A revision of the pycnodontid fish Coelodus subdiscus Wenz, 1989, from the Early Cretaceous of Montsec (Lleida, Spain)

Abstract

The revision of Coelodus subdiscus Wenz 1989 (Early Cretaceous of Montsec, north-eastern Spain) has yielded new information on its anatomy, notably on cranial and caudal skeletons and cloaca. The parietal bone has a brush-like extension, the parietal process, and seems to consist of two different fused portions, parietal and supratemporal. The identification of the bone in the postero-dorsal margin of the orbit is discussed. It was described as dermopterotic, but seems to be a complex bone consisting of dermopterotic plus dermosphenotic. This is evident by the junction of the infraorbital and supraorbital sensory canals in this bone. The prearticular and vomerine dentitions are figured, and the presence of large, hookshaped branchial teeth is indicated. The caudal skeleton, ridge scales, and cloaca are described in detail for the first time. To avoid forcing homologies that are not established yet with teleosts, the terms “epi- and hypochordal elements” are used for the caudal endoskeleton. There are 4 epi- and at least 12 hypochordal elements, and two large, tightly articulated urodermals. Fringing fulcra are absent. The cloaca is formed by one anterior and two posterior differentiated scales. A taxonomical review and a new diagnosis of Coelodus subdiscus are presented.