Szabó János szerk.: Fragmenta Mineralogica Et Palaentologica 20. 2002. (Budapest, 2002)

44 Ko: (KRETZOI 1941; KORDOS 1981), (2) type of Paralitherium tarkanyense, Late Eocene, Felsőtárkány (KORDOS 1977), (3) srxcimen of the Legányi Coll., Late Eocene, Eger - Kis-Eged (KORDOS 1985), (4) "Sirenavus or Eotheroides", MTM V.60.685, Middle Eocene, Tatabánya Basin (KORDOS 1983), (5) "Eotherium or Prototherium", Late Eocene, Kolozsvár [ClujNapoca], (TULOGDY

1944). Cranium — The premaxillae contact frontals; the zygomaticorbital bridge of the maxilla is low, less than 1 cm above the palate; the nasals are large and meet in the midline; the supraorbital process of the frontal is well developed and has a prominent, dorsoventrally flattened posterolateral comer, the frontal roof is convex; the sagittal crest is probably absent [According to KRETZOI (1941), but recendy this part of the bone is missing]; the mckxranial sagittal suture is well developed; the post-tympanic process of the squamosal is absent; the sigmoid ridge is present and well developed; the retroversal process of the squamosal is probably present and moderately inflected; the medial side of the zygomatic process of the squamosal is not swollen, appears relatively concave and inclined inward dorsally; the posterior process of the jugal is lower than the diameter of the orbit; the posterior border of the palatine is not incised but slighdy concave; the palatines extend anteriorly beyond the posterior edge of the zygomatic/orbital ridge. Mandibles — The mandibular symphysis is anteroposteriorly elongated, laterally compressed, with narrow masticatory surface; the symphyseal surface is deflected at about 45° to the occlusal plane; the mental foramen is large; the number of accessory mental foramina is three to four, the horizontal ramus of the mandible is relatively short anteroposteriorly, compressed laterally; the coronoid process is high, very narrow and extends anterior to its base above MJ; the mandibular canal is large, bean-shaped in cross-section, and opens posteriorly. Dentition — Among the upper molars M

2 is the largest as determined by the alveolar surface; among the lower molars Mi is the largest; shape of M3 is elongated with alternate lophid system; in M3 the proto- and metalophulids are well developed and they are separated by a deep transverse crest; the hypoconulid of Mb is an independent, asymmetric, divided or undivided cusp; four premolars (represented as roots) and three molars are present on the masticatory surface of the mandible; the dental formula is probably 3.1.5.3 both in the upper and lower jaws. Thoracic vertebrae — The corpus is relatively short anteroposteriorly and broad transversaly; the centrum is dorsoventrally compressed, with a concave dorsal and convex ventral surface. The neural canal is dorsoventrally low. On the ventral side it has an arched, flat crest that is crescent-shaped in cross section. The diapophyses are extremely short and dropshaped. In the dorsal part of the diapophysis a slight depression separates the mdiments of the anapophysis and metapophysis. The anterior and posterior zygapophyses are short. The neural spine is probably well developed. Ribs — The cross-section of the distal and middle parts of the ribs is rectangularly arched and compact. The proximal part is narrower than the thicker middle or distal ones. The capitulum is divided by the capitis into two fades of unequal size. Distally from the tuberculum the corpus is gradually increasing in diamater. According to MOTTL (1944) the ribs of the type specimen of Sirenavus hungaricus had a low degree of pachyostosis, their cross section was compressed anteroposteriorly and elliptical. Innominate bone — It has a rod-like ilium, a flattened and well-developed ischium and pelvis; the acetabulum is large, distinct and elliptical; the obturator foramen must have been present. Femur — The shaft of the femur is straight, anteroposteriorly flattened; the caput femoris is well-developed, elliptical with distinct margins; the neck is short; the femur has a distinct greater and probably a lesser trochanter; the patellar surface is present. Discussion and conclusion — The following minor morphological differences exist between the type specimen of the Middle Eocene Sirenavus hungaricus and the Late Eocene "Parditherium" individuals: (1) The distance between the posterior end of M3 and the anterior margin of the coronoid process is greater with the Middle Eocene holotype than with the Late Eocene specimens. (2) The deep crest between the postero- and mesolophids of Mi is intermpted by a cristid that does not form a connection between them in the 5. hungaricus type specimen. The same cristid is better developed with the MAFI V. 15359 specimen and connects the postero- and mesolophids. (3) The M3 hypoconulid lophule is undivided in the type specimen of S. hungaricus whereas it is divided in two parts in MÁFIV. 15359. The differences in character states between the Sirenavus hungaricus holotype and the type srx^cimen of Paralitherium tarkanyense, and the other specimens discussed above are not significant. Consequendy, Paralitherium tarkanyense is a synonym of Sirenavus hungaricus and not a separate spedes of Sirenavus as stated before (KORDOS 1999). Among the Eocene taxa, Sirenavus stands closest to the cranium of Eotheroides aegyptiacum (OWEN) figured by ABEL (1913, Taf. I. 2., Taf. H 1-2., Ind. Dl.) as conduded from the shared morphological characters, which are as follows: (1) the premaxillae contact the frontals; (2) the zygomatic-orbital bridge of the maxilla is low; (3) the nasals meet in the midline; (4) the supraorbital process of the frontal is well-developed with a prominent, dorsoventrally flattened posterolateral comer, (5) frontal roof is convex; (6) the sigmoid ridge is present and welldevdoped; (6) the processus retroversus of the squamosal is present and moderately inflected; (7) the posterior process of the jugal is lower than the diameter of the orbit; (8) the posterior border of palatine is not incised but slighdy concave; (9) the palatines extend anteriorly beyond the posterior edge of the zygomatic-orbital bridge. Important difference between the skulls of both taxa is that the frontal roof of Sirenavus hungaricus is deeper in comparison with Eotheroides aegyptiacum. The very evolved, recendy described Halitherium taulannense SAGNE, 2001 from the Upper Eocene of France has some morphological similarities with the Sirenavus.