Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 10. 1981. (Budapest, 1981)
FRAGMENTA MINERALOGICA ET PALAEONTOLOGICA Some complements to the knowledge of a Middle Eocene Sirenia, Sirenavus hungaricus Kretzoi, 1941 By L. KORDOS (Received February 15, 1981) Abstract: The article contains the results of the revision of a new Eocene Sirenia described by M. KRETZOI in 1941. The total preparation of the type specimen performed recently leads to the discovery of the mandibles that had been covered before. Besides the completing of the type description we could state that Sirenavus did not belong to the Prorastomidae but represented an independent highly specialised branch of development. In 1941 M. KRETZOI published the Sirenia find of Felsögalla (Kálvárla-hlll, Tatabánya, Transdanubian Middle Mountains), which had come to light from nummulitic limestone of MiddleEocene (Lutetian) age. He introduced the find to the literature as Sirenavus hungaricus n.g.n.sp. (KRETZOI 1941). When Sirenavus hungaricus was described the find was only partially preparated, thus KRETZOI could draw his conclusions from the dorsal structure of the skull only. In the course of a systematic elaboration of the Hungarian finds the revision of this extremely important type became indispensable for the study of the origin of Sirenia. Therefore, in 1978 P. SOLT preparated the type specimen following the instructions of the author. The bones, stored in the Geological-Palaeontological Department of the Hungarian Natural History Museum, Budapest, gave further pieces of information on the building of the skull and the mandibulae and the M 3 , that had been covered before the preparation. In the course of the revision the large, pachyostotic ribs mentioned in the original diagnosis were not found in the collection. COMPLEMENTS TO THE TYPE-DESCRIPTION OF SIRENAVUS HUNGARICUS KRETZOI' s description can be completed after the preparation with the following: Cranium (Pl. I, Fig. 1-4): nasal region is incomplete due to original fracture. The right orbital cavity is filled with rock material, the left one Is totally cleaned. The cranium is saggitally extended and dorso-ventrally flattened. The width of the nasal and zygomatic region and its narrowing towards the small calvaria is striking. The probably narrow nasalia is separated from the maxilla by a very simple run-off sutura. The trapeze-shaped os zygomaticum (7.0 cms x 3.9 cms) came to light in the course of preparation from the bones of the arcus zygomaticus which is starting with a wide arch, then getting narrow, runs off collaterally. The continuati on of the os zygomaticum, the processus around the orbits is of slim and high construction (maximal lenght 10.2 cms, height 3.6 cms). The arcus zygomaticus protrudes to the line of M 3-M 2 , and it is connected to the forepart of the skull with a wide base. The rest of the osseous components of the cranium cannot be reliably separated due to the bad state of the suturae. Dimensions of the skull are shown on Figure 1. The maxilla contains on both sides the rooted alveoli of M, M 2 and M 1 (Fig. 2). The row ot teeth shows a slightly convex arch in buccal and ventral direction, respectively. Lenght of
