REEVALUATION OF THE CRETACEOUS MARINE LIZARD ACTEOSAURUS CRASSICOSTATUS CALLIGARIS, 1993

Abstract

A CTEOSAURUS CRASSICOSTATUS Calligaris, 1993 was erected based on a partial skeleton of a small lizard found in marine carbonate rocks from the Cretaceous (Upper Cenomanian-Lower Turonian) of Comen, Slovenia. Here, we show that the holotype and only known specimen cannot be assigned to the genus Acteosaurus (Calligaris, 1993), but instead is referable to and indistinguishable from Adriosaurus suessi Seeley, 1881. Acteosaurus crassicostatus is therefore a junior objective synonym of Adriosaurus suessi . The holotype of Acteosaurus crassicostatus is in a small block of rock that is split horizontally into part and counterpart (MCSNT 9400a & b). The material consists of an articulated portion of the anterior postcranial skeleton. Photographs of both part and counterpart have been published (Calligaris, 1993), however, these photographs were small and not easily interpreted. We illustrate the “part” (MCSNT 9400a) of the specimen using drawings and a photograph (Fig. 1.1–1.3 ) as the part contains the skeletal remains while the counterpart is a natural mold. Figure 1 — 1–3, Acteosaurus crassicostatus Calligaris, 1993 (MCSNT 9400a—part); 1, photograph of the holotype; 2, line drawing of the holotype; 3, line drawing of left forelimb. Abbreviations: h, humerus; in, intermedium; r, radius; rad, radiale; ul, ulna; uln, ulnare; i–v, digits one through five. A series of 13 anterior dorsal vertebrae is preserved on MCSNT 9400a, with further portions of two extra vertebrae at both ends (Fig. 1.1, 1.2). All are exposed only in dorsal view. The neural arches are wide, with the anterior and posterior zygapophyses projecting laterally giving them a “butterfly” shape in dorsal view. They are all pachyostotic, with the neural arches swollen and heavily ossified. Adjacent neural spines interlock, indicating the presence of zygosphene-zygantral articulations, but the precise morphology of these joints cannot be determined as no one vertebra is isolated. …