The Armored Dinosaurs of Mongolia T.A. Tumanova

1987 The Joint Soviet-Mongolian Paleontological Expedition Transaction vol. 32, 76p.

Translated by Ruth Griffith, edited by Kenneth Carpenter and T. A. Tumanova

i Editor's Comments

There are two major philosophies regarding translations, one which literally translates the words (transcription) and the other the implied meaning. The problem with transcription is that words, sentence structure, punctuation, grammar, etc. (i.e., everything that makes each language unique), is often unintelligible or confusing. This is especially true from Russian to English. Anyone who has taken a foreign language knows that a word-by-word transcription to English seldom makes sense. To avoid this problem and to make this translation of " The Armored Dinosaurs of Mongolia " readable, I have edited the translation by my collaborator Ruth Griffith as I would a manuscript written by a colleague for whom American English is not a first language. I do so on the basis that American English rules of grammar are not identical to those of Russian. In a few places, words have been added for clarification; these are inserted in brackets, [ ]. In addition, most Russian names for localities and formations have been standardized to Jerzykiewicz and Russell (1991) because these names are more readily understood among English-speakers. As parts of the translation were completed, they were checked by Tatyana Tumanova for accuracy. The resulting translation tries to be true to the original.

Kenneth Carpenter Denver, 1999

Reference: Jerzykiewicz, T., and Russell, D.A., 1991, Late Mesozoic stratigraphy and vertebrates of the Gobi Basin. Cretaceous Research 12 :345-377.

[Originally, this translation was sold and the proceeds used to pay for Dr. Tumanova's membership in the Society of Vertebrate Paleontology. Now, funds are available elsewhere, so this important monograph is being released more broadly - Kenneth Carpenter, 2008]

ii CONTENTS Introduction ...... 1 Material ...... 3 Chapter 1 A brief history of ankylosaur studies ...... 5 Chapter 2 Systematic description ...... 8 Suborder Ankylosauria ...... 8 Family Nodosauridae Marsh, 1890 ...... 9 Family Ankylosauridae Brown, 1908 ...... 9 Subfamily Ankylosaurinae Brown, 1908 ...... 11 Subfamily Shamosaurinae Tumanova, 1983 ...... 19 Chapter 3 Morphology ...... 22 Skull...... 22 Shape and external features ...... 22 Cranial armor ...... 23 Structure of the Skull roof ...... 27 Morphology of the Nasal Cavity ...... 29 Palatal area ...... 31 Ossifications of the quadrate complex ...... 31 Braincase ...... 33 Ethmosphenoidal section ...... 33 Otico-occipital section ...... 33 Maxilla ...... 38 Mandible ...... 41 Teeth...... 41 Hyoid apparatus ...... 42 Muscles, glands, nerves and vessels of the head ...... 43 Musculature of' the head ...... 43 Lateral nasal gland and Jacobson's organ ...... 44 Circulatory system ...... 45 Cranial nerves ...... 46 Chapter 4 Dermal armor ...... 48 Chapter 5 Phylogeny of ankylosaurs ...... 51 Chapter 6 Some morphological features of ankylosaurs and their systematic significance ...... 55 Chapter 7 Ecology ...... 59 Chapter 8 Geological and geographical distribution of ankylosaurs ...... 63 Localites of the Mongolian ankylosaurs ...... 67 Lower Cretaceous sites ...... 67 Upper Cretaceous sites ...... 68 Summary ...... 72 References ...... 72 Plate Captions ...... 81

iii INTRODUCTION

The Ankylosaurs are a separate group of dinosaurs known from the Cretaceous Period and widespread throughout practically the entire World. Ankylosaur morphology reveals their extreme specialization, as well as primitiveness compared to the rest of the dinosaurs. Until recently, the discoveries of these animals consisted, as a rule, of scutes and spines from armor or of fragments of the postcranial skeleton; characteristically, cranial material was poorly preserved. Because of this, knowledge of the group remained rather limited and descriptions were basically of a superficial character. Only in recent years have a monograph and some separate papers appeared in which the morphology of Mongolian (Marya ńska, 1971, 1977) and North American (Coombs, 1972a,b,c, 1979) armored dinosaurs were treated in more detail. A major obstacle to the study of ankylosaur cranial morphology was found to be the massive overlapping of the cranial surface by osteodermal plates which are firmly fused with the underlying bones. In this connection, was a lucky find by the Polish Mongolian Paleontological Expedition to Bayn Dzak (MPR) of a young specimen of Pinacosaurus grangeri (Marya ńska, 1971, 1977); on the skull sutures were still visible. A detailed study of ankylosaur morphology and comparisons with other dinosaurs and reptiles enable us to solve more definitely the problems of their systematic position, relationships, and origins of both North American and Asian specimens, and allows us to raise questions concerning dinosaur evolution as a whole. The aim of the present work is an attempt to make a detailed study of ankylosaur morphology, especially of the skull, so it provide us with the key to clarifying the origin and phylogeny of this independent group of animals. Because of the poor state of previous ankylosaur morphology studies, there were still problems concerning their origin and connection with related groups, and even about relationships within the group. In the present work, only the least studied specimens of ankylosaurs from Mongolia are considered in detail, including Talarurus known almost solely by the postcranial skeleton, and the new genus Amtosaurus , the same age as Talarurus . A revised diagnosis of the genus Maleevus is also presented. A new Early Cretaceous genus of ankylosaurid, Shamosaurus , is also established. The family Ankylosauridae is divided into two subfamilies, the Shamosaurinae and the Ankylosaurinae. Shamosaurinae, the more primitive, is represented at present by only one genus, Shamosaurus , from the Lower Cretaceous; the Ankylosaurinae includes all the rest of the known ankylosaurids. Sauroplites , from the Lowest Cretaceous of China, possibly belongs to the Shamosaurinae, but we can not resolve the problem definitively because its remains are incomplete (Bohlin, 1953). As criteria for this division [into two subfamilies], we have the following: difference in form of the preorbital section of the skull, orientation of the orbits, relative distance of the orbits from the occiput, and also some structures of the skull of Shamosaurus that are intermediate between

1 Ankylosauridae and Nodosauridae. These include the construction of the premaxillary section of the muzzle, the large curves anterior to the pterygoid flanges, contact of the pterygoids with the basisphenoid, the structure of the quadrates and paroccipital process, and the circular shape of the occipital condyle. All of these intermediate traits are obviously due to the very great age of Shamosaurus and its proximity to the ancestry of both families. The study of the discoveries, including some preliminary material we received, supports the claims of W. Coombs for the extremely isolated position of the ankylosaurs within the ornithischian dinosaurs, their peculiar morphology, and, consequently it is possible to consider the phylogeny of ankylosaurs to some extent. A detailed morphological study is also important for paleoecological research. Naturally, the results of a morphological analysis must be augmented by stratigraphy, lithology, etc. Obviously, the more a group is studied, the greater importance these [ankylosaur] specimens have for biostratigraphy. In recent years, the remains of ankylosaurs were found in all Upper Cretaceous strata discovered in the territory of the Mongolian Peoples Republic. This makes it possible to consider ankylosaurs in fauna complexes for correlation of Cretaceous deposits in Mongolia and other Asiatic regions, but also of Asia and North America (ankylosaurid remains are also found in the territory of Kazakhstan, but due to their fragmentary state, they have not been studied at the present). The study of Mongolian ankylosaurs is very important for several reasons. First, they provide clues about the evolution of groups, assuming they are representative samples. The work in recent years by expeditions from several countries (including the Joint Soviet-Mongolian Paleontological Expedition) has shown Mongolian ankylosaurs to be numerous and the discoveries comparatively complete. In addition, the quality of preservation makes the Mongolian material unique, and is perhaps better than any other specimens of these animals in the world. The major collection [of Mongolian ankylosaurs] is in the Paleontological Institute of the Academy of Sciences, USSR. It contains material belonging to seven genera, three of which were established by the author. [The taxonomic description of] two genera were revised, and the description of the other genera were expanded from more complete material. In addition, we utilized for comparison the discoveries of the Polish-Mongolian Paleontological Expedition; these are preserved in Warsaw in the Museum of Earth and in the Institute of Paleobiology, and were kindly offered for study by the Polish Academy of Science. This work was completed in the laboratory of Lower Tetrapods of the Paleontological Institute, Academy of Sciences, USSR, under the guidance of Academician L. P. Tatarinov, to whom the author expresses heartfelt thanks. The author is deeply grateful to A. K. Rodzdestvensky for thesis definition and guidance in the first stages of the study. The author sincerely thanks the coworkers in the Paleontological Institute for valuable advice. Besides, I would like from all my heart to thank the Assistant Director of the Museum of Earth, Dr. T. Marya ńska, for her help and valuable consultations. Drawings for the paper were completed by artists T. D. Rakova, K. P. Meshkov and V. D. Kolganov.

2 MATERIAL

Shamosaurus scutatus

3779/2 - skull with incomplete postcranial skeleton and part of the armor. Khamareen Us, Lower Cretaceous, Dzun Bayn Formation.

?Shamosaurus

3779/1 - portion of skull, Khamareen Us, Lower Cretaceous, Dzun Bayn Formation.

?Shamosaurus

3101 - lower mandible, separate fragments. Khovboor, Lower Cretaceous.

Talarurus plicatospineus

557 - partial postcranial skeletons of 6 individuals and two fragments of skulls. Bayn Shiren, Eastern Gobi, Upper Cretaceous, Bayn Shiren Formation. (Cenomanian - Lower Santonian according to Barsbold, 1972). 3780/1 - incomplete skull with skull roof, part of occiput and braincase. Baynshin Tsav, Southeast Gobi, Upper Cretaceous, Bayn Shiren Formation.

Maleevus disparoserratus

554/1-2 - fragments of right maxilla. 554/1-1 - left maxilla of specimen described by E. A. Maleev (1952b) as the holotype Syrmosaurus disparoserratus . Shiregin Gashun, Mongolia, Upper Cretaceous, Bayn Shiren Formation. 554/2-1 - endocranial fragment with occipital condyle.

Amtosaurus magnus

3780/2 - part of skull - endocranium. Amtgai, Upper Cretaceous, Bayn Shiren Formation.

Pinacosaurus grangeri

614 - complete postcranial skeleton of animal, described by E. A. Maleev (1952) as the holotype

3 Syrmosaurus viminicaudus . Bayn Dzak, Upper Cretaceous, Djadokhta Formation, Santonian according to Kielan-Jaworowska (1974a, b). 4043 - cranial fragments. Baga Tarjach, Upper Cretaceous. 3780/3 - skull, Shilt-Ula, Upper Cretaceous. 3144 - cranial fragments and fragments of postcranial skeleton. Alag Teg, Upper Cretaceous.

Saichania chulsenensis

3142/251 - complete skeleton with skull. Khermeen Tsav II, Upper Cretaceous, Barun Goyot Formation.

Tarchia gigantea

3142/250 - skull with incomplete postcranial skeleton. Khermeen Tsav, Upper Cretaceous, Nemegt Formation. 551-29 - disarticulated caudal vertebrae, metacarpals and phalanges manus, fragments of armor plate. This specimen was described by E. A. Maleev as holotype Dyoplosaurus giganteus . Nemegt, Upper Cretaceous, Nemegt Formation.

4 Chapter 1

A BRIEF HISTORY OF ANKYLOSAUR STUDIES

Before proceeding into the history of research on the Ankylosauridae of Asia, it is necessary to say a few words about the history of the classification of ankylosaurs as a whole. This is necessary because the first studies of armored dinosaurs debated the validity of the group. When the first ankylosaurid Stereocephalus (Lambe, 1902) was discovered in the Oldman Formation in North America, ankylosaurs were placed in three families of the suborder Stegosauria. They were united with the stegosaurs because of the armor (Marsh, 1895, 1896). Gradually, within the suborder [Stegosauria], groups of genera stood out - the future families of the ankylosaurs. The new family, Ankylosauridae Brown, 1908, was established on a new genus Ankylosaurus , which was based on a cranium and an incomplete post-cranial skeleton. This one family of ankylosaurs contained, according to modern classification (Coombs, 1978a), Ankylosaurus and Euoplocephalus (formerly named Stereocephalus , Lambe, 1910). For several decades, no significant changes were proposed in the systematics of ankylosaurs as a whole, and in the Ankylosauridae in particular. Ankylosaurs were still closely linked to stegosaurs as a different family. In 1923, F. Nopsca (1923) proposed to equalize the ranks of the three groups of quadrupedal ornithischians: stegosaurs, ankylosaurs, and ceratopsians. They were reduced in taxonomic rank [from individual suborders] and placed [together] in the suborder Thyreophora. A. Romer (1927) adopted the separation of ankylosaurs within the boundaries of the Ornithischia and of the separation from Stegosaurs. No detailed explanation was given for his change of Ankylosauria as a suborder, but the difference in pelvic structure was emphasized because its unique structure did not occur among the other Ornithischians. The differences between the armor of ankylosaurs and stegosaurs were also apparent. The main emphasis in subsequent papers focused on the distribution of genera within the Ankylosauria (Nopsca, 1929; Gilmore, 1930). Gilmore joined all the European genera into the family Acanthopholidae, which corresponds to the Nodosauridae. A. Romer (1956) retained the suborder rank of Ankylosauria and divided them into the [families] Acanthopholidae and Nodosauridae. The first family included the primitive taxa, the last included the most derived forms. Romer noted that the proposed scheme was provisional because of insufficient study of the group. The suborder rank for the Ankylosauria was maintained in "Fundamentals of Paleontology" (Maleev, 1964). The group was divided into three families: Acanthopholidae, Nodosauridae and Syrmosauridae. One of the recent systematic revisions of the suborder Ankylosauria was produced by W. Coombs (1978a). He divided all Ankylosaurs into two families. The family Nodosauridae, where he placed the family Acanthopholidae and part of the Nodosauridae, included representatives

5 with remarkably narrow skulls from North America and Europe. The second family, Ankylosauridae, included two North American genera, Ankylosaurus and Euoplocephalus , and all Asiatic armored dinosaurs. Asian Ankylosaurs were first mentioned in 1923 by S. Matley (1923), who described Lametesaurus indica from the Turonian deposits of the Jabbalpur (India) region. The affiliation of Lametesaurus with armored dinosaurs, based on the a sacrum, an ilium and tibia, turned out to be debatable (Chakravarti, 1935). Actual ankylosaurs [from Asia] were described from China (Wiman, 1929; Gilmore, 1933a), but their remains were too fragmentary for an detailed identification. Thus, Pinacosaurus grangeri (Gilmore, 1933b) is considered to be the first discovery of an Asiatic armored dinosaur; it was described from the deposits of the Upper Cretaceous (Djadokhta Formation, Bayn Dzak) of Mongolia. In 1935, Young Chung-Chien (1935) described another species of this genus - P. nighsiensis , from the Cretaceous deposits of China. A. N. Ryabinin (1938) discovered in the Cretaceous fauna of the Sary Agach area in Kazakhstan, the remains of ankylosaurs. The fragments, which he attributed to ceratopsians (Ryabinin, 1939), proved to be from armored dinosaurs (Marya ńska, 1977). Over a period extending from 1930 - 1931, broken fragments of poorly preserved ankylosaur skeletons, were collected by the Swedish-Chinese Expedition in China. B. Bohlin (1953) established three new genera and species: Sauroplites scutiger , Heishansaurus pachicephalus and Peishansaurus philemis , and also a new genus and species, Stegosaurides excavatus , which he assigned to Stegosauria. Because the material is so fragmentary, the validity of his taxa is questionable. Nevertheless, E. A. Maleev (1956), A. S. Romer (1966) and R. Steel (1969) believed that Stegosaurides excavatus belonged to the Ankylosauria. Later, the Soviet-Chinese Paleontological Expedition (Rozhdestvenskii, 1961) added to the collection of ankylosaurs from China. But we still hardly have any descriptive papers on ankylosaurs of China. One practically complete skeleton and scattered remains of other specimens from Ala-Shan have up to now not been described and are in the collections at Peking (Beijing) (Marya ńska, 1977). The phylogenetic scheme for dinosaurs presented at the II Symposium on Mesozoic Terrestrial Ecosystems (Chao Shichin, 1981) reviewed ankylosaur phylogeny and they were united with stegosaurs into the same suborder. During the Mongolian Paleontological Expeditions of the USSR (1946,1949), a variety of nearly complete ankylosaur material was collected (Maleev, 1952a, b, 1953, 1954, 1956). From the expedition's discoveries in the Upper Cretaceous Bayn Shiren Formation, E. A. Maleev (1952a, b, 1956) described a new genus and species Talarurus plicatospineus . The author created a new family, Syrmosauridae (Maleev, 1952b, 1954) for the genus Syrmosaurus, with two species: S. viminicaudes and S. disparoserratum based on the upper jaws and postcranial skeletons. The age of the Shiregin Gashun locality [where Talarurus was collected] was initially determined to be early Late Cretaceous (Maleev, 1954). As a result, this family [Syrmosauridae] was placed intermediately between the stegosaurs and the ankylosaurs. In the taxonomic classifications of that time, the new family was used (Lapparent and Lavocat, 1955; Maleev, 1964). But now, based on more complete discoveries of better preserved specimens, S. vimicaudus is a synonymy of Pinacosaurus grangeri (Marya ńska, 1971), and the family Syrmosauridae was a synonymy of the family Ankylosauridae Brown. S. disparoserratus was to

6 become a new species or even genus of this family. Another discovery of ankylosaurid in the Nemegt strata was determined by Maleev to be a new species of the American genus Dyoplosaurus - D. giganteus . Supplemental material after this discovery permitted us to establish a new Mongolian genus, Tarchia (Marya ńska, 1977, Tumanova, 1977). The remains belonging to this genus were described earlier (Marya ńska, 1970), but under the original designation of Dyoplosaurus sp. In 1963-1971 , the Polish-Mongolian Paleontological Expedition worked in Mongolia (Kielan-Jaworowska, Dovchin, 1969; Marya ńska, 1970, 1971, 1977). Based on the collections from the Barun Goyot strata, two new genera of Ankylosauria were identified: Saichania (from a complete skeleton) and Tarchia (based on a partial braincase). From the work of Marya ńska, the evolution of the ankylosaurs as determined, their relationship with other ornithischian dinosaurs, and the distinct features of their life styles. The latest ankylosaur classification was proposed by W. Coombs (1978a). He reviewed the diagnostic traits of the subdivisions within the suborder Ankylosauria and concluded that there were two families: 1) family Nodosauridae, which included all the European forms (formerly the family Acanthopholidae), and the narrow-skull ankylosaurs from North American with large armor plates on the skull roof; 2) family Ankylosauridae, included the North American ankylosaurs with broad triangular heads, the skull roof of which are covered by a large number of small osteodermal scutes, and the Asiatic specimens of the suborder. Besides the shape of the head and the size and amounts of armor on the top of the skull, Coombs points out a series of important differences between specimens of the two families, for example, the presence of cranial sinuses and the complex nasal cavity of the Ankylosauridae. Coombs established a phylogenetic scheme for the ankylosaurs and, based on the uniqueness of the group relative to the other ornithischians, he discusses the exceedingly remote connection of ankylosaurs with them. It seems to us that the proposition of Coombs for the division of ankylosaurs into two families is reasonable based on the few differences already mentioned, i.e., head shape, size and amount of armor scutes on the skull roof, the presence or absence of sinuses and the degree of complexity of the nasal passage, etc. But it is impossible to be conclusive about the Nodosauridae because there has not been very much research on the specimens. For example, the structure of their skull roof is unknown, there has not been a complete description the braincase, etc. The situation for the Ankylosauridae is better in more recent times, thanks to the work of T. Marya ńska (1977) and W. Coombs (Coombs, 1978).

7 Chapter 2

SYSTEMATICS SECTION

Suborder Ankylosauria 1 Ancylosauria: Huene, 1914, p. 7 Ankylosauria: Osborn, 1923, p. 3 Apraedentalia: Huene, 1948, p. 95 Apraedentalidae: Huene, 1952, p.;50 Diagnosis. A quadrupedal animal of large dimensions. Skull covered with osteodermal plates which are fused with the underlying bones in the adults. There is one temporal fenestra, located near the bottom [i.e. subtemporal fenestra]. The skull roof is almost flat, low; the basi-occipital bone and the basisphenoid are rotated downwards, the angle formed by the base of the cranium and the floor of the cranial cavity ranges from 150-170 o; the inner carotid artery arises from the dorsal surface of the basipterygoid process. Contact of quadrate with paroccipital process is characteristic; retroarticular and coronoid process are weak; dental row is curved, teeth are small, compressed laterally, with denticles on margins, with cingulum; only one row of teeth functional; pubis reduced; the acetabulum is un-perforated. Armor plates covered the entire dorsal section of the skull and also the trunk; it did not extend to the abdomen. Contents. Two families: Nodosauridae Marsh, 1890; Middle Jurassic to Cretaceous Europe, North America, South America, Australia, and Antarctica; Ankylosauridae Brown, 1908; middle Jurassic to Cretaceous, North America, Asia. Comparison. Ankylosaurs differ from other types of dinosaurs in the presence of osteodermal armor plates distributed on the creature's trunk and head. The dorsal osteodermal spines of Stegosaurus are not comparable to the armor plates of the ankylosaurs. Instead of two temporal fenestra typical for dinosaurs, ankylosaurs have one, the lower temporal fenestra. The braincase of armored dinosaurs is lower, so there is a tendency for the basioccipital and basisphenoid to be displaced downward. The angle between the base of the cranium and the cerebral cavity is 15 o- 17 o, whereas in other dinosaurs the basioccipital and basisphenoid slope posteriorly and the angle ranges from 50 o-55 o. The internal carotid artery in ankylosaurs extends from the dorsal surface of the basipterygoid process, but in other dinosaurs it extends ventrally below the process. The quadrate contacts the paroccipital process, while in all other dinosaurs these bones are usually separated by the squamosal. The coronoid process in ankylosaurs is weak compared with the strong development in ornithopods and ceratopsians. One row of comparatively small teeth was functional, differing from the hypsodont condition in ornithopods and ceratopsians.

1 Diagnosis of the suborder and the families and divisions of all ankylosaurs into two families after Coombs (1971, 1978).

8 Ankylosaurs have similar locomotion as stegosaurs; however, they differ from stegosaurs in the greatly reduced pubis and the non-perforation of the acetabular cavity.

FAMILY NODOSAURIDAE MARSH, 1890 Nodosauridae: Marsh, 1890, p. 425 Acanthopholidae: Nopcsa, 1902, P. 9 Polacanthidae: Wieland, 1911, P. 118 Hylaeosauridae: Nopcsa, 1917, p. 210 Palaeoscincidae: Nopcsa, 1918, P. 328 Acanthopholinae: Nopcsa, 1923a, P. 199 Nodosaurinae: Nopcsa, 1923a, p. 199 Struthiosaurinae: Nopcsa, 1923a, p. 2126 Panoplosaurinae: Nopcsa, 1929, P. 70 Edmontoniinae: Russell, 1940, p. 25 Diagnosis. Ankylosaurs with narrow skulls, the length of which is distinctly greater than the width (Fig. 1); bones of the skull roof are covered by a few large plates; spines over the orbits are absent; nostrils are latero-terminal; no supplemental nasal sinuses, respiratory tract is straight, usual; occipital condyle is round, on a ventrally directed short neck; pterygoids fused with the basipterygoid processes; lateral temporal fenestra and quadrate condyle are not closed laterally by osteodermal armor plates; ends of paroccipital processes make contact further back behind the posterior border of the skull roof; pterygoid flanges directed forward; teeth large. Content. Hylaeosaurus Mantell, 1832 (= Polacanthus Hulke, 1874; Polacanthoides Nopcsa, 1929), Lower Cretaceous, Western Europe; Palaeoscincus Leidy, 1856 (in part), Upper Cretaceous, USA; Acanthopholis Huxley, 1867, Upper Cretaceous, England; Struthiosaurus Bunzel, 1871 (= Crataeomus Seeley, 1881; Danubiosaurus Bunzel, 1871; Leipsanosaurus Nopcsa, 1918; Pleuropeltis Seeley, 1881; Rhodanosaurus Nopcsa, 1929), Upper Cretaceous, Western Europe; Nodosaurus Marsh, 1889 (= Stegopelta Williston, 1905; Hierosaurus Wieland, 1909), Upper Cretaceous, USA; Hoplitosaurus Lucas, 1902, Lower Cretaceous, North America; Sauropelta Ostrom, 1970, Lower Cretaceous, USA; Panoplosaurus Lambe, 1919 (= Edmontonia Sternberg, 1928), Upper Cretaceous, North America; Silvisaurus Eaton, 1960, Lower Cretaceous, North America. Distribution. Lower and Upper Cretaceous; Europe, North America.

FAMILY ANKYLOSAURIDAE BROWN, 1908 Ankylosauridae: Brown, 1908, p. 187; Coombs, 1978, p. 14 Ancylosauridae: Huene, 1909, p. 17 Syrmosauridae: Maleev, 1952, p. 131 Diagnosis. Ankylosaurs with skull greatly expanding in orbital and postorbital regions, width is equal or greater than length (Figs. 2, 3); bones of skull roof covered by many small scutes, which may be posterior to the orbits, change from pyramidal osteoderms into spines; nostrils large and terminal; additional sinuses in nasal cavity present; respiratory tract is flexed; occipital condyle oval, without neck; lateral temporal fenestra and quadrate condyle (except Shamosaurus ) closed laterally with osteodermal scutes; scutes also on the the maxilla and expanded from the squamosal into spines; paroccipital processes projects laterally, ends not reaching posterior of skull roof; pterygoid flanges, mandibular branch of pterygoid and ectopterygoid project

9 Fig. 1. Skull of Panoplosaurus mirus Lambe. After W. Coombs (1978). A, ventral; B, dorsal; C, lateral; D, detail showing contact between quadrate and paroccipital process. ch - choanae; Mx - maxilla; Pmx -premaxilla; Poc - paroccipital process; Pt - pterygoid; Qu - quadrate. laterally; teeth are small. Content. Two subfamilies: Ankylosaurinae and Shamosaurinae. Comparison. The Ankylosauridae differ from the Nodosauridae in the greater width of the skull, greater number of small osteodermal scutes on the skull surface; presence of supplementary sinuses of the nasal cavity; modification and curvature of the respiratory tract; shape of the occipital condyle and absence of a neck for condyle; extensive growth of osteoderms causing the lateral temporal fenestra and quadrate condyles to not be visible laterally; by the lateral direction of the paroccipital processes, the borders of which do not protrude to the end of the skull roof; in the lateral direction of the pterygoid flanges; in the much smaller teeth. Distribution. Upper Jurassic, and Lower and Upper Cretaceous, North America, Asia, Antarctica.

10 Fig. 2. Schematic reconstruction of the cranial bones of Pinacosaurus grangeri Gilmore. From T. Marya ńska (1971). Fr - frontal; Na - nasal; Os - osteoderm; Par - parietal; Pf - prefrontal; Po - postorbital; Pof - postfrontal; Sq - squamosal; Tb - tabular

SUBFAMILY ANKYLOSAURINAE BROWN, 1908 2 Type Genus. Ankylosaurus Brown, 1908; Upper Cretaceous, North America. Diagnosis. Ankylosaurs with wide skull, width of which is slightly less or equal to the length; broad snout; orbits oriented slightly forward; angle of orbital plane with long axis of skull about 30 o; anterior wall of pterygoids sometimes inclined somewhat sharply posteriorly, but more often inclined anteriorly; occipital condyle oval; basipterygoid process contacts with pterygoid by suture; orbits in posterior half of skull length. Contents of Subfamily. Eight genera: Ankylosaurus Brown, 1908; Euoplocephalus Lambe, 1910, Upper Cretaceous, North America; Pinacosaurus Gilmore, 1933; Talarurus Maleev, 1952; Maleevus Tumanova, gen. nov.; Saichania Marya ńska, 1977; Tarchia Marya ńska, 1977; Amtosaurus Kursanov and Tumanova, 1978, Upper Cretaceous, Mongolia. Distribution. Upper Cretaceous, North America, Asia.

Genus Ankylosaurus Brown, 1908 Ankylosaurus: Brown, 1908, p. 188; Coombs, 1978, p. 145. Ancylosaurus: Huene, 1909, p. 17; Sternberg, 1917, p. 257 Type Species. Ankylosaurus magniventris Brown, 1908; Upper Cretaceous; Maastrichtian; North America. Diagnosis. Premaxillary beak wide, anterior oval-shaped, width less than distance between rear maxillary teeth; anterior and posterior maxillary shelves well developed, especially anterior; palatal bones and structures raised horizontally; medial section of anterior wall of pterygoids inclined posteriorly; plane of occiput inclined posteriorly; paroccipital processes inclined laterally; occipital condyle broad oval shape, inclined postero-ventrally; quadrate and paroccipital processes do not fuse. Species Content. One species. Distribution. Upper Cretaceous, Maastrichtian, North America.

2) the diagnosis for the subfamily Ankylosaurinae is based on the diagnosis of genera given by T. Marya ńska (1977).

11 Genus Euoplocephalus Lambe, 1910 Stereocephalus : Lambe, 1902, p. 55 Eupolocephalus : Lambe, 1910, p. 151; 1920, p. 42; Nopcsa, 1923, p. 197; 1928, p. 185. Dyoplosaurus : Parks, 1924, p. 5; Hay, 1929, p. 236 Scolosaurus : Nopcsa, 1928b, p. 54; Mehl, 1936, p. 19 Anodontosaurus : Sternberg, 1929, p.28 Type Species. Stereocephalus tutus Lambe 1902; Upper Cretaceous, Campanian-Upper Maastrichtian, North America. Diagnosis. Premaxillary beak very wide, anterior blunt, width equal to or exceeding space between rear [maxillary] teeth; maxillary shelves well developed; plane surface of palatal bone tilted laterally; anterior wall of medial section of pterygoids slanted forward; paroccipital processes laterally oriented; occipital condyle broad oval, oriented posteroventrally; quadrate and paroccipital processes not fused; occipital plane tilted slightly forward. Species Content. One species. Comparison. Differs from Ankylosaurus in the noticeably wider premaxillary beak, with rounder anterior edge and in the width as compared to the space between the rear maxillary teeth; in the development of the anterior maxillary shelf; in the obliquely placed palatal structure; in the anterior, forward inclined pterygoid wall; and in the forward slant of the occipital plane. Distribution. Upper Cretaceous, Campanian-Maastrichtian, Canada (Alberta), North America (Montana).

Genus Pinacosaurus Gilmore, 1933 Pinacosaurus : Gilmore, 1933b, p. 3; Young, 1935, p. 5; Marya ńska, 1971, 45; 1977, p. 101 Syrmosaurus : Maleev, 1952, p. 137; 1954, p. 147. Type Species. Pinacosaurus grangeri Gilmore, 1933, Upper Cretaceous Djadokhta Formation; from Bayn Dzak in Gobi Desert, Mongolia. Diagnosis. Small ankylosaurid; three pairs of openings in nostril region, no osteoderms in area; two pyramidal scutes above orbits elongated into supraorbital spine; posterior and lateral corners of skull with upper and lower postorbital spines; osteoderms do not project over occiput so occipital condyle visible from top; premaxillary rostrum rounded, width greater than space between the last maxillary teeth; anterior and posterior maxillary shelves poorly developed; palatal bones raised; medial section of anterior wall of pterygoids inclined forward; plane of occiput perpendicular to plane of the skull roof; occipital condyle broadly oval, with posteroventral orientation; contact of quadrate and paroccipital processes not ossified; quadrate inclined slightly forward, [articular] condyle below rear orbital border; ventral surface of basisphenoid without sharply defined relief; fenestra ovalis not joined to jugular foramen. Species contents. One species. Comparison. Differs from the North American Ankylosaurus and Euoplocephalus in its rounded anterior edge of the premaxilla, the poorly developed maxillary shelves, occiput perpendicular to the skull roof. Unlike Euoplocephalus , the width of the premaxillary shelf exceeds the space between the last upper maxillary teeth. In contrast to Ankylosaurus , the medial section of pterygoidal wall is inclined forward.

12 Pinacosaurus grangeri Gilmore, 1933 Plate V, figs. 1-2 Pinacosaurus grangeri : Gilmore, 1933b, p. 3; Marya ńska, 1971, p. 45; 1977, p. 101. Pinacosaurus ninghsiensis : Young, 1935, p. 5 Syrmosaurus viminicaudus : Maleev, 1952, p. 131; 1954, p. 147. Holotype. AMNH 6523, deteriorated skull and maxilla, first cervical vertebrae, some dermal scutes; Upper Cretaceous Djadokhta Formation of Bayn Dzak, Mongolia. Material. PIN (Paleontologicheskii Institut) 614, complete post skull skeleton, Upper Cretaceous Djadokhta Formation at Bayn Dzak, Mongolia; PIN 4046, fragmentary section of skull, Upper Cretaceous Djadokhta Formation at Bara Tarjach, Mongolia; PIN 3780/3, skull in concretion, Upper Cretaceous at Shilt-Ula, Mongolia; PIN N 3144, fragmentary remnants of skull and post skull skeletons of a few specimens, Upper Cretaceous of Alag Teg, Mongolia. Diagnosis. Premaxillary processes separate nostrils and elevate them, extend posteriorly between nasals, not covered by osteoderms; osteoderms do not project over medial portion of occiput; occipital condyle visible from above. Distribution. Djadokhta Formation, Bayn Dzak, Mongolia.

Genus Talarurus Maleev, 1952 Talarurus : Maleev, 1952, p. 273; 1956, p. 56; 1977, p. 99; Kurzanov, Tumanova, 1978, p. 90. Type Species - Talarurus plicatospineus Maleev, 1952, Upper Cretaceous Bayn Shiren Formation at Bayn Shiren, Mongolia. Diagnosis. Distinct pyramidal scutes distributed above and behind orbits; skull roof covered with small tubercular osteoderms; occipital plane perpendicular to skull roof; paroccipital processes inclined somewhat posterolaterally; occipital condyle narrow oval, posterolaterally inclined; quadrate not attached to paroccipital processes; basioccipital with medial protuberance, depressions on sides of protuberance; floor of skull cavity straight; fenestra ovalis not fused with jugular foramen. Species content. One species. Comparison. Differs from Ankylosaurus , Euoplocephalus and Pinacosaurus in the narrow, oval occipital condyle; in the posterolaterally inclined paroccipital processes; in the shape of the ventral surface of the basioccipital, by a sharp, symmetrical depression located approximately in the middle of the protuberance. It differs from Ankylosaurus and Euoplocephalus in the occiput perpendicular to the skull roof. Observations. A second species, T. disparoserratus , was [originally] described by E. A. Maleev (1952) as Syrmosaurus disparoserratus .The differences between it and T. plicatospineus warrant placing it in a level higher than species [i.e., a separate genus (see below)].

Talarurus plicatospineus Maleev, 1952 Plate III, fig. 1-2; Plate IV, fig. 1-3 Talarurus plicatospineus Maleev, 1952, p. 273; 1956, p. 54; Marya ńska, 1977; p. 99; Kurzanov and Tumanova, 1978, p. 78. Holotype. PIN 557/91, occipital section of cranium, part of skull roof and post skull skeleton; Upper Cretaceous Bayn Shiren Formation at Bayn Shiren, eastern Gobi Desert, Mongolia. Material. Besides the holotype, specimen PIN 557, fragments of post skull skeletons of 6 individuals from the same location; PIN 3780/1, skull roof with occipital section and brain case;

13 Upper Cretaceous, Bayn Shire Formation at Baynshin Tsav, southeastern Gobi, Mongolia. Diagnosis. Osteoderms of skull roof overhangs medial region of the occiput; premaxillary covered with osteoderms. Distribution. Upper Cretaceous, Bayn Shiren Formation at Bayn Shiren and Baynshin Tsav, eastern and southeastern, Mongolia.

Genus Amtosaurus Kursanov and Tumanova, 1978 Amtosaurus : Kurzanov and Tumanova, 1978, p. 91. Type Species. Amtosaurus magnus Kursanov and Tumanova, 1978; Upper Cretaceous Bayn Shiren Formation at Amtgai, Mongolia. Diagnosis. Occipital condyle a narrow oval and inclined posteroventrally; basioccipital with two elongated, sloping basitubera distributed symmetrically with respect to the ventromedial depression; floor of braincase with few flexions in anterior section; foramen in endocranium large; fenestra ovalis not joined with jugular foramen. Species content. One species. Comparison. Differs from Euoplocephalus , Ankylosaurus and Pinacosaurus in the narrow, oval occipital condyle. Also, in the presence of a medial depression on the ventral surface of the basioccipital, and sloping raised area. It differs from Talarurus also in the structure of the basioccipital, in the larger size of the skull cavity, and the presence of some flexures in the floor of the skull cavity.

Amtosaurus magnus Kursanov and Tumanova, 1978 Plate V, fig. 3-4 Amtosaurus magnus : Kursanov and Tumanova, 1978, p. 92 Holotype: PIN 3780/2, cerebral case, Upper Cretaceous Bayn Shiren Formation at Amtgai, Mongolia. Material: Holotype. Diagnosis: Occiput high, endocranial cavity large. Distribution. Upper Cretaceous Bayn Shiren Formation at Amtgai, Mongolia.

Genus Maleevus Tumanova, gen. nov. Syrmosaurus : Maleev, 1952, p. 134; 1954, p. 63. Talarurus : Marya ńska, 1977, p. 100 (partim) Type Species. Syrmosaurus disparoserratus Maleev, 1952; Upper Cretaceous Bayn Shiren Formation at Shiregin Gashoon, Mongolia. Diagnosis. Occipital condyle almost round and ventrally oriented; basioccipital with two small projections ventrally that diverge forwards; depression located in middle more pronounced towards occipital "swelling"; floor of skull cavity almost straight; maxillary shelves poorly developed. Species Contents. One species. Comparison. Differs from all ankylosaurs described above in its almost round, ventrally oriented occipital condyle. It differs from Talarurus in the ventral surface of the basioccipital in which there is medially located a grooved neck flanked on both sides by slight elevations; this condition is reversed in Talarurus . The lateral depressions symmetrically diverge relative to the

14 medial protuberance. Remarks. Despite the proximity of the localities for Maleevus and Talarurus and their occurrence in the same formation, we cannot agree that both [genera] belong to the genus Talarurus (See Marya ńska, 1977). Pinacosaurus is much closer to Maleevus in the structure of the brain case. [It differs from Maleevus ] in its larger dimensions, and the sharper angle between the axis of the basioccipital and the "parabasisphenoid complex", and in the anteroposteriorly longer articulate surface of the occipital condyle.

Maleevus disparoserratus (Maleev, 1952) Plate VI, fig. 1-3; plate VII, fig. 1-8 Syrmosaurus disparoserratus : Maleev, 1952, p. 134; 1954, p. 162 Talarurus disparoserratus : Marya ńska, 1977, p. 100 Holotype: PIN 554/1, two fragments of right and left maxilla; Upper Cretaceous Bayn Shiren Formation at Shiregin Gashoon, eastern Gobi, Mongolia. Material. Besides the holotype, specimen PIN N 554/2-1 - fragment of basicranium with occipital condyle, same location. Diagnosis. Upper maxillary teeth with cingulum separated from crown by a W-shaped swelling on the external side. Distribution. Upper Cretaceous Bayn Shiren Formation, eastern Gobi Desert, Mongolia.

Genus Saichania Marya ńska, 1977 Saichania : Marya ńska, 1977, p. 103. Type Specimen. Saichania chulsanensis Marya ńska, 1977; Upper Cretaceous Barun Goyot Formation at Khulsan, Mongolia,. Diagnosis. Large ankylosaurid with distinctly isolated osteodermal plates on skull roof, spine- shaped postorbital osteoderms; nostrils large, terminally located, separated by horizontal partitions dorsally in the true respiratory canal from ventromedial canal leading into the premaxillary sinus; premaxillary beak is oval shaped, width equal to space between last maxillary teeth; palate with well developed anterior and posterior maxillary shelves; medial section of anterior wall of the pterygoids inclined forwards; plane of occiput perpendicular to plane of skull roof; paroccipital processes low, upper part perpendicular to skull roof, lower part inclined forwards; occipital condyle wide oval, slightly convex; articular surface inclined vertically; quadrate and paroccipital process fused; maxillary condyle of quadrate at level of central part of orbits; ossification of anterior and posterior walls of orbits; basioccipital has no sharply defined relief; fenestra ovalis fused with jugular foramen. Species Contents. One species. Comparison. Saichania differs from every representative of the subfamily [Ankylosaurinae] in the fusion of the quadrate and paroccipital processes. Also, in its unique and extremely complex structure of the paroccipital processes "with the underlying folds beneath the ventral border". In contrast to Talarurus , Amtosaurus and Pinacosaurus , Saichania has a single foramen for the jugular and the fenestra ovalis. The occipital condyle is less convex than in all the rest, its articular surface is inclined vertically. Distribution. Upper Cretaceous Barun Goyot Formation, Gobi Desert, Mongolia.

15 Saichania chulsanensis Marya ńska, 1977 Saichania chulsanensis : Marya ńska, 1977, p. 103. Holotype. GI SPS 101/151 (Museum of Earth, Warsaw), skull with mandibles and anterior part of post skull skeleton; Upper Cretaceous Barun Goyot Formation at Khulsan, Mongolia. Material. PIN N 3142/251 - complete skeleton with skull and lower jaw; Upper Cretaceous Barun Goyot Formation at Khermeen Tsav, Mongolia. Diagnosis. Premaxillary bones partially covered by osteoderms descending from nasal bones. Distribution. Upper Cretaceous Barun Goyot Formation at Khulsan and Khermeen Tsav, Gobi Desert, Mongolia.

Genus Tarchia Marya ńska, 1977 Dyoplosaurus : Maleev, 1956, p. 78; Marya ńska, 1970, p. 24. Tarchia : Marya ńska, 1977, p. 105 ; Tumanova, 1977, p. 92. Type species. Tarchia gigantea (Maleev, 1956); Upper Cretaceous Nemegt Formation at Nemegt, Gobi Desert, Mongolia. Diagnosis. Premaxillary part of beak oval in shape, width equal to distance between rear maxillary teeth (fig. 3); anterior and posterior maxillary shelves well developed; plane of palatal bone raised horizontally; anterior wall of pterygoids inclined forwards; plane of occiput slightly inclined posteriorly; occipital condyle widely oval with articular area slightly projecting and oriented posteroventrally; paroccipital process high, short, perpendicular to skull roof; quadrate and paroccipital process not fused; maxillary condyle of quadrate on level of rear border of orbit; ventral surface of basioccipital without distinct relief. Species contents. Two species: T. gigantea (Maleev, 1954); T. kielanae Marya ńska, 1977. Comparison. Differs from Euoplocephalus , Pinacosaurus and Saichania in the narrower premaxillary part of the snout. Besides this, it differs from Euoplocephalus in the horizontally placed palatal bones. It differs from Ankylosaurus in the forward inclined anterior wall of the pterygoid; also in the greater length of the paroccipital processes, and the expansion and lengthening of the ventral part of the basioccipital. It differs from Talarurus , Amtosaurus and Pinacosaurus in joining of the jugular foramen with the fenestra ovalis. Distribution. Upper Cretaceous, Barun Goyot and Nemegt Formations; Nemegt, Khermeen Tsav, Khulsan, Mongolia.

Tarchia gigantea (Maleev, 1956) (Plate I, fig. 1-4; Plate II, fig. 1-2) Dyoplosaurus giganteus : Maleev, 1956, p. 78. Tarchia gigantea : Tumanova, 1977, p. 92. Holotype. PIN N 551/29, series of caudal vertebrae, metacarpals and phalanges, fragments of armor plate; Upper Cretaceous Nemegt Formation at Nemegt, Gobi Desert, Mongolia,. Material. PIN N 3142/250 - skull with incomplete post skull skeleton; Mongolia, Khermeen Tsav; Upper Cretaceous, Nemegt Formation. Diagnosis. Large ankylosaurid with sharply defined osteoderms on skull roof, postorbital spine-shaped osteoderms; nostrils large, terminal; premaxilla without osteoderms, rises high between nasal bones. Distribution. Upper Cretaceous Nemegt Formation at Nemegt and Khermeen Tsav, Gobi Desert, Mongolia.

16 Tarchia kielanae Marya ńska, 1977 Tarchia kielanae : Marya ńska, 1977, p. 108. Holotype. Tarchia kielanae , fragment of skull roof with brain case and occipital section, Upper Cretaceou Barun Goyot Formation at Khulsan,Gobi Desert, Mongolia. Material. Holotype. Diagnosis. Height of large foramen magnum exceeds width, endo skull cavity very high; foramen for nerves large; single foramen for last skull nerves posterior to fenestra ovalis.

Fig. 3. Skull and lower jaw of the ankylosaurid Tarchia gigantea (Maleev). Sp. PIN N 3142/250. Khermeen Tsav, Upper Cretaceous Nemegt Formation. A, dorsal; B, ventral; C, anterior; D, posterior; E, lateral; F, mandible in lateral view; G, mandible in medial view. Art - articular; Bo - basioccipital; C - coronoid; ch - choanae; Ecp - ectopterygoid; Ex - exoccipital; f. mech - Meckelian foramen; f. sang - surangular foramen; lps - lower orbital spine; Ju - jugal; Mx - maxilla; O - orbit; Os - osteoderm; Pl - palatine; Pmx - premaxilla; Poc - paroccipital process; R - retroarticular process; Pt - pterygoid; Qu -quadrate; Sa - surangular; So -supraoccipital; Sp - splenial; Sps - supraoccipital spines

17 18 Remarks. Comparison of T. kielanae with T. gigantea is impossible because T. kielanae was described from fragments of the skull roof and brain case, the structure of which is similar to those of T. gigantea . It is possible that both species can be classified with T. gigantea , but identification is difficult because material for T. kielanae is insufficient. Distribution. Upper Cretaceous Barun Goyot Formation at Khulsan, Gobi Desert, Mongolia.

SUBFAMILY SHAMOSAURINAE TUMANOVA, 1983

Type genus: Shamosaurus Tumanova, 1983. Diagnosis. Ankylosaurids with anterior part of snout narrow; angle of orbital plane with skull axis less than 25 o; anterior wall of pterygoids inclined to the rear; occipital condyle wide oval to round; pterygoids fused with basisphenoid; interpterygoid fenestra very small; orbits at midpoint of skull length.

19 Contents of Subfamily. One genus Shamosaurus Tumanova. Comparison. The Shamosaurinae differs from Ankylosaurinae in the narrow premaxillae, the orbits are laterally oriented on the midpoint of the skull length; by its almost round, ventrally oriented occipital condyle; in the fusion of the pterygoid with the basisphenoid; and in the smaller dimensions of the interpterygoid fenestra. Distribution. Lower Cretaceous, Gobi Desert, Mongolia.

20 Shamosaurus scutatus Tumanova, 1983 (Plates VIII, X) Holotype. PIN N 3779/2, skull, Lower Cretaceous Khukhtekskaya Svita [Dzunbayn Formation] at Dorngov, Ovorkhangai [Khamryn-Us], Mongolia. Material. Besides the holotype, specimen PIN N3779/2 - partial skull, from same location?; PIN N3101 - lower mandible, fragments; Lower Cretaceous Khukhtekskaya Svita [Dzunbayn Formation] at Khovboor, Gobi Desert, Mongolia. Diagnosis. Upper portion of premaxillary bones covered with osteoderms. Occipital condyle projects to end of skull roof. Distribution. Lower Cretaceous Dzun Bayan Formation, Southern Gobi, Mongolia.

21 Chapter 3

MORPHOLOGY

SKULL

Shape and External Appearance The length of the cranium in adult specimens ranges from 20 to 50 cm. The width of the orbital region can exceed skull length. In design (Fig. 1b, 3a, 4a), the cranium appears as either an isosceles triangle (Family Nodosauridae) or equilateral triangle (Family Ankylosauridae). Anteriorly, the cranium is slightly depressed dorsoventrally. There are a few “swellings” over the orbits, and furthermore, the anterior of the premaxilla is sharply truncated in Ankylosauridae and is gradual sloped in Nodosauridae. The external nares, as a rule, are large, terminal or latero-terminal (in Ankylosaurus they are so overgrown with osteoderms that they are only small lateral openings). In the majority of the ankylosaurs, there is one pair of external nostrils. In a young specimen of Pinacosaurus , T. Marya ńska (1971, 1977) recorded three pairs of openings in this region, of which the dorsal-most pair correspond to external nares. The orbits of ankylosaurs are of average dimensions, arranged laterally, and oriented in most cases somewhat forward; but in Shamosaurus , they are laterally oriented (see Fig. 4). Supratemporal fenestrae were not discovered in any of the ankylosaurs studied. There is a hypothesis that osteoderms have overgrown the fenestra (Eaton, 1961), but the opening does not appear even in the young specimen of Pinacosaurus ; its skull roof has an incomplete osteoderm covering (Marya ńska, 1971). The lateral temporal fenestrae are posterior to the orbits, distributed between the quadrate and quadratojugal (see Fig. 1c), but in the family Ankylosauridae they are covered by osteoderms.

Cranial Armor Armor on the skull are either separate and assume the typical form in the postorbital region, or they are united without any clear boundary as a continuous covering of the cranial bones and fusing with them. The premaxillary bones may be completely overlapped by osteoderms (see Fig. 1b); in the majority of cases only the lowest part of the premaxilla remains free of them, and sometimes osteoderms do not even cover the high ascending process of the premaxillaries that divides the nares medially (e.g. Tarchia , Euoplocephalus , and Pinacosaurus ). The dimension, location, and quantity of the osteoderms depends on the development of the osteoderms in the region of the external nares. Iin Ankylosaurus , the osteoderms almost completely overlap the large terminal nostrils (which are characteristic of the majority of ankylo- saurs), leaving only a pair of small lateral, external narial openings. Farther back on the snout,

22 the scutes in the Nodosauridae are large (see Fig. 1b), sharply demarcated from each other by deep furrows and bilaterally distributed in a comparatively symmetrical manner among three central scutes; in the Ankylosauridae, the scutes (if they are discernible and have an identifiable outline) are small, and are arranged symmetrically on each side of a relatively medial furrow that reaches approximately to the level of the posterior border of the orbits (see Fig. 3a). Posterior to the orbits, the osteoderms fuse, producing a “radical-type relief”. The rearmost scute, or scutellum, extends transversely (see Fig. 3 a) and can overhang the occiput, as, for example, in Talarurus and to some degree in Euoplocephalus and Shamosaurus , or may terminate at the level of the occiput; this scutellum may be high and may occupy about 1/3 the height of the occiput (Tarchia ), or may be the same thickness as the other cranial plates ( Panoplosaurus , Talarurus , Euoplocephalus , Ankylosaurus ). In Ankylosaurus magniventris, it is clearly evident (Coombs, 1978, p. 146, text-Fig. 1) that this scutellum is formed by the fusion of four osteoderms located along the posterior border of the cranium. The lateral surface of the skull in Ankylosaurids is covered with rather large osteoderms. Above the orbits in ankylosaurids are two elongated, low keel-shaped scutes (see Fig. 3, e ). These appear under the name of palpebral in Coombs (1978), and supraorbitals by Gilmore (1914). A considerably amount of variability is observed in the size of the supraorbital spines in the posterolateral corner of the skull and on the quadratojugal. In Nodosaurids, the spines are absent (see Fig. 1c). In Shamosaurus there is only a pyramidal osteoderm, which grows under and fuses with a narrow, keel-shaped plate that lies on the quadratojugal; the laminal keel is inclined laterally anteroposteriorly. The upper supraorbital plate in Talarurus also have. the shape of a triangular pyramid. In very late ankylosaurids ( Pinacosaurus , Saichania , Tarchia , Ankylosaurus , and Euoplocephalus ) the supraorbital spines are modified into corneous spines inclined at the edges dorsolaterally and ventrolaterally. Above the orbits in nodosaurids there is only a narrow, lateral strip of osteoderms that do not extend farther back than the quadratojugal and does not cover the lower border of the quadrate condyle. The result is that the lateral temporal fenestra is open and the quadrate condyle is visible (see Fig. 1c). In the family Ankylosauridae, there is a considerable expansion of osteoderms so that the lateral temporal fenestra and quadrate condyle are not visible laterally (see Fig. 3e). Shamosaurus is exceptional in that , although as in all ankylosaurids the lateral temporal fenestra is covered by osteoderms, the quadrate condyle is visible laterally (see Fig. 4e). Covering of the skull bones by osteoderms is characteristic for all the Ankylosauridae, but in young individuals (for example, Pinacosaurus grangeri , Marya ńska, 1971) the osteoderms fuse with the growing bones only on the anterior part of the nasal bones, between the nostrils. Small medially located osteoderms also occur between the posterior ends of the nasal bones, and also above and posterior to the orbits. In the postorbital region, the edges of the bones in this specimen are unusual as compared with other dinosaurs, and therefore it is not unusual that even now we are not dealing with actual bones, but with complex bone and osteoderms.

Structure of the Skull Roof The structure of the skull roof in Nodosaurids has been little studied because the cranial surface of all specimens are covered with osteoderms. In Ankylosaurids the external surface of the skull roof is comparatively free from osteoderms in Pinacosaurus (Marya ńska, 1971, 1977).

23 Fig. 5. Skull of the ankylosaurid Talarurus plicatospineus Maleev. Sp. PIN N 3780/1. Baynshin Tsav, Upper Cretaceous Bayn Shiren Formation. A, dorsal; B, ventral; C, lateral; D, posterior. add. con. - additus conchae; art. max. - foramen for the maxillary artery; f. add. - adductor fossa; f.q. - fossa for quadrate head; latr. - anterior transverse lamina; Natu - nasoturbinalia; posh - postorbital shelf; sul. proc. sulcus for paroccipital process; zan - annularis zone; I - groove for olfactory nerve.

The ventral or interior region is exposed in Talarurus (Spec. No. 3780/1) (Fig. 5b). Identification of the bones is taken from Marya ńska. The anterior section of the snout, formed by the premaxillary bones in ankylosaurids, is blunt (see Fig. 3b). The premaxillaries surround the external nares and divides them medially by the narrow dorsal process; the premaxillaries contact the nasals beneath the thickened osteoderm covering. The nares terminate about mid-length of the skull roof where the nasals are thickest (see Fig. 3c). The maxillaries, which border the nostrils posterolaterally in Tarchia (Tumanova, 1977), do not contribute to the any of the three openings in Pinacosaurus ; both the supplementary openings are bordered only by the premaxillaries (Marya ńska,.1971). The surface of the

24 premaxillary, which are free of osteoderms in ankylosaurs, has a few large external fenestrae for blood vessels (see Fig. 3c) providing evidence for the probable presence of a corneous covering of the premaxillaries into a , a beak. Anteromedially, there is a notch that conforms to the projection on the dorsal surface of the predentary (see Fig. 3f). There is also a small posterolateral process of the premaxillary that is wedged between the nasals and maxilla. Laterally on the skull, there are nodes of osteoderms that extend outward slightly from between the nares and upper part of the maxilla. The maxillaries are placed laterally and their sutures are not distinct; in height they reach the level of the orbits. They have a short contact with nasals. Posteriorly, the maxillaries contact the jugals, and posterodorsally, they unite with the lachrymals. The nasal bones are large and occupy a large part of the anterior half of the skull roof. They slope laterally downwards to the mid-level of the orbit. Anteriorly, the nasals are covered by nodes of osteoderms so that the suture can not be seen, even in Pinacosaurus (see Fig. 2); the suture of the posterior edge can be seen . Here, the nasal bones contact the frontals and prefrontals; on the lateral surface of the skull, they contact the lachrymals and upper part of the maxillaries. Ventrally, the nasals form part of a pair of maxillary sinuses (see Fig. 5b) that are offset laterally relative to the main channels of the respiratory tract; in these sinuses there are some depressions located anterodorsally and posterodorsally, and anterolaterally. In the dorsoposterior wall of the sinuses , a fenestra opens ventrally to where numerous small grooves radiate out across the surface of the sinus walls. On the medial section of the posterior-most sinus wall is a horizontal sutural surface for the maxilla. Laterally on this wall, are two depressions that taper postero-medially. Posterior-most one is wider and is formed in part by the posterolateral section of the nasals and the horizontal part of the prefrontals. The depressions and the structure of the sinus walls represent impressions of the cartilaginous nasal capsule and parts of its bone structure. These features are only known from skull roof fragment of Talarurus . The ossification of the sinus walls are moderately developed in Talarurus . Other ankylosauids had more extensive ossification of the nasal cavity: Saichania (Marya ńska, 1977), Tarchia (see Fig. 3c) and Euoplocephalus (Coombs, 1978). These sinus walls may be absent, as in all Nodosauridae (Coombs, 19781). The degree of ossification of the inner nasal walls probably depends upon the corneous attachments and the age of the individual. It is difficult to give a single interpretation for the degree of ossification in the inner nasal cavity because maturity changes are not known for ankylosaurs. The prefrontals overlie the posterolateral border of the nasals anteriorly and extend to the frontal, and posteriorly, contact the postfrontals and the supraorbital osteoderms. Laterally, the prefrontals descend to mid-orbital height where the contact the lachrymals; the lachrymals form part of the anterior wall of orbits Anteriorly, the lachrymals contact the nasals and ventrally the maxillaries; they form the middle of the anterior wall of the orbits; ventroposteriorly they contact the jugals, but medially they contact the accessory ossification of the anterior orbital wall, which is a new structure according to T. Marya ńska (1977). However, a lateral outgrowth forms on the sphen-ethmoid at this spot and, probably, the described accessory ossification may be this growth. On the anterior orbital wall, approximately in the center of the lachrymals, are two foramina of the lachrymal duct, one of which may extend into the upper part of the maxillaries and the

25 other which opens into a channel in the wide maxillary sinus. The frontals are located in the middle of the skull roof and are bounded anteriorly by the nasals, posteriorly the parietals, laterally with the pre- and postfrontals; posterolaterally, they probably contact the postorbitals (Marya ńska, 1977), but the suture is covered by osteoderms. The ventral surface of the frontals have crests (cristae frontalis) attached to the center of the septum, the sphenethmoid and its lateral enlargement. Laterally, where the septum attaches, are two grooves anteriorly and posteriorly, possibly for the olfactory nerves to enter the nasal capsules (see Fig. 5b). The postfrontal bones are clearly present (Marya ńska, 1977, pl.20) in contrast to the majority of dinosaurs in which they unite with the postorbital bones (Romer, 1956). They are located lateral to the frontals and are bounded anteriorly by the prefrontals, posteriorly by the postorbitals, and laterally, by the supraorbital osteoderms. The parietals form the central part of the posterior part of the skull roof. They have a short contact laterally with the postorbitals, squamosals and tabulars. Their ventral surface forms the roof of the cerebral cavity. A pear-shaped depression is present in ventral view (Fig. 5b), which is expanded anteriorly for the procephalon and diencephalon. Laterally, on the level of the postorbital shelf, the bone is expanded for the epipterygoids. These expanded surfaces contact the upper end of the epipterygoids. The posterior section of the parietals are also expanded for contact of the upper and lateral occipital bones. The anterior section of these expansions and the posterolateral corners of the parietals, where they contact the squamosals, form the medial border of the adductor fossa. The skull roof and braincase of Pinacosaurus from Bayn Dzak, do not fuse with each other and the post-temporal fenestra is present, whereas in all other ankylosaurs, these structures fuse and the post-temporal fenestra overgrown. The sutural contacts between the prefrontals, frontals, parietals, and postorbitals is difficult to establish, because even in the young specimen of Pinacosaurus (Marya ńska, 1971, Fig. 1, pl. VI) the osteoderms are already developed in this region. It is obvious, however, that the postorbitals form the rear wall of the orbits and extend medially as the postocular shelf (Haas, 1969). This shelf forms the anterior wall of the adductor fossa. The squamosals occupy an unusual position on the skull roof, not extending laterally. They are located between the postorbitals anteriorly and laterally, the parietals medially, and the tabulars and osteoderms posteriorly (see Fig. 2). The squamosals and the osteoderms cover the adductor fossa dorsally. The adductor cavity is formed medially by the parietals and, apparently, the prootic. The anterior wall of the cavity is formed by the ventral portions of the parietals and the medial section of the postorbitals, the lateral and posterior walls are formed by the posterior portion of the squamosals. In Talarurus , a small fossa is present ventrolaterally on the posterior part of the squamosal. The depression is triangular in shape and is for the upper end of the quadrates. The paroccipital processes are hidden in a sloping transverse furrow, concealing it in dorsal view. The presence of a fossa on the ventral surface of the squamosal for the dorsal head of the quadrate is a characteristic feature in the majority of dinosaurs. However, the occurrence of depressions for the paroccipital process posterior to the quadrate fossa distinguishes ankylosaur from all other dinosaurs. In the other dinosaurs, the squamosals contact the upper part of the paroccipital process only, stopping at the anterior wall and separating them from the quadrates

26 (Rozhdestvensky, 1964; Ostrom, 1961). Interestingly, traces of the squamosals, which are evident on the skull roof of Pinacosaurus (see Fig. 2), are similar in shape and location of the supertemporals of primitive tetrapods. The tabulars (Marya ńska, 1971) found in Pinacosaurus are small bones that lie along the posterior edge of the skull roof. They were identified based on their topographical position. It is possible that the formation of osteoderms normally occurred in this area in the majority of ankylosaurs, but the fusion of the osteoderms with the bones of the skull roof in Pinacosaurus proceeded selectively, mainly where large osteoderms occurred. The jugals make up the lower border and lower base of the orbits and anteriorly contacts the maxillae, anterodorsally the lachrymals, posteriorly the quadratojugals and postorbitals, and anteromedially, with the pterygoids. The jugals are partially free osteoderms, even in Saichania and Tarchia , and only slightly approaches the osteoderm on the lateral surface of the maxilla.

Morphology of the Nasal Cavity In ankylosaurs, the external nasal openings are usually large and in the majority of the species, the borders are framed by osteoderms; therefore, the shape and dimensions of the external nares are in direct proportion to the degree of osteodermal growth. The narial openings are, as a rule, located terminally on the snout. The exception, is Ankylosaurus , in which the small round nostrils are located more laterally. This position is because of the extreme growth of osteodermal lamina so that the osteoderm covers the entire anterior section of the snout, leaving only small anterolateral openings. In Tarchia , the external nares are large and divided by the dorsal process of the premaxillaries, which are covered only by osteoderms on the dorsal-most portions. On the dorsolateral edge of the narial opening there is a notch, probably for one of the branches of the maxillary artery (see Fig. 3c). In Saichania , T. Marya ńska (1977) observed the presence of two pairs of ducts inside the external nares. These openings are divided by a horizontal process of he premaxilla. Technically, the upper pair of openings correspond to the nares. The septum between the openings may be the septomaxilla, which gives the impression of a splitting of the external nares in half. For Pinacosaurus , T. Marya ńska ascertained that three pair of openings were present in the nasal region: two medial, which are divided by a horizontal septum and corresponding to that in Saichania , and one lateral, which is surrounded by the flat, outer surface of the premaxilla, to house the lateral nasal glands. On the other hand, it may be possible that the septomaxilla is present and that the lateral nasal gland is situated in it, adjoining the maxilla laterally. The third pair of openings may be a strongly hypertrophied exit for one of the alimentary vessels for the blood supply of that region (perhaps due to the immaturity of the specimen). In adult specimens, no traces of these openings were discovered. The internal, medial bony septum in the nares of Pinacosaurus and Talarurus is incomplete and consists of a vertical plate extending up from premaxillary and a vertical plate extending down from the nasal bones; in Talarurus , these extensions do not occur and the height of the bony septum does not exceed 0.7 - 1 cm. The dorsal edge of the medial septum terminates where the anterior portion of the nasals contacts the premaxilla. From that point, the septum is reduced in height posteriorly to about the middle of the nasal capsules at the expense of the medial extension of the sphen-ethmoid where it attaches to the facial bone. The nasal septum of

27 Saichania and Tarchia is distinctly more massive and solid. As in Pinacosaurus , it consists of the premaxillary and nasals anteriorly, which are elongated as thin walls along the midline and forward of the vomer keel; posterodorsally, the ethmoid ossification also forms part of the septum. A thin bony lamina, which extends horizontally from the nasal septum to a projection on anterior of the inner surface of the maxilla may be the septomaxilla. Ventral to the septomaxilla is the Jacobson's organ, probably located between the septomaxilla and the horizontal portion of the premaxilla. Laterally, somewhat posterior to the external edge of the external nares, is probably located the nasal gland. In the anterior section of the respiratory tract in Pinacosaurus and Saichania , Marya ńska (1971) noted some structures that are related to those in theriodonts and mammals. A crest which extends along the maxillaries is called the crista maxillo-turbinale, and the structures connected to it are called the maxillo-turbinals (the author notes a greater degree of ossification in the nasal region of Saichania ). The crest on the nasal bones of Pinacosaurus was compared to crista naso- turbinale in mammals and so may have also been equipped with naso-turbinals (Marya ńska, 1971) In Saichania , few of such crests were found. Thinner turbinals were found, which were comparable to the ethmoturbinals in mammals. Marya ńska describes the formation of various sinuses due to the ossification of turbinals: the maxillary and the premaxillaries. She compares the anterior dorsomedial section of the respiratory tract in Saichania with the meatus nasi superior of mammals, based on the fact that the air from here may enter immediately into the olfactory section of the nasal capsules. According to her the ventrally located air passage leading from the supplementary opening through the maxillary sinus into the nasal cavity, corresponds to the meatus nasi medium, where the air originated in the respiratory section of the nasal cavity. W. Coombs (1978), in the North American Euoplocephalus , pointed out the large quantity of sinuses in the nasal cavity of this species of the family Ankylosauridae. He considers this a diagnostic trait of the family Ankylosauridae which separates them from Nodosauridae and other reptiles. Neither the inflection of the respiratory tract nor of the supplementary cranial sinuses were discovered in Nodosauridae. The general structural plan of the nasal section of the skull as seen in the ankylosaurs, is not known for any other group of dinosaurs or extant reptiles (Marya ńska, 1977). The normal condition, which is similar to extant reptiles in the opinion of T. Marya ńska, is the dorsal nasal channels that lead from the external nares to the rear section of the so-called nasal capsules. Their dorsomedial location and opening in the nasal cavity resembles the vestibule in extant iguanids and agamids that live in sandy locations. On the other hand, by detailed study of the ventral area of the skull roof of Talarurus (see Fig. 5b), there can be found more similarities in the structure of the nasal capsules between ankylosaurs and lizards. Based on separate structures for this region, it is possible to utilize the terminology used for lizards (Oelrich, 1956). The nasal region of ankylosaurs was very spacious, occupying in length over half the cranium. Medially, the respiratory tract is bounded immediately by the bones of the skull roof; laterally, by elongated crests extending on the ventral side of the nasals; posteriorly, by the depression in the anterior wall of the medial thickness on the nasal crest. On the anterior wall of the sinuses there is a groove, evidently for a branch of the maxillary artery, which passes over to the upper

28 border of the bony nostril where it may form the circum-narial anastomosis with a branch of the frontal artery. Transverse crests serve as the rear wall of the sinuses on the ventral surface of the nasals, terminating in oval horizontal expansions of bone that are probably homologous with the nasoturbinals according to Marya ńska. The structures possibly represent the upper section of the maxillary sinuses and may be filled partially by the expanding venous channels of the palatal vein, proceeding along the dorsal surface of the maxillas. The large part of these cavities was evidently filled with air. Ventrally to the anterior rostrum of the vomers, extends a thin wall from the premaxillaries in a position comparable to that of the septomaxilla, and extending farther posterolaterally to the maxilla. Ventral to this septum rests the Jacobson’s organ, which probably had openings on the palatal portions of the premaxillaries as pointed out by Marya ńska (1977). Posterior to the the respiratory section [(i.e., where air is inhaled)] is the region of the cartilaginous nasal capsules. The skull roof in this section has a few crests which possibly delineate the boundaries of the cartilaginous structures. And if we use the terminology that is applied to lizards (Oelrichs, 1956), we may propose the presence of structures here comparable to zona annularis, aditus concha and lamina transversalis anterior (see Fig. 5b). The ossification of this region is developed to a rather large extent in Pinacosaurus . It reaches its maximum development in Saichania , manifesting itself by the presence of a large number of sinuses (Marya ńska, 1977).

Palatal Area The premaxillary bones (see Fig. 3b)in ankylosaurs are well developed in the palatal area, forming a scoop-shaped beak; in nodosaurids it is narrow (see Fig. 1 a) and in ankylosaurids it is wide (see Fig. 3b). The bone surface, as a rule, is depressed and somewhat concave; only in Pinacosaurus is it somewhat convex, probably due to the immaturity of the specimen. The anterior border of the premaxillary bones may take on a different form: narrow-oval in Shamosaurus, wide-oval in Tarchia , Saichania and Ankylosaurus, round in Euoplocephalus, and square in Pinacosaurus . Medially, along the suture between the premaxillaries, near the cutting edge of the beak are located a pair of openings, probably serving as outlets for the ethmoid branch of the trigeminal nerve (V 1). The ventral laminae [(i.e., palatal portion)] of the pre- maxillaries, especially in the rear section, are very thin, easily fractured. The vomers contact approximately 1/3 to 1/4 the length of the premaxilla; the vomers also extend some in the horizontal plane. Posterolaterally on the premaxilla lie the maxillaries; depending upon the development of the anterior maxillary shelf, the maxilla may displace the premaxilla laterally (in Pinacosaurus and probably Maleevus ) and even the anterior edge of the choanae ( Saichania , Euoplocephalus and Ankylosaurus ). In the nodosaurid Silvisaurus (Eaton, 1960) premaxillary teeth are present, in a row on each side along the edge of the premaxilla. In later species of the Nodosauridae, the premaxillary teeth are lost, but the crest along the lateral margins is retained, uniting the premaxilla with the front of the maxillary teeth. In ankylosaurids, neither premaxillary teeth nor crests are formed. The maxilla are lengthened, outwardly curved, and bear teeth. Anteromedially, they may unite with the vomers ( Saichania , Tarchia , Euoplocephalus , Ankylosaurus ). The anterior section of the maxillae form the anterior maxillary shelf, which is not very well developed and is present

29 only near the first maxillary teeth in Maleevus and Pinacosaurus , but is well developed in Saichania and Euoplocephalus . It is very well developed and begins at the midpoint of the maxilla in Ankylosaurus and Tarchia . Thus, in Late Cretaceous ankylosaurids, the secondary palate gradually expands at the expense of the anterior maxillary shelf. The Early Cretaceous Shamosaurus appears to be an exception, since it has a well developed shelf beginning at the midpoint of the dental row. We may define two ankylosaurid groups based on the development of the posterior part of the maxillary shelf. In the first are included Euoplocephalus , Saichania , and Shamosaurus ; they have a well developed shelf located on a laterally inclined surface. The second group includes the remaining ankylosaurids; their maxillary shelf is weak developed and appears only as a palatal outgrowth of the maxilla and are inclined upwards. In each group there is also a suborbital fenestra [(posterior palatal foramen of Marya ńska)] that differs in each group. In the first group, the fenestra is located near the posterior portion of the maxillary shelf, which is inclined laterally. The maxilla frame the fenestra in anteriorly and laterally; the palatines bones frame it medially, and the ectopterygoids frame it posteriorly. In Shamosaurus , this fenestra is greatly expanded. In specimens of the second group, the suborbital fenestra lies a little more posteriorly, and is expanded as depressions in the pterygoids. Pinacosaurus is an exception in that the suborbital fenestra differs sharply in position with the first group, and differs from the second in that the fenestra is small and located in the rear lateral wall of the pocket formed in the pterygoids. The entry to the pocket is bounded anteriorly by the maxilla, by the ectopterygoids laterally, by the palatines medially, and the pterygoids posteriorly. A small suborbital fenestra lies between the maxilla bones, the ectopterygoids and the palatines; it opens into the adductor fossa by means of a narrow channel with a foramen for the infraorbital artery, which is located at the in the maxilla near its contact with the ectopterygoids. The palatines are located high in the base of the oral cavity. Ventrally, they are inclined laterally in different degrees. Medially, they unite with the vomers and laterally contact the palatine process of the maxilla. Posteriorly, the palatines overlap the descending wall of the pterygoids, forming the ventral part of the posterior wall of the palatal cavities; in the North American ankylosaurids, Saichania and Tarchia , the palatines only contact the mid-section of the pterygoids at a right angle. The anterior portion of the palatines delineates the posterior edge of the choana (internal nares). With the lateral edge, they border the suborbital fenestra and contact the posterior part of the maxillary shelf. This contact is usually with the palatine process of the upper maxilla, which is expanded to contact the palatines. The surface of the palatines is uneven ventrally. In Saichania , there are symmetrically arranged depressions. Also in Saichania , near the contact of the palatines with the pterygoids, there are round openings called postero- palatal formania (Marya ńska, 1977). In Tarchia , there are elongated fossae in this area (See Fig. 3b). The vomers unite along a thin vertical partition that divides the palatal cavities. Anteriorly, the vomers extend dorsally to the internarial septums and forms its rear section. Ventrally, they lie on the premaxillary bones and contact a well developed anterior maxillary shelf and anterolaterally with the maxilla. The lower border of the vomer keel may be split ( Tarchia , Euoplocephalus ) showing that it is actually formed of two bones. The dorsal contact with the palatines in Euoplocephalus and Pinacosaurus is expanded slightly in the horizontal plane.

30 Posteriorly, the vomers contact the palatine process of the pterygoids, which are a continuation of the septum. The pterygoid flanges form a vertical structure perpendicular to the vomer keel which consists of the palatine processes of the pterygoids and vomers. The pterygoid flanges in the Ankylosauridae are directed laterally (see Fig. 3b), and, as in Nodosauridae, they extend forward parallel to the vomers (see Fig. 1a). The pterygoids, as usual, form the rear wall of the palatal cavities. In Pinacosaurus, anteriorly they may contact the palatines on the along the midline (Marya ńska, 1977). In the dorsal corner of the vertical wall, the pterygoids have a posteriorly facing pocket. Medially, the pterygoids are separated by an interpterygoidal vacavity (see Fig. 3b). In the Early Cretaceous Shamosaurus, this vacuity is very small or absent (see Fig. 4b), much like in the family Nodosauridae (see Fig. la). Just lateral to the vacuity, the pterygoids are pierced by two foramina arranged symmetrically. The contact between the pterygoids and the brain case is seen as a seam in Ankylosauridae (Fig. 6a), except for Shamosaurus, in which these two structures are completely fused (Fig. 6b), as in Nodosauridae (see Fig. la). In ankylosaurids, the quadrate process of the pterygoids is long, occupying about half of the quadrate-pterygoid processes; in Shamosaurus , the quadrate-pterygoid processes are shorter and higher. The ectopterygoids lie in front of the pterygoids and contact the outer, anterior section of the pterygoid flanges. The anterior and lateral parts of the ectopterygoid contacts the maxilla. Dorsally, they contact the palatines and form the upper ( Tarchia ) or most ( Pinacosaurus ) of the rear wall of the posterior palatal cavities posterior to the suborbital opening.

Ossification of the Quadrate Complex The epipterygoids in ankylosaurs were first found in Saichania (Marya ńska, 1977) and in all probability are characteristic of all ankylosaurs. The position of these bones is very unusual in that they are not arranged vertically as in the majority of dinosaurs. Instead, they are strongly inclined dorsoposteriorly at about 45 o and are almost parallel to the brain case. They begin near the front of the basipterygoid and extend towards the ventral surface of the parietal bones opposite the mid-section of the postorbital shelf. These bones are thin rods, flattened dorsoventrally, and expanded at the ends. The quadrates are broad, flat, inclined slightly forward, and triangular in shape. A wide process extends anteriorly and medially to contact the pterygoids; only in young individuals of Pinacosaurus , is the quadrate process of the pterygoid and the pterygoid process of the quadrate not fused. The head of the quadrate rises to the skull roof and in the majority of ankylosaurids contacts the anterior side of the paroccipital processes (see Fig. 6). W. Coombs (1978) places great emphasis on this contact and considers it a characteristic feature of the family Ankylosauridae, because in all specimens of the family Nodosauridae the dorsal process of the quadrate head fuses with the ventral part of the distal ends of the paroccipital process. An exception to the typical ankylosaurid arrangement is Saichania (Marya ńska, 1977) in which the dorsal head of the quadrate and paroccipital processes fuse (see Fig. 6d) as in the Nodosauridae. Fusion of the two bones also occurs in the Lower Cretaceous Shamosaurus (see Fig. 6b). In addition, specimen PIN N 3779/1 (see Fig. 6c) has a double dorsal process pf the quadrate head: one is parallel to the anterior surface of the paroccipital process, the second is fused along the lower edge of the paroccipital process. Evidently, the cartilage in this region may ossify at

31 Fig. 6. Types of contact of the quadrate and paroccipital process in ankylosaurids. A, Tarchia ; B, Shamosaurus ; C, Shamosaur sp. PIN N3770/1; D, Saichania (after Marya ńska, 1977). See Fig. 3 for abbreviations. different degrees: in the majority of ankylosaurids, the anterior section of cartilage was more ossified; in the Nodosauridae, Saichania and Shamosaurus it is the posterior section, but in specimen N 3779/1 (probably also Shamosaurus ) both sections ossified. Thus, the peculiar contact between the quadrate and the paroccipital process, may not serve as a concrete systematic criterion for the family Ankylosauridae. The extreme upper end of the quadrate, as a rule, is fused to the ventral surface of the cranial roof, but in the young specimen of Pinacosaurus (Marya ńska, 1977) and in Talarurus (Sp. N 3780/1; see Fig. 5,i) there is no fusion, the contact is free. In the place of fusion there is a fossa on the ventral surface for the quadrate head. The boundary between the quadrate and the quadratojugal in the Ankylosauridae is seen as a transverse band which unites the quadrate condyle with the quadratojugal lying on the lateral surface of the cranium (not expressed in the Nodosauridae; see Coombs, 1978). The band extends with the jugal to its contact with the maxilla. The ventral articular condyle is oval, oriented with its long axis perpendicular to the axis of the cranium and is narrow laterally.

32 BRAINCASE

Ethmo-sphenoid Section The basisphenoid is short, massive, and slightly ossified. The basioccipital tubera are shaped more or less like crests, most clearly visible in Talarurus (Sp. N 3780), and are directed antero- medially-posterolaterally (Fig. 7c). The basioccipital tubera are very comparable to the basipterygoid tubera, which are small, positioned anteriorly and contact the pterygoids. The suture with the pterygoids in Ankylosauridae not fused, in contrasted with Nodosauridae, in which the basisphenoid section is greatly compressed against the pterygoids and fusion is well developed; exceptions are seen in Saichania and Shamosaurus . In the latter, there is a spot, which is the same as in Nodosauridae, where the basisphenoid complex is fused into the pterygoids. In this area, well defined sutures were not found in any of the specimens. Anteriorly, and rather more dorsally of the basisphenoid is the basisphenoid rostrum, which underlies sphen-ethmoid. We may assume its existence because of the remnants of the structures preserved on the ventral surface of the skull roof in the specimen of Talarurus, N 3780/1,: two of these structure are on the lateral walls, located near the medial border of the anterior wall of the orbit and one is medial, beneath the small osteoderm on the skull roof tentatively identified as the ethmoid in Pinacosaurus (Marya ńska, 1971). On the lateral surface of the contact with the sphen-ethmoid is an area which, in lizards, is where the fascia of the optical muscles attach.

Otic-Occipital Section The prootic, opisthotic and exoccipital are completely fused, except in Pinacosaurus (Sp. N 4046) from Baga Tarjach, where there is a vertical suture between the prootic and the paroccipital process about at the approximate level of the lacuna (Fig. 8). The anterior part of the prootic fuses with the laterosphenoids, with the projection from the ventral surface of the parietals and the medial elongation of the postorbital shelf. The inner ear (see Fig. 7d) is open in to the brain cavity because its medial wall is not ossified. The lagena are large. The vestibule is located in the lateral wall of the brain case. The tubes of the semicircular canals are clearly distinguishable: the posterior one appears as a distinct widening of the rear and horizontal ends of the semicircular canals; the anterior and horizontal ones are near by. The horizontal semicircular canal is located somewhat below and medial to the anterior one. The anterior semicircular canal pierces the inner ear capsule and exits at the upper section on its inner surface and unites with the posterior semicircular canal. Here in the endocranial wall there is a a depression which is inclined to the rear and upwards and terminates blindly. Probably this structure enclosed the thickened upper section, the crus communis, which extended through the un-ossified wall of the brain case. It may have had no connection with the membraneous labyrinth (Kurzanov and Tumanova, 1978), but may be similar to the recessus interacusticus of the predatory dinosaur Itemurus (Kurzanov, 1976). Above the cavity of the inner ear on the edge of the endocranial wall runs a fissure, evidently of the endolymphatic duct, which is divided into two branches: the posterior branch, which does not extend far, and an anterior branch, which enters into the inner ear cavity at the dorsal edge of the horizontal semicircular canal. From the

33 Fig. 7. Braincase of the ankylosaurid Talarurus plicatospineus Maleev. Sp. PIN. N 3780/1; Baynshin Tsav; Upper Cretaceous Bayn Shiren Formation. A, lateral; B, dorsal; C, ventral; D, reconstruction showing the inner ear. aa - anterior ampule; aci - internal carotid artery; ae - external ampule; aoph - opthalmic artery; ap - posterior ampule; btb - floor of braincase; cinf - crista interfenestralis; csa - anterior semicircular canal; cse - horizontal semicircular canal; csp - posterior semicircular canal; ds - spine of sella turcica; fj - jugular foramen; fo - fenestra ovalis; fp - hypophysis fossa; la - lacunae; rca - M. rectus capiti anterior; ria - inner auditory chamber; sv - foramen for vein; tha - facet for proatlas; tsph - basioccipital tubera; vp - pituitary vein; II-XII - cranial nerves. edge of the endocranial cavity, the furrow can be traced to the upper edge of the paroccipital process where the endolymphatic duct may have passed outside. The ankylosaurid occiput is wide (see Fig. 3d; 4d) and the bones are fused together. The post- temporal opening exists in Pinacosaurus in the form of a gap, but is completely closed over

34 Fig. 8. Braincase of the ankylosaurid Pinacosaurus grangeri Gilmore (ventral). Sp. PIN N 4043; Baga Tarjach, Upper Cretaceous Djadokhta Formation. See Fig. 7 for abbreviations.

in the other ankylosaurids. The formamen magnum is prominent and occupies over a third of the height of the occiput; it is circular-rhomboid in shape, and horizontally elongated in Pinacosaurus , Saichania and Amtosaurus (Fig. 9a) and is more vertical in Talarurus and Tarchia (see Figs. 3d, 5d). The paroccipital processes, which are less than twice the height of the occiput, extend perpendicularly to the sagittal axis of the cranium (see Fig. 3b); in the Nodosauridae, they extend at an angle (see Fig. la); in Saichania, they are very low and angle beneath the edge of the skull . The paroccipital processes in Tarchia (see Fig. 3,d) are at approximately the same height for their entire length, but in Talarurus (see Fig. 5d) and usually in Shamosaurus (see Fig. 4d), they are wider distally and proximally they extend forwards. As a result, the osteoderm rim of the skull roof slightly overhangs the middle of the occipital region. In Talarurus (see Fig. 5d), the ends of the paroccipital processes are bent downwards like a hook; in the majority of ankylosaurs they are only slightly bent. In Talarurus (sp. 3780/1), there is incomplete fusion of the occiput to the ventral side of the skull roof. There is also a transverse slot behind the fossa for quadrate heads that encloses the dorsal edge of the paroccipital processes. The "tabular" was identified in the skull of Pinacosaurus grangeri (Marya ńska, 1971, 1977). It seems to be an element hanging over the rear border of the skull roof consisting of osteoderms. The supraoccipital contacts the foramen magnum dorsally. In all ankylosaurs, except for the young specimen of Pinacosaurus , the supraoccipital is strongly fused with the skull roof (see Fig. 3d 4d). The exoccipital bones are completely fused with the opisthotic. Near the edge of foramen magnum, there is a pair of raised facets on the exoccipitals that are apparently for the neural arches of the first cervical vertebra (i.e., proatlas), but in the base of the raised facets is a furrow in which the occipital vein may have extended. The basioccipital covers the rear section of the brain cavity and borders the foramen magnum from below, forming the occipital condyle. The occipital condyle ranges from a narrow oval in Talarurus and Amtosaurus (see Fig. 7c) to a wide oval in Saichania and Tarchia (see Fig. 3d), and round in Pinacosaurus , Maleevus and Shamosaurus (Fig. 10a, 4b). The articular surface is inclined more or less posteroventrally. On the dorsal side of the basioccipital is a shallow depression. On the ventral surface of the basioccipital, between the condyle and the basioccipital tubera,

35 is the attachment site for the M. rectus capitis anterior. The appearance of this part differs greatly: in Shamosaurus it is a comparatively narrow, ventrally convex, round area; in Talarurus, a keel occupies the central position and is bounded by lateral depressions; in Amtosaurus there is a depression in the center bounded laterally by ridges extending from the front to the rear. In Pinacosaurus , the surface is very smooth and concave with a sharp depression between the basioccipital tubera; in Maleevus , the ventral surface of the basioccipital is also smooth, expands anterolaterally and curves down sharply at the basioccipital tubera; in Saichania and Tarchia , this region is short and even. On the contact of the basioccipital with the basisphenoid, between the basioccipital tubera, there is a depression. It is very large in Saichania and Tarchia (see Fig. 3b). Endocranial cavity. The posterior part of the lateral wall of the brain case shows formanina for two branches of the XII nerves; on the contact of exoccipital and opisthotic there is a round jugular foramen through which the IX, X, and XI cranial nerves enter. A little anterior and

36 Fig. 10. Braincase of the ankylosaurid Maleevus disparoserratus (Maleev). Sp. PIN. N 554/2-1; Shiregin Gashun; Upper Cretaceous Bayn Shiren Formation. A, ventral; B, dorsal. See Fig. 7 for abbreviations. separating the crista interfenestralis, is an oval opening. In Amtosaurus (see Fig. 9c, d) the crista interfenestralis is thick and unbroken; in Talarurus (Fig. 7a,c) it is incomplete; in Tarchia , the jugular foramen and the fenestra ovalis completely fuse. The endocranial cavity is not large in volume. Its height increases in front. The floor of the cavity is level and straight; it rises only slightly in the front half of the cavity in Amtosaurus , just anterior to the pituitary fossa. The angle between the basisphenoid and the basioccipital varies from 120 o for Amtosaurus (see Fig. 9d) and 150 o for Talarurus (see Fig. 7a). Along the front half of the brain cavity base extends the crest, which is comparable to the basis tuberculi basalis of the turtle (Gaffney, 1972) which, in Amtosaurus , ends with a triangular knob at the upper wall of the sella turcica (see Fig. 9c). At the base of the rear wall, along the sides of the basis tuberculi basalis, there are depressions (distinct in Amtosaurus ) for attachment of a fascia “rod” supporting the oblongatal medulla. The sella turcica is well defined. Its anterior wall is inclined forward and it makes an acute angle with the posterior surface of sella turcica; at approximately midheight (in Pinacosaurus and Maleevus , a little lower), it becomes vertical. Anterolaterally, the foramina of the VI nerve pierces the wall of the sella turcica. There is also a small foramen for a branch of the trigeminal nerve; a little more posteriorly, are foramina for two maxillary branches of the n. trigeminus (V 2, 3 ). A little to the rear and above is the smaller foramen for the VII nerve. By the shape of the foramen, we can determine that one branch of the facial nerve, the hyomandibular, exits and extends posteriorly, and the other, the palatal, extends ventroanteriorly along a groove to the palatal branch of the internal carotid artery. The meeting of the palatal branch of the facial nerve with the palatal branch of the internal carotid artery is on the dorsal surface of the paroccipital process; the parabasal canal is absent. From the foramen into the channel of the VII nerve on the inner surface of the braincase lies the channel of the VIII nerve, which is directed into the labyrinth of the inner ear. Posterior to the palatal branches of

37 the carotid artery and the facial nerve, is a vertically oval foramen for the cerebral branch of the internal carotid artery. Dorso-anteriorly, the foramina of different dimension are arranged into an irregular oval with its axis inclined posteriorly. At this point, the pituitary vein possibly exits from the brain case. Small foramina pierce the anterolateral wall of the hypophyseal fossa and are directed outwards and upwards. Apparently they are for the a. ophtalmica and have a separate and lower exit. In front of the hypophyseal fossa, a large furrow for the optic nerve extends in a transverse direction. Great morphological distances separate the ankylosaurs and other ornithischians, and a hypothesis regarding their early separation was present based on the ancestral condition of the pseudosuchians (Coombs, 1978a). The morphology of the cranium served as the basis for this hypothesis, but there are also structural details of the postcranial skeleton. The study of the endocranial structure corroborates this hypothesis. By comparison of the morphological patterns of brain case in dinosaurs (Osborn, 1912; Brown and Schlaikjer, 1940; Ostrom, 1961; Russell, 1969; Kurzanov, 1976), and comparison of the patterns characteristic of Mongolian Ankylosaurs discussed above, it is obvious that the brain case of ankylosaurs is different from any other dinosaur. To some extent, the specific structures of the ankylosaur braincase indicate the correctness of this hypothesis.

Maxilla The row of teeth is straight in Pinacosaurus ; in all the others it is arced (see Fig. 3b), and includes a varied number of undifferentiated teeth: in Maleevus , 19; in the young Pinacosaurus , 17; there are 18 in Tarchia ; 22 in Saichania and Euoplocephalus , and 35 in Ankylosaurus . There is only one row of functional teeth.

Mandible The height of the mandible is about 1/3 its length. The anterior edge is curved laterally in dorsal view (Fig. 11) forming a spade-shaped surface; the narrow symphysis is horizontally inclined meeting on the midline. There are no teeth in this part of the dentary. The upper border of the mandible is concave internally so that the distance between the front teeth of the dentaries is greater than the distance between the rear teeth. The lateral wall of the adductor fossa is convex inside. Posterior to the adductor fossa, the upper edge of the mandible is flattened and extends into the articular area, where it contact quadrate (Fig. 12d). The lower border of the mandible is straight, except in the central third where it is somewhat convex ventrally. The right and left symphyses are securely joined at the midline. Each symphysis is low, with the height approximately 1/4 the dentary height. The lower part of the lateral surface of the mandible is covered with osteoderms. This armor has a very irregular, ornamented surface and in the majority of cases completely conceals the underlying bones. Along the lower border of the mandible is a narrow projection that is inclined laterally (see Fig. 3,e); it completely covers the external surface of the angular. In Pinacosaurus , this bone is not covered with osteoderms and is keel shaped. The armor on the mandible in Tarchia does not cover the region of the symphysis (Fig. 3f), nevertheless edges of the bone and sutures cannot be observed here. The sculpturing fades away on

38 Fig. 11. Tarchia gigantea (Maleev). SP. PIN N 3142/250. Khermeen Tsav, Upper Cretaceous Nemegt Formation. A, mandibles in dorsal view; B, predentary in dorsal view; C, maxillary tooth; D, dentary tooth. c -crown; cla - labial cingulum; cli - lingual cingulum the dentary and supra-angular. The coronoid is rather large and posteriorly contacts supra- angular (see Fig. 3g). The coronoid process is poorly defined and low. W. Coombs (1978) does not consider it to exist in ankylosaurs. The coronoid rises above the alveolar border on average of about 15 mm, but its dimensions are rather large; it overlies anteriorly the dentary, and it extends half the tooth row as a narrow tongue. The bones described have a keel, extending approximately over an angle of 45 o relative to the tooth row. Anteriorly and dorsally, the coronoid is contiguous with the supra-angular and contacts its anterior edge. The coronoid forms a strip on the inner wall of the adductor fossa. The dentary forms most of the mandible. Its anterior part is flexed laterally in a spade shape; near the symphysis, it is almost perpendicular to the main arch of the dentary. On the external side, near the anterior end of the dentary, is a fissure for the lateral process of the predentary containing foramina for blood vessels and nerve branches to the predentary; this indicates the presence of a corneous covering in this region. However, striations similar to those on the anterior part of the cranium, which are due to the comparatively rapid rate of

39 Fig. 12. Right mandible of Shamosaurus scutatus Tumanova. Sp. PIN N 3779/2-2; Khamareen Us, Lower Cretaceous, Dzun Bayn Formation. A, lateral; B, medial; C, occllusal; D, ventral. lops - insertion for M. pseudotemporalis superficialis and M. pseudotemporalis profundus; lopt - insertion for M. pterygoideus; lp - internal process. See Fig. 3 for other abbreviations.

growth of the corneous covering, have not been found. The supra-angular forms the outer wall of the adductor fossa and appears on the outer surface of the mandible of Tarchia (see Fig. 3e) as a region with poorly defined sculpturing. The bone resembles an uneven oval in shape. Anteriorly, near where it contacts the coronoid, it contacts the dentary. Ventrally, it’s contact with the angular is covered with osteoderms in

40 ankylosaurs. Posteriorly, the supra-angular extends to the articular. The prearticular overlaps the coronoid bone with its upper edge and forms the inner border of the adductor fossa; it also forms the “inner process” (see Fig. 12b) and part of the articular fossa; on the upper boundary it fuses with the articular. Ventrally, where the lower edge of the mandible extends downward, the prearticular contacts the angular. The articular is wide, fused with the angular bone posteriorly and to the prearticular near the “inner process” in the region of the adductor fossa (see Fig. 11a). Posteroventrally, on the poorly developed retroarticular process, is located a irregular texture that probably indicate the insertion of the depressor musculature. On the inner surface of the mandible, along the lower anterior half of the dentary, is a band 5 mm wide that extends to the end of the symphysis. Evidently, this is the imprint left by the Meckelian cartilage (sulcus Meckelii). At this level, beneath the anterior part of the adductor fossa, is a foramen, the foramen Meckelianum posterior, through which the mylohyoid artery and vein, and branch of the lower mandibular nerve exits. On the internal surface of the lateral wall of the adductor fossa, there is the foramen in the supra-angular for N. recurrens cutaneous, and on the outside, an anterior supra-angular foramen for the n. cutaneous externus.

Teeth The teeth of the maxilla (see Fig.11c) have an asymmetrical, leaf-shaped crown and a cylindrical root. The lower anterior angle of the crown is smooth. On the border with the root the crown forms a "little collar" (cingulum). The lingual cingulum is continuous with the root; the labial cingulum is not continuous, but has a groove; in Maleevus there is a W-shaped swelling. The margin of the crown is serrated (8-10 denticles). The denticles are small along the anterior edge and are arranged transversely to the crown in alignment with the tongue; the cingulum also does not have a folded border with the posterior denticles. The labial cingulum projects away from the crown more than does the lingual. This occurs because of the more convex lingual surface of the crown and the more even and flat labial surface. On the teeth of ankylosaurs there are no evidence of extensive wear similar to that seen on the crowns of Protoceratops and hadrosaur teeth. But some wear is seen on the serrations of some teeth of Tarchia . Teeth of lower jaw (see Fig. 11d). The alveolar border of the dentary has a length of about 120 mm in Tarchia and Saichania , and 160 mm in Shamosaurus (approximately equal in cranial dimensions). As a whole, the dental row is concave; under each of the functioning teeth there is no less than one alveolus for the replacement teeth (see Fig. 3g). The labial cingulum is more convex than the lingual. The labial cingulum in the Late Cretaceous ankylosaurids is split. Teeth of stegosaurid type: The crown is spatulate in shape, compressed lateromedially. The upper edge is split into denticles. The apex of the tooth is located approximately in the center, but the crown is not symmetrical on each side of it. The ribbing on the crown face is fan-shaped, especially near the apex, and it does not extend down farther than to the center of the crown (here there appear only faint wrinkles). Along the anterior edge the denticles are

41 arranged transversely with the tongue and the most anterior serration does not border with the cingulum.

Hyoid Apparatus Remains of the hyoid apparatus are presently known in only two Mongolian ankylosaurids: Saichania (Marya ńska, 1977) and Tarchia (PIN 3142/250-5). In ankylosaurs (Fig. 13) it consists of an unpaired hyoid body (basihyal), a pair of ceratobranchyals and a pair of ceratochyals. These are practically the first examples in dinosaurs of such well ossified hyoid apparatus (Marya ńska, 1977). The body of the hyoid is rather narrow, of triangular outline with a rather thin lingual process (see Fig. 13). Ceratohyals (see Camp, 1923) or hyoid prongs, for which only the base remains in Saichania , probably functioned to support the sublingual muscles. The keel-shaped ceratobranchyals serve as the main origin site for the fascia of this muscle. These ceratobranchyals elements of the hyoid taper distally. They are bowed rods with three sharp keels, between which are depressions of differing degrees of development (Table II). On the proximal end is the articular surface for contact with the hyoid body. Perhaps the musculature for this region in ankylosaurs was not strong because the ceratobranchyals are not firmly attached in comparison those of the hadrosaur Corythosaurus casuarius (Ostrom, 1961). The second of the pair of ceratobranchyals, found in the hyoid apparatus of Protoceratops and Psittacosaurus (Colbert, 1945), is not found in ankylosaurs. For this reason, and because of the rather thin hyoid body with narrow lingual processes, the hyoid apparatus of ankylosaurs are compared with those of lizards rather than with crocodiles as was done with Psittacosaurus and ceratopians (Goodrich, 1930).

Fig. 13. Hyoid apparatus of the ankylosaurid Saichania chulsanensis Marya ńska. From Marya ńska (1977). bh - hyoid body; cb - ceratobranchial; ceh - ceratohyal

42 MUSCLES, GLANDS AND VESSELS OF THE HEAD

Musculature of the Head The only attempt to reproduce the adductors of the mandibles is by Haas (1969). The reconstruction was based on comparison of the mandible of Ankylosaurus with contemporary reptiles. While comparing the cranial structure of Ankylosaurus and of contemporary lizards, possible attachment sites of muscles were hypothesized, as were their degree of development and those of other muscles of the head. Depressor of the mandible. The origin of the mandibular depressor was probably on the upper, posterolateral part of the quadrate and the distal ends of the paroccipital process. Insertion on the mandible was on a convex oval fossa on the inner process (see Fig. 11a and 12b). Adductors of the mandible. Judging by the small teeth, the ankylosaur jaws was not subjected to powerful stresses in contrast to animals whose jaws produce crushing, grinding, tearing, etc., motions. On the other hand, the jaws themselves are high and massive, the adductor fossa large; consequently, it is most likely that the adductors in ankylosaurs were rather strongly developed. The posterior portion of the M. adductoris mandibularis originated on the anterior part of the paroccipital processes and adjacent crest on the vertical process of the quadrate, and also on the ventral part of the prootic. One slip of the adductor may have also originated where the quadrate and paroccipital process meet with theskull roof. On the mandible, the M. adductor mandibulae externus medialis inserts on the upper, inner surface of the supra-angular, but the M. adductor mandibulae profundus inserted deeper on the lower section of the external wall of the adductor fossa. In lizards, the M. pseudotemporalis superficialis and M. pseudotemporalis profundus originate on the anteromedial partr of the supratemporal fenestra, the surface of the pterygoid (alar) process on the pro-otic, and on the upper third of the epipterygoid. In ankylosaurs, the supratemporal fenestrae are absent, therefore these muscles probably originate in the upper, anterior parts of the narrow adductor [(=temporal)] fossa, (see Fig. 3b); it is bounded anteriorly by the rear wall of the orbit and the postorbital shelf, and posteriorly by the dorsal process of the quadrate. On the mandible, insertion is on the internal border of the adductor fossa and the coronoid process (see fig 3g). This area of insertion is well developed in Shamosaurus , in which the keel on the coronoid is low, but the insertion area is wider and deeper (see Fig. 12c), as compared with Tarchia (see Fig. 3g). The pterygo-mandibular (pterygoid) muscle in lizards originats along the lateral edge of the quadrate processes of the pterygoids. In ankylosaurs, the homologous area lacks any structure to speak of for muscles. But a little more anteriorly on the lateral edge of the pterygoids is a depression that might correspond to the location of this muscle. On the mandible, the pterygoideus inserts on the posteromedial surface, and probably passing around the lower edge to the lateral side (see Fig. 3g) . In Shamosaurus , insertion is along the dorsoposterior section of the mandible because a portion of the depressor descends to insert on the inner processes. M. adductor mandibularia posterior in ankylosaurs may originate from the medial surface

43 of the quadrate and quadrate process of the pterygoids and insert on the inner surface of the lateral wall of the adductor fossa. "Optical" muscles. M. bursalis and M. retractor bulbi probably originated on the lateral part of the laterosphenoid. The basic muscular mass of the "optic" group, including the M. rectus superior, originates in a pronounced medial depression on the rear wall of the orbit. The M. oblique inferior and M. oblique superior originate as narrow bundles from the fossa on the orbital wall. Cervical Musculature. Part of the muscle groups M. rectus capitis and M. longissimus capitis attached tot the basiosphenoid tubercles; these tubercles are variably developed to varying degrees in ankylosaurs and indicate different degrees of muscular development. In Amtosaurus , the basisphenoid tubercles are poorly developed (see Fig. 9 b). In Talarurus , the tubercles are prominent crests (see Fig. 7c) suggesting the insertion of correspondingly powerful muscles. In Tarchia and Saichania , they are also crest shaped (see Fig. 3b), but are not so prominent and are oriented differently. Straight Muscles of the Head (M. rectus capita), probably attached to the ventral surface of the basioccipital, and the difference in the degree of development among the different genera shows the contrasting degree of development of these muscle; In Amtosaurus (see Fig. 9b), there are two sloping, elongated keels or ridges about the same relief as those in Tarchia , although not as pronounced (see Fig. 3b). In Talarurus , between the occipital condyle and the basisphenoid tubercles, the keel occupies a medial position (see Fig. 7 b). In Shamosaurus , this area has no relief, but is rounded (see Fig. 4 b), therefore it is hard to judge the distribution of the muscule bundles.

Lateral Nasal Gland And Jacobson’s Organ The lateral nasal gland is probably one of the few glands in ankylosaurs whose position can be determined with any degree of reliability. It probably occupied a place on the dorsal surface of the septomaxilla (see Fig. 3 b) adjoining the external wall of the external nares. Marya ńska (1977) described one of three ducts, the most laterally placed one in the nostril region, and assumed that it served as a receptacle for the lateral nasal gland. But it is unclear why the gland just developed in an external position on the premaxillaries, nor why a corresponding duct was not discovered in Talarurus . In Talarurus , on the nasals just above the homologous position for the lateral nasal gland, there is a sinus with two dorsal depressions, the function of which is unclear. The Jacobson's Organ, proposed for akylosaurs (Marya ńska, 1977), may have been placed in the cavity under the septomaxilla, which served as the base and posterior wall of the cavity. In addition, the cavity was bounded by the anterior section of the vomers, and laterally, the maxilla. Based on the size of the cavity, the Jacobson's Organ was not large. It may open into the anterior, horizontal part od the premaxilla by a small duct. The septomaxilla and Jacobson's Organ is not known for all archosaurs, therefore it is difficult to prove their presence in ankylosaurs. But based on other structures in the skull, there is indirect evidence for the presence of the septomaxilla and Jacobson's Organ.

44 Circulatory System Arterial system. The arterial system of the head can be reconstructed based on the presence of furrows, impressions, and foramina for the vessels on the bones. The circulatory system of contemporary lizards can be used in making the reconstruction. From the internal carotid artery in the periotic region, the stapedial artery branches out from either near to the small auditory bone or through an opening in it. Among ankylosaurs, the auditory bone is found only in Pinacosaurus , but because of its poor preservation it is not possible to determine whether there was a foramen (duct) for the artery. One of the branches of the stapedial artery, the mandibular, branches downward into the adductor fossa of the mandible, where it divides into the anterior and posterior branches. Part of the posterior branch in ankylosaurs entered the supra-angular; within the jaw it branches with the main branch exiting the mandible through the supra-angular foramen on the lateral surface. The other part of the posterior branch in the articular extended posteriorly and exited on the medial surface of the internal process. In lizards, the anterior branch provides a branch into the Meckelian canal. It is probable that it also followed that route in ankylosaurs. In them, the Meckelian canal is well formed, and decreasing in diameter anteriorly. In Tarchia , a band of ossified cartilege separated the Meckelian canal from an underlying depression having less ossified cartilage (see Fig. 3g). In Shamosaurus , the Meckelian canal is obvious only in the anterior section of the mandible (see Fig. 12b). Along the entire length of the Meckelian canal, the mandibular artery gives off branches at the teeth. On the external surface, the arteries exit the anterior section of the mandible through foramina in the vertical grooves on the edge of the dentary (see Fig. 12a). - On the internal surface of the mandible, the ossified Meckelian cartilage is pierced approximately at the midpoint of the mandible for the ventral (medial, in lizards) branches of the posterior section of the mandibular artery. In Shamosaurus , near the internal margin of the adductor fossa, below the depression for insertion of the pseudotemporal muscle, there is a foramen for the arterial branches supplying the muscles. The mandibular artery is accompanied by branches of the trigeminal and facial nerves. The temporal artery is the other branch of the stapedial artery and is divided into three branches: the frontal, the suborbital, and the supraorbital. The most dorsal branch of the temporal artery, the frontal, passes high under the skull roof and in ankylosaurs leaves hardly any traces on the ventral surface. Thin furrows on nasals formed by longitudinal and transverse crests, probably belong to one of the branches of the arteries diverging in the region of the nasal capsule. The frontal artery opens in the apex of the nares and formed an anastomosing network with the subnarial branch of the maxillary artery. The frontal artery is accompanied by the optic branch of the trigeminal nerve. The first of the orbital branches arising from the temporal artery, Art. orbitalis superior, produces branches at the eye and "optic" musculature; the second, Art. orbitaliste main part of the artery extended along the roof of the maxillary sinus to the dorsoanterior wall of the nasal sinus where it formed the circumnarial anastoming network with the frontal artery. The second, the upper maxillary branch of the trigeminal nerve accompanies the maxillary artery. The internal carotid artery, at approximately the level of the basipterygoid processes, forks

45 in two: the cerebral artery, which penetrates the basisphenoid through the foramen at the bottom of the hypophyseal fossa; and the palatal, which extends with the palatal branch of the facial nerve along the dorsal surface of the basipterygoid processes. One branch of the palatal artery extends posteriorly in lizards along the ventral surface of the basisphenoidal complex, while the other rises at the basisphenoidal rostrum and extends along the interorbital septum into the nasal capsule where it terminates in the olfactory region. A similar situation may be assumed for ankylosaurs. The main and largest branch of the artery (lateral) extended to the infraorbital fenestra. There it branched, as in Procolophon (Ivakhnenko, 1978), with the anastomosis branch entering the maxilla at the union with the suborbital artery, and the branch that supplies the ventral surface of the palate. Farther forward, the palatal artery in ankylosaurs can not be traced in the cranial material.

Cranial Nerves The olfactory nerves (I) in ankylosaurs are large. They extend from the olfactory lobe of the cerebrum along a large furrow on the underside of the frontals to the nasal capsules (see Fig. 5). Optic nerves (II) are located at the base of the diencephalon and extend through large foramina in the anterior lateral walls of the brain case. Nerves of the optic muscles: n. oculomotoris (III) diverges away from the ventral surface of the midbrain through a small foramen in the braincase wall at midlevel to the hypophyseal fossa to the inner surface of the eye where it innervates the upper, lower, oblique, and inner rectus muscles of the eye; n. trochlearis (trochlear nerve) (IV) extends from the dorsal surface of the midbrain through a small foramen in the braincase wall near the muscle group M. oblique superior; n. abducens (VI) extends from the ventral surface of the diencephalon by a small channel which penetrates the posterior border of the sella turcica and exits it under the foramen of nerve III. From there it extends to the inner surface of the eye, innervating the muscles of the rectus posterior group. N. trigeminus (V) is a large nerve which starts in the medulla oblongata and exits the braincase through a rather large foramen and divides into three branches: optical (n. ophthalmicus), maxillary (n. maxillaris or infraorbitalis), and mandibular (n. mandibularis).

The optic branch (V 1) proceeds high under the skull roof with the frontal artery to the nasal capsule, where it divides into the medial and lateral branches. The lateral ethmoid nerve in lizards exits into the upper section of the lateral nasal gland; it is possible that it also took that path in ankylosaurs. The medial ethmoid nerve, as in all reptiles, extends from the anterior wall of the nasal capsule to the anteroventral surface of the premaxilla near their medial contact, where in ankylosaurs there is a small foramen..

The maxillary branch (V 2) penetrates the maxilla through the infraorbital fenestra, but before it does, it branches under the base of the orbit and anastomoses with the facial nerve. Its main trunk proceeds to the maxilla with the maxillary artery, but one of the branches could lie on the surface.

The mandibular branch (V 3) extends to the mandible, and into the adductor fossa where it splits into an anterior and a posterior section. The anterior branch forks into a lingual nerve, which with a branch of the facial nerve, innervates the tongue; the other branch proceeds to

46 the dentary where it innervates the teeth and skin. The posterior branch, together with the branch of the mandibular artery, exits in a foramen in the retroarticular process and where the n. cutaneous forks off and exits through a foramen in the supra-angular. The facial nerve (VII) n. facialis is not large and exits the brain cavity through a venrolaterally facing foramen in front of a lagena. Based on the furrow at the exit of the nerve onto the external surface of the endocranial wall, it immediately forks into a palatal and a hyomandibular branch. The palatal branch extends forward and down to a similar branch of the internal carotid artery; after they meet, this branch proceeds to the palate, branching and extending by a plexus in ear the base of the orbit. The hyomandibular branch divides into two stems, just as in lizards - a ramus hyoideus and chorda tympani. The hyoid branch, passing the structure encircling the hyoid apparatus, did not leave any traces. The chorda tympani enters the mandible in the region of the articular and accompanies the mandibular branch of the trigeminal nerve forward. The auditory nerve (n. acusticus) exits the cavity of the inner ear and closely joins the facial nerve; they run together inside the endocranial cavity as indicated by traces on the inner surface of the endocranial wall. The glossopharyngeal, vagus and supplemental nerves leave the brain cavity through the jugular opening, which in Saichania and Tarchia unite with the fenestra ovalis. The sublingual nerve, as a rule, exits laterally by two branches through comparatively large openings in the exoccipital.

47 CHAPTER 4

DERMAL ARMOR OF ANKYLOSAURS

The armor plate is a complex of osteodermal elements, partially fused with each other and arranged on the torso in a rigidly determined pattern. Because of the combination of separate elements, the torso of ankylosaurs, lacking uniform armor like that of tortoises, appeared practically "armor clad.". The plates, differing in shape and dimensions, and the spines, diverse in height, dimension, and degree of symmetry, show the original construction of all armor. The main part of the armor is represented mainly by these elements, which are independently located in the skin ([i.e., not fused into a carapace]). They may be divided into six main types of armor: large cariniform [(=keeled)], thin-walled, pointed plates; smaller cariniform, thin-walled plates; conical plates, somewhat concave at the base; crest-shaped, laterally depressed, large spines with narrow base and pointed tip located peripherally on the body; oval, low, asymmetrical, sharply tipped plates; and different small ossifications. Consolidation of armor exists to different degrees in different ankylosaur genera. In Talarurus , the plates of carinate shape fuse into a narrow semicircle [(i.e., transverse band)], enveloping the torso dorsolaterally. The most vulnerable spots - over the neck and shoulders - in the majority of ankylosaurs are protected by powerful cervical and shoulder or pectoral armor bands. The cervical bands are distinguished by a two-layered structure: the lower layer is a transverse band of bone formed of several fused, flattened, osteodermal bones; the upper layer consists of a band of three large keeled plates, fused one with another by a narrow zone of oval, nodule-like ossifications. Both layers of the band are fused by connecting ossified strips, while in more posterior bands, the fusion is less extensive. The fused zones of the lower ossified band are thickened, which in all probability, are for reinforcing the base of the uniquely arched structure [(i.e., the cervical band)]. The cervical and shoulder bands are indented. The keeled plates of the upper layer in the pectoral band are distinctly larger than the plates of the cervical band, but they are not so ordered in rows as in the cervical bands. In nodosaurids, the plates of the upper layer are low (only on the sides of the torso do the terminal plates acquire the form of spines), and lie tightly next to each other so that the small ossicles are absent between them. The osteodermal cervical bands of a young Pinacosaurus (Marya ńska, 1971) are represented only by the upper layer, which is arranged as described above, the lower layer either was absent or not preserved (the fusion between the layers were not found) (Marya ńska, 1977). In Shamosaurus of the Lower Cretaceous, growths of similar dermal bands - cervical and shoulder - exist, but the upper and lower layers are completely fused together. The thickness of the osteoderms is greatly increased along the edges, and the armor bands are inclined

48 anteriorly. With regards to the complete fusion of the layers, this will be discussed in Tarchia . Wieland (1911), based on an example from North American, dermined that the armor plates of the upper layer were arranged on the body in seven rows: single - neural and adjacent areas, pleurals, suprapleurals and marginals. The structure of the armor bands in Mongolian dinosaurs does not have a neural row, but does have pleural, suprapleural and marginal paired rows. Posterior to the bands described, are odd osteoderms [(i.e., ossicles)] that differ in form and dimensions and lie immediately on the skin; they are arranged in elongated and transverse bands, but do not have a lower layer beneath and, as a rule, do not fuse with each other; in Saichania , an overgrowth of small round ossicles is seen around the edges of the large spines (Marya ńska, 1977). The presence of spines on the ankylosaur body is distinctive, but their height in the majority of cases increases laterally. This increase may be seen in the cervical and shoulder bands of Tarchia , Saichania and Shamosaurus . A good example of this increase along the margins is seen in the nodosaurid Paleoscincus [(= Edmontonia) ] (Sternberg, 1946), and in the reconstruction of Talarurus (Maleev, 1954). However, for North American Scolosaurus (Swinton, 1929) and the European Polacanthus (Nopsca, 1905), the spines are tallest near the middle of the back and form a structure like the medial row of plates in Stegosaurus . Opinions on the orientation of the spines on the flanks of the body are controversial. In the reconstruction of Paleoscincus [(= Edmontonia )] (Brown, 1908) long, sharp spines are located on the anterior of the animal and along the flanks. Ostrom (1970) suggested that the spines of the shoulder region in Sauropelta edwardsi were rotated. Marya ńska (1977) supposes that in Saichania the spines, which are arranged laterally on the body in elongated rows, projected posteriorly in one row and anteriorly in the next. The armor of the sacral region in Mongolian ankylosaurs is insufficiently studied. In Talarurus , Pinacosaurus and Saichania , there are separate spines in this region; there is no evidence for any underlying constructions. It is entirely possible that there are none at all. Saichania differs from the North American Sauropelta in that the armor in the sacral region lie closely side by side. In Shamosaurus , an armor type previously unknown in Mongolian ankylosaurs was discovered: well developed ilia covered by a single thin osteodermal sheet, similar in position and distribution to the sacral armor of the European Polacanthus . It is possible that because of its thinness, this sheet was not always preserved and, therefore, was not found in other ankylosaurids. The distal section of the ankylosaurid tail has an interesting construction. It consisted of vertebrae with ossified tendons united for the whole length. On the end of this unusual "digit" is an armored structure. The Nodosauridae did not have a terminal caudal armor. W. Coombs (1978) expressed doubt that Struthiosaurus (Nopsca, 1929) had a multi-ringed, powerful tail. The presence of such rings is doubtful in Dyoplosaurus (Parks, 1929), Scolosaurus (Nopsca, 1928) and Talarurus (Maleev, 1956) because the construction of the tail in all ankylosaurids is in general similar and differences are in details of the terminal club. Returning to the similarity in the distribution of the spines on the body of Stegosaurus and some ankylosaurs, these spines were one of the reasons ankylosaurs were originally referred to the stegosaurs. But ingnoring the differences between their cranial structure and postcranial

49 skeleton, there are obvious differences between the armor plates of these creatures in morphology and function. The cutaneous covering ankylosaurs is consolidated, continuous, genuine armor, and in this respect is comparable not only with Stegosaurus but with such typical armored creatures as tortoises and glyptodonts. The structure of the spines differ, although they are externally similar, in stegosaurs and ankylosaurs. In Stegosaurus they are covered with a branched network of surface grooves which supply the skin covering the spines during life. The armor of ankylosaurs were pierced by grooves noticeably deeper, but on the surface there are furrows for the branches to the corneous cover that covered the ankylosaur spine during life. Therefore, if the large armor plates of Stegosaurus functioned as part of the thermoregulatory mechanism (Farlow, Thompson, Rosner, 1976), then the spines of ankylosaurs may have had a similar function, although weaker. We will discuss this in the chapter "Ecology." It is possible that the armor, having originated in the evolution of this branch of creatures, may have been adapted for many functions. Thus, besides being a defense against enemies and damage [to the body], the armor may have partially moderated excessive body heat or may have prevented the excessive emissions of heat. The participation of armor in heat exchange, originating on the head (Kozatskii, 1965; Trusova, Kozatskii, 1970), was possible because of the covering of the individual armor in ankylosaurs by an unbroken corneous sheath, which isolated the living organism from its environment. The armor was useful for protection from unsuitable changes of the surrounding environment such as, harmful solar radiation. Regardless of the extreme variability of armor plate shape and height of the spines in relation it position on the body, we may note some diagnostic generic features. The manifestations are as follows: ribbed and grooved ornamentation of the spines in Talarurus , perforated large spines in Tarchia, and small anastomosing sculpturing of the armor surface with thick walls in Shamosaurus . There are some indications for the structure of the armor as established by W. Coombs (1978b) at the family level (the presence on the dorsal surface of the body of high, narrow spines in ankylosaurids and their absence in nodosaurids). The construction of the epithecal layer of the armor cervical bands consists in ankylosaurids of spined plates, slightly differing in height from the marginal ones, and between which may be small plates and ossicles. In nodosaurids, the upper armor consists of low spined plates packed tightly against one another, and marginally becoming long, narrow spines that noticeably exceeding in height the armor of the pleural and suprapleural rows.

50 CHAPTER 5

PHYLOGENY OF ANKYLOSAURS

The ancestor of the ankylosaurs was long thought to be among the stegosaurs. This group is closer to the ankylosaurs than to any other dinosaur. They both share in the presence of armor; the narrow triangular skull of Stegosaurus is similar to that of the nodosaurids; some similarities are also found in the structure of the palate and of the basisphenoid region. The genus Scelidosaurus (Romer, 1968; Thulborn, 1971) is considered to be a very likely ancestor because of the primitive structure of the pelvic girdle. On the other hand, Coombs (1978) considers the structural features of the scelidosaurid postcranial skeleton, such as the long posterior process of the pubis, the perforated acetabular cavity, the short preacetabular section of the ilium and its deep postacetabular section, does not support this hypothesis. Besides, the pelvic material referred to Scelidosaurus on the basis of the similarity of the short anterior pubic process to that of Ankylosaurus , is disputed (Rixon, 1968; Charig, 1972). The discovery in Mongolia of a new Lower Cretaceous ankylosaur Shamosaurus might corroborate Coombs’ opinion in that it has the typical ankylosaur pelvic girdle, with a very long preacetabular section of the ilium expanded horizontally. Shamosaurus raises doubt as to whether the comparatively sudden change in this region of the ankylosaur pelvis could have happened during their relatively slow evolution with minor morphological changes (Coombs, 1978) that occurred between the Jurassic (when Scelidosaurus existed) to the Early Cretaceous. In other words, an ankylosaur or ankylosaur ancestor may have been a contemporary of Scelidosaurus in the Jurassic. Besides, it is possible to add features to the skull to differentiate ankylosaurs from stegosaurs as follows: unbroken covering of armor on the skull and their fusion with the underlying bones; the absence of the upper temporal fenestra, a small one which is present in Stegosaurus ; the unusual contact of the quadrate bones with the paroccipital processes. T. Marya ńska proposed that the ancestor of ankylosaurs was in all probability quadrupedal, in contrast to the ornithopods and the bipedal ancestor of the ceratopsians. It is possible that, if we take into account the ancestors of all ornithischian dinosaurs, the Triassic ornithopods like Fabrosaurus (Galton, 1974) might have been the origin of the first bipedal ornithischians. But in any case, it is necessary to agree with Coombs (1978) concerning the large morphological differences of between ankylosaurs and stegosaurs. The most probable ancestors of ankylosaurs were quadrupeds with a primitive cranium, noticeably less flexed in comparison with typical Mesozoic dinosaurs (iguanodonts, hadrosaurs, ceratopians) and apparently, with Triassic ornithopods ( Fabrosaurus ) and even with Triassic pseudosuchians ( Erythrosuchus ). Otherwise, during the evolution of the ankylosaurs, among the many morphological changes, we would have to accept a

51 Fig. 14. Phylogeny of ankylosaurid genera. straightening of the cranium, which is not typical for any other group of dinosaurs. The interrelationships of the two families of ankylosaurs has not been resolved according to Coombs (1978) because specific features prevent their development from one another. These features include the fusion of the upper end of the quadrate with the paroccipital process, and the presence of a scapular crest near the glenoid in the nodosaurids, and the corneous armor in the posterolateral corners of the skull; the lateral temporal fenestra closed by armor; the complex system of sinuses in the nasal cavity, and terminal caudal club in ankylosaurids. Now, after the discovery of the skull of Shamosaurus , the first definite ankylosaurid from the Lower Cretaceous of Mongolia, a hypothetical relationship of the families may be presented (Fig. 14). In Shamosaurus , which has a typical ankylosaur palate, the premaxillary section is narrow showing that the narrow snout is the original condition of all ankylosaurs. The narrow snout does not prevent the origin of ankylosaurs from stegosaurs as A. Romer (1968) thought; the differences mentioned are evidence against the union of both groups. The presence in early nodosaurids ( Silvisaurus ) of premaxillary teeth, of which only the cutting margin of the premaxilla remain in later representative families; this cutting margin is continuous with the maxillary tooth row, but in ankylosaurids it is not. This difference suggests the primitive state exists in ankylosaurids. In cranial morphology, similar features between Shamosaurus and nodosaurids may indicate a transitional position for the Early Cretaceous ankylosaurids, the Shamosaurinae. These features include fusion of the quadrate with the paroccipital process, immovable contact of the pterygoids with the basisphenoid,

52 round, vertically oriented occipital condyle, and partial covering by armor of the laterally sloping quadrate condyle. The similar features of the nodosaurids and Shamosaurinae apparently reveal characters of their ancestors, although these appear more stable and fixed in the nodosaurids. In ankylosaurs, the cranial morphology changed significantly from the original condition: early disappearance of the premaxillary teeth, modification of the cranial shape, the complete fusion of the quadrate bones with the paroccipital processes, and pterygoids with the cranium; all of these features are seen in the two specimens of Shamosaurus ). In nodosaurids, features are observed which, in my opinion, may be primitive; for example, the premaxillary teeth in early specimens, and the open lateral temporal fenestra (in ankylosaurids lateral temporal fenestra is covered by armor overgrown anteriorly and dorsally over the squamosal, and covering the quadrate condyle in the lateral aspect; in Shamosaurus , this armor covering is not as extensive and the quadrate condyle is visible in lateral profile). The condition in Shamosaurus condition may be considered primitive and similar to that in nodosaurs. The significant differences in ankylosaur morphology probably occurred by their early branching from the ancestral dinosaur stem and by adapting to some different habitat and manner of life. The fusion of the quadrate with the paroccipital process, and of the pterygoids and the skull in the majority of the ankylosaurs, may explain the absence of kinesis in nodosaurids. Among the Nodosauridae, W. Coombs (1978) noted the following evolutionary branches: the most primitive, Hylaeosaurus and Struthiosaurus , are characterized by a small body size, the presence of teeth in the premaxillary, and unfused coracoid and scapula; the second branch is represented by the North American Nodosauridae, in which fusion of the scapula with the coracoid is characteristic. Early genera of the second branch - Sauropelta and Silvisaurus - retain premaxillary teeth, but in a later genus - Panoplosaurus - they are absent. Not one ankylosaurid genus has premaxillary teeth. There is a series of other morphological traits by which ankylosaurids may be divided into two groups. Two genera of ankylosaurids may be referred to the first group: Shamosaurus , as the most ancient representative of the family, and Saichania , which possesses the more primitive structural features, such as a comparatively narrow premaxillary section of the snout, fusion of the quadrate with the paroccipital process, fusion of the pterygoids with the brain case, and small interpteryoidal fossa. The second group includes all the rest of the Mongolian ankylosaurs, the ancient representatives of which, were probably the ancestors of the North American Euoplocephalus and Ankylosaurus . Evidently, the first group has a very close morphological relationship with the Nodosauridae, which were apparently extremely close in appearance to their ancestor. In the transition to Shamosaurus , such alterations in cranial morphology arose, such as the broadening of the postorbital region, the covering of the lateral temporal fenestra by armor, and the conversion of the armor on the posterolateral corners of the skull into horns. The typical ankylosaurid palate, which is present in Shamosaurus , differs in the transverse orientation of the pterygoids and ectopterygoids. The occipital condyle in Shamosaurus is similar to that of nodosaurids in that it is rotated downwards, but it lacks a neck on which it sits, i.e., it is closely attached to the basicranium. Saichania may be the direct descendent of

53 the Shamosaurinae. In the lineage of Shamosaurus to Saichania , there arose the following developments: widening of the premaxillary section of the snout, overgrowth of the armor from the squamosals downwards, covering of the quadrate condyle, transformation of armor in the posterolateral corners of the cranium into spines, a more anterior position of the orbits and an inclination of the vertical plane of the orbits somewhat towards the front [(i.e., the orbits face slightly forwards)], expansion of the secondary palate, and shortening of the maxilla. But there remains unchanged the fusion of the quadrate with the paroccipital process and the pterygoids with the braincase. It is probable that all remaining ankylosaurids may be derived from this line. During the evolution of the other branch, at the base of which is Talarurus (the oldest Late Cretaceous ankylosaurid), occurred changes in the contact of the quadrate with the paroccipital process and the pterygoids with the braincase. Also, there was an increase in the size of the interpterygoid gap. The upper process of the quadrate in these ankylosaurs do not fuse with the lower section of the paroccipital processes, but just contact them in Tarchia , the youngest Mongolian ankylosaur. Obviously, the contact was made by ligaments. On the basipterygoid process in all ankylosaurids there are articular areas. The tendency to strengthen the armor plate by fusion of the armor (Marya ńska, 1977; Coombs, 1978) suggests that primitively, armor consisted of separate osteodermal elements that were not fused with each other. In Shamosaurus a rather high degree of fusion of armor has occurred with two rings (cervical and shoulder) present, which also exist in the later Saichania and Tarchia, and also a thin sacral armor shield; in the remaining Mongolian ankylosaurs not mentioned, other structures of fused armor elements are encountered. Based on these facts, it is clear that Shamosaurus may not be at the base of the ankylosaurid branch. Because of this conclusion, and also because of the absence of teeth on the premaxilla and the covered lateral temporal fenestrae, I propose that the ancestral species was nodosaurid-like, not Shamosaurus -like, even though in both groups there are equally primitive features and the Shamosaurinae exhibit some sets of morphological features which would be expected for the ancestor. The separation of nodosaurids and ankylosaurids arose, presumably, in the Jurassic, since Early Cretaceous specimens of these branches already have the typical structure of their family. As a result of this study of the morphology and the possible relationships of the species, the following diagram (see Fig. 14) was compiled.

54 CHAPTER 6

SOME MORPHOLOGICAL FEATURES OF ANKYLOSAURS AND THEIR SYSTEMATIC IMPORTANCE

One of the characteristic features of dinosaurs, as diapsid reptiles, is the presence of two temporal fenestrae on the skull. There are isolated deviations from this rule. For example, in some Pachycephalosaurs ( Prenocephale prenes ), the upper temporal fenestra is closed because of the strong increase in the thickness of the parietal bone. There is even an example of the overgrowth by the upper temporal bone in the crocodile ( Palaeosuchus ). Here, the covering occurs on the ventral side of the former temporal fenestra because of the formations of bony rings to which the adductor muscles were attached. The thickness of the bones of the cranial roof in ankylosaurs are entirely comparable to those in the majority of the other dinosaurs. It is further proposed that the uneven striated surface of the ankylosaur cranium is not due to the overlapping by armor which is fused with the underlying bones, but to a thickening of the bones. This change is comparable to the swelling of the parietal bones in Pachycephalosaurus , which are capable of overgrowing the adjoining bones and covering the temporal fenestra. The area where the upper temporal fenestra is located in the skull of ankylosaurs is overlain by an armor covering (Eaton, 1960). In all specimens of ankylosaurs, the bones and armor in this region are so very strongly attached that it is not possible to establish whether the overgrowth of armor occurred first, or closure of the upper temporal fenestrae. But in the unique specimen of the young Pinacosaurus (ZPAL MgD-11/1), most of the bones of the cranial roof are free from armor overgrowth and the upper temporal fenestra is also absent. It follows that if the reconstruction of the Pinacosaurus cranial roof was reliably done (Marya ńska, 1977), then the upper temporal fenestrae might be absent in ankylosaurs. Furthermore, no traces of the fenestrae are seen on the ventral side of the cranial roof [(in Pinacosaurus )]. In this region, the apex of the adductor fossa is present as a small depression having sloping walls between the rear wall of the orbits and the paroccipital process. The smooth, unmarked surface of this region, and the absence of any armor gives evidence in favor of the primary of absence of the upper temporal fenestrae. The attachment of the adductor muscles was probably redistributed to the crest on the quadrate and the anterior surface of the paroccipital processes; it is possible that the ventral surface of the prootic bones were involved also. The lower or lateral temporal fenestra in ankylosaurids is covered externally with armor overlapping the squamosal. In specimens of the Nodosauridae, the lateral temporal fenestra open laterally. At the rear, the lower temporal fenestra of ankylosaurs is oval and is formed by the postorbital and quadratojugal anteriorly and ventrally, and by the quadrate and apparently

55 the squamosal posteriorly and dorsally. The distal end of the paroccipital process also forms the posterior part of the lower temporal fenestra. In the braincase of ankylosaurs, there are also a whole series of features that are significantly different than in other dinosaurs. In dinosaur braincases, the basipterygoid processes characteristically protrude downwards. Therefore, the angle formed by a baseline through the foramen magnum and another line connecting lowest point of the basipterygoid, is rather obtuse. In ankylosaurs, the basipterygoid processes are pulled up to the poorly developed basioccipital tubercles. Therefore, the angle is very acute, not exceeding 15 o-17 o. Furthermore, the axis of the endocranium in the majority of dinosaurs is depressed ventrally, posterior to the hypophysis fossa, forming a step-like inflection ( Jaxartosaurus , Corythosaurus , Anatosaurus [(= Edmontosaurus )], Triceratops ). In ankylosaurs the entrance to the hypophysis fossa lies in the floor of the endocranium. Farther forward, the axis of the endocranial floor rises slightly. Obviously among dinosaurs, there are cases where the cranial flexion is not so sharp, possibly hypsilophodonts (Galton, 1974). However, because of the poor preservation of Hypsilophodon specimens, it is difficult to verify this. It would be logical to think that the base of the braincase, being more straight than in typical dinosaurs, was present in some [primitive] Triassic groups, such as Pisanosaurus (Bonaparte, 1976). This feature is not mentioned for [these primitive groups], although, judging by illustrations of incomplete braincases, nerve foramina were arranged in almost a straight line along the wall of the braincase, i.e., some straightening of the braincase floor may have taken place. Also, it is apparent in the illustrations of these primitive groups that the angle between the floor of the braincase and the basipterygoid is obtuse. This angle is also present on the braincase of the Triassic pseudosuchians, for example, in Erythrosuchus . The erect braincase with a very low angle is characteristic for reptiles that are organized below and phylogenetically distant from ankylosaurs, as pareisaurs and tortoises. Finally, another feature of the braincase separates the ankylosaurs from the typical dinosaurs. In ankylosaurs, the inner carotid artery passes by the dorsal surface of the basipterygoid processes. There, as in the majority of dinosaurs, it travels farther ventrally under the processes (Kurzanov, 1976). The skull of ankylosaurs have another feature that differs from typical dinosaurs. This probably plays a secondary role, but must be mentioned. In spite of the strong similarities in the quadrate region of most dinosaurs (Ornithopoda, Stegosauria, Ceratopsia), there is no contact of the quadrate and paroccipital process. Usually, there is a strip of the squamosal separating the quadrate head and the paroccipital process. In all known ankylosaurs, either the quadrate passes under the cranial roof and contacts the anterior part of the paroccipital processes ( Ankylosaurus , Euoplocephalus , Talarurus , Pinacosaurus , Tarchia ), or the lower border of the paroccipital process fuses with the head of the quadrate ( Saichania , Shamosaurus and all Nodosauridae). In other instance, both forms of connection occur (Shamosaurinae from Khamryn-Us, PIN N 3779/1). The outline, shape and contacts of the squamosal of ankylosaurs also reveal some differences from some typical dinosaurs. Typically, the squamosal is usually narrow, located dorsal to the cheek region, and does not reach the dorsal surface of the cranial roof except at

56 the upper margin of the paroccipital process. The squamosal of ankylosaurs is not located dorsally on the cranial roof, but laterally. On the ventral surface, there is a fossa for the head of the quadrate (if fusion did not completely occur), as in all other dinosaurs (Ornithopoda, Stegosauria, Ceratopsia). But the low transverse crest or strip separating the quadrate from the paroccipital process in other dinosaurs is reduced in ankylosaurs. As a result, the paroccipital process fits into the fossa in the squamosal, where it is slightly overlapped along its upper border. W. Coombs (1978a) points out that the pterygoid contact with the braincase is a family trait. In Nodosaurids he notes the complete fusion of these structures; in ankylosaurids, he notes the union via the tubercles on the basipterygoid processes. But recent discoveries of ankylosaurid specimens ( Saichania , Shamosaurus ) also have the immovable contact of the pterygoids with the basisphenoid; i.e., the basisphenoid joint is completely fused. Therefore, fusion of the pterygoids to the braincase may not be used as a family trait. But the fusion of the pterygoids with the braincase is more typical for an individual genus of ankylosaurs and separates this suborder from the other ornithischians and all other dinosaurs (regretfully, the character of the basisphenoid joint is not known in Stegosaurus and to state anything with regards to this group is premature). From the above discussion, we arrive at the following conclusions: 1) If the features are secondary, then the ankylosaurs represent a group of ornithischian dinosaurs that are very unusual because of their cranial morphology and greatly specialized. They separated very early from the basic stem of dinosaurs. But, considering the formation of the ornithischians, it is difficult to demonstrate how the transformation of the dinosaur ancestral traits may have resulted in the ankylosaur cranial construction. The reason is that in the three listed periods (Jurassic, Lower and Upper Cretaceous), we must propose changes that are the reverse of the evolutionary trend in the ornithischians; 2) If the various traits of ankylosaurs discussed above are assumed reflect the ancestral condition, then it is logical to search for the ancestor among the early pseudosuchians (probably still unknown to us). These pseudosuchians probably did not have the cranial features that were characteristic of their Triassic representatives and for early dinosaurs arising from them. It is possible that the separation of this particular branch arose in the Permian. In this case, we propose that the separation of ankylosaurs from the pseudosuchian already took place in the Permian when they acquired characteristic features of their ornithischian ancestors. But it is clear that to confirm the absence of a general ancestor with other ornithischian dinosaurs, is to deny the placement of the ankylosaurs with the Ornithischia. And, although ankylosaurs do not comply with contemporary opinion concerning the ornithischians, it is premature to state more definitively their systematic position. The reason is that there are no criteria for determining primary or secondary morphological differences in the skulls of ankylosaurs and other dinosaurs. Also, the early dinosaur specimens are still poorly known, the study of their detailed morphology should eventually help resolve the problem. To the listed differences we may add the characteristics shown by W. Coombs (1978a) which serve to differentiate ankylosaurs from other ornithischian dinosaurs. The specific nature of ankylosaurs includes the skull roof is overlapped by armor strips that fuse, as a rule,

57 with underlying bones; the whole surface of the torso is also covered with armor plate and spines, which are very short in comparison with those of Stegosaurus . The strong ossification of the inner walls of the orbit and the formation of the postorbital shelf are also specific for ankylosaurs. In the postcranial skeleton, the unusual structure of the pelvic bones among ornithischian dinosaurs, has attracted attention: the ilium has grown into the horizontal plane and have greatly elongated and widened in the preacetabular region. The pubes are small, rectangular with a short posterior process; the prepubic processes are absent (they are not found in any of the Mongolian specimens.) The distinctive features of ankylosaurs may be explain as features of adaptation. The presence of body armor, and the covering of the skull roof by armor are examples. We may also explain the unique pelvic girdle as originally primitive in ornithischians. But the features referred to by us as significant are unlikely to be due to adaptation; rather, they have deeper roots which are yet to clarified.

58 CHAPTER 7

ECOLOGY

There are a few points of view available about the Ankylosaur way of life. On the one hand, they are considered terrestrial animals found near water only when necessary to drink and eating in littoral ponds. On the other hand, some of their structural characteristics, such as large bulk and slow locomotion, indicate a very close connection with water. Structurally, some morphological features indicate an amphibious lifestyle. These features include the barrel-shaped or widened torso formed by ribs that wrap ventrally; the presence in Saichania of processes on the ribs that expand in a curve and overlap the adjacent ribs; the large nostrils that are elevated slightly (it is possible that muscles were present at the inner border of the nasals and closed a valve to protect the respiratory tract from water); small teeth capable of masticating only soft aquatic vegetation; wide spread phalanges terminating in wide, flat unguals for locomotion in soft ground. The mass accumulation of ankylosaur remains at one site supports such an amphibious hypothesis. For example, in 1969, a site was found at Alar-Teg [(Mongolia)], eleven ankylosaur skeletons in various degrees of preservation, were found in an area less than 30 m2. About six incomplete skeletons were found side by side in an area less than 14 m 2. Taphonomic analysis of the site (Tverdokhlebov and Tsybin, 1974) indicates that the rocks, which contain the large number of skeletal remains of ankylosaurs, appeared to be a dried section of a beach. Based on the unique texture of the rocks, the area was a marsh before the climate subsequently dried,. A similar mass of ankylosaur remains are also characteristic for such sites as Khongil- Tsav, Bayn-Shiren, and especially Baga Tarjach. In these large mass accumulations, two genera are represented: Pinacosaurus and, less common, Talarurus . Obviously, the nature of large mass accumulations of ankylosaurs, not seen in any other group of dinosaur, may be explained as most likely the close association of the animals to water. A concentration of individuals at one site gives solid support that ankylosaurs led a semi-aquatic way of life. We base this conclusion on morphological analysis of the skeleton that is an absolutely reliable for reconstructing a animal’s way of life. In appearance, ankylosaurs were rather large animals. Their body length reached 4 to 5 m, and sometimes 8-9 m. Under the corneous surface layer, which covered the torso and head of the animal, lay the bony armor plates. The armor bands and spines may have occasionally fused together, but the individual elements remained distinct. The armor never reached the degree of co-ossification seen in the tortoise shell, but is reminiscent of the protective armor of armadillos. Often, two layers were seen in the ankylosaur armor. Such a pattern is seen in the cervical and pectoral half rings of Saichania and Tarchia . In these double layered

59 structures, the lower layer consisted of a comparatively thick and solid band and the upper layer is thinner and is composed of plates. In later ankylosaurids ( Pinacosaurus , Saichania , Tarchia ), the sides of the plates are thin, porous, and are pierced by numerous foramina for blood vessels. The armor of ankylosaurs formed a protective cover against unfavorable environment conditions (for example, desiccation or predators), but may have also had other functions as well. For example, although bone is not the best conductor of heat, the armor plate might still have served as a regulatory apparatus for heating and cooling the body. Considering that both the plates of Stegosaurus and the plates of ankylosaurs increased the surface area of the body, it is logical to assume that if the Stegosaurus plates served to release or absorb heat (Farlow, Thompson, Rosner, 1976), that they may have served a similar function if ankylosaurs as well. It would be unlikely that in the process of evolution, ankylosaurs plates became thinner and more delicate for a strictly defensive role. The impression from the number of ducts permeating the walls of the plates is that they clearly exceed what is necessary for the blood supply to the corneous covering. If we employ the analogy with Stegosaurus , the well developed vascularized surface is best explained by an increased blood supply to the skin over the armor. The strongly vascularized skin, together with armor elements, may represent a primitive thermoregulatory system. When the temperature of the surrounding environment exceeded the creature's body temperature, the surface of the animal heated up. The vessels located on the upper layer of the skin above the armor expanded, causing the blood to start flowing rapidly. With increased flow, there was an increased transfer of heat from the body to the environment. In this manner, the animal did not overheat. When the environmental temperature sharply decreased and the animal was threatened with hypothermia, the vessels contracted restricting blood flow to the surface layer of the skin and the exchange of heat with the atmosphere declined. The effectiveness of the system was increased because under the plates, as mentioned above, were usually located bone bands, which when fused, could work passively to release or absorb heat. In other words, inside the armor, the temperature was stable because of its passive isolation> However, because of the strongly vascularized skin that covered the body and increased the surface of the plates, a remarkably active temperature regulation was accomplished. The differences in the surfaces of the plates in Stegosaurus and ankylosaurs may be explain as follows. In Stegosaurus , the branching of the blood vessels issues from the surface of the plates in the section which was covered only by skin during life. In ankylosaurs, the plates also have a corneous cover. The blood vessels branch in the thick layer of skin that separates the armor from the corneous material. In ankylosaurs, the blood vessels are not confined to the surface of the plates. Because the thermoregulatory system suggested might have been perfected only in advanced ankylosaurs with very porous plates, it is possible that the armor originally played a passive thermoregulatory role by slowing down excessive heat production, because, as L. Khozatzkii (1965) hypothesized, this occurs in tortoises while also acting as protection. The body shape of ankylosaurs varies, but the barrel shape predominates with different degrees of lateral compression. In Pinacosaurus , the torso is flattened dorso-ventrally in a manner that is unique for Mongolian ankylosaurs.

60 The structure of the girdles and limbs do not show any adaptations in ankylosaurs for rapid motion. The front limbs, as T. Marya ńska (1977) showed in Saichania , were extremely flexed: the humerus was oriented almost horizontally and slightly rearwards, while the ulna and radius were inclined to a great degree in a medial direction. Obviously on such limbs, a heavily-armored body might not move with any remarkable speed. The study of the limb musculature of Euoplocephalus (Coombs, 1978B) leads to the same conclusion.'The fused coracoid and scapula and the supplementary union of the coracoid with the dorsals (Marya ńska, 1977), also indicate an absence of motion in the pectoral girdle. Because of the strong flexion of the front limbs, the anterior part of the body was slightly closer to the ground and was about 35 cm from it (Marya ńska, 1977); i.e., as a whole the body was very low. The rear extremities were more normal because the pelvic girdle is located higher than the pectoral girdle. Ankylosaurs were quadruped animals. And if ceratopians are secondarily quadrupeds based on the structure of the acetabulum, then Marya ńska (1977) believes that the un- perforated acetabulum in ankylosaurs indicates that they were originally quadrupeds. The head was united to the body by a rather long neck (seven vertebrae). The posteroventrally oriented occipital condyle suggests that the atlas articulated with the skull from behind and below; i.e., at an angle relative to the cranial axis. As a result, the head does not sit on a stick-shaped, drawn out neck as shown in some reconstructions (Lull, 1922). The neck shows some downward flexion based on the angles of the cervical vertebrae (slightly, in Talarurus , more in Pinacosaurus and Tarchia ). This construction prevents stress fracture of the neck, which inevitably arose due to a heavily armored head, and the downwards flexion acted as shock absorbers. Because of the shape of the occipital condyle (the articular surface faces more ventrally), the head had greater motion in the horizontal plane than in the vertical. This was of prime importance because of the lateral placement of the eyes in the head. Movement of the lower jaw was restricted by the construction of the quadrate and pterygoid process. The mandibles were limited to only cutting motions in the vertical plane. The tooth row is slightly inset, and the teeth in the majority of ankylosaurs do not show any reliable traces of wear. The animal broke up soft, succulent aquatic plants with a beak that was probably covered during life with a corneous cover and processed the food with a primitive dental system. In this manner, damage to the dental enamel was averted. Analyzing the structure of the hyoid apparatus of Saichania , Marya ńska (1977) concluded that it was most similar to that of the monitor lizard, i.e., it is possible that ankylosaurs were not exclusively herbivores and might have fed on insects or their larvae (Nopcsa, 1928). A long tongue may have been present (based on the analogy with monitors) to assist in searching for and catching food. The probable presence of a Jacobson's organ (Marya ńska, 1971, 1977) also suggests, that the food of ankylosaurs was not confined only to plants, although undoubtedly they made up the principal part. The eyes of ankylosaurs shifted somewhat posteriorly during their evolution, changing their direction from perpendicular to the long axis of the skull, to one somewhat forward and at an acute angle with the of the long axis of the skull. Because of similar inclination, the

61 planes of the orbits increased the area of visibility by overlapping their field of vision (Fig.15).

Fig. 15. Inclination of the plane of the orbits in ankylosaurids. A, Saichania ; B, Tarchia

Marya ńska (1977) analyzed the hypothesis first advanced by E. A. Maleev (1954), based on Syrmosaurus (= Pinacosaurus ), of digging by ankylosaurs. She concluded that the dorsoventrally flattened body of Pinacosaurus and the presence of armor on the ventral surface supported this hypothesis. Furthermore, the short keel-shaped scutes are located laterally, and the probable presence of a bony eyelid (Coombs, 1972) that might have been adapted for protection of the eyes during digging. However, no bony eyelid similar to Euoplocephalus has been found for Pinacosaurus or for any other Mongolian ankylosaurs, although they exist in many other dinosaurs. Besides, in the majority of dinosaurs, the body is laterally compressed. Because ankylosaurs were such large animals, I cannot accept the hypothesis of digging by ankylosaurs. The ankylosaurid tail had a very unusual structure. Only its proximal section is mobile, while the distal section was formed by greatly transformed vertebrae, articulated not only by pre- and post-zygapophyses and haemal arches, but also by elongated ossified tendons (Plate 11). The end of the tail has an armor disk in the form of a club that served as a percussive weapon. Rozhdestvenskii (1974) suggested that the long, powerful tail may have served ankylosaurs as an active defense structure. Although ankylosaurids have a passive defense mechanisms in the form of body armor, it is difficult to find another function for the tail club.

62 CHAPTER 8

GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION OF ANKYLOSAURS

At the present, we may now discuss the global distribution of ankylosaurs. The largest concentration of sites occurs in North America, Asia and, to a somewhat lesser degree, Europe. There are isolated reports about ankylosaur remains from Africa (Lapparent, 1958), South America (Huene, 1929) and Australia (Molnar, 1980). In North America, specimens of the family Nodosauridae are found, starting with the lowest deposits, from the Neocomian or Aptian (Arundel Formation) to the to the Campanian or the lowest Maastrichtian (Edmonton Formation); there is a single tooth from the latest Maastrichtian that may be nodosaurid (Coombs, 1979). All the ankylosaurid finds in this region are confined to the Campanian (Two Medicine, Judith River, Oldman formations) and the Upper Maastrichtian deposits. The South American finds are very fragmentary, although it is possible that there was a time of distribution of some ankylosaur families into this territory. The isolated ankylosaur remains found in Africa were provisionally identified by Lapparent (1958) as Nodosauridae. In Europe, the Nodosauridae are found from the Neocomian (Wealdian) to the Campanian (middle strata of Gosau[, Romania]). More recently, some of the original identifications of stegosaur remains from the Jurassic deposits of Europe were questioned. It was proposed that these some of these remains were those of Jurassic ankylosaurs (Galton, 1980a, b). This material is currently under further research and preparation. Ankylosaurids are absent in Europe. In Asia, there are no nodosaurids, and ankylosaurids are widely distributed. With regards to the discovery of Asian ankylosaurs, there are reports from India (Matley, 1923), China (Bohlen, 1953; Young, 1935, 1958), and Mongolia (Maleev, 1952a,b,c; Marya ńska, 1970, 1971, 1977). Incomplete ankylosaur remains have also been found in the territory of the Soviet Union, in Kazakhstan (Ryabinin, 1938). All the material described in this paper was collected from the Aptian-Albian (Djun-Bayn stratum) and Maastrichtian deposits (Nemegt stratum) in the Mongolian territory. Because of the investigations of American, Soviet and Polish specialists, many paleontological and stratigraphical works will appear in the future. A series of stratigraphical charts for Cretaceous deposits of the Mongolian Peoples Republic (MNR) has been prepared by different authors (Fig. 16). The upper Cretaceous deposits in the Mongolian territory were identified by the American geologists C. Berkeley and F. Morris (1927). They made cross sections at the siteopened by the American expedition at Shabarak-Usu (Bayn Dzak), Djadokhta Formation. Except for a

63 series of skeletons of archaic horned dinosaurs, Protoceratops andrewsi , and the remains of small carnivorous dinosaurs, the skull of an armored dinosaur was found, which was described by C. Gilmore (1933) as Pinacosaurus grangeri . Shortly after this, Soviet scholars began paleontological studies and produce geological papers. During this time, stratigraphic charts of this region were developed (Fig. 16). The efforts of the Paleontological expedition of 1946-1948 not only resulted in a huge, unique collection of different dinosaurs skeletons, mostly very large (carnosaurs, ornithopods, ankylosaurs, etc.) , but also the stratigraphy of bone layers in the Upper Cretaceous and other geochronological deposits in the territory of MNR. Based on the initial paleontological charts and the charts of formations by the American investigators (see fig. 16), there developed a sequence of fauna complexes for Mesozoic and Cenozoic vertebrates. The stratigraphic diagram, published by E. A. Efremov in 1954 (see fig. 16), was the basis for all subsequent diagrams that augmented and improved on it. A refinement of the geochronology of the main bone-bearing horizons was proposed by A. K. Rozhdestvenskii (1957). This was possible only a study of the material collected by the expeditions and comparisons with similar groups from other Asiatic regions and from other continents. Furthermore, the correlations filled in the gap that existed between the discovery of Turonian- Lower Santonian Mongolian dinosaurs, with the fauna complexes of the territory of the Soviet Union (Rozhdestvenskii, 1957, 1971). Using the geological data and the scientific results of the paleontological expeditions of the USSR, N. A. Marinov compiled a basic paper on the stratigraphy of MNR, publishing it in 1957 (see fig. 16). He recognized two series within the Upper Cretaceous: the lower Sayn- Shand, and the upper Bayn Shiren. The presence at that time of two dinosaur complexes served as the basis for the subdivisions. This division was later confirmed by the discovery of mollusks and ostracods, and by data from petroleum geologists. The two-fold stratigraphic division is based upon mapping of the Upper Cretaceous deposits in the eastern Gobi, as well as in the extreme eastern regions of the Gobi part of the MNR. Regretfully, the stratigraphical boundaries remain unclear and the descriptions of the stratotype cross-sections were not given. After 60 years in Mongolia, paleontological studies by by Soviet paleontologists were renewed (Kramarenko, 1974), yielding new, valuable paleontological materials. It is important to note that the papers by scientists during this time involve more joint research (Kalandadze and Kurzanov, 1974; Martinson, Sochava and Barsbold, 1969; Tsybin and Kurzanov, 1979). Besides the Soviet-Mongolian expeditions, were the Polish-Mongolian Paleontological Expeditions (Kielan-Jaworowska, Dovchin, 1969; Kielan-Jaworowska, Barsbold, 1972). Along with the paleontological papers, geologists from these nations also published on the stratigraphy (Marinov et al., 1973; Tverdokhlebov and Tsybin, 1974; Shuvalov, 1974, 1975; Gradzinski, 1970; Lefeld, 1971; Gradzinski and Jerzykiewicz, 1972. As a result of the combined studies in the stratigraphy, lithography, and paleontology of invertebrates, which wre carried out by the Combined Soviet-Mongolian Geological Expedition, G. G. Martinson, A. V. Sochava and R. Barsbold in 1969 proposed separating the Upper Cretaceous deposits of the Eastern Gobi into three strata, and the Trans-Altaic

64 65 Gobi into two strata. A short time later, R. Barsbold (1970) unified this system by proposing a single division for both the eastern and southern regions of the Gobi. The lower and upper layers of Nemegt were divided accordingly by R. Gradzinski (1970). The lists of author names was supplemented by further research by the Soviet-Mongolian geological expeditions, and revised by G. G. Martinson (1973). He divided the Eastern, as well as the Trans-Altaic Gobi, into four strata(see fig. 16). The following stratigraphical chart indicates the chronological history of the of the bone beds and is accepted as the most current work. But it is impossible not to note that the Polish researchers (Gradzinski et al., 1977) divided the Djadokhta into separate litho- and bio- stratigraphic subdivisions. Thus, it is possible that the upper section of the chart provided by Martinson should accepted with modification.

LOCALITIES OF MONGOLIAN ANKYLOSAURS Lower Cretaceous Sites In the Lower Cretaceous deposits of Mongolia, ankylosaur remains are comparatively rare. They were first found at Khovboor (Shuvalov, 1974). Here a cross section showed the interstratification of gray sandstone, yellowish sand, and blue and reddish clay. In the bands of sandstone, sand and silt, mammal bones were discovered: multituberculates, triconodonts, symmetrodonts and insectivores; reptiles: lizards; dinosaurs: Psittacosaurus mongoliensis , sauropods, large and small predatory dinosaurs; and various fish teeth. At this site in 1972, the Combined Mongolian-Polish Expedition (CMPE), discovered the remains of a new ankylosaur enclosed in a nodule. A large number of large and small nodules here are similar to those from Oshi-Naru, where ankylosaur sites are also known (Kalandadze and Kurzanov, 1974). The site has presumably of lacustrine-alluvial origin (Shuvalov, 1974). A more discovery of a Lower Cretaceous ankylosaur was made in 1977 at Khamareen-Us. Here, in the gray sandstones of the Upper Dzun-Bayn strata, a skeleton was found with a cranium and the lower jows, indented as those from Khovboor. The skeletal material was enclosed in a large lens of coarse-grained sand, with spots of gravel. In all, the cross section of the bone-bearing sandstone layer, which lay on an unfossiliferous red layer, consisted of of sandstone and clay, with scattered bands of conglomerate, gravel and limestone. In the cross section, a very coarse unit, approximately 10 meters thick, stands out. It consists of layers of gravel, sandstone and conglomerates; it is here that the most interesting paleontological discoveries were made. For the most part, dinosaur bones are found more or less uniformly throughout the whole cross section. From the assembled fauna, Psittacosaurus sp., sauropods, carnosaurs, lizards of the families Iguanidae and Varanidae, were identified, and also a new genus of ankylosaurid, Shamosaurus , and a Triconodont subfamily, Amphilestinae (determined by B. A. Trofimov). The fauna at Khamareen-Us (as well as the lithology and origin of the sediments) is similar to that at Khovboor, and indicates that both sites are the same age: Aptian-Albian. Analysis of the different fauna of the Lower Cretaceous deposits indicates slopewash as the origin of the red-colored deposits of at Khamreen-Us. The origin of the gray bone beds appears to be more complex. Both lacustrine and riverine fauna are present in them, with cross-grained, alluvial sandstone layers of secondary i

66 Fig. 17. Distribution of Mongolian ankylosaurids by formation importance. The change from lacustrine fauna to riverine is probably the result of periodic reduction of the lake basin. Most discoveries of complete dinosaur skeletons and isolated skulls and of fossil lizards were confined to the lacustrine deposits. The burial sites for ankylosaurs formed under some unique conditions suitable for developing the riverine fauna. The result was prolonged [fluvial] transport with accompanying maceration, complete breakup of the skeletons and, finally, burial of mainly bone fragments.

Upper Cretaceous Sites Bayn-Shiren is the site where Talarurus plicatospineus Maleev (1954) was first discovered. The stratigraphy of the upper part of the Bayn-Shiren Formation consists of three strata: a conglomerate; varied, light colored sand and sandstone; and red colored clays. At this site, other dinosaurs besides ankylosaurs were also found. From the lower stratum, a bivalve fauna was collected, among which is a species of thick walled massive shell that was named Protounio carbiculoides by G.G. Martinson. Originally, Bayn-Shiren was thought to be Maastrichtian, hence the youngest site in Mongolia (Fig. 17) (Maleev, 1952; Efremov, 1954). However, this conclusion was not supported by subsequent studies; G. G. Martinson (1973, 1975) concluded the age of Bayn- Shiren as Late Cenomanian - Early Santonian. The remains of Talarurus (skull roof with braincase) were discovered slightly to the southwest at Baynshin-Tsav. Here, according to I.U. Tsybin and S.M.Kurzanov (1979), the stratigraphy is more or less cyclic consisting of conglomerates, gravels, sandstones, siltstones

67 and clays, with a characteristic thinning of material from lower to upper cycle layers. The rocks contained the remains of a new form of flat-headed dinosaurs, Paralligator sp., Alectrosaurus sp., Archaeornithomimus sp. (determined by S. M. Kurzanov). The fauna suggests a typical Bayn-Shiren accumulation of mixed remains (Tsybin and Kurzanov, 1979). Also in the deposits of this formation [(Bayn-Shiren)] in the Shiregin Gashun valley, were found the maxilla fragments and the occipital condyle of the ankylosaur Maleevus disparoserratus (Maleev 1952). The Bayn-Shiren Formation, according I.A. Efremov (1949), consisted at this site of interstratified marly clay, conglomerates and gray, clayey-sandstone. The ankylosaur remains were associated with fragments of tortoises, and crocodiles that were described by E. D. Kohzhukova (1954) as Paralligator gradilifrons. The dinosaurs Microceratops gobiensis , ornithomimids and hadrosaurs (Marya ńska and Osmolska, 1974). Mollusks, according to Martinson, are represented by Pseudohyria cardiiforma and P. mongolica . The age of the Shiregin Gashun fauna is uncertain. Obviously, the stratigraphy of Shiregin Gashun includes some strata from the first half of the Upper Cretaceous. E. A. Maleev (1952) and E. D. Konzhukova (1954) stated that the rocks enclosing the fauna correspond to the Nemegt Formation, and are one of the youngest deposits, i.e., Maastrichtian. A. K. Rozhdestvenskii (1971, 1974) dated them as Campanian. A. Sochava (1975) compares the Shiregin Gashun with the Barun-Goyot Formation. According to Marya ńska and Osmolska (1975), it is doubtful that the deposits, which contain remains of Microceratops gobiensis and Maleevus dispareserratus , are younger than Santonian. In any case the deposits are older than the Djadokht Formation, and include in their fauna Protoceratops andrewsi (Marya ńska, 1977). In the Bayn-Shiren formation at Amtgai, a new genus of ankylosaur was found, Amtosaurus , based on a braincase (Kurzanov, Tumanova, 1976). Here in the gravels and conglomerates, besides the ankylosaur, were found tortoise shells, crocodile skeletons and the remains of bivalves that Martinson named as Sainsandia robusta , S. cf. hongiliabica , Pseudohyria sp. The rocks of Baynshin-Tsav and Amtgai are lacustrine for the most part. Sediments originated in small lacustrine shoal waters, with periodic fluctuating water levels (Tsybin, Kurzanov, 1979). The first ankylosaurs in the MNR were found in deposits of the Djadokhta Formation (at Bayn Dzak) (Gilmore, 1933b). According to Barsbold (1969), the stratigraphy of the deposits in the northwest part of the escarpment of Bayn Dzak consists of alternating porous sandstone and calcareous clay (which is lenticular and thins), and brownish-gray and orange sandstone with 5-7 layers of calcareous nodules. Martinson (1973, 1975) and Shuvalov (1975) are of the opinion that the deposits of Bayn Dzak are the lower part of the Barun-Goyot Formation. But the Americans (Berkeley and Morris, 1927) and the Polish scientists (Gradzinski et al., 1969; Gradzinski and Jerzykiewicz, 1972; Kielan-Jaworoska, 1974, 1975a, 1975b; Marya ńska, 1977; Osmolska and Marya ńska, 1975) conclude that the strata are a distinct litho- and biostratigraphical subdivision, older than the Barun-Goyot Formation. In the stratigraphy of Bayn Dzak, many remains of dinosaurs, crocodiles, lizards and tortoises have collected by different explorers. The dinosaur fauna of the Djadokhta deposits is distinct. It includes the armored dinosaur Pinacosaurus grangeri (Gilmore, 1933;

68 Marya ńska, 1971), many skeletons of Protoceratops andrewsi (Granger, Gregory, 1923), skulls of small dinosaurs - predators ( Velociraptor mongoliensis (6sborn, 1924) and remains of crocodiles (Mook, 1924), Gobiosuchus kielanae (Osmolska, 1972) and also the lizard Adamisaurus magnidentatus (Sulimski, 1972), Microcephalosaurus fessugenous (Gilmore, 1943) and others. Besides these, there are also discoveries from Bayn Dzak of mammals: Djadochtatherium matthewi (Simpson, 1925; Kielan-Jaworowska, 1970), Kryptobaatar dashzevegi (Kielan-Jaworowska, 1970), Deltatheridium pretrituberculare (Kielan- Jaworowska, 1975a), Zalamdalestes lechei (Kielan-Jaworowska, 1968), Z. grangeri (Kielan- Jaworowska, 1969), and Kennalestes gobiensis (Kielan-Jaworowska, 1969). Gradzinski et al. (1977) tentatively suggested a Late Santonian and/or Early Campanian age for the Bayn Dzak rocks. In contrast to the contradictory opinions about the age and distinctness of the Bayn Dzak strata, almost all scientists agree that the sediments are lacustrine in origin. The remains of some ankylosaurs, in particular Pinacosaurus , often form massive accumulations. For example, at Alag Teg, which is located a little to the west of Bayn Dzak and lying farther to the east, Baga Tarjach. At Alag Teg, besides ankylosaurs, are found scattered skeletons of large carnivorous dinosaurs, sauropods and tortoises (Tverdokhlebov and Tsybin, 1974). The bones are enclosed in the lower member consisting of alternating layers of reddish brown and gray, clayey, fine-grained sandstone beneath a gray sandstone At Baga Tarjach, along with fragmentary Pinacosaurus remains, were found scattered bones of crocodiles and theropods. From a higher level of the Upper Cretaceous Barun-Goyot Formation, came the ankylosaurids Saichania and Tarchia (Marya ńska, 1977). Both skeletons were found at the Khulsan site. Among the vertebrate fauna were the dinosaurs ? Protoceratops kozlowskii , Tylocephale gilmore , Velociraptor sp., carnosaurs and sauropods, the birds Gobipterix minuta (Elzanovski, 1974, 1977), the tortoise Zangerlia testudinimorpha (Mlynarski, 1972), the lizards Natansaurus chulsanensis and Macrocephalosaurus (Marya ńska, 1977), the mammals identified by Kielan-Jaworowska (1974) include Djadochtatherium catapsaloides , Nemegtbaatar gobiensis , and also Asioryctes nemegtensis and Barunlestes butleri (Kielan- Jawoworska, 1975). The remains of Saichania also were found in the layers of red sandstone in the deposits at Khermeen-Tsav. Here, according to the Polish paleontologists (Marya ńska and, Osmolska, 1975), they co-occurred with other dinosaurs such as Bagaceratops rozdestvenski , small therapods and oviraptors, and the lizards Cherminsaurus kozlowskii , Erdenetsaurus robinsonie , Darchansaurus estesi , and Macrocephalosaurus gilmorei , etc. Kielan- Jaworowska (1974) identified the mammals Djadochtatherium catapsaloides , Nemegtbaatar gobiensis , etc. In the highest levels of the Upper Cretaceous, the Nemegt Formation, was found another species of Tarchia , T. gigantea . It was first described by E. A. Maleev (1956) from the Nemegt under the name Dyoplosaurus giganteus . Tarbosaurus baatar was named by E. A. Maleev (1955) and Saurolophus angustirostris was named by A. K. Rozhdestvenskii from the same stratigraphic level. Later, Gallimimus bullatus (Osmolska et al., 1972) was found here. More complete remains of Tarchia (skull with skeletal bones) were found somewhat later, in

69 1975, in the Nemegt Formation at Khermeen Tsav (Tumanova, 1977). In addition, the dinosaurs Tarbosaurus baatar (according to Marya ńska, 1977), hadrosaurs, and sauropods. Turtles include Mongolemys sp according to V.M. Chkhikvadze, and Trionyx sp. (Shuvalov and Chkhikvadze, 1975). Skeletal remains were discovered in an outcrop of the Nemegt near the Barun-Goyot Formation, and included the remains of the protoceratopian, Protoceratops andrewsi, and shells of dinosaur eggs (Shuvalov and Chkhikvadze, 1975). The Nemegt was represented by two layers. The lower layer consisted of sandstone with lenses of gravel and sandy clay, and yielded the shell remains of the freshwater mollusk, Pseudohyria autochthona , which, according to Martinson, is characteristic of the Maastrichtian. The upper layer consists of interstratified sandstone, gravel and sandy clay. In the gravel beds were found mollusk shells similar to those mentioned above and skeletal remains of dinosaurs, among which are Tarchia gigantea and some tortoises. Based on the strata at Khermeen-Tsav, sedimentation took from the Campanian to the Maastrichtian (Shuvalov and ChKhikvadze, 1975). The highest strata, the Nemegt Formation, is no doubt dated as Maastrichtian, not only by the presence of bivalves that are characteristic of this age, but also by the grade of ankylosaur evolution. Ankylosaurs are an integral component of the faunal complex for eash formation (Fig. 17), from the Dzun-Bayn to the Nemegt (the only exception is the Sayn-Shand [(which is unfossiliferous)]). Consequently, they can play an important part in the stratigraphy of the Upper Cretaceous deposits in the Gobi. They can be used, by their unique morphology, to determine the age of rocks [(i.e., biostratigraphy)], and can supplement data provided by other vertebrates and invertebrates for Mongolian stratigraphy. Besides, it is now possible to use ankylosaurs to correlate deposits from different regions in Asia, and also between Asia and North America.

70 SUMMARY

1. Ankylosaurs are a primitive, greatly specialized group of dinosaurs. Many structural features (lower part of the braincase, the absence of the upper temporal fenestra, the contact of the quadrate bone and the paroccipital process) indicate the extreme primitivity in comparison with other dinosaurs. Ankylosaurs originated from quadruped ancestors and persisted up to the end of the Cretaceous period. The ancestor could have been more primitive than Fabrosaurus morphologically, which is considered one of the possible groups established as the basal ornithischian dinosaurs. 2. Based on the development of morphological features, ankylosaurs are divided into the more primitive Nodosauridae and the more specialized Ankylosauridae. The principal differences include the shape and proportions of the skull, the pattern of the armor covering the skull roof, the size of the teeth, the structure of the palate and the braincase, and the occipital region. The ancestors of both families had skull structure similar to the nodosaurids. 3.Based on the type of contact between the pterygoids and the basisphenoid, the proportions and some features of the structure of the palate, ankylosaurids are divided into two subfamilies: Shamosaurinae, which appeared relatively early, and the subfamily Ankylosaurinae, which includes all Late Cretaceous ankylosaurs. The early specimens of ankylosaurids - Shamosaurinae - possessed characteristics intermediate between the two families, Ankylosauridae and Nodosauridae. On the one hand, they already have the ankylosaurid proportions of the skull, small teeth, and the lower (lateral) temporal fenestrae covered by a sheet of armor. On the other hand, they preserved the ancestoral narrow premaxillary region, the more posterior position of the orbits, the more poorly developed postorbital horn, some structural traits of the palate, and the type of contact between the quadrate and the paroccipital processes. 4. The primitive ankylosaur, Saichania , illustrates the evolutionary changes, such as the widening of the premaxillary region, the shortening of the maxilla, some rotation of the snout in front of the orbits, the further growth of the armor in the postorbital region into horn- shaped growths. 5. The Ankylosaurinae developed towards an increase in the armor covering of the skull roof, in the development of armor in the posterolateral corners of the skull into horn-shaped growths, in development of the secondary palate, and the complicated structure of the nasal region. The contact of the quadrate with the paroccipital processes remained weak. The functional analysis carried out for the inner nasal region indicated the presence on the ventral surface of the ankylosaur skull roof cap, structural vestiges partly comparable to those of contemporary lizards. Along with this similarity, the nasal region in ankylosaurids distinct in having a large number of septa and sinuses. It is difficult to explain their function. In the

71 paper, the circulatory system of the head, the cranial nerves, and the structure of the inner ear were presented for the first time for this group. Particular attention was paid to characteristics of ankylosaurids, which were unusually primitive. This allowed us to contrast them with the other dinosaurs. 6. Ankylosaurs were, in all probability, less aquatic than hadrosaurs. Their connection with water was, perhaps, more like that of the contemporary hippopotamus, which come out to feed on dry land. Ankylosaurs probably led a large part of their lives in the water based on the bulkiness and great weight of the animals. It was difficult for them to travel on dry land and more difficult to hide from predators. Their simple dental system, the small primitive teeth with finely notched edges and practically without traces of abrasion, suggest that the animal’s food was soft succulent plant life, and most of all, the number of discoveries of ankylosaur remains in certain sites in Mongolia reveals an aquatic way of life that we rarely see in connection with other dinosaurs.

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78 Oelrich Th.M. The anatomy of the head of Rixon, A.E. The development of the remains Ctenosauria pectinata (Iquanidae). Misc. of a small Scelidosaurus from a Lias Publ. Mus. Zoo]. Univ. Mich. 1956. N nodule. Mus. J. 1968. N 67. P. 315-321. 94. P. 1-122. Romer, A.S. The pelvic musculature of the Osborn, H.F. Integument of the iguanodont ornithischian dinosaurs. Acta zool. 1927. dinosaur Trachodon . Mem. Amer. Mus. Vol. 8, N 2/3. P. 225-275. Natur. Hist. N.S. 1912. Vol. 1. P. 33-54. Romer, A.S. Osteology of the reptiles. Osborn, H.F. Two Lower Cretaceous Chicago: Univ. Chicago press, 1956. P. dinosaurs of Mongolia. Amer. Mus. 1-772. Novit. 1923. N 95. P. 1-10. Romer, A.S. Vertebrate paleontology. Osborn, H.F. Sauropoda and Theropoda, Chicago; L.: Univ. Chicago press, 1966. Protoceratops zone, Central Mongolia. P. 1-468. Ibid. 1924. N 144, P. 1-12. Romer, A.S. Notes and comments on Osmólska, H. Preliminary note on a vertebrate paleontology. Chicago: Univ. crocodilian from the Upper Cretaceous Chicago press, 1968. P. 5-304. of Mongolia. Results Pol.-Mongol. Russell. D.A. The dinosaurs of Central Asia. Paleontol. Exp. IV. 1972, P. 33-47. Canad. Geogr. J. 1969. Vol. 81, N 6. P. (Paleontol. Pol.; N 24.) 208-215. Ostrom, J.H. Cranial morphology of the Russell, L.S. Edmontonia rugosidens hadrosaurian dinosaurs of North (Gilmore), an armoured dinosaur from America. Bull. Amer. Mus. Natur. Hist. the Belly River series of Alberta. Univ. 1961. Vol. 122. P. 33-186. Toronto Stud. Geol. Ser.1940. N 43. P. Ostrom, J.H. Stratigraphy and paleontology 1-27. of the Cloverly Formation (Lower Seeley, H.G. Index to the fossil remains of Cretaceous) of the Bighorn Basin and Aves, Ornithosauria and reptilia from the Wyoming and Montana. Bull. Peabody Secondary Strata arranged in the Mus. Natur. Hist. Yale Univ. 1970. Vol. Woodwardion Museum of the University 35. P. 1-152. of Cambridge. Cambridge, 1869. 143 p. Owen, R. Monograph on the fossil reptilia of Seeley, H.G. On the Dinosauria of the the Wealden and Purbeck formations. Cambridge Greensand. London. Quart. J. Part IV. Dinosauria ( Hylaeosaurus ). Geol. Soc. 1979. Vol. 35. P. 591-636. Paleontogr. Soc. Monogr. 1858. Vol. 10, Seeley, H.G. On the reptile fauna of the pt. 4. P. 8-26. Gosau Formation preserved in the Owen, R. Monograph on the fossil reptilia of Geological Museum of the University of the Liassic formation. Part 1, II A Vienna. Ibid. 1981. Vol. 37. P. 619-707. monograph of a fossil dinosaur Simpson, G.G. Mesozoic mammal skull (Scelidosaurus harrisoni Owen) of the from Mongolia. Amer. Mus. Mus. Novit. Lower Lias. Ibid. 1863. Vol. 14. P. 1-26, 1925. N 201. P. 1-11. Parks, W.A. Dyoplosaurus acutosquameus , Steel, R. Ornithischia. Kuhn 0. Handbuch a new genus and species of armoured der Paläoherpetologie. Jena, 1969. Bd. dinosaur; and notes on a skeleton of 15. S. 1-67. Prosaurolophus maximus . Univ. Toronto Sternberg, C.M. A new armoured dinosaur Stud. Geol. Set. 1924. N 18. P. 1-35. from the Edmonton Formation of

79 Alberta. Trans. Roy. Soc. Canada. Sect. 111. 1928. Vol. 22. P. 93-106. Thulborn, R.A. Origins and evolution of Sternberg, C.M. A toothless armoured ornithischian dinosaurs. Nature. 1971. dinosaur from the Upper Cretaceous of Vol. 234, N 5324. P. 75-78. Alberta. Bull. Nat. Mus. Canada. Dep. Wiman, C. Die Kreide-Dinosaurien aus Mines. 1929. N 54. P. 28-33. Schantung Paleontol. sin. C. 1929. Vol. Sternberg, C.M. Canadian dinosaurs. Ibid. 6, fasc. 1. P. 1-67. 1946. N 103. P. 1-20. Young CC. On a new Nodosaurid from Swinton, W.E. A Canadian armoured Ninghsua. Palaeontol. Sin. 1935. Vol. dinosaur. Natur. Hist. Mag. 1929. Vol. 2. 11, fasc. 1. P. 1-28. P. 67-74. Young C.C. The dinosaurian remains of Sulimski, A. Adamisaurus magnidentatus n. Laiyang, Shautung. Palaeontol. Sin. gen., n. sp. (Sauria) from the Upper N.S.C. 1958. Vol. 16. P. 1-139. Cretaceous of Mongolia. Results Pol.-Mongol. Paleontol. Exp. IV. Warszawa - Kraków, 1972. P. 33-40. (Palaeontol. Pol.; N 27.)

80 PLATE CAPTIONS

Plate I Fig.1-2. Tarchia gigantea (Maleev). PIN 3142/250, skull. Khermeen Tsav, Upper Cretaceous, Nemegt Formation. 1 - dorsal; 2 - ventral Fig. 3. Tarchia gigantea (Maleev). PIN 3142/250, mandible in lateral view. Khermeen Tsav, Upper Cretaceous, Nemegt Formation. Plate II Fig. 1. Tarchia gigantea (Maleev). PIN 3142/250, skull in lateral view. Khermeen Tsav, Upper Cretaceous, Nemegt Formation. Fig. 2-3. Saichania chulsanensis Marya ńska. PIN 3142/251. Khermeen Tsav II, Upper Cretaceous, Barun Goyot Formation. 2- hyoids; 3 - distal part of tail with club. Plate III Fig. 1-2. Talururus plicatospineus Maleev. PIN 3780/1, skull roof. Baynshin Tsav; Upper Cretaceous Bayn Shiren Formation. 1 - dorsal; 2 - ventral . Fig. 3. Tarchia gigantea (Maleev). PIN 3142/250, hyoids. Khermeen Tsav, Upper Cretaceous, Nemegt Formation. Plate IV Fig. 1-3. Talarurus plicatospineus Maleev. PIN 3780/1, braincase. Baynshin Tsav; Upper Cretaceous Bayn Shiren Formation. 1 - ventral; 2 - dorsal; 3 - anterior Plate V Fig. 1-2. Pinacosaurus grangeri Gilmore. PIN 4043, braincase. Baga Tarjach, Upper Cretaceous Djadokhta Formation. 1 - ventral; 2 - ventral Fig. 3-5. Amtosaurus magnus Kursanov and Tumanova. PIN 3780/2, braincase. Amtgai, Upper Cretaceous Bayn Shiren Formation. 3 - ventral; 4 - dorsal; 5 - lateral Plate VI Fig. 1-3. Maleevus disparoserratus (Maleev). PIN 554/2-1, braincase. Shiregen Gashun, Upper Cretaceous Bayn Shiren Formation. 1 - ventral; 2 - dorsal; 3 - lateral Fig. 4-5. Talarurus plicatospineus Maleev. PIN 557-51, braincase. Baynshin Tsav; Upper Cretaceous Bayn Shiren Formation. 4 - ventral; 5 - lateral Plate VII Fig. 1-2. Maleevus disparoserratus (Maleev). PIN 554/1-1, maxilla . Shiregen Gashun, Upper Cretaceous Bayn Shiren Formation. 1 - lateral; 2, ventral

81 Fig. 3-6. Maleevus disparoserratus (Maleev). PIN 554/1-1, maxillary fragments. Shiregen Gashun, Upper Cretaceous Bayn Shiren Formation. 3, 4 - ventral; 5, lateral; 6, medial Fig. 7-8. Shamosaurus scutatus Tumanova. Kharareen Us, Lower Cretaceous Dzun Bayn Formation. 7 - skull PIN 3779/2-1, dorsal; 8 - mandible PIN 3779/2-2, lateral Plate VIII Fig. 1-4. Shamosaurus scutatus Tumanova. PIN 3779/2-1, skull. Kharareen Us, Lower Cretaceous Dzun Bayn Formation. 1- ventral; 2 - lateral; 3 - posterior; 4 -detail of premaxillaries.

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