[D] Ichthyovenator laosensis [Sa][sG][T]
Allain, Xaisanavong, Richir, Khentavong 2012
Cretaceous Early Aptian
Saurischia Theropoda Tetanurae Spinosauroidae Spinosauridae
Grès supérieurs Formation, Ban Kalum, Tang Vay area, Savannakhet Province, Laos
Spinosaurids are among the largest and most specialized carnivorous dinosaurs. The morphology of their crocodile-like skull, stomach contents, and oxygen isotopic composition of the bones suggest they had a predominantly piscivorous diet. Even if close relationships between spinosaurids and Middle Jurassic megalosaurs seem well established, very little is known about the transition from a generalized large basal tetanuran to the specialized morphology of spinosaurids. Spinosaurid remains were previously known from the Early to Late Cretaceous of North Africa, Europe, and South America. Here, we report the discovery of a new spinosaurid theropod from the late Early Cretaceous Savannakhet Basin in Laos, which is distinguished by an autapomorphic sinusoidal dorsosacral sail. This new taxon, Ichthyovenator laosensis gen. et sp. nov., includes well-preserved and partially articulated postcranial remains. Although possible spinosaurid teeth have been reported from various Early Cretaceous localities in Asia, the new taxon I. laosensis is the first definite record of Spinosauridae from Asia. Cladistic analysis identifies Ichthyovenator as a member of the sub-clade Baryonychinae and suggests a widespread distribution of this clade at the end of the Early Cretaceous. Chilantaisaurus tashouikensis from the Cretaceous of Inner Mongolia, and an ungual phalanx from the Upper Jurassic of Colorado are also referred to spinosaurids, extending both the stratigraphical and geographical range of this clade.
The generic name is derived from ichthos (ancient Greek word for fish), and from venator (Latin word for “hunter”). The generic name is in reference to the predominantly piscivorous diet of Spinosauridae. The specific name is derived from the name Laos.
Partially articulated skeleton, curated at the Dinosaur Museum, Savannakhet (MDS BK10-01 to 15), including the antepenultimate dorsal vertebra, the neural spine of
the last dorsal vertebra, the first and the second caudal vertebrae, five incomplete sacral vertebrae found in articulation, ilia, the right pubis, ischia, and a posterior dorsal rib (Figs. 1, 2. 3 and 4) (See ESM, for a complete description of the bones).
Horizon and locality
Ban Kalum, Tang Vay area, Savannakhet Province, Laos; Grès supérieurs Formation; Early Cretaceous (Hoffet 1937; Allain et al. 1997, 1999). The Grès supérieurs Formation is considered here the lateral equivalent of the Khok Kruat and Phu Pan formations in neighbouring Thailand and is probably late Barremian to
early Cenomanian in age (Buffetaut 1991; Allain et al. 1999;Sha 2007; Racey and Goodall 2009). The non-marine Cretaceous bivalve Trigonioides kobayashi–Plicatounio suzuki assemblage (Hoffet 1937) which is the only known assemblagerecovered in Tang Vay area suggests that Ichthyovenator is Aptian in age (Allain et al. 1999; Sha 2007).
A baryonychine spinosaurid with the following autapomorphies: a dorsosacral sinusoidal sail; penultimate dorsal neural spine is 410 % of centrum length with anterodistal finger-like process; fanshaped sacral neural spines 3 and 4; transverse processes of first caudal vertebra with sigmoid profile in dorsal view; deep prezygapophyseal centrodiapophyseal fossae the first caudal vertebra; long iliac blade with ilium/pubis length ratio highest than in any other theropods. Moreover, I. laosensis is characterized by some features unknown inother tetanuran theropods: posterior dorsal ribs articulated with sternal complex (ESM); proximal pubic plate with obturator and pubic notches; large ischial plate with ischial foramen; and mediolaterally flattened ischial shaft.