Examples of pathologies in the Middle-Upper Jurassic ammonites from Poland

Total of 445 ammonites bearing pathological deviations of their shells, have been sorted out from a rich (about thousand of specimens) ammonoid collection belonging to the present authors. The specimens are derived from two regions, where Jurassic rocks outcrop: Mesozoic border of the Holy Cross Mountains (Callovian) and the Polish Jura Chain (Bajocian to Oxfordian), situated in Central Poland. Additionally, 27 specimens from classical locality at Łuków Podlaski (Callovian) were also studied: these specimens come from archival collection of late Prof. Henryk Makowski, housed in the Faculty of Geology, Warsaw University. Pathological deviations of ammonite shells might be interpreted as an effect of the mantle epithelium damage caused by exogenous injuries (e.g. during predatory attacks, collision with substrate or even mating and feeding), parasitism or genetic aberrations. The resulted pathologies occur as discontinuation of shell ornamentation, secondary ornamental features, abrupt shift of symmetry of the shell or atrophy of regular sculpture. Considering the exogenous injury (e.g. attack of a predator) as a primary cause, the resultant pathologies indicate, that ammonites survived and healed the mantle epithelium wounds. Therefore, some kinds of shell pathologies may be a good indicator of predatory intensity. Pathological ammonites are derived from various stratigraphic intervals: Middle Jurassic – Bajocian (Parkinsoni Zone), Bathonian (Zigzag, Tenuiplicatus, Morrisi and Bremeri zones) and Callovian (Jason, Coronatum, Athleta and Lamberti zones); Upper Jurassic – Oxfordian (Mariae, Cordatum, Plicatilis, Transversarium and Bifurcatus zones). They represent 9 families (Stephanoceratidae, Parkinsoniidae, Kosmoceratidae, Cardioceratidae, Perisphinctidae, Morphoceratidae, Tulitidae, Reineckeiidae and Aspidoceratidae), including 15 genera and 25 species. Within the ammonites studied, 12 types of pathologies were recognized (see Hengsbach 1996 for details): "forma verticata" (47 specimens), "forma substructa" (2 specimens), "forma juxtasulcata" (1 specimen), "forma circumdata" (1 specimen), "forma chaotica" (5 specimens), "forma inflata" (2 specimens), "forma undatispirata" (3 specimens), "forma undaticarinata" (1 specimen), "forma calcar" (4 specimens), "forma cacoptycha" (1 specimen), "forma abrupta" (3 specimens), "forma seccata" (379 specimens). The frequency of occurrences of the above mentioned pathologies changes in particular ammonite families, but "forma seccata" and "forma verticata" sensu Holder (non Keupp; see Hengsbach 1996) clearly predominate in the Bathonian, Callovian and Oxfordian families Perisphinctidae, as well as subfamilies Cardioceratinae and Peltoceratinae.