Genus Eckhardites Mitta (Cardioceratidae, Ammonoidea) from the Lower Callovian of the Subboreal Jurassic V
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ISSN 0031-0301, Paleontological Journal, 2009, Vol. 43, No. 1, pp. 50–58. © Pleiades Publishing, Ltd., 2009. Original Russian Text © V.V. Mitta, 2009, published in Paleontologicheskii Zhurnal, 2009, No. 1, pp. 47–53. Genus Eckhardites Mitta (Cardioceratidae, Ammonoidea) from the Lower Callovian of the Subboreal Jurassic V. V. Mitta Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya 123, Moscow, 117997 Russia e-mail: [email protected] Received July 2, 2007 Abstract—The genus Eckhardites Mitta 1999, with the type species Macrocephalites pavlowi Smorodina, 1928 is discussed and its diagnosis and assignment to the family Cardioceratidae are substantiated. Eckhardites is compared to the genus Macrocephalites Zittel (family Sphaeroceratidae), to which some workers presently assign the type species of Eckhardites. Three species of Eckhardites are recorded from the basal Callovian elat- mae Zone of the Russian Platform, one of which (E. menzeli (Mönnig)) was originally described from the syn- chronous beds in Germany. A new species E. dietli sp. nov. is described. DOI: 10.1134/S0031030109010055 Key words: genus Eckhardites, Cardioceratidae, Ammonoidea, Lower Callovian, subboreal Jurassic. INTRODUCTION Gulyaev (1999) described several specimens of Several years ago (Mitta, 2000) described the genus Eckhardites (from Ivkino on the Unzha River in the Eckhardites Mitta, 1999 with the type species Macro- Kostroma Region and from Prosek-Isady on the Volga cephalites pavlowi Smorodina and containing two River in the Nizhnii Novgorod Region) as Macroceph- other species identified in open nomenclature alites (Macrocephalites) pavlowi Smorodina and (Eckhardites sp. and E. aff. menzeli (Mönnig)) in the M. (M.) ex gr. jacquoti Douvillé. Later (Gulyaev, 2001) family Cardioceratidae Siemiradzki, 1891. However, some of the specimens were refigured. M. prosekensis some workers did not accept this genus and continued Gulyaev (= nom. nov. pro Macrocephalites (M.) ex gr. assigning the type species and its close allies to the jacquoti sensu Gulyaev, 1999, pl. 1, fig. 1). was estab- genus Macrocephalites, following N.S. Smorodina lished based on a specimen less than 50 mm in diame- who worked at the beginning of the 20th century. In ter. Later, Gulyaev (2007) figured but did not describe addition, recently, Eckhardites has also been recorded three specimens of E. pavlowi from Churkina on the in various sections and horizons of the Lower Callovian Pizhma River (Pechora River basin) as Macrocepha- of European Russia. Therefore, it has become neces- lites (M.) pavlowi, M. (M.) cf./aff. jacquoti and M. (M.) sary to reexamine this genus, especially its differences prosekensis. from Macrocephalites. Gulyaev did not discuss Eckhardites in the above In 1928, Smorodina described a new species Macro- papers, but recently in their joint papers, Kiselev and cephalites pavlowi, based on three specimens (from the Rogov (2007a, 2007b) discussed matters regarding this Unzha River basin in the Kostroma Province, collected genus. The above workers have no doubts concerning by M.I. Sokolov and M.A. Veidenbaum; from the Sura the validity of the lineage Macrocephalites jacquoti River basin in the Nizhnii Novgorod Region, collected M. cf./aff. jacquoti M. prosekensis M. pav- by A.P. Pavlov) in a paper on the genus Chamoussetia lowi, and they propose the first species as an index spe- (Cadoceratinae, Cardioceratidae) and discussed its cies of the basal faunal horizon of the Callovian on the relationships with the closely related taxa. At the end of Russian Platform. The state of preservation of their the 20th century I discovered and refigured two of material is poor (which was also acknowledged by the Smorodina’s syntypes in the collections of the Vernad- authors themselves) and in most cases does not allow sky State Geological Museum, in Moscow (Mitta and specific identification. Therefore I reidentify “Macro- Starodubtseva, 1998, pl. 1, fig. 1; pl. 2, figs. 1, 2). cephalites jacquoti” (Kiselev and Rogov, 2007b, pl. 2, A third syntype, which had not been previously figured, figs. 3–7) as Eckhardites sp. juv., whereas “M. prosek- was discovered later (Mitta, 2000, pl. 7, fig. 2). The ensis” (Kiselev and Rogov, 2007b, pl. 5, fig. 2), appar- reexamination of the type series and other material, ently belongs to E. pavlowi. including specimens collected by myself, allowed the The confusion displayed above shows that a com- conclusion that this species belongs to a new genus in parative study of Eckhardites and Macrocephalites is the family Cardioceratidae (Mitta, 1999), which necessary to resolve difficulties in identifications of received the name Eckhardites. genera and families in this group. In the Callovian of 50 GENUS ECKHARDITES MITTA (CARDIOCERATIDAE, AMMONOIDEA) 51 the Russian Platform, representatives of the genus Mac- Specimen no. Dm WH WW Du WH/Dm WW/Dm Du/Dm rocephalites are found across a large territory, but are rare. Representatives of Macrocephalites from central SMNS 62500 154 93 75 16 0.6 0.49 0.1 Russia were previously considered by me (Mitta, 1998; 127 71 58 15 0.56 0.46 0.12 2000). The Lower Callovian beds in this region defi- SMNS 67152 64 35 29.5 7 0.55 0.46 0.11 nitely contain M. pila (Nikitin, 1885), M. verus Buck- 5029/074 45 23 23 9 0.51 0.51 0.2 man, 1922, M. zickendrathi Mitta, 1998 (including 32 17 17 7 0.53 0.53 0.22 M. volgensis Gulyaev, 1999, as a junior subjective syn- 5029/072 25 12 14 5 0.48 0.56 0.2 onym), and, apparently, M. krylowi (Milachewitsch, 5029/067 21 10 10 4 0.48 0.48 0.19 1879) (the holotype of the latter species is lost). Several 5029/066 20 10 11 4 0.5 0.55 0.2 other forms are described in open nomenclature. All these ammonoids are readily distinguished from Eck- 5029/078 20 11 10 3 0.55 0.5 0.15 hardites by the shell shape and ornamentation. There- 14 6 8 2 0.43 0.57 0.14 fore, for comparison, it is suitable to consider Macro- 5029/065 17 8 10 3 0.47 0.59 0.18 cephalites jacquoti, which, in my opinion, has been erroneously recorded from the Russian Platform. The ornamentation at early stages is represented by relief, mainly bifurcating ribs, equally high along their The name Ammonites jacquoti was proposed by entire length, which run radially across the flanks, and Douvillé (1878, p. 570; cit. after Callomon, 1971) for are slightly bent orad on the venter. The bifurcation Ammonites macrocephalus compressus Quenst. (Quen- point lies in the lower third–middle zone of the flanks. stedt, 1849, p. 182, pl. 15, fig. 1; the lectotype was AS the shell grows, the ribs become weaker, but are refigured by Thierry (1978, pl. 27, fig. 1). The type usually well pronounced almost until the end of the series comes from Southern Germany (Swabia). I had phragmocone (Fig. 1), which on average reaches an opportunity to study the extensive material on this 175 mm in diameter (see Dietl and Gygi, 1998, pl. 3). species from the Swabian Alps (Swäbische Alb) in the Usually, in Macrocephalites, the adult shell with the Stuttgart Museum of Natural History. G. Dietl kindly body chamber occupies 0.8 of the whorl, reaching gave me for examination several specimens of M. jac- 200 mm or more in diameter. The aperture in these quoti from the “Macrocephalen-Oolith” (faunal hori- forms is simple, with a small ventral projection. zon keppleri) from the Albstadt–Pfeffingen Section. In G. Schweigert (pers. comm.) informed me that the col- addition, an amateur paleontologist N. Wannenmacher lection of the Stuttgart Museum of Natural History con- donated an excellent collection of juvenile specimens tains a specimen of M. jacquoti from the locality Albs- of this species from the Bisingen–Thanheim locality in tadt–Pfeffingen, 240 mm in diameter, with a complete the valley of the Klingenbach River (see Dietl, 1981 for body chamber, occupying about 0.8 of the whorl and the section description). Like the previous, the latter without a well-developed preapertural constriction. collection comes from the main bed of “Macroceph- At a diameter 15–35 mm, Eckhardites (see dimen- alen-Oolith.” This allowed the comparison of the Swa- sions below, in the description of a new species) are bian and Central Russian material. characterized by flattened or moderately wide whorls, with high, arrow-shaped cross section, and with a nar- row venter (Pl. 6, fig. 6; pl. 7, figs. 4–6). The whorl DISCUSSION height is considerably greater than its width (by 40– In Jurassic ammonites, differences of the generic 50%). As the shell grows, the whorls become wider, rank and more so of the familial rank are usually well and some species have a weakly inflated body chamber. pronounced at early stages, at a diameter of 15–20 mm. The umbilicus is narrow or moderately narrow. At this ontogenetic stage, M. jacquoti is characterized At early stages, the ornamentation is represented by by strongly inflated whorls with a rounded cross-sec- relatively thin ribs, arranged in bunches of 3–5 branches, tion with a wide venter (see Pl. 6, figs. 1–3; pl. 7, fig. 2). running across the flanks with a strong inclination orad. The whorl height is slightly less (at Dm less than At Dm > 15–25 mm the ribs in the umbilical zone and 15 mm) or equal to the whorl width (Dm = 5–25 mm). most of the flanks are smoothened. Thus, in the last With age, (Pl. 7, figs. 1, 4) the shell becomes less 1.5–2 whorls of the phragmocone, the ribs are observed inflated, with the height exceeding the width by 20% at mainly in the ventrolateral region. The body chamber the most. At early stages, the umbilicus is moderately can be smooth, possessing only growth lines (Pl.