| Species | Ectocentrites petersi (HAUER) |
| Author | HAUER |
| Group | Lyctoceraten |
| Horizon | rotiformis-horizon subsalinarius-horizon atanatense-horizon pachygaster-horizon seebachi-horizon curviornatum-horizon |
| Zone | rotiformis-zone marmoreum-zone megastoma-Zone |
| Stage | Lower Sinemur Upper Hettangian Middle Hettangian |
Description
The cross-section of the coils is circular to slightly oval, becoming increasingly oval in larger cases, i.e. typically lytoceratid. Ectocentrites can become very large in the horizons with Angulaticeras marmoreum and D. atranatense. In younger horizons like the cylindricum horizon, where predominantly all ammonites are very small, only very small shells are found.
Characteristic are the constrictions on the innermost coils, which occur in this form only in Ectocentrites.
The ribs are fine and run straight or slightly curved over the flanks. They reach their greatest height near the external side and end in a spine. These spines usually disappear in larger cases, where the ribbing then simply ends in a point on the outer third of the flank.
It is not uncommon to find specimens together with Angulaticeras marmoreum, but Ectocentrites is also a typical element in much younger horizons (cylindricum horizon). Apparently the species is very long-lived.
Compare
At first glance, small specimens are very easy to confuse with Schlotheimia or Angulaticeras, where the external side also remains smooth.
So be careful with the determination! An indeterminable Schlotheimia could be an Ectocentrites. However, the constrictions on the inner coils and the lytoceratid cross-section are unambiguous.
Similar is Pleuracanthites, which, however, has no constrictions and also no fine ribbing. The lobe line is also different. Wähner describes Ectocentrites in great detail.
Dimension
Dimensions with D= 42mm
Nw % v. D: ca. 35%
Wh % v. D: ca. 36%
Wb % v. D: ca. 36%
Literature
- 1890 Lytoceras articulatum Sow. (Orb.) – Wähner S. 255, Taf, 54.3, 58.1-5, 59.1-15, 60-1-2
- 1993 Analytoceras articulatum Sowerby – Rakus & Lobitzer, S. 924, Abb. 11
- 2000 Analytoceras articulatum Sowerby – Kment S. 194
- 2021 Ectocentrites petersi (HAUER) – KMENT S. 269, Fig. 10.5-7, 12.5
