Proceedings of the Zoological Institute RAS Vol. 313, No. 2, 2009, рр. 153–167 УДК 57.072:551.762.2 STEGOSAUR REMAINS FROM THE MIDDLE JURASSIC OF WEST SIBERIA A.O. Averianov1* and S.A. Krasnolutskii2 1Zoological Institute of the Russian Academy of Sciences, Universitetskaya Emb. 1, 199034 Saint Petersburg, Russia; e-mail: [email protected] 2Sharypovo Regional Museum, 2nd microrayon 10, Sharypovo, 662311 Krasnoyarsk Territory, Russia; e-mail: [email protected] ABSTRACT The Middle Jurassic (Bathonian) Itat Formation at Berezovsk Quarry, Krasnoyarsk Territory (West Siberia, Russia) has produced abundant remains of stegosaurs. Numerous isolated teeth are found at various microvertebrate sites, and associated skeletal remains, mostly vertebrae, ribs, and ilio-sacral block fragments were excavated at the Stegosaur Quarry. These remains likely belong to one taxon which is characterized by numerous secondary ridges on one crown side in cheek dentition, six vertebrae in the synsacrum, four sacral and one dorsosacral ribs, lack of dorsal process on the transverse process in anterior caudals, moderately expanded tops of the neural spines in anterior caudals, and large triangular transversely thin dorsal dermal plates. The combination of these and other features is not characteristic for any other known stegosaur taxon and the Berezovsk stegosaur likely represents a new taxon. Among known stegosaurs it is most similar with Stegosaurus from the Late Jurassic and Early Cretaceous of North America and Asia by having numerous secondary ridges on teeth, a right angle between the supraacetabular flange and the anterior iliac process of ilium and in the structure of the dorsal dermal plates. It differs from Stegosaurus by plesiomorphically unexpanded tops of the neural spines and lack of dorsal process on the transverse processes in the anterior caudal vertebrae. The Berezovsk stegosaur is among the oldest stegosaurs in the fossil record. Key words: Dinosauria, Middle Jurassic, Russia, Stegosauria, West Siberia Submitted March 10, 2009; accepted April 27, 2009. ОСТАТКИ СТЕГОЗАВРОВ ИЗ СРЕДНЕЙ ЮРЫ ЗАПАДНОЙ СИБИРИ А.О. Аверьянов1* и С.А. Краснолуцкий2 1Зоологический институт Российской академии наук, Университетская наб. 1, 199034 Санкт-Петербург, Россия; e-mail: [email protected] 2Шарыповский краеведческий музей, 2-й микрорайон 10, Шарыпово, 662311 Красноярский край, Россия; e-mail: [email protected] РЕЗЮМЕ Многочисленные остатки стегозавров обнаружены в отложениях среднеюрской (бат) итатской свиты, вскрытой в Березовском карьере Красноярского Края (Западная Сибирь, Россия). Многочисленные изоли- рованные зубы происходят из различных местонахождений микропозвоночных в карьере. Ассоциированные скелетные остатки (в основном позвонки, ребра и фрагменты подвздошно-крестцового блока) найдены в “стегозавровом раскопе”. Эти остатки, вероятно, принадлежат особям одного таксона, который характеризу- * Corresponding author / Автор-корреспондент. 154 A.O. Averianov and S.A. Krasnolutskii ется многочисленными вторичными гребнями на одной стороне коронки щечных зубов, шестью позвонками в сложном крестце, четырьмя крестцовыми и одним спино-крестцовым ребрами, отсутствием дорсального отростка на поперечных отростках передних хвостовых позвонков, умеренно расширенными вершинами остистых отростков передних хвостовых позвонков и большими треугольными поперечно тонкими спин- ными костными пластинками. Комбинация этих и других признаков не характерна для какого-нибудь из- вестного таксона стегозавров, и, поэтому, Березовский стегозавр, вероятно, принадлежит к новому таксону. Среди известных стегозавров он наиболее сходен с Stegosaurus из поздней юры и раннего мела Северной Америки и Азии по наличию многочисленных вторичных гребней на зубах, по прямому углу между над- вертлужным флангом и передним отростком подвздошной кости и по строению спинных костных пласти- нок. Березовский стегозавр отличается от Stegosaurus такими примитивными чертами, как слабо поперечно расширенные вершины остистых отростков и отсутствие дорсального отростка на поперечных отростках передних хвостовых позвонков. Березовский стегозавр является одним из наиболее древних стегозавров из- вестных в геологической летописи. Kлючевые слова: Dinosauria, средняя юра, Россия, Stegosauria, Западная Сибирь Представлена 10 марта 2009; принята 27 апреля 2009. INTRODUCTION The Middle Jurassic (Bathonian) beds of the Itat Formation, revealed in the Berezovsk Quarry on the south of Krasnoyarsk Territory, West Siberia (Fig. 1) has produced a diverse fauna of vertebrates, including fishes, salamanders, turtles, choristoderes, lizards, crocodiles, pterosaurs, dinosaurs, tritylo- dontids, and diverse mammals (see Averianov et al. 2005 for details). This fauna is known mostly from small sized disarticulated specimens obtained during underwater screen-washing at various fossiliferous strata within the Itat Formation, but in one place, called the Stegosaur Quarry (Fig. 2), associated but usually not articulated larger dinosaur bones were excavated by S.A. Krasnolutskii and his assistants during three field seasons (2005–2007). Majority of dinosaur bones from this quarry belong to stegosaurs, and at least two individuals are present. The bones are irregularly scattered along the surface indicat- ing a long period of sub-aerial exposure. The burial was biased to mostly vertebrae, ribs, and ilio-sacral blocks. The limb bones and dermal plates are known from single specimens and the cranial bones are lack- ing altogether. The purpose of this paper is to give a detailed morphological description to the stegosaur remains from this quarry and the microvertebrate sites. In the taxonomy of Stegosauria we follow the recent revision by Maidment et al. (2008). Tooth measurements. BCW, basal crown width; FABL, fore-aft-basal length; TCH, tooth crown Fig. 1. Geographic position of Berezovsk Quarry (asterisk) on height. All linear measurements are in mm. the map of Russia (top, Krasnoyarsk Territory is in green) and in Institutional abbreviations. SHRM, Sharypovo the vicinity of Sharypovo city (bottom; the map is modified from Regional Museum, Krasnoyarsk Territory, Russia. http://maps.google.ru/maps). Middle Jurassic stegosaurs of West Siberia 155 Fig. 2. Stegosaur Quarry map (left) and S.A. Krasnolutskii excavating the stegosaur bones at this site (right) in the Berezovsk Quarry, Krasnoyarsk Territory, Russia. ZIN PH, Paleoherpetological collection, Zoological 214/1, fragment of left anterior process of ilium; Institute of the Russian Academy of Sciences, Saint SHRM 40/1, ungual phalanx; SHRM 212/1, dorsal Petersburg, Russia. dermal plate. Description. Several dozens of isolated stegosaur SYSTEMATICS teeth were found during screen-washing at various microvertebrate sites within the fossiliferous bed of the Itat Formation; no teeth have been found at the Dinosauria Owen, 1842 Stegosaur Quarry. The tooth morphology is typical Ornithischia Seeley, 1887 for stegosaurs (Fig. 3; Galton and Upchurch 2004). Stegosauria Marsh, 1877 The crown is covered with enamel on both sides and Stegosauria indet. slightly asymmetrical. The mesial side is more convex (Figs. 3–13) and bears a greater number of denticles, five to eight compared with three to five on the distal side. As a Material. ZIN PH 1–2/117 and numerous un- result, the median cusp is slightly posterior to the catalogued specimens, isolated teeth; SHRM 205/1, midline of the crown. The cingulum is robust and al- posterior cervical(?); SHRM 203–204/1, anterior- most complete, except a short interval on one side of most dorsals; SHRM 8/1, 9/1, 11/1, 103/1, 104/1, the crown (labial or lingual), where it is very weak or 122/1, 123/1, 206/1, dorsals; SHRM 3/1, 5/1, 6/1, absent. The median cusp is closer to this crown side 14/1, 15/1, 28/1, 109/1, dorsal neural arches; SHRM than the lateral denticles, giving to the denticulated 12/1, dorsal neural arch with ankylosed rib; SHRM ridge a wide V-shape in occlusal view (Fig. 3A, D). 52–56/1, 58/1, 59/1, 63/1, dorsal ribs; SHRM On this crown side there is a “complex network of 17–26/1, 95–99/1, 106/1, 120/1, 121/1, caudals; secondary ridges” (Fig. 3B), which among stegosaurs SHRM 10/1, 30/1, 200/1, 201/1, 207/1, caudal cen- was noted previously only for Stegosaurus (Galton tra; SHRM 31/1, 208/1, chevrons; SHRM 210/1 and and Upchurch 2004, p. 350). Also the enamel ap- 211/1, fragmented ilio-sacral blocks; SHRM 45/1, pears to be more wrinkled on this side (compare Fig. fragment of right anterior process of ilium; SHRM 3E, F). On the opposite side, there are fewer ridges, 156 A.O. Averianov and S.A. Krasnolutskii Fig. 3. Isolated teeth of Stegosauria indet. from Berezovsk Quarry, Krasnoyarsk Territory, Russia (Itat Formation, Middle Jurassic) in occlusal (A, D) and two side (other figures) views: A–C — ZIN PH 1/117; D–F — ZIN PH 2/117. Scale bar = 1 mm. and groves between denticles are more consistent, condition. Specimens SHRM 204/1 and SHRM extending to the base of the crown (Fig. 3F). But on 205/1 were found in association, but SHRM 203/1 other specimens (Fig. 3C) there are secondary ridges was found in a different place and may not belong to on this side also, which are, however, confined to the same individual. The parapophysis is not clearly the basal and central part of the crown. The root is discernible on these specimens, but in SHRM 205/1 cylindrical, distinctly narrower than the crown and it is possible just below the neurocentral suture. If this is correct, this vertebra would be a posterior cervi- slightly constricted below the cingulum. Some teeth cal. Two other specimens are likely the most anterior have facets on the cingulum closer to the mesial or dorsals. The neural arch in SHRM 203/1 is high, as distal side caused apparently by occlusion with the in typical dorsals (the height of pedicel is ~1.4 times neighboring teeth and indicating some overlap of the the height of the centrum). In two other specimens teeth in the dental series. The largest complete tooth the neural canal is wider, and in SHRM 205/1 the in the sample (ZIN PH 1/117; Fig. 3A–C) has FABL neural arch is relatively low, as in the anterior dorsal 6.7, BCW 4.5, and TCH 6.4. There are many teeth of Huayangosaurus (Maidment et al. 2006, fig. 2A, B). of various sizes and with different states of dental The centrum is relatively short; the centrum length wear, some of which are completely eroded. Appar- is approximately equal to centrum width in SHRM ently, these teeth were swallowed and digested by 204/1 and SHRM 205/1 and little smaller in SHRM the animal. Some teeth were in use until the crown 203/1. In SHRM 204/1 and SHRM 205/1 the in- was completely worn dawn and represent fungus-like tercentral articulation surfaces are more squarish structures with a thin apically concave cap. compared to the rounded surfaces in SHRM 203/1 In all dorsal vertebrae the centra are spool-shaped and typical dorsals. The anterior margin of the neural and amphiplatyan. The vertebrae SHRM 203–205/1 arch pedicel is with level with the centrum anterior (Fig. 4) differ from the typical dorsals by an asym- surface and vertical with or slightly overhanging the metrical centrum in lateral view. In SHRM 204/1 latter. The posterior margin of the neural arch pedicel the anterior intercentral articulation surface projects is sloping towards the posterior centrum surface. The ventrally below the posterior intercentral articulation transverse process, preserved completely on right side surface, while two other specimens show the reversal of SHRM 203/1 (Fig. 4G–I), is short and oriented at Middle Jurassic stegosaurs of West Siberia 157 70° to the sagittal plane. The prezygapophyseal articula- tion surfaces are not fused ventrally and are oriented at about 45° to the sagittal plane. The postzygapophysis, best preserved in SHRM 203/1 (Fig. 4G, H), is anteroposte- riorly elongate and projects posteriorly beyond the poste- rior intercentral articulation surface. The neural spine, preserved in SHRM 203/1 (Fig. 4G–I), is a low plate triangular in lateral view and not widened dorsally. The other dorsals (Figs. 5–6) show typical stegosau- rian morphology (Galton and Upchurch 2004). The ventral margin of the centrum is slightly concave or almost straight in lateral view. The lateral side of the centrum is smooth, without a longi- tudinal ridge or depression. The neural canal varies in width and height (the latter is 29–71% of the centrum height, measured along the anterior side). In most speci- mens it is relatively low and tear-drop shaped (Fig. 5). In some specimens with a broken thin plate above the canal it appears very high and narrow Fig. 4. Posterior cervicals or anterior dorsals of Stegosauria indet. from Be- rezovsk Quarry, Krasnoyarsk Terri- tory, Russia (Itat Formation, Middle Jurassic): A–C — SHRM 205/1, in anterior (A), lateral (B), and poste- rior (C) views; D–F — SHRM 204/1, in posterior (D), lateral (E), and anterior (F) views; G–I — SHRM 203/1, in posterior (G), lateral (H), and anterior (I) views. Abbreviations: di — diapophysis; nc — neural canal; ns — neural spine; prz — prezygapophysis; psz — postzy- gapophysis. Scale bar = 5 cm. 158 A.O. Averianov and S.A. Krasnolutskii Fig. 5. Dorsals of Stegosauria indet. from Berezovsk Quarry, Krasnoyarsk Territory, Russia (Itat Formation, Middle Jurassic): A–D — SHRM 11/1, in posterior (A), ventral (B), lateral (C), and anterior (D) views; E–H — SHRM 8/1, in posterior (E), ventral (F), lateral (G), and anterior (H) views. Abbreviations: di — diapophysis; nc — neural canal; ns — neural spine; pa — parapophysis; prz — prezygapophysis; psz — postzygapophysis. Scale bar = 5 cm. Middle Jurassic stegosaurs of West Siberia 159 Fig. 6. Dorsals of Stegosauria indet. from Berezovsk Quarry, Krasnoyarsk Territory, Russia (Itat Formation, Middle Jurassic): A–C — SHRM 123/1, in posterior (A), lateral (B), and anterior (C) views; D–F — SHRM 206/1, in posterior (D), lateral (E), and anterior (F) views. Abbreviations: di — diapophysis; nc — neural canal; ns — neural spine; pa — parapophysis; prz — prezygapophysis; psz — postzygapophysis. Scale bar = 5 cm. 160 A.O. Averianov and S.A. Krasnolutskii Fig. 7. Isolated dorsal ribs of Stegosauria indet. from Berezovsk Quarry, Krasnoyarsk Territory, Russia (Itat Formation, Middle Jurassic) in anterior or posterior views: A — SHRM 63/1; B — SHRM 53/1; C — SHRM 54/1; D — SHRM 58/1; E — SHRM 55/1; F — SHRM 59/1; G — SHRM 52/1. Scale bar = 10 cm. (e.g., SHRM 206/1; Fig. 6D, F), which is an artifact verse processes to the sagittal plane varies from 20° of preservation (some postmortem compression of to 65°; in the specimens with the low angle they are vertebrae is also likely). The height of the pedicel almost as high as the neural spine. These specimens varies from 138% to 204% of the centrum height (the possibly come from the middle of the dorsal series. mean value is 170% for nine measurements). There The prezygapophyses are joined ventrally and form is a deep pocket-like depression on the posterior side a U-shaped common articulation surface in most of the neural arch pedicel above the neural canal and specimens but are separated by a deep groove in between the lateral columnar buttresses support- SHRM 109/1. The articulation surfaces are oriented ing the postzygapophyses. The anterior side of the from 31° to 55° to the sagittal plane. Usually there pedicel above the neural canal is flat and with level is a prominent ridge between the prezygapophyseal with the lateral buttresses supporting the prezygapo- articular surface and the base of the neural spine. The physes. The parapophysis is placed approximately at anterior base of the neural spine is positioned level the level of prezygapophyses. It has a short pedicel with the centrum midline. The anterior and posterior in SHRM 5/1 and SHRM 8/1 (Fig. 5E, H). The margins of the neural arch pedicel converge towards transverse processes are robust and T-shaped in cross the base of the diapophysis and zygapophyses, in section, with the longitudinal supporting ridge ex- contrast with the anteriormost dorsals described tending ventrally between the parapophysis and the above, where the anterior margin is subvertical. The diapophysis. As typical for stegosaurs, the transverse postzygapophysis is elongated and projects posteri- processes are united between the prezygapophyses orly beyond the centrum. The postzygapophyseal and the neural spine. The orientation of the trans- articular surfaces are separated by a ventral groove. Middle Jurassic stegosaurs of West Siberia 161 The vertical ridge between the postzygapophyses and the top of the neural canal is variably developed. The neural spine is completely preserved in SHRM 8/1 and SHRM 123/1 (Figs. 5E, G, H and 6A–C). It is a plate like-structure extending between the posterior ends of the prezygapophyses and postzygapophyses and slightly tapering dorsally. There are several isolated dorsal ribs (Fig. 7). SHRM 63/1 (Fig. 7A) with a relatively large and massive capitular process and wider rib shaft could be among first dorsal ribs or even the posterior cervical ribs. The tuberculum is relatively small in all speci- mens. SHRM 52/1 (Fig. 7G) with the longest and straightest shaft apparently comes from the middle of dorsal series. The rib shaft has a T-shape in cross section as in Stegosaurus (Gilmore 1914; Ostrom and McIntosh 1999, pl. 20), with a perpendicular lateral lamina in the proximal part forming a ridge in ante- rior view. The sacral vertebrae are known from two frag- mentary ilio-sacral blocks (SHRM 210/1 and SHRM 211/1). In SHRM 210/1 there are six coosified cen- tra (Fig. 8), the two anterior of which are apparently dorsosacrals. The second dorsosacral appears to share the sacral rib with the first sacral, as in Stegosaurus (Ostrom and McIntosh 1999, pl. 24). The first dor- sosacral has a round intercentral articulation surface which is flattened dorsally. The second dorsosacral centrum has a prominent ventral keel. The sacral cen- tra are longer than wide and are approximately equal in length. The sacral neural arches are better preserved in SHRM 211/1. The neural arch is transversely about twice as wide in the third vertebra (sacral 1) compared with the first vertebra (dorsosacral 1), indicating widening of the sacral neural canal, simi- larly to that of Stegosaurus and Kentrosaurus. SHRM 211/1 preserves four sacral ribs and one dorsosacral rib attached to the ilium (Fig. 12C). Stegosaurs usu- ally have four robust sacral ribs, but in some there is an additional slender dorsosacral rib (Gilmore 1914, fig. 23; Galton and Upchurch 2004, p. 353). SHRM Fig. 8. SHRM 210/1, coosified dorsosacral and sacral centra of Stegosauria indet. from Berezovsk Quarry, Krasnoyarsk Territory, 211/1 agrees with this condition: the dorsosacral Russia (Itat Formation, Middle Jurassic) in anterior (A), ventral rib is slender and anteromedially directed, while the (B), and lateral (C) views. remaining sacral ribs are more robust and directed Abbreviations: ds1–ds2 — dorsosacrals one and two; s1–s4 — more medially. sacrals one to four; sr — sacral rib. Scale bar = 10 cm. Caudal vertebrae are common at the Stegosaur Quarry. The specimens SHRM 95–99/1 were found among the first three or four caudals. They are simi- in association and apparently represent a continu- lar to the third caudal of Stegosaurus (Ostrom and ous caudal section of one individual. The vertebrae McIntosh 1999, pl. 25) in having a short and wide SHRM 22/1 and SHRM 120/1 (Fig. 9A–C) are centrum and long transverse processes directed vent- 162 A.O. Averianov and S.A. Krasnolutskii Fig. 9. Anterior caudals of Stegosauria indet. from Berezovsk Quarry, Krasnoyarsk Territory, Russia (Itat Formation, Middle Jurassic): A–C — SHRM 120/1, in posterior (A), lateral (B), and anterior (C) views; D–F — SHRM 121/1, in posterior (D), lateral (E), and anterior (F) views. Abbreviations: nc — neural canal; ns — neural spine; prz — prezygapophysis; psz — postzygapophyses; trpr — transverse process. Scale bar = 10 cm.