Kiaeroceras Strand, 1934

Kröger, Björn, 2025, The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia, European Journal of Taxonomy 978, pp. 1-169 : 106

Genus Kiaeroceras Strand, 1934

Type species

Kiaeroceras frognoyense Strand, 1934 , from Frognoyøa island, Ringerike, Norway, “ Trinucleus limestone, (4cβ)” ( Strand 1934: 98), SØrbakken Formation, Late Katian; by original designation.

Diagnosis

Orthocones with ovate conch cross section, narrower ventral conch margin; mature body chamber slightly bulbous, with shallow constriction near aperture; aperture with deep and broad hyponomic sinus; sutures with lateral lobes and pronounced ventral saddle; siphuncle close to ventral conch margin, with broadly expanded siphuncular segments, with prominent bullettes. (Adopted from Strand 1934.)

Remarks

The diagnosis of the genus given in Kröger (2013) is imprecise, it is corrected herein and features now the important characters described in Strand (1934). Moreover, the relatively rich Estonian material described herein reveals a few features, not known from type material of the type species. These include the shape and dimensions of the more apical phragmocone parts, variability in conch cross section shape as well as the extent and development of endosiphuncular deposits. Consequently, species are included here, which have conch cross sections with a CHI of nearly 1, although possessing the characteristically narrow margin on the prosiphuncular side. Additionally, the hyponomic sinus which is deep in the type species, does not seem to be deep in all species. Finally, the more complete specimens of this genus reveal that the curvature is endogastric and that the suture develops a lateral lobe during the latest growth stages (compare, e.g., Fig. 34H , and Strand 1934: pl. 9 fig. 4 and pl. 12 fig. 2). The genus is interpreted here sensu lato, to include these deviations from the original diagnosis.

The genus was placed within the Cyrtogomphoceratidae by Teichert (1964b) and has been compared to Protophragmoceras by Strand (1934). This was based on the presence of heavy endosiphuncular bullettes in the type-material. The new material, described herein, shows that in specimens assigned to Kiaeroceras transitions exist from typical discosorid-like bullettes toward valcouroceratid-like actinosiphonate deposits (see below in description of K. kaebliki sp. nov.).

Moreover, Strand (1934) described Mixosiphonoceras norvegicum Strand, 1934 from late Katian strata in Norway. The type species of Mixosiphonoceras is mid Silurian in age and the genus is placed within the Brevicoceratidae , which are known otherwise only from the mid Silurian to Devonian. Therefore, it is likely that the Norwegian species represents another Kiaeroceras .

The presence of actinosiphonate deposits in endogastrically curved Kiaeroceras , in orthocones ( Mixosiphonoceras norvegicum Strand, 1934 ), and in exogastrically curved valcouroceratids suggests either multiple independent origins of this type of endosiphuncular deposit or a close relationship between these taxa. A detailed phylogenetic, or cladistic analysis of the oncocerid-discoserid groups, which could help to solve this open question (suggested also by Pohle et al. 2022) is beyond the scope of this work.

Below, four species of Kiaeroceras are described in open nomenclature. These are known almost exclusively from their mature body chambers. Their differing sizes and shapes are unique, and they differ from species described in the literature and herein. However, the relatively low number of known specimens of Kiaeroceras does not permit evaluation of the intraspecific and interspecific variability in, e.g., mature body chamber size, and CHI. The possibility therefore exists, that some of these species, represent intraspecific variability.

Figures

Fig. 34. Dalecarlioceras Frye, 1987 of the Vormsi–Pirgu regional stages, Estonia. A–B. Dalecarlioceras constrictum Frye, 1987, specimen GIT 878-251, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. A. View of the prosiphuncular side. B. Lateral view. C. Dalecarlioceras sp., specimen GIT 878-250, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage, lateral view. D–F. Dalecarlioceras bodense Frye, 1987, specimen TUG 1745-213, from Saaremõisa (Lyckholm), Vormsi Regional Stage. D. Adapical view. E. Lateral view. F. View of the antisiphuncular side. Scale bar = 20 mm in all figures, same scale in A–C, and in D–F.