Isorthoceras Flower, 1962
|
publication ID |
https://doi.org/10.1186/s13358-025-00374-5 |
|
persistent identifier |
https://treatment.plazi.org/id/66120869-FFB1-FFDE-BDFD-E006FD74FE1E |
|
treatment provided by |
Felipe |
|
scientific name |
Isorthoceras Flower, 1962 |
| status |
|
Genus Isorthoceras Flower, 1962
Type species: Orthoceras sociale Hall in Miller, 1877, from the Katian Stage , Upper Ordovician Series, Maquoketa Shale, Iowa, USA .
Diagnosis: Smooth or cancellate orthocones with subcircular transverse section. Siphuncle subcentral; early segments barrel-shaped and slender, expanding abruptly at septal foramina with cyrtochoanitic to suborthochoanitic septal necks; during ontogeny, later segments become subcylindrical with suborthochoanitic to orthochoanitic septal necks. Endosiphuncular annuli grow forward and backward, joining those of adjacent segments to form continuous parietal lining of nearly uniform thickness throughout segments (after Ghavidel-Syooki et al., 2015).
Remarks: Typical specimens of Isorthoceras display a cancellate sculpture, and longitudinal lirae on the conch surface ( Ghavidel-Syooki et al., 2015; Kröger et al., 2009, 2011). According to the spatial and temporal distribution of Isorthoceras, Niko (2008) suggested that the taxa should arise from Laurentia and spread around Baltica during the Boda Event. However, Ghavidel-Syooki et al. (2015) compiled all the occurrences and records of Isorthoceras around the world, e.g., Sandbian and Katian of Laurentia, Sandbian of Avalonia and Baltica, and Katian of Arabia and Baltica ( Iran and Bohemia). Te latter authors accordingly suggested that this genus might have originated from Baltica, or it might be Laurentia. Te distribution pattern agrees with the habit of Isorthoceras (Kröger et al., 2009) .
Figure 3 View Fig
Locality and horizon: Tanout el Fecht, northeastern Anti-Atlas region, Morocco. Upper Tiouririne Formation, Katian Stage, Upper Ordovician Series.
Material: Two specimens, NIGP207332 View Materials and NIGP207333 View Materials , at Tanout el Fecht, northeastern Anti-Atlas , the Upper Tiouririne Formation, Katian Stage, Upper Ordovician Series .
Description: One specimen, NIGP207332 ( Fig. 3A, B View Fig ), comprises portions of the phragmocone and part of the body chamber, 55 mm in maximum diameter and 195 mm in length. Te apical angle slightly exceeds 7°. Te shell ornament cannot be studied due to the poor preservation of the shell surface. Te conch cross-section is circular. Te cameral height varies from 6.3 to 13.1 mm (0.18–0.25 of the corresponding conch diameter). Te siphuncle is subcentral at the dorsal–ventral median section. Te siphuncle is barrel-shaped and expands abruptly at the septal foramen, with a diameter at the septal foramen of 0.07 of the corresponding phragmocone diameter. Septal necks are suborthochoanitic. Siphuncular and cameral deposits are not presented.
The other specimen, NIGP207333 ( Fig. 3C, D View Fig ), comprises portions of a phragmocone 41 mm in maximum diameter and 114 mm in length. The apical angle could not be determined due to the poor preservation of the specimen. The surface of the conch is unknown. The conch cross-section is circular. The cameral height varies between 6.1 and 10.6 mm (0.16–0.27 of the corresponding conch diameter). The siphuncle is subcentral, barrel-shaped, and expands abruptly immediately after the septal foramen, with a diameter at the septal foramen of 0.06 of the phragmocone diameter
( Fig. 3D View Fig ). Septal necks are suborthochoanitic. Connecting rings are adnate at the episeptal surface of the septa. Endosiphuncular and cameral deposits are visible and more developed on the ventral side of the siphuncle and camerae.
Remarks: Te material described above does not appear to differ significantly from other specimens of Isorthoceras in most internal characters measured, i.e., the large size and abrupt expansion of the siphuncular segments. Although the present specimens share many characters with the genus Isorthoceras , we assign it only in open nomenclature. Furthermore, the species and have been suggested to need revision ( Ghavidel-Syooki et al., 2015; Kröger et al., 2011).
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.