Arasella, Ghaderi & Leda & Schobben & Korn & Ashouri, 2014

Ghaderi, A., Leda, L., Schobben, M., Korn, D. & Ashouri, A. R., 2014, High-resolution stratigraphy of the Changhsingian (Late Permian) successions of NW Iran and the Transcaucasus based on lithological features, conodonts and ammonoids, Fossil Record 17 (1), pp. 41-57 : 54-55

Arasella n. gen.

Derivation of name: after the Aras Valley, the locality of the type material.

Type species: Sinoceltites minutus Zakharov, 1983 .

Diagnosis: genus of the Dzhulfitidae with small conch reaching 30 mm diameter. Conch widely umbilicate with circular whorl cross section. Ornament with sharp ribs. Suture line with short external lobe, which reaches only 50 % of the depth of the adventive lobe. Adventive lobe and lateral lobe rounded and unserrated.

Discussion: Zakharov (1983) described the species as belonging to Sinoceltites , a genus belonging to the family Tapashanitidae and known from occurrences in South China. The species has a particular position in two respects: (1) it is obviously the stratigraphically youngest ammonoid to appear before the end-Permian mass extinction event in the NW Iranian sections, and (2) it has a morphology characterized by reduction of morphological characters such as the suture line and thus is difficult to interpret in terms of phylogeny. Two possible phylogenetic origins may be discussed:

(2) A paratirolitid origin – this would imply a simplification of conch and suture morphology. Indeed, obvious phylogenetic relationships occur between the stratigraphically older Paratirolites towards the younger Abichites in the reduction of size, the change from trapezoidal towards quadrate whorl cross sections, the disappearance of strong nodes in the sculpture and the reduction of sutural notching. Arasella has some similarities with the stratigraphically younger species of Abichites and may thus be an advanced but morphologically simplified descendent.