of mesencephalic vein; II-VII) carnial-nerve openings. Remaining ... is the very large passage for the mesencephalic vein, connected with an arcuate groove on ...
UDC 568.192.1:551.763.3(517)
A NEW SAUROPOD FROM THE UPPER CRETACEOUS OF MONGOLIA S.M. Kurzanov and A.F. Bannikov Paleontological Institute of Academy of Sciences of the USSR
ABSTRACT: A description is given of Quaesitosaurus orientaLis gen. et sp. nov., assigned to the subfamily Dicraeosaurinae. Brief data about its living habits are presented.
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The saurian dinosaurs are a constant element of dinosaur faunas of all continents. However, complete skeletons are extremely rare, as are isolated cranial discoveries. For instance, from Cretaceous deposits of Asia, only two species have been described on the basis of a complete skull, and only one, on the basis of a brain case and cervical vertebrae. The remaining species of Asiatic sauropods are known only from fragments of the post-cranial skeleton or from isolated teeth. Therefore the discovery by the Combined Soviet-Mongolian Paleontological Expedition of an almost complete skull of a sauropod, belonging to the new genus Quaesitosaurus, is of particular interest. The skull was discovered in the western part of the Shara-Tsav bluffs, located 8 km to the north of the well-known Upper Cretaceous reptile locality at Bayshin-Tsav [2]. The bluffs consist of mottled marls, clays, siltstones, sandstones, and grits of the Barungoyot Formation. Besides the Quaesitosaurus skull, the locality yielded a skeleton of the ornithomimid GaLLimimus sp. and a substantial part of the skeleton of the theropod Avimimus portentosus [1], which also place the deposits in the Barungoyot. Family CETIOSAURIDAE Owen, 1841 Subfamily Dicraeosaurininae Janensch, 1929 Genus Quaesitosaurus Bannikov et Kurzanov [sic], gen. nov. Name of genus from quaesitus, Lat. - abnormal, and saura, Gk. - lizard. Tipe species. Quaesitosaurus orientaLis sp. nov., Upper Cretaceous, Barungoyot Format on, Mongolia. Dia~nosis. Skull high, short, with wide snout. Squamosal bone not in contact with qua ratojugal. On the posterior side of the quadrate bone, there is a large "resonator" depression. Parietal aperture absent. Occipital condyle rounded. A canal passes posteriorly from the pituitary depression in the base of the occipital bone, opening immediately below the occipital condyle. Alveolar segment of lower jaw strongly bend inwards. Maxilla bears nine teeth.
Species composition.
Type species.
Comparison. Besides Quaesitosaurus, the subfamily includes a further two genera; one of them, Diaraeosaurus [3], is known from the Upper Jurassic of East Africa, and the other, Nemegtosaurus [4], comes from the Upper Cretaceous of Mongolia. From the skull shape, Quaesitosaurus is closer to Nemegtosaurus, although in the latter, the snout is significantly narrower. The squamosal bone of Quaesitosaurus is considerably shorter, a different shape than in Nemegtosaurus, and is not in contact with the quadratojugal. In the skull of Quaesitosaurus, there are no traces of a parietal aperture, which is present in Nemegtosaurus. The occipital condyle of the latter is oval, in contrast to the rounded shape in Quaesitosaurus. The "resonator" cavity in the posterior side of the quadrate bone is completely undeveloped in Nemegtosaurus. In the maxilla of the latter, there are eight, and not Translated from:
NOvyy zavropod iz verkhnego mela MNR.
Paleont. Zhur., No.2, pp. 90-96, 1983.
Paleont. Jour. 1983, no. 2
91 ISSN0031-0301/83/0002-0091$7.S0/0 ~ 1983 Scripta Publishing Co.
nine teeth. The alveolar segment of the mandible in Quaesitosaurus is longer and more deflected inwards than in Nemegtosaurus. Perhaps the most original feature of Quaesitosaurus is the inclined canal in the base of the occipital bone, opening into the pituitary depression. There is nothing similar in Nemegtosaurus, nor in Dicraeosaurus, nor in any of the sauropods in general. The same features also distinguish Quaesitosaurus from Dicraeosaurus. In particular, there is a parietal aperture in Dicraeosaurus, but no canal in the base of the occipital bone, and there are 12 teeth in the maxilla. The structure of the quadrate and quadratojugal bones in Dicraeosaurus is known. Quaesitosaurus orientaZis Bannikov et Kurzanov, sp. nov.
Name of species - orientaZis, Lat., eastern. Holotype. PIN, No. 3906/2, incomplete skull; Mongolia, Southeastern Gobi region, Shara-Tsav; Upper Cretaceous, Barungoyot Formation. Description (Figs. I and 2). Skull massive, high, expanded in the occipital region. Facial portion elongate. Outer nasal openings were probably shifted posteriorly, since there are no traces of them in the considerable amount of maxillary bones preserved. The upper temporal vacuities are small, transversely elongate, whereas the lateral vacuities are narrow, and drawn out dorsoventrally. The position of the occipital condyle indicates that during natural lowering of the head, its long axis was directed ventrally forward. Premaxillary bones elongate, triangular, with long, thin nasal processes. Outer side slightly convex in lower part, concave in upper. On the inner side, there is a broad hollow in the upper part for attachment of the anterior process of the maxillary bone. Each premaxilla bears four teeth. Maxillary bones form a massive "scoop" at the end of the snout, open downwards. From the upper margin to the posterior part of the premaxilla, a short, massive transverse process projects. Palatal process extends posteriorly and laterally, covered ventrally by the apterior part of the palatal bone. A substantial part of the outer surface of the bones is pitted with numerous openings and strong grooves of feeding vessels, elongated parallel to one another. In both maxillae, there are up to nine teeth. The flat frontal bones form the larger part of the skull roof. A weak transverse ridge extends along the mid-line. In the posterior half, the frontal bones expand and form part of the upper margins of the orbit, and also the anterior and inner walls of the upper temporal vacuities. The frontal bones have grown into the laterosphenoids without visible suture. Prefrontal bones preserved only in the parts adjacent to the frontals, and all we can say about them is that they were massive. Post-orbital bones triradiate. The upper short and broad process is directed inwards, is in contact with the frontal bone, and along with the other short process (also directed inwards and in contact with the parietal bone) forms the outer wall of the upper temporal fenestra. The third process, the thinnest and longest, is directed downwards and forwards, and separates the posterior wall of the orbit from the lower temporal fenestra. Outer surface of the bones rough and coarse. Parietal bones form the posterior part of the skull roof. Along the lower flexure in the suture with the upper occipital bone, there is a longitudinal depression, probably corresponding to the cervical ligament. Squamosal bones massive and elongated, posteriorly abutting the paroccipital processes. From the anterior surface, a thin process extends downwards, articulating with the quadrate bone. Dorsal and posterior surfaces intensely roughened. Quadratojugal bones flat, outwardly convex. Two processes extend from the posterior end: one, wide and short, extends posteriorly, and the other, longer and rapidly narrowing, extends upwards. Along the upper margin there is a furrow for articulation with the zygomatic bone. Quadrate bones massive and high. Their upper ends lie between the paroccipital processes and the squamosal bones. Along the middle of the posterior side, there is a large "resonator" depression with thin walls, occupying a third of the entire height of the bone. Posterior margin of the depression rounded, and in the anterior part there is a small longitudinal ridge. In the middle of the bone, from its
Par
p OC
CDC
,
, ,,, , ,,,
II
processu~ D;c~ou"
Fig . 1 • Quaesitosau ype cons u truction) and l"US orientaU pper Cre t mandible ' 8 , sp . n cond yle , Batungoyo;n , 'de v iev (sketch)' ov . ; holot e nt ary, Formation. M . 3906/2 " paroccipit IPa" " r) Q) parietal Aon)gO No lia. Sh ara : T sku l' l (rea • P1IlX) Symbols' , quadtate . pr emaxilla , nang P u 1ac, coc ) sav 0 ' . . Sq) s ,QJ) quadratoj 0) postorbital cC 1pl.tal lar. quamosal. ugal . Sa) sup raangu • poe)
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Soc
poe
Eu
o
5 em
Fig. 2, a
inner margin, there projects a thin, wide, wing-like process, the lateral surface of which is coarsely roughened. Lower articulation surface of the quadrate has the shape of a convex crescent and faces forwards and outwards. Palatine bones comparatively small and thin, oriented along the longitudinal axis of the skull. The expanded and compressed anterior ends are in contact with the palatine processes of the maxillary bones, apparently being a natural prolongation of the latter. At the rear, the palatine bones narrow laterally and markedly expand dorsoventrally, and the outer side abuts against the pterygoid. Pterygoid bones elongate, triradiate, rising from the palatine bones almost at right angles. Anterior process oriented upwards and inwards, and joining with its partner of the opposite side. The ventral process, thickened at the end, abuts the palatine bone. The third process is directed almost vertically backwards. Its posterior margin is strongly concave on the inside, and is connected here with the basipterygoid process. The main occipital bone forms only the lower margin of the large occipital opening. The occipital condyle, distinctly separated from the remaining part of the bone, is inclined downwards. The neck of the condyle is short and broad, and slightly compressed dorsoventrally. Its upper side is broadly concave. At the junction with the basisphenoid, into which the main occipital bone passes without a visible suture, there are clearly-defined clinooccipital tubercles. Immediately beneath the occipital condyle, there is a wide canal passing to the pituitary depression of the brain cavity (Fig. 2a). The canal is very short and separates the lower part of the bone as it were into two processes. The massive basisphenoid is involved in the formation of the lower part of canal of the main occipital bone mentioned above. Short basipterygoid processes extend downwards and somewhat posteriorly. The processes are broad and compressed laterally, their posterior margins are rounded, and the anterior margins angular. They 94
UGm
Fig. 2. 3906/2:
Quaesitosaurus orientalis, sp. nov., holotype, No. a) [po 94] skull, posterior view;
case, side view;
Mongolia, Shara-Tsav;
b) [po 95] brain
Upper Cretaceous, Barun-
goyot Formation. Symbols: Boc) basioccipital, Bs) basisphenoid, cac) canal of inner carotid artery, Exo) exoccipital, fo) fenestra oval is, fp) pituitary depression, pbpt) processus basipterygoideus, Pt) pterygoid, rb) impression of mus. retractor bulbi, Soc) supraoccipital, tsph) clinooccipital tubercle, vcm) opening of mesencephalic vein; II-VII) carnial-nerve openings. Remaining symbols as for Fig. 1.
are oriented at about 45° to each other. The convex ventral ends of the basipterygoid processeS articulate with the concave surface of the posterior ends of the pterygoids, forming a joint with some mobility. A broad and flat presphenoid process extends from the anterior part of the basisphenoid. On the upper end, it is thickened and strongly tuberculate, and bears a low ridge on each side. A concave triangular area is developed between these three processeS. The lateral occipital bones grow into each other above the large occipital opening, isolating the upper occipital bone from it. The paroccipital processes have been expanded vertically on the ends. Their inner surface, abutting the quadrate and squamosal bones, is roughened, and bears several depressions. The lower part, located directly on the floor of the brain case, is pierced by openings for cranial nerves IX-XI and XII. The small upper occipital bone is separated from the large occipital opening. In the lower half, fine lateral processes extend from it, separating the parietal and lateral occipital bones. In the upper part, a low ridge passes along the suture with the parietal bones. 95
The bones of the brain case are so intergrown that sutures are virtually not visible, so that it is difficult to discuss either individual bones, or even the regions corresponding to them. Therefore, the brain case will be described as a whole (Fig. 2b). In front, the brain case opens in the large heart-shaped opening of the olfactory passage. Immediately below it, in the anterior lateral wall, there is a large circular opening of the optic nerve, continuing downwards as a short, wide furrow. Immediately behind the opening for nerve II, the wall of the brain case is pierced by a further two large openings. The first of them was probably associated with nerve III, and the second and larger, with nerve V. From the opening of the trigeminal nerve, two grooves pass downwards, the anterior one corresponding to the maxillary, and the posterior to the mandibular branches of the trigeminal nerve. Above and between openings for nerves III and V, there is yet another opening, the high position of which indicates that it evidently belongs to nerve IV. Above them is the very large passage for the mesencephalic vein, connected with an arcuate groove on the inner wall of the brain case. At the base of the crista prootica, there is a very small opening for nerve VII, from which a very fine groove extends downwards. Immediately behind the crista prootica lies the foramen ovale. The excurrent nerve passed out from the brain case below the occulomotor. In front of it lies a broad depression, most probably associated with attachment of the eye muscles (m. retractor bulbi and m. bursalis). The pituitary (hypophysial) depression is located approximately at the level of nerve III and it opens outwards through the canal mentioned in the base of the wedge-like and main occipital bones. It seems that this is the only path, along which the cerebral branches of the inner carotid artery penetrated into the brain case. Allowing for the shortening of the brain cavity of Quaesitosaurus, it is difficult to imagine another route for the cerebral branches, even considering the absence of analogies among remaining sauropods. This shortening of the brain case leads to the situation in which the openings for IX-XII pairs of nerves, and in part the fenestra ovalis, have been shifted onto its occipital side. The lower jaw is U-shaped in plan. The symphysis is arranged almost perpendicularly to its longitudinal axis. Since the contact between the jaws and remaining bones of the skull is lacking, the general dimensions of the skull may be deduced from the length of the lower jaw (380 mm). The dentary bone is long and high in the posterior part. The ventral margin is broad, rounded anteriorly and angular posteriorly. The alveolar portion is curved. Posteriorly, the dentary is divided into two branches: an upper branch that is short and overlaps the supraangular bone, and a lower branch that is long, covering about half of the length of the angular bone. The inner surface is even, convex only in the alveolar segment, and in the posterior part scarcely covered by the lamina bone. The upper margin bears the alveoli of 13 teeth. The tooth series occupies half the length of the bone and about a third of the overall length of the lower jaw. The coronary bone is narrow and long. The upper margin lies on the posterior extension of the alveolar margin of the dentary. The lower margin forms the upper part of the adductor depression. The supraangular bone is an elongate, slightly laterally convex plate. The anterior end is set between the coronary and dentary bones. Behind the adductor depression, the upper margin is bent inwards and articulates closely with the angular bone. The angular bone is flat, with an expanded posterior margin. The anterior end is set between the lower branches of the dentary and lamina bones. The teeth occur only in the most anterior portion of the jaw. The largest teeth are in front, and they become smaller behind. The teeth of the upper jaw are larger than those of the lower jaw. They are all cylindrical, and taper slightly towards the top. The maxillary teeth are somewhat bent inwards. Lingually, the crowns of all teeth are compressed, whereas the labial surface is convex. On each crown there are two small lateral ridges. The roots are cylindrical, with an open lower end. The enamel is covered with longitudinal grooves. Distribution. Upper Cretaceous, Campanian, Barungoyot Formation; Southeastern Gobi region. Material.
Mongolia,
Holotype.
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Some structural characteristics of the skull of Quaesitosaurus can be used to draw conclusions about its ecology. One of the most significant features is the abnormally large cavity of the middle ear, formed by the quadrate bone. This resonator space, which undoubtedly increased the perception of sound signals, probably indicates the very sensitive hearing of Quaesitosaurus and favors hypotheses as to its terrestrial form of life. However, the jaw musculature and the structure of the jaw in Quaesitosaurus lead to completely different conclusions. The temporal depressions are very small 96
with respect to the size of the jaw and skull and reflect an extremely small muscular mass for the adductors of the lower jaw and consequently, their weakness. At the same time, the broad jaw scoop with little-worn teeth was clearly adapted to the collection of large volumes of some sort of soft vegetation. These properties of the jaw suggest that the vegetation was aqueous. Feeding with the head semi-submerged in water is also indicated by the length of the facial part of Quaeaitoaaurus, which was possibly associated with the marked reduction of the cranial part. The very distinct system of impressions of blood vessels on the jaws, especially the upper ones, must be noted. It clearly reflects an intensified blood-supply in the anterior part of the snout. It is likely that its covering was distinguished by certain peculiarities. Furthermore, in the lower jaw, the character of the impressions of blood vessels are different, which strongly suggests that the covering in the lower jaw was less developed, or even of another kind; the latter, it is true, is unlikely. It is completely possible that this covering was a thickened horny layer, useful for collecting large masses of soft, aquatic vegetation. The brief analysis of the jaw structure of Quaesitosaurua leads to the conclusion that there is here a combination of a semi-aquatic and terrestrial form of life. However, it is more likely that Quaesitosaurus was amphibious. There is no doubt whatsoever that some of its features are unique, and therefore the conclusion cannot be extended to all sauropods. Some of the characteristics are present in other sauropods, but are completely absent in others. And with such variability in characters, it is completely logical to suggest the existence of groups of sauropods with a totally different ecology, both terrestrial, and also semi-aquatic. REFERENCES 1.
2.
3.
4.
Kurzanov, S.M., 1981, Unusual theropods from the Upper Cretaceous sequence of Mongolia, Trudy Sovmestn. Sov.-Mongol. Paleont. Eksped., Vol. 15, pp. 36-45, Tsybin, Yu.I. and S.M. Kurzanov, 1979, New data on the Upper Cretaceous vertebrate localities near Bayshin-Tsav. In: Fauna mezozoya i kaynozoya Mongolii (The Mesozoic and Cenozoic Fauna of Mongolia), pp. 108-112, Moscow, Nauka. Janensch, W., 1935/1936, Die Schadel der Sauropoden Brachiosaurus, Barosaurus und Dicraeosaurus aus den Tendaguru-Schichten Deutsch-Ostafricas, Palaeontographica, Suppl. 7, Vol. I, 2, pp. 145-297. Novinski, A., 1971, NemegtoBaurus mongoZienais n. gen., n. sp. (Sauropoda) from the uppermost Cretaceous of Mongolia, Palaeontol. polon., Vol. 25, pp. 57-81.
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