Siamosaurus

Siamosaurus (meaning "Siam lizard") is a potentially dubious genus of spinosaurid dinosaur that lived in what is now Thailand and possibly China during the Early Cretaceous period (Barremian to Aptian) and is the first reported spinosaurid from Asia. It is confidently known only from tooth fossils; the first were found in the Sao Khua Formation, with more teeth later recovered from the younger Khok Kruat Formation. The only species Siamosaurus suteethorni, whose name honours Thai palaeontologist Varavudh Suteethorn, was formally described in 1986. In 2009, four teeth from China previously attributed to a pliosaur—under the species '"Sinopliosaurus" fusuiensis'''—were identified as those of a spinosaurid, possibly Siamosaurus. It is yet to be determined if two partial spinosaurid skeletons from Thailand and an isolated tooth from Japan also belong to Siamosaurus.

Since it is based only on teeth, Siamosaurus body size is uncertain, though it has been estimated at between in length. The holotype tooth is long. Siamosauruss teeth were straight, oval to circular in cross-section, and lined with distinct lengthwise grooves. Its teeth had wrinkled enamel, similar to teeth from the related genus Baryonyx. As a spinosaur it would have had a long, low snout and robust forelimbs, and one possible skeleton indicates the presence of a tall sail running down its back, another typical trait of this theropod family. Siamosaurus is considered by some palaeontologists to be a dubious name, with some arguing that its teeth are hard to differentiate from those of other Early Cretaceous spinosaurids, and others that it may not be a dinosaur at all. Based on dental traits, Siamosaurus and "S." fusuiensis have been placed in the subfamily Spinosaurinae.