Armoured Dinosaurs from the Cretaceous of Mongolia

Armoured dinosaurs from the Cretaceous of Mongolia

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Introduction were collected and later described by Gillnore (1933) as Pinacosnuvusgm?zgeri.Abundant reniains of ankylo- .\nkylosaurs, onc of the main suborders of ornithis- saors were excavated by the Palaeontological chian dinosaurs, were distributed world-wide in tlie Expedition of the USSR Academy of Sciences and Mesozoic: their remains are tbund ill Europe, Asia, described by hlaleev (1952a, 11, 19.54, 1956). North and South America, Australia and .\ntarctica Subsequently, new and well preserved ankylosaurs (see Coon~bsand Maryariska (1090) for the most were discovered in the Upper Cretaceous of Mongolia recent comprehensive review of the group). The earli- by the Polish-Mongolian Palaeontological Expedition est rcpresei~tativesof ;inkvlosaurs are known from the in the years 1963-1971 (Marva~iska,1960; 1071; 1977). Middle Jurassic (Galton, 1080; Dong, 1993), while the Rich collections, including numerous interesting latest are Idate Cretaceous (hlaastrichtian) in age (e.g., specimens of Upper Cretaceous ankylosaurs and the Carpenter and Brcithaupt, 1986). However, despite its first Lo\vcr Cretaceous representatives of the group wide distribution and representation by numeroils were excavated by the Soviet-Mongolian Expedition fossil specimc~ls,this group is still not well under- (now Mongolian-Russian Paleontological Expedi- stood. tion) during the past 20 years ('T~~rnanova,1077; 1987; In tlie former USSR remains of ankylosaurs were 1903; Kurzanov and 'l'umanova, 1978). Material col- found in t~vo1,ower Cretaceous sites, one in Yakutia lected by these t~voexpeditions and described by (now the Republic Sakha) the other in Buryatis. 'l'liey bfaryariska (1977) and Tulrianova (1987) are the prin- have also been recovered from various Upper cipal sources for the generic diagnoses of the Cretaceous horizons at 26 localities in Kazakhstan, Mongolian ankylosaurs presented in this chapter. UzOekistan (Kyzylkurn Desert) and Russia The currently accepted systematic arrangement of (Ryabinin,l939; Kozhdestvenskii, 1964; Nesov, 199.5). ankylosaurs was developed b17 Coombs (I 97 1, 1978a), -51 hese remains arc represented by fragmentary who proposed that ankylosaurs should be divided into material, usually disarticualated bones of the postcra- two families: Nodosauridae and .\nkylosauridae. So nial skeleton, arrnour, and, typically, tccth. far, all ankylosaurs found in Mongolia have been 'This article is devoted to the armoured dinosaurs of assigned to the family :inkylosauridae. Mongolia, one of the most representative collections The oldest mongolian ankylosaur, Sbn~rrosnt~rus.rcu- of ankylosaurs from Asia. 'The first disco\rerics of tatus (see Figures 26.1-26.3), is the only member of the Mongolian ankylosaurs were made by the Central Linkylosauridac known so far from the Early Asiatic Expedition of the American Museum of Cretaceous (;\ll)ian-L4ptian) of Asia. 'The construction Natural History (1 91 8-1930). Among large numbers of the skull of Shamos~~urusistypical for ankylosaurids, of skeletons belonging to \rarious dinosaurs from the although it also exhibits some plesioniorphic features. highly fossiliferoi~slocality of Bayan Zag, a skull and For this reason, Sbattto.muru.r was placed in a new sub- fragments of the postcranial skeleton of an ankylosaur family, Shamosaurinae (Tumano\,a, 1987). Owing to errors in the choice of characters, the genus Saichafzin (ankylosaurids have smaller teeth) and in the width of was also included in this subfamily, but this the muzzle led Carpenter (1982) to conclude that rep- classification of ankylosaurs at the suprageneric level resentatives of the two families employed different has not been supported bj7 other specialists (e.g. modes of feeding. Quite possibly, the nodosaurs, with Coomhs and Maryanska, 1990). their narrow muzzles, were more selective in their Upper Cretaceous ankylosaurs are common in all choice of vegetation, while the broad muzzled ankylo- non-marine regional stratigraphic units. The oldest of saurids were less so. '4 similar functional analogy can these, the Bayanshiree Svita (Cenomanian-Turonian) be found among African ungulates (Carpenter, 1982). contains remains of Tnlavurus plicatospineu~;Malcevus In any case, an herbivorous mode of feeding for anky- dispnrosevvntu.~; A~ntosauvus magnus and possibly losaurs seems to be clear, although their long, move- Tragaalztegia lnngicvanialis (see Figure 26.4). The suc- able tongue and some peculiarities in the mobility of ceeding unit, the Djadokhta Svita (?Late the mandibles suggests the possibility that their diet Santonian-Early Campanian), yielded Pinacosaurus also included insects and larvae (Nopcsa, 1928; gvangeri, while the slightly younger Baruungoyot Svita Maryahska, 1977; Coombs and Maryanska, 1990). (?Middle Campanian) produced Saichania chulsanensis. The pectoral and pelvic girdles, like the limbs, were The youngest Mongolian anky losaur, Tnrchin gigantea, well adapted to redistributing the body weight. The is known only from the Nemegt Svita (?Middle scapula and coracoid were usually coossified, the Campanian-Early Maastrichtian). ilium was widely expanded in the horizontal plane, and the acetabulum was imperforate. Indeed, the con- struction of the pelvic girdle is so consistent with Rcpo~itoryabbreviations quadrupedality that it is difficult to imagine transi- AMNH, &4mericanMuseum of Natural History, New tional forms from a bipedal ancestor, though according York; G1 SPS, Geological Institute, Section of to current models of the monophyletic origin of all Palaeontology and Stratigraphy, Mongolian Academy ornithischians this must have been the condition of of Sciences, Ulaanbaatar; PIN, Palaeontological the ancestral form. The short massive limbs were situ- Institute, Russian Academy of Sciences, Moscow. ated beneath the body and moved mainly in a parasag- gital plane. The forelimbs were shorter than the hind limbs resulting in a somewhat arch-like dorsal bend in The anatomy of ankylosaurs the pelvic region. Coombs (1978b) concluded that ;inkylosaurs were usually large, reaching up to 7-8 m ankylosaurs were mediportal, like the rhinoceros and long, though some adults did not exceed 2.5 m in hippopotamus, rather than graviportal like the ele- length. They were quadrupedal animals, heavily con- phant. structed, and with a broad body. Ankylosaur skulls are The armour of ankylosaurs consists of flat, keeled low, wide and rectangular in occipital view, with the or spiked plates arranged in transverse and longitudi- long axis horizontal. The antorbital and supratempo- nal rows. The plates, whose shape, size, height and ral fenestrae are closed and the bones of the skull roof symmetry vary in different parts of the armour, are are covered by dermal plates which fuse with the surrounded by small, irregular, oval or tubercular ossi- underlying bones in adults, resulting in an even cles. Distribution of the plates over the armour is also heavier, more massive skull. The special construction uneven. Usually, the keels of large plates are higher of the short neck, wherein the centra of the posterior and sharper towards the flanks of the body and the cervical vertebrae have cranial and caudal faces of direction of the plate tips differs in alternating longi- different height, enabled the huge weight of the heavy tudinal rows (Maryanska, 1977). armoured head and dermal 'half-ring' to be supported. Unlike other thyreophorans, the armour elements Differences in the size of teeth of the two families of ankylosaurs did fuse to each other. The commonest Armoured dinosaurs from the Cretaceous of Mongolia constructions of the postcranial armour of ankylo- margin above the orbit is flat. The near-horizontal saurs, and of Mongolian ankylosaurs in particular, are epipterygoid contacts the pterygoid and prootic. cervical and pectoral half-rings, each consisting of two Dorsal surface of the skull roof covered by a large bony layers. The deeper half-ring is constructed of number of small scutes. Scute pattern poorly defined fused plates, while the upper layer is formed from in the supraorbital region. Prominent, wedge-shaped three pairs of sharply pointed large plates lying sym- caudolaterally projecting quadratojugal dermal plate. metrical to the mid-line. The arrangement of the Large, wedge-shaped, caudolaterally projecting squa- armour elements follows the same general pattern for mosal dermal plate. The infratemporal fenestra, each ankylosaur family, but there are distinctive pecu- paroccipital process and quadratojugal are hidden in liarities in each species. For example, keeled plates lateral view by the united quadratojugal and squarno- with thick and dense walls occur in Sbamosaurus sal dermal plates. There is a sharp lateral rim and low (Figure 26.1 1A) and rih and groove ornamentation is dorsal prominence for each lateral supraorbital found in Talarurus, while thin and strongly perforated element. Coronoid process lower and more rounded spine walls are typcial of species of Tarcbia (Figure than in nodosaurids. Small teeth. Distal caudal verte- 26.1 1B) and Saicbania. brae with centra partially or completely fused and The peculiarly constructed tail of ankylosaurs, with elongate prezygapophyses that are broad dorso- which could be used as a weapon of defence, is ventrally and elongate postzygapophyses that are morphologically different in the representatives of united to form a single dorsoventrally flattened, both families. In Mongolian ankylosaurs, as in the tongue-like process. Haemal arches of distal caudals group as a whole, the proximal part of the tail was elongate, with zygapophysis-like overlapping pro- flexible while the distal third consisted of a stiff rod cesses and elongate bases that contact to form a fully formed from coossified posterior caudals in which enclosed haemal canal. Fused sternal plates. Coracoid long prezygapophyses and postzygapophyses over- small relative to scapula. Scapular spine located on lapped each other up to the heavy, terminal tail club. extreme anterior edge of scapular blade (see Pipre 26.2). Acromion projects laterally and does not project ahove the dorsal margin of the scapular blade. Systematic survey Postacetabular process of ilium short. lschium near Suborder Ankylosauria Osborn, 1023 vertical below acetabulurn. Pubis reduced to nubbin Family Ankylosauridae Brown, 1908 and fused to other pelvic elements. Deltopectoral Diagnosis (based on Coombs and Maryanska, 1900). crest and transverse axis through distal humeral con- Skull broad and triangular in dorsal view. Skull width dyles in same plane. Fourth trochanter on distal half of more or less equal to length. Snout arches above the femur. Terminal tail club consisting of large pair of level of the postorbital skull roof. 'l'he caudal process lateral plates and two smaller plates. Ossified tendons of the premaxilla along the rnargin of the beak extends surround distal caudal vertebrae. Keeled armour lateral to the most medial teeth. Paired sinuses in the plates usually have deep internal hollow (Figure premaxilla, maxilla, and nasal. The external nares are 26.1 1'4). divided by a premaxillary septum with a ventral or lateral opening leading into a maxillary sinus. No Sbamosaurus'rumanova, 1 983 ridge separating the premaxillary palate from the Type species. Sbamo.raurus scutatus Tumanova, 1083. lateral n~axillaryshelf. 'l'he complex secondary palate Holo~ypt~.PIN N 377912, complete skull and jaw; twists the respiratory passage into a vertical S-shaped Khamaryn Us, ov~rkhangai, Dornogov' Aimag; bend. The postorbital shelf, composed of postorbital Hiihteeg Svita, Lower Cretaceous (Aptian-Albian). and jugal bones, extends farther medially and ven- Kcfirred material. In addition to the holotype a partial trally than in nodosaurids. The lateral supraorbital skull from the holotype locality (Tumanova, 1987) and T.A. TUMANOVA

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Figure 26.1. Shamosaurusscutatu.r, Tumanova, 1983. PIN 377912-1, holotype skull in (A) dorsal and (B) lateral view. Mandible in (C) right lateral and (D) internal view. After Tumanova, 1987, p. 24, fig. 4, p. 42, fig. 12. Abbreviations: ips, quadratojugal (lower postorbital) dermal plate; o, orbit; os, dermal plate; pmx, premaxilla; sps, squamosal (upper postorbital) dermal plate. Scale bar = 100 mm. an undescribed mandible from Hoovor are also bones and paroccipital process are coossified and the referred to this taxon. ventral surface of the basioccipital is round and narrow. Description. The length of the body reaches about 7 m. The walls of armour elements are thick and dense. The skull is up to 360 mm in length and 370 mm width. The dorsal surface of the of the skull was completely Talarurus Maleev, 1952 covered by osteodermal plates (Figure 26.1) bearing a Type species. Talarurus plicatospineus Maleev, 1952. sculpture pattern of small excrescences. Plates in the Holotype. PIN N 557191, occipital section of cranium posterolateral corners of the skull do not develop into a with part of the skull roof. Bayan Shiree, Eastern Gobi scute and the quadratojugal and squamosal dermal desert; Bayanshiree Svita, Upper Cretaceous plates do not hide the quadrate condylus. The anterior (Cenomanian-Turanian). part of the snout is oval and narrow, and it is a little nar- Referred material. A skull roof with occipital section rower than the distance between the posteriormost (Kurzanov and Tumanova, 1978) and fragmentary maxillary teeth. The posterior maxillary shelf is well remains of the postcranial skeletons of a number of developed and the ventral surfaces of the palatal bones individuals have been found at the same locality are inclined laterally. The mandibular condyle of the (Maleev, 1952a, b). quadrate is situated behind the posterior margin of the Description. The body length of this ankylosaur orbit. The occiput is inclined posteriorly and the reached about +5 m. The skull (Figure 26.5) is about occipital condyle is oriented ventrally. The quadrate 240 mm long, and approximately 220 mm wide. Armoured dinosaurs from the Cretaceous of Mongolia

skull; Tsagaan Teeg, Southeastern Gobi; Bayanshiree Svita, Upper Cretaceous (Cenomanian-Turonian). Description. Large ankylosaur with a body up to 6-7 m long and a skull (Figure 26.4) about 300 mm long and 250 mm wide. The skull roof is covered by numerous small osteoderms with a weakly expressed relief. The upper postorbital spines are not developed and osteo- derms do not expand above the occiput. The orbits are situated posterior to the middle of the skull length. The osteodermal ring around the orbit is separated from the other osteoderms by a prominent furrow. The orbit size is slightly reduced due to the presence of the osteodermal ring. The premaxillary beak is trapezoid and the anterior and posterior maxillary shelves are weakly developed. The medial part of the anterior wall of the pterygoid is inclined posteriorly and the basisphenoid and pterygoid are fused. The occipital surface is perpendicular to the skull roof and the lower side of each paroccipital process is directed a little Figure 26.2. Shamosaurus scutatus Turnanova, 198 3. PIN medially, while the distal ends are bent slightly ven- 377912-1, scapulocoracoid in (A) lateral and (B) medial view. trally. The prootic, opisthotic and exoccipital bones Scale bar = 100 rnm. are united, but with prominent borders between them. The occipital condyle is wide-oval and directed poste- roventrally. The quadrate and paroccipital process are Pyramidal plates occur above and behind the orbits coossified and the mandibular condyle of the quadrate and the entire surface of the skull roof is covered by is situated level with the posterior margin of the orbit, osteoderms ornamented with small tubercles (Figure or further posteriorly. The ventral surface of the 26.5A). The occipital surface is perpendicular to the basioccipital bears a central depression, separated by skull roof and the paroccipital processes are directed a gentle crests from the lateral depressions. The cingu- little posterolaterally. The occipital condyle is lum and lingulum of the maxillary teeth are separated directed posteroventrally and there is no fusion of the by a vertical furrow. quadrate bones and paroccipital processes. Anterior to the condyle the ventral surface of the basioccipital Maleevus Tumanova, 1987 bears a medial eminence with depressions on both Type species. Maleevus disparoserratus (Maleev, 1952b) sides. The fundus of the brain cavity is level. The pec- Holotype. PIN N554/1, fragments of a right and toral glenoid is deep and short and the humeral head is left maxilla; Shireegiin Gashuun, Eastern Gobi situated dorso-terminally. The manus is pentadactyl, Desert; Bayanshiree Svita, Upper Cretaceous the pes tetradactyl. Armour elements bear a 'furrow- (Cenomanian-Turonian). rib' type of ornamentation and the tail-club is weakly Referredmaterial. A fragment of a basicranium from the developed. type locality (Figure 26.6). Description. Anterior maxillary shelf weakly devel- Tsagantegia Tumanova, 1993 oped and originating from a point near the start of the Type species. Tsagantegia longicranialis Tumanova, 1993. tooth row. The maxillary teeth have a 'w'-shaped cin- Holotype (and only known specimen). GI SPS N 70011 7, gulum. The occipital condyle is almost hemispherical T.A. TUMANOVA

Figure 26.3. Sbamosaurusscutatus, PIN 377912: A-B. Isolated dorsal vertebra in (A) lateral and (B) anterior view. Isolated dorsal vertebra with ankylosed rib in (C) lateral and (D) anterior views. Scale bar = 50 mm. Armoured dinosaurs from the Cretaceous of Mongolia

Figure 26.4. Tsagantegia longicvanialisTumanova, 1993. GI SPS 70011 7, holotype skull in (A) dorsal and (B) palatal view. After Tumanova, 1993. Scale bar= 100 mm.

and ventrally directed. The ventral surface of the basi- Amtosaurus Kurzanov and Tumanova, 1978 cranium bears two weakly expressed longitudinal Type species. Amtosaurus magnus Kurzanov and ridges which diverge anteriorly (Figure 26.6A). The Tumanova, 1978. medial depression upon the basicranium gradually Holotype (andonly known specimen). PIN N 378012, brain transforms into a depression at the level of the sphe- case (Figure 26.7); Amtgai, Omnogov', Gobi Desert; noccipital tubercles. The fundus of the brain cavity is Bayanshiree Svita, Upper Cretaceous almost level. (Cenomanian-Turonian). Comments. The holotype of this genus was first Description. This taxon is represented by a fragmen- described by Maleev (1952a, b) under the name of tary basicranium. The occiput is high and the brain Syrmosaurus disparosewatus. However, the type species cavity is large. The occipital condyle is oval and of this genus, Syrmosaurus viminicaudus, proved to be a directed posteroventrally. The ventral surface of the junior synonym of the genus Pinacosaurus and S. dis- basioccipital bears two gentle longitudinal elevations parosewatus was assigned by Maryahska (1977) to the situated symmetrically on either side of the medial genus Talarurus. However, as the basicranium of depression (Figure 26.7A). The hndus of the brain Syrmosaurus disparoserratus is different from that of cavity is slightly flexed anteriorly. Talarurus and as the type material of Talarurus does not include the upper jaw, S. dirparosewatus cannot be Pinacosaurus Gilmore, 1933 assigned to this genus and Maleevus was chosen as a Type species. Pinacosaurus grangeri Gilmore, 193 3. replacement name. Holotype. AMNH 6523, incomplete skull and maxilla,

Armoured dinosaurs from the Cretaceous of Mongolia A B

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Figure 26.6. Maleevus disparoserratus(Maleev, 1952). PIN 55412-1, partial braincase in (A) ventral and (B) dorsal view. After Tumanova, 1987, p. 39, fig. 10. For abbreviations see Figure 26.5. Scale bar= 50 mm.

Figure 26.7. Amtosaurus magnus Kurzanov and Tumanova, 1978. PIN 378012, holotype braincase in (A) ventral and (B) dorsal view. After Tumanova, 1987, p. 38, fig. 9). Abbreviations as in Figure 26.5, and: cint, crista intervenestralis; fj, jugular foramen. Scale bar = 50 mm. T.A. TUMANOVA

tsph

rca

Figure 26.8. PinacosaurusgrangeriGilmore, 193 3. PIN 4043, braincase in ventral view. After Tumanova, 1987, p. 37, fig. 8. For abbreviations see Figure 26.5. Scale bar = 50 mm. first cervical vertebra and some dermal scutes; Bayan Zag, Gobi Desert; Djadokhta Formation, Upper Cretaceous (?Late Santonian-Early Campanian). Rq5erred material. A well preserved skull and almost complete postcranial skeleton of a young individual, another complete postcranial skeleton (Maleev, 1952a, 1954) and fragmentary remains of postcrania and armour (Maryanska, 1971, 1977) all from the type Figure 26.9. Pinacosaurusgrangeri Gilmore, 193 3. PIN 3 144. locality; a basicranium from Baga Tariach (Kurzanov Left humerus (A) in dorsal view. Right femur (B) and coracoid and Tumanova, 1978); an undescribed skull in a con- (C) in posterior view. Scale bar = 50 mm. cretion from Shilt Uul; and undescribed fragmentary remains of a few individuals from Alag Teeg. maxillary beak is quadrato-spherical in shape and Description. A medium sized ankylosaurid with a body broader than the width of the skull between the pos- length of about 5 m and a skull 300 mm long and 340 teriormost maxillary teeth. Both anterior and poste- mm wide. The nostrils are divided by a horizontal rior maxillary shelves are weakly developed, the septum and in a superbly preserved skull there is a palatal bones are elevated, and the medial part of the third pair of openings that lead into the premaxillary anterior wall of the pterygoid is inclined anteriorly. sinus. Ascending processes of the premaxillary bones The occipital condyle is wide-oval and directed pos- divide the nostrils, penetrating between the nasal teroventrally. The contact between the quadrate and bones and are not covered by osteoderms. Plates the paroccipital process remained unossified. The above the orbits develop into a longitudinal supraor- quadrate bones are slightly inclined anteriorly and bital spine consisting of two pyramidal plates and the the mandibular condyle of the quadrate is located at posterolateral corners of the skull are marked by the level of the posterior margin of the orbit. The upper and lower postorbital spines. Osteoderms do ventral surface of the basisphenoid does not exhibit not overhang the medial part of the occiput, thus the any marked relief (Figure 26.8). The postcranial occipital condyle is visible in dorsal view. The pre- skeleton (Figure 26.9) is relatively light, the limb Armoured dinosaurs from the Cretaceous of Mongolia

hones are slender, the manus is pentadactyl and the Tavchia Maryanska, 1977 pes tetradactyl. Type species. Tavchia gigantea (Maleev, 1956). Holotype. PIN 551/29, a series of caudal vertebrae, Saichania Maryanska, 1977 metacarpals and phalanges, and fragments of armour Typespecies. Saichania chulsanensis Maryariska, 1977. plates; Nemegt, Gobi Desert; Nemegt Svita, Upper Holotype. GI SPS 101/151, skull with mandibles and Cretaceous (?Middle Campanian-Early the anterior part of the postcranial skeleton and Maastrichtian). armour in natural articulation; Khulsan, Gobi Desert; Rtfivved matevial. Fragmentary remains of distal parts Baruungoyot Svita, Upper Cretaceous (?Middle of tails and fragments of armour from the Nemegt Campanian). Basin (Maryanska, 1977), an incomplete skull with Refevvedmaten'al. Fragments of a skull roof and armour skull roof, occiput and brain case from Khulsan from the type locality (Maryanska,l977) and an unde- (Maryanska, 1977) and a well preserved skull scribed skull, mandibles and almost complete postcra- (Tumanova, 1977; 1987) with incomplete postcra- nial skeleton from Hermiin Tsav. nium. Descviption. Large ankylosaur with a body length up to Descviption. This is the largest, but stratigraphically, 7 m, and a skull about 450 mm long and 480 mm wide. the youngest Mongolian ankylosaur. The body length The skull roof exhibits prominent osteodermal plates reached 8 m and the skull (Figure 26.1 0) was up to 400 and spinous postorbital osteoderms. The nostrils are mm long and 450 mm wide. 'The premaxillary part of large, terminally situated, and divided by a horizontal the snout forms a rounded oval, and is as broad as the septum. '4 dorsal opening leads to a respiratory canal distance between the posteriormost maxillary teeth. and a ventral one to a ventromedial canal which enters The anterior and posterior maxillary shelves are well the premaxillary sinus. The premaxillary beak has a developed. The plane of the palatine bones is horizon- round-oval shape and is almost as broad as the distance tally elevated and the anterior wall of each pterygoid between the posteriormost maxillary teeth. The pala- is inclined forward. The occiput is inclined slightly tine has strongly developed anterior and posterior posteriorly and the occipital condyle is brachy-oval maxillary shelves. The medial part of the anterior wall with a slightly protruding joint surface that is directed of the pterygoid is inclined anteriorly. The plane of posteroventrally. The paroccipital process is high, the occiput is perpendicular to the skull roof and the short, perpendicular to the plane of the skull roof and paroccipital processes are low and perpendicular to does not fuse to the quadrate. The mandibular condy- the skull roof in their upper part, while their lower lus of the quadrate lies at the level of the posterior portion is deflected anteriorly. The occipital condyle is margin of the orbit. The ventral part of the basioccipi- oval, weakly convex and directed ventrally. 'She quad- tal has no marked relief. The height of the foramen rate and paroccipital process are coossified. The man- magnum exceeds its width, the hrain cavity is very dibular cotylus of the quadrate is located at the level of high and the openings for the cranial nerves are of the middle part of the orbit. The anterior and posterior large size. The pes is tetradactyl and the tail-club is walls of the orbit are heavily ossified. The ventral large. surface of the basioccipital has no marked relief. The Comments. The type species of the genus Tavchia, T. premaxillary bones are partially overlapped by osteo- kielanae, was established on the basis of an incomplete derms growing downward from the nasal bone. skull with skull roof, occiput and brain case Strongly developed secondary plate-like intercostal (Maryanska, 1977). However, more comprehensive ossifications occur along the lateroventral side of the material has shown that Dyoplosauvusgiga~zteus(Maleev, trunk. The postcranial skeleton is extremely massive 1956) and T. kielanae belong to the same species: with strong ossification of the sternal complex. The Tavchia gigantea (Maleev, 1956) (see Tumanova, 1977, manus is pentadactyl and the tail-club is large. 1987; Coombs and Maryariska, 1990). T.A. TUMANOVA

Figure 26.10. Tarchiagigantea(Maleev, 1956), PIN 31421250. Skull in (A) dorsal, (B) palatal and (C) lateral view. Left mandible in (D) external and (E) internal view. Mandible in (F) dorsal view. After Turnanova, 1987, p. 19-21, fig. 3, p. 41, fig. 11. For abbreviations see Figure 26.5, and: art, articular; c, coronoid; f. meck., Meckelian foramen; f. sang, foramen supraangulare; os meck, Meckel's cartilage; pr, retroarticular process; sa, surangular. Scale bar = 100 mm. Armoured dinosaurs from the Cretaceous of Mongolia

- Figure 26.10. (cont.) T.A. TUMANOVA

Jurassic of China has greatly expanded the known t~merange of ankylosaurs from Asia Surprisingly, however, although T nedegoapeferzma exhibits prim~tive features of the mandibles and postcranial skeleton, it has a small, flat, tail club that is characteristic for anky- losaurlds Thus all ankylosaurs from Asia seem to belong to the Ankylosauridae Besides the Aslatic genera, the Ankylosauridae ~ncludestwo North American forms Euoplocephalus and Ankylosaurus Euoplocephalus is represented by numerous specimens and has the following characters the external nares face rostrally and are divided by a vertical septum and the width of the beak is equal to or greater than the distance between the caudalmost maxillary teeth. Ankylosaurus, the youngest and largest ankylosaurid is distinguished by a strong expansion of the dermal armour in the nasal region that restricts the external nares to small circular openings. Interrelationships within the Ankylosauridae remain unclear. However, by taking into account the older age of Shamosaurus, one can suggest the follow- Figure 26.1 1. Different types of dermal scute surface: (A) ing general evolutionary transformation in the lineage SbamosaurusscutatusTumanova, 1983, PIN 377912-1, Shamosaurus-Ankylosaurus: holotype. (B) Tarcbiagiantea(Maleev,1956), PIN 31421250. Scale bar = 50 mm. 1. quadratojugal and squamosal dermal plates become more horn-like. They are weakly expressed in Talarurus (Figure 26.5A, C), Shamosaurus (Figure Discussion 26.1 A, B), and in Tsagantegia (Figure 26.4 A), but At present, the fossil material of Mongolian ankylo- are well developed and moderately pointed in saurs is the most representative for this group in Asia. Tarchia (Figure 26.10 A, C) and Euoplocephalus, and Ankylosaur remains from the territory of the former take the form of horns in Ankylosaurus and Saichania; Soviet Union (FSU) are fragmentary, scattered and 2. development of the quadratojugal plate tends to because of the nature of their preservation: mainly hide the mandibular condyle of the quadrate in teeth, armour and poorly preserved postcranial ele- lateral view; ments, they cannot be identified to the generic level. 3. widening of the premaxillary beak; The oldest ankylosaur so far known from Mongolia is 4. the plane of the orbits rotates forwards while the Shamosaurus from the late Lower Cretaceous orbits shift posteriorly; (Aptian-Albian). In the Upper Cretaceous assemblages 5. the tooth rows shorten; from most of the regional stratigraphic subdivisions 6. there is some increase in skull kinetism because of usually contain ankylosaurs. Thus they are known from the weakening of the basipterygoid joint: in the Cenomanian-Turonian ( Talarurus, Amtosaurus, Shamosaurus the pterygoids and basisphenoid were Maleevus) up to the Maastrichtian (Tarchia). fused, but all isolated basicrania of Talarurus, The recent discovery of the ankylosaur Tianchia- Maleevus and Amtosaurus exhibit articular surfaces saurus nedegoapeferima (Dong, 1993) in the Middle for the contact with the pterygoids. Armoured dinosaurs from the Cretaceous of Mongolia

Some morphological features of Sbamosaurus, for -Kirkland, J., Miles, C. and Cloward, K. 1996. example, fusion of the quadrate with the paroccipital Evolutionary significance of new .Ankylosaurs process can be observed in later ankylosaurs such as (Dinosauria) from the Upper Jurassic and Lower Tsagantegia and Saicbania. Often, however, the nature Cretaceous, Western Interior. 3ournal o/- Vevtebrate of this contact is rather different: the upper process of pale onto log^, 19 (Suppl. to nb. 3): 25.4. Coombs, W.P., Jr. 1971. The Ankylosauria. Ph.D. thesis, the quadrate reaches the skull roof anterior to the Columbia University, New York, NY, 487 pp. paroccipital process and contacts the latter to various -1978a. The families of the ornithischian dinosaur order degrees: close in 'Ihlarurus, and, probably, with liga- 24nkylosauria.Palaeof~tology 2 1: 143-1 70. ments in Tarcbia. 1978b. Theoretical aspects of cursorial adaptations in Some features in the n~orphologyof Sbamosaurus dinosaurs. Quarterly Review of Biology 53: 393-418. can be considered as intermediate between -and Maryanska, T. 1990. Ankylosauria, pp. 456-483 in Ankylosauridae and Nodosauridae. These include: a Weishampel, D.B., Dodson, P. and Osmhlska, H. (eds.), narrow premaxillary beak; immohile basipterygoidal 'I%e Di~osauria. University of California Press: contact; a quadrate condyle partially visible in lateral Berkeley. view; and a round, vertically oriented occipital Dong, Z.M. 1993. An ankylosaur (Ornithischian dinosaur) condyle. These features suggest that these families are from the Middle Jurassic of the Junggar Basin, China. monophyletic and this is strongly supported by the firtebrata PaMsiatica 3 1 (4): 258-266. Galton, P.M. 1980. Armored Dinosaurs (Ornithischia: discovery of Jurassic ankylosaurs in North America .inkylosauria) from the Middle and UpperJurassic of (Kirkland and Carpenter, 199% Carpenter etal., 1996). England. Geobios 13: 82.5-837. Study of the new Jurassic ankylosaurs may help to Gilmore, C.W. 1933. Two new dinosaurian reptiles from clarify phylogenetic relationships, both within fami- Mongolia with notes on some fragmentary specimens. lies and at the family level. Amelcan Museum Novitates679: 1-20. Kirkland, J.I. and Carpenter, K. 1994. North America's first Acknowledgments. pre-Cretaceous ankylosaur (Dinosauria) from the Upper Jurassic Morrison Formation of Western am deeply grateful to Teresa Maryanska and Walter I Colorado. Brigham Young Cnivesity Geoloir~yStudies 40: P. Coombs, Jr., for their careful reading of the manu- 2 5-42. script, which has been greatly improved by their com- Kurzanov, S.M. amd Tumanova, T.A. 1978. [On the struc- ments, and I thank Ken Carpenter for helpful ture of the endocranium in some ankylosaurs from information on new Jurassic ankylosaur specimens, hlongolia.] Paleontologicheskii Zkurnal1978: 90-96. and David Unwin for his useful comments during my hlaleev, E.A. 1952a. [A new family of armored dinosaurs work on this manuscript. from the Upper Cretaceous of Mongolia.] Doklady AN SSSR87: 131-1 34. -1952b. [A new ankylosaur from the Upper Cretaceous of References Asia.] Doklady AN SSSR 87: 2 73-2 76. Carpenter, K. 1982. Skeletal and dermal armor reconstruc- 1954. [New turtle-like reptile in Mongolia.] Priroda tion of Euoplocephalus tutus (Ornithischia: 1954: 106-108. Ankylosauridae from the Late Cretaceous Oldman 1956.[Armoured dinosaurs from the Upper Cretaceous Formation of '4lberta. Canadian.~ournalof Sciences 19: of Mongolia.] Trudy Paleontologicheskugo Institutu AN 689-697. SSSR62: 51-91. -and Breithaupt, B. 1986. Latest Cretaceous occurrence Maryanska, T. 1969. Remains of armored dinosaurs from of nodosaurid ankylosaurs (Dinosauria, Ornithischia) the uppermost Cretaceous in Nernegt Basin, Gobi in western North America and the gradual extinction Desert. Pakontologia Polonica 2 1: 22-34. of the dinosaurs. 3ournal of firtebrate Paleontology 6: 1971. New data on the skull of Pinacosaurus panpi 251-257. (Ankylosauria). Paleontologia Polonica 25: 45-53, -1977. ;\nk!llosauritlae (1linosauri:l ) from Ylongolia. 'lsrtrlrou .\cruch~io-l.s.cl~~/ovutcl:skugo G~'r~~lugo- I'nlr~o~itulo~~inPulouicu 3 7: 8.j-I 5 I . KULUPL~S~C~~IO~OIfi.s/it~i/u1 18: 1-40, Nesov, L.A. 199.j. [Diuosaurs o/- ,\'utht~ni Iu4 I