Ivanites, Randolfe & Rustán & Bignon, 2022

Randolfe, Enrique A., Rustán, Juan José & Bignon, Arnaud, 2022, New dalmanitid trilobite taxa from the Lower Devonian of Argentina: comments on spinosity in endemic taxa from southern high paleolatitudes, Comptes Rendus Palevol 21 (2), pp. 17-38 : 21-22

Ivanites n. gen.

( Figs 3; 4)

urn:lsid:zoobank.org:act:05E3FE79-071D-4804-8373-F32E8FD7C6F6

TYPE AND ONLY SPECIES. — Ivanites leonorae n. sp.

TYPE LOCALITY. — Quebrada de Talacasto, San Juan Province, Argentina.

ETYMOLOGY. — Belonging to Ivan, for Ivan Grunewald, EAR’s cousin.

OCCURRENCE. — Lochkovian-Pragian, lower part of the Talacasto Formation, Quebrada de las Aguaditas, Quebrada de Talacasto and Loma de los Piojos sections, San Juan Province, Argentina.

DIAGNOSIS. — Dalmanitid with a smooth, widely subparabolic, cephalic margin. Very narrow sag. and exsag. anterior border, with a shallow epiborder furrow. Absence of preglabellar field. Glabella piriform-shaped, nearly flat in the mid-posterior portion; with frontal lobe slightly inflated and less convex sagitally in lateral view, nearly oval to sub-rhombic and evenly convex anteriorly in dorsal view. S1-S2 nearly straight and transversal, without contacting the axial furrows, with the adaxial portion apodemal and incised. Apodems of S1 slightly convex forward, located nearly at the same exsagittal distance to SO and apodems of S2. Eye maximum length exsag. nearly 40% of maximum cranidium length sag. Ocular surface anteriorly taller, with approximately 45 vertical rows of no more than 16 lenses each. Pygidium without ornamentation, broadly subtriangular with 18-20 axial rings and 14 pleurae. Five to six anteriormost pleurae sinuous (more convex forward at level of fulcrum), then tending to be evenly curved backward. Anterior and posterior pygidial pleural bands of equal length exsag. Pygidial pleural furrows incised and symmetrical in cross-section exsag. Pygidial interpleural furrows incised, approximately parallel to pleural furrows. Pygidial border and distal part of pleurae steeply inclined downward. Post axial region ridge-like dorsally, as a stout mucro in posterior view.

REMARKS

The material used to define Ivanites was doubtfully assigned to Kasachstania Maksimova, 1972 by Rustán (2016). Ivanites differs from Kasachstania , based on our recent emendation of its diagnosis ( Randolfe et al. 2020), in having shorter exsag. eyes, S1 and S2 without contacting axial furrows, subtriangular pygidium (not heart-shaped), higher number of axial rings and pleurae, pleural bands and furrows parallel and more sinuous, pleural bands of equal width exsag., and pleural furrows symmetrical in cross-section.

Ivanites challenges the current classification of subfamilies because it possesses diagnostic characters of both Dalmanitinae and Synphoriinae. The lack of well-developed cephalic and pygidial borders, the location of eyes and the width of pygidial pleural bands resemble the synphoriinines but the spacing between glabellar apodems, the number of pygidial segments and the presence of an epiborder furrow are characteristic of dalmanitines. This particular combination of characters supports Ivanites as a new genus and encourages a taxonomic revision of dalmanitid subfamilies.