Report of shell paleopathologies in Antarctic ammonoids of the López the Bertodano Formation (Late Cretaceous, Antarctic Peninsula)

MORÓN-ALFONSO, DANIEL; LUCI, L.; HOFFMANN, RENÉ; VENNARI, V.V.; CICHOWOLSKI, MARCELA

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2024

0002-7014

This study documents ten potential paleopathologies observed in Antarctic ammonoids from the López de Bertodano Formation. Specifically, four cases are identified in the species Grossouvrites joharae, while Maorites densicostatus shells exhibit six . The observed pathologies vary in severity, ranging from minor lesions along the apertural margin to more extensive abnormalities or injuries affecting up to 180° of the whorl. These anomalies include alterations in ribbing patterns, small constrictions, and malformation of ornamental elements. Various interpretations have been proposed to explain these pathologies, such as fractures or injuries that could affect the shell-secreting soft tissues (resulting in recurrent anomalies during healing), illness, toxicity, and/or environmental stress. A specific case involving a M. densicostatus specimen is described, wherein three enigmatic annular traces were observed in the ventral region of a steinkern of the body chamber. These traces were interpreted as likely attachment sites of an unknown organism following the ammonoid soft-tissue degradation. The discovery of these paleopathologies can be attributed to several factors, including the excellent preservation state of the available specimens, which retained multiple layers of the original shell wall, the utilization of methodologies aimed at enhancing the visualization of surface features (such as Reflectance Transformation Imaging), and specific characteristics of the cartographic unit (Klb9) of the López the Bertodano Formation from which the majority of the specimens were recovered.