Crickites – investigation of a unique extinction taxon of Palaeozoic goniatites (Ammonoidea)

The extraordinary genus Crickites is chronologically restricted to the uppermost Frasnian (Upper Devonian, UD I–L), occurring exclusively during the Upper Kellwasser Crisis, often in large numbers and with remarkable body size (> 40 cm). Morphological features place it within the Gephuroceratidae, distinguished particularly by its characteristic suture with a high ventrolateral saddle. Unlike most other representatives of this family, which exhibit biconvex growth lines, Crickites - along with its much thinner sister genus Clauseniceras - is characterized by exclusively convex growth lines. Additionally, the conch is unusually wide and becomes progressively wider through ontogeny. Crickites ranks among the largest known ammonoids of the Devonian, thriving during a time of severe ecological changes now recognized as one of the major mass extinction events in Earth’s history. This apparent paradox of a global spreading followed by rapid extinction, raises significant evolutionary and palaeoecological questions. The genus shows a wide distribution, from Cr. lindneri in the Canning Basin (NW Australia), to Cr. holzapfeli in the Rhenish Mountains (Germany), and supposed Cr. rickardi in the Appalachians (North America). A major challenge, however true for all gephuroceratids, is the unresolved taxonomy and systematic classification. Contributing factors include a historically fragmented and inconsistent research history, the loss of type material, and the lack of precise diagnoses. To date, it remains unclear how many and which species are validly assigned to Crickites. Therefore, this study provides the first comprehensive revision of this important yet poorly understood fossil group.