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From the Early Cretaceous of Laos

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From the Early Cretaceous of Laos Naturwissenschaften DOI 10.1007/s00114-012-0911-7 ORIGINAL PAPER The first definitive Asian spinosaurid (Dinosauria: Theropoda) from the early cretaceous of Laos Ronan Allain & Tiengkham Xaisanavong & Philippe Richir & Bounsou Khentavong Received: 25 November 2011 /Revised: 19 March 2012 /Accepted: 22 March 2012 # Springer-Verlag 2012 Abstract Spinosaurids are among the largest and most spe- from Asia. Cladistic analysis identifies Ichthyovenator as a cialized carnivorous dinosaurs. The morphology of their member of the sub-clade Baryonychinae and suggests a crocodile-like skull, stomach contents, and oxygen isotopic widespread distribution of this clade at the end of the Early composition of the bones suggest they had a predominantly Cretaceous. Chilantaisaurus tashouikensis from the Creta- piscivorous diet. Even if close relationships between spino- ceous of Inner Mongolia, and an ungual phalanx from the saurids and Middle Jurassic megalosaurs seem well estab- Upper Jurassic of Colorado are also referred to spinosaurids, lished, very little is known about the transition from a extending both the stratigraphical and geographical range of generalized large basal tetanuran to the specialized morphol- this clade. ogy of spinosaurids. Spinosaurid remains were previously known from the Early to Late Cretaceous of North Africa, Keywords Cretaceous . Savannakhet basin . Theropoda . Europe, and South America. Here, we report the discovery Spinosauridae . Asia of a new spinosaurid theropod from the late Early Creta- ceous Savannakhet Basin in Laos, which is distinguished by an autapomorphic sinusoidal dorsosacral sail. This new Introduction taxon, Ichthyovenator laosensis gen. et sp. nov., includes well-preserved and partially articulated postcranial remains. The spinosaurids are among the most bizarre dinosaurs. The Although possible spinosaurid teeth have been reported morphology of their superficially crocodile-like skull from various Early Cretaceous localities in Asia, the new (Taquet 1984; Charig and Milner 1997; Sereno et al. 1998; taxon I. laosensis is the first definite record of Spinosauridae Sues et al. 2002; Dal Sasso et al. 2005), as well as the stomach contents of the holotype of Baryonyx walkeri Communicated by: Robert Reisz (Charig and Milner 1997), the biomechanical data (Rayfield et al. 2007), and the oxygen isotopic composition of the Electronic supplementary material The online version of this article (doi:10.1007/s00114-012-0911-7) contains supplementary material, bones (Amiot et al. 2010) of spinosaurs suggest they had a which is available to authorized users. predominantly piscivorous diet, even if it appears that they also fed on ornithopods (Charig and Milner 1997)and R. Allain (*) : P. Richir Département Histoire de la Terre, Centre de Recherches sur la pterosaurs (Buffetaut et al. 2004). Spinosauridae is mainly Paléobiodiversité et les Paléoenvironnements (CR2P), Muséum known from the Early Cretaceous Wessex Formation of National d’Histoire Naturelle, Europe (Charig and Milner 1986) and from the late Early UMR 7207 du CNRS CP 38, 57 rue Cuvier, and early Late Cretaceous of Gondwana (Stromer 1915; 75231 Paris cedex 05, France e-mail: [email protected] Sereno et al. 1998; Taquet and Russell 1998; Sues et al. : 2002). Furthermore, the first-described spinosaurid, Spino- T. Xaisanavong B. Khentavong saurus aegypticus, which was destroyed during World War Science and Technology Office, Savannakhet Dinosaur Museum, II in an Allied bombing raid of Munich, is famous for its Khanthabouly Road, Thamouang Village, Savannakhet, Kaisonphomvihan DistrictPO Box 739, République hypertrophied dorsal neural spines forming a high median Démocratique Populaire Lao sail on its back (Stromer 1915, 1934; Smith et al. 2006). Naturwissenschaften Except for the close relationships with Middle Jurassic “hunter”). The generic name is in reference to the predom- megalosaurs (Sereno et al. 1998; Allain 2002; Holtz et al. inantly piscivorous diet of Spinosauridae. The specific name 2004; Benson 2010), early evolution of the Spinosauridae is derived from the name Laos. remains enigmatic as the first appearance datum of the taxon is in Early Cretaceous deposits. Holotype Partially articulated skeleton, curated at the Dino- The presence of spinosaurid theropods in Asia has been saur Museum, Savannakhet (MDS BK10-01 to 15), includ- tentatively reported on the basis of several isolated teeth ing the antepenultimate dorsal vertebra, the neural spine of from Cretaceous units in Thailand (Buffettaut and Ingavat the last dorsal vertebra, the first and the second caudal 1986), China (Buffetaut et al. 2008; Hone et al. 2010), and vertebrae, five incomplete sacral vertebrae found in articu- Japan (Hasegawa et al. 2003). An as-yet-undescribed partial lation, ilia, the right pubis, ischia, and a posterior dorsal rib postcranial skeleton from the Aptian Khok Kruat Formation (Figs. 1, 2. 3 and 4) (See ESM, for a complete description of of Thailand has also been referred to Spinosauridae (Milner the bones). et al. 2007; Brusatte et al. 2010). Our recent excavations in the Early Cretaceous “Grès supérieur” Formation of the Horizon and localit Ban Kalum, Tang Vay area, Savanna- Savannakhet Basin of southern Laos recovered the skeleton khet Province, Laos; “Grès supérieurs” Formation; Early of a new unquestionable spinosaurid that exhibits an ex- Cretaceous (Hoffet 1937;Allainetal.1997, 1999). The traordinary dorsosacral sail. The presently known postcra- “Grès supérieurs” Formation is considered here the lateral nial material was found in close association within a layer of equivalent of the Khok Kruat and Phu Pan formations in red sandstone, on a surface area of less than 2 m2. Pending neighbouring Thailand and is probably late Barremian to further excavations, a preliminary account of the postcranial early Cenomanian in age (Buffetaut 1991; Allain et al. 1999; skeleton of this new spinosaurid is described here. Sha 2007; Racey and Goodall 2009). The non-marine Cre- Dinosaurs from Southeast Asia have been known since taceous bivalve Trigonioides kobayashi–Plicatounio suzuki the 1930s based on the work of the French geologist J. H. assemblage (Hoffet 1937) which is the only known assem- Hoffet in the Savannakhet Basin, in Laos (Hoffet 1942; blage recovered in Tang Vay area suggests that Ichthyove- Hoffet 1944; Taquet 1994). It was not until the 1980s that nator is Aptian in age (Allain et al. 1999;Sha2007). joint Thai–French projects led to new discoveries of verte- brate assemblages from various formations of the western Diagnosis A baryonychine spinosaurid with the following part of the Khorat Plateau in Thailand (e.g., Ingavat et al. autapomorphies: a dorsosacral sinusoidal sail (Figs. 2 and 1978; Buffetaut et al. 2009). In 1991, a French–Lao team 6); penultimate dorsal neural spine is 410 % of centrum resumed research in the “Couches Rouges” from the Early length with anterodistal finger-like process (Fig. 1); fan- Cretaceous Savannakhet Basin of Laos. Since then, skeletal shaped sacral neural spines 3 and 4; transverse processes remains and tracks of sauropod, theropod and ornithischian of first caudal vertebra with sigmoid profile in dorsal view; dinosaurs, as well as turtles, bivalve, and plant fossils have deep prezygapophyseal centrodiapophyseal fossae the first been collected from the Tang Vay area (Plate 1A–B) (Taquet caudal vertebra (Fig. 3); long iliac blade with ilium/pubis et al. 1995; Allain et al. 1997, 1999; de Broin 2004). Among length ratio highest than in any other theropods. Moreover, them are the type specimens of the basal titanosauriform I. laosensis is characterized by some features unknown in sauropod dinosaur Tangvayosaurus hoffeti (Allain et al. other tetanuran theropods: posterior dorsal ribs articulated 1999) and the turtle Shachemys laosiana (de Broin 2004). with sternal complex (ESM); proximal pubic plate with Further locality information is given in the electronic sup- obturator and pubic notches (Fig. 4); large ischial plate with plementary material (ESM). ischial foramen; and mediolaterally flattened ischial shaft. Systematic palaeontology Description Dinosauria Owen 1842 Theropoda Marsh 1881 The 12th dorsal vertebra is one of the most unusual dorsal Tetanurae Gauthier 1986 vertebrae known in theropods except for those of the lost holotype of Spinosaurus aegyptiacus (Fig. 1). The amphi- Spinosauridae Stromer 1915 coelous centrum is slightly longer than high, but wider than Baryonychinae Charig and Milner 1986 long. The neural arch is characterized by the presence of Ichthyovenator laosensis gen et sp nov. accessory centrodiapophyseal laminae and a set of faint ridges that joins the base of the transverse processes to the Etymology The generic name is derived from ichthos (an- neural spine. The hypertrophied neural spine is neither in- cient Greek word for fish), and from venator (Latin word for clined anteriorly nor posteriorly, as in Spinosaurus (Stromer Naturwissenschaften Fig. 1 Twelfth dorsal vertebra (BK 10-01) of I. laosensis. a Lateral posterior centrodiapopyseal lamina, pisl distal extent of the posterior view. b Posterior view. c Anterior view. d Dorsal view. e Detailed interspinous ligament scar, podl postzygodiapophiseal lamina, poz lateral view (with the distal part of the neural spine removed). aisl postzygapophysis, pp parapophyses, ppdl parapodiapophyseal lamina, distal extent of the anterior interspinous ligament scar, al accesory prdl prezygodiapophyseal lamina, prpl prezygoparapophyseal lamina, lamina,
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