iran, Alborz Range (Seyed-Emami et al. 2008); Georgia ( Topchishvili 1998); Portugal ( Mouterde 1967); Morocco, Moyen-Atlas ( Morard 2004);Siberia ( Dagis 1976); Italy, Lombardy Basin ( Wiendenmayer 1980); North America, Stikinia allochthonous terrane and Arctic-Alaska craton ( Smith et al. 2001); Tunisia ( Fauré et al. 2007).

DESCRIPTION

Ľe whorl section is compressed with the whorl heigth matching at least twice the whorl breadth. Ľe umbilical edges are angular. Ribbing is weak and does not develop any spines or tubercles. Ľese diagnostic character states must be observed on adult whorls because some A. margaritatus have inner whorls (D <2-3 cm) showing the morphologies of A. gibbosus or A. gloriosus .

DISCUSSION

Ľis is the most common Amaltheidae species. Amaltheus margaritatus can be distinguished from the other Amaltheus species because of the absence of spines or tubercles and the important reduction of ribbing strength starting from a diameter of around 25 mm.

Amaltheus gibbosus ( Schlotheim, 1820) ( Figs 4 C-F; 5I, J; Table 3)

Ammonites amaltheus gibbosus Schlotheim, 1820: 66 .

Amaltheus turgidus Hyatt, 1867: 90 .

Amaltheus margaritatus var. muntjanae Tietze, 1872: 102 , pl. 2, fig. 5.

Amaltheus gibbosus – Howarth 1958: 17, text-fig. 10.

Amaltheus (Amaltheus) gibbosus – Tintant et al. 1961: pl. 1, fig. 4. — Mattéi 1985: pl. 1, fig. 1H.

TYPE MATERIAL. — Ľe lectotype chosen by Howarth (1958) is the specimen n°2.4.Q.K. (Berlin University Museum) figured in Schlotheim (1820: 66). It is refigured in Howarth (1958: 17, text-fig. 10).

SPECIMENS AVAILABLE. — UPMC-100, 103, 106, 107, 111, 114, 115, 116, 126, 128, 132, 138, 146, 148, 150, 152, 153.

STRATIGRAPHICAL DISTRIBUTION. — Late Pliensbachian, Margaritatus chronozone, base of Gibbosus subchronozone up to the top of Gibbosus subchronozone. Haute-Marne: bed 3 to bed 5.

GEOGRAPHIC DISTRIBUTION. — South-East France, Causses ( Monestier 1913, 1916, 1928; Mattéi 1985; Meister 1989; Morard 2004); North-West France, Paris Basin, Normandy ( Dommergues 2008); eastern France, Burgundy ( Tintant et al. 1961; Lablanche et al. 1997) and Haute-Marne (this work); North-West Germany ( Jordan 1971); South-West Germany ( Frentzen 1934; Urlichs 1977); Austria, northern Calcareous Alps (Meister & Böhm 1993); England and Scotland ( Howarth 1958).

DESCRIPTION

Ľe shell is moderately evolute with a subelliptic whorl section. Up to a diameter of about 20 mm, whorls are larger than high and a tubercle is present on each rib (stadium coronatum, Quenstedt, 1885). From a diameter of 20 mm, a strong tubercle develops near the ventro-lateral edge every two or three ribs (stadium gibbosum, Schlotheim, 1820). Sometimes a later ontogenetic stage occurs, tending towards the character states of A. margaritatus , i.e. lack of tubercles and ovate whorl section (stadium nudum [Quenstedt 1885]).

DISCUSSION

Amaltheus gibbosus differs from A. salebrosum because of the stronger involution and its higher whorl section. Ľe adult size of A. gibbosus is smaller than that of A. salebrosum . Amaltheus gibbosus differs from A. gloriosus because of both the stronger involution and the presence of the stadium gibbosum, which consists of a tubercle every two or three ribs.

Amaltheus salebrosum Hyatt, 1867 ( Figs 5K, L ; 6H, I ; Table 3)

Amaltheus salebrosus Hyatt, 1867: 90 (nom. nov. for Quenstedt, 1849: 95, pl. 5, fig. 4b; 1856: 168, pl. 20, fig. 8). Ammonites amaltheus spinosus Quenstedt, 1849: 95 , pl. 5, fig. 4b; 1856: 168, pl. 20, fig. 8; 1885: 321, 322, pl. 41, fig. 5.

Amaltheus armiger Buckman, 1911 (nom. nov. for Quenstedt 1885: 321, 322, pl. 41, fig. 5).

Amaltheus bechteri Frentzen, 1934: 40-42 (nom. nov. for Quenstedt 1885: 321, 322, pl. 41, fig. 5); 1937: pl. 5, figs 6, 7, 10-12.

Pleuroceras salebrosum – Howarth 1958: 34, text-fig. 13. — Tintant et al. 1961: pl. 1, fig. 10.

Amaltheus postremus Mattéi, 1985: 117 , pl. 12, fig. 1.

TYPE MATERIAL. — Buckman designated Quenstedt 1856: 168, pl. 20, fig. 8 lectotype of A. salebrosum . Ľis specimen is assumed to be lost, thus Howarth (1958) designated a topotype as neotype (Tübingen Museum Ce 5/41/5, text-fig. 13).

SPECIMENS AVAILABLE. — UPMC-225, 173, 188, 192.

STRATIGRAPHICAL DISTRIBUTION. — Upper Gibbosus subchronozone – base of Hawskerense subchronozone. Haute-Marne: bed 7 to 13.

GEOGRAPHIC DISTRIBUTION. — England and Scotland ( Howarth 1958); eastern France, Burgundy ( Tintant et al. 1961; Lablanche et al. 1997) and Haute-Marne (this work); North-west Germany ( Jordan 1971); South-West Germany ( Frentzen 1934); South-East Germany (Hoffman et al. 2007); Italy, Lombardy Basin ( Wiendenmayer 1980).

DESCRIPTION

Evolute shell with a whorl section similar to that of the inner whorls of Pleuroceras (presence of sulci formed on both sides of the keel by strong ribbing).In the last whorls, the section is nearly circular.Strong tubercles near the ventro-lateral edge are developed every two or three ribs. Ľe expression of this tuberculate stage seems to be very irregular. In the classical specimens of A. salebrosum (i.e. Neotype: Howarth 1958: textfig. 13), tubercles develop all along the growth. In some specimens, especially German faunas(Quensted 1885; Frentzen 1937), this stage can be reduced to only three tubercules(i.e. Frentzen 1937:pl.VI, fig.2).

DISCUSSION

Ľis species can be confused with A. gibbosus , which does not exceed a diameter of 70 mm, whereas A. salebrosum can reach 150 mm. Amaltheus salebrosum is more evolute than A. gibbosus in the adult whorls. From the stratigraphic point of view, A. salebrosum appears together with P. transiens after the disappearance of A. gibbosus .

Figures

FIG. 4. — Amaltheus margaritatus Montfort, 1808: A, B, specimen UPMC-137, Outcrop 1, bed 3, Amaltheus gibbosus (Schlotheim, 1820); C, D, specimen UPMC-100, Outcrop 1, bed 3; E, F, specimen UPMC-138, Outcrop 1, bed 3. Scale bar: 1 cm. The arrows indicate the beginning of the body chamber.

FIG. 5. — Amaltheus margaritatus Montfort, 1808:A, B, specimen UPMC-104, Outcrop 1, bed 3; E, F, specimen UPMC-147, Outcrop 1, bed 5. Amaltheus gibbosus (Schlotheim, 1820); I, J, specimen UPMC-148, Outcrop 1, bed 5; Amauroceras ferrugineum (Simpson, 1855); C, D, specimen UPMC-140, Outcrop 1, bed 3; G, H, specimen UPMC-139, Outcrop 1, bed 3. Amaltheus salebrosum Hyatt, 1867; K, L, specimen UPMC-225, Outcrop 1, bed 7. Pleuroceras transiens (Frentzen, 1937); M, O, specimen UPMC-174, Outcrop 1, beds 8, 9. Scale bars: 1 cm. The arrows indicate the beginning of the body chamber.

FIG. 6. — Pleuroceras transiens (Frentzen, 1937): A, B, specimen UPMC-175, Outcrop 1, bed 8, 9; C, D, E, specimen UPMC-176, Outcrop 1, bed 8, 9. Amaltheus margaritatus Montfort, 1808; F, G, specimen UPMC-187, Outcrop 1, bed 13. Amaltheus salebrosum Hyatt, 1867; H, I, specimen UPMC-188,Outcrop 1, bed 13. Scale bar: 1 cm.The arrows indicate the beginning of the body chamber.