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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.
Siamosaurus specimens tended to have the largest difference from the ratios of other theropods, and Spinosaurus tended to have the least difference. The authors concluded that spinosaurids, like modern crocodilians and hippopotamuses, spent much of their daily lives in water.
[5] [22] More fragmentary spinosaurids such as Siamosaurus and "Sinopliosaurus" fusuiensis are based only on teeth, making them difficult to separate from other taxa. The habit of naming theropods from isolated teeth or tooth fragments has resulted in many invalid and synonymous genera; it has also occurred with spinosaurids and is compounded ...
Spinosaurus is known to have eaten fish and small to medium terrestrial prey as well. [5] Evidence suggests that it was semiaquatic; how capable it was of swimming has been strongly contested. Spinosaurus's leg bones had osteosclerosis (high bone density), allowing for better buoyancy control.
Though prior spinosaurids had been named from the continent—including Siamosaurus from Thailand's Barremian Sao Khua Formation and "Sinopliosaurus" fusuiensis from China's Aptian Xinlong Formation—the authors noted that palaeontologists have debated the validity of these taxa because they are only confidently known from isolated teeth.
Irritator is further distinguished from Baryonyx, Suchomimus, and Cristatusaurus by having slightly over half as many teeth in the maxilla, and from Spinosaurus due to its comparatively larger and more forwardly positioned nostril openings, which, unlike in Spinosaurus, are also formed by the premaxilla.
Spinosaurus teeth, like those of typical theropods, were usually smooth, and Asian forms like Siamosaurus exhibited an increase in the amount of dental ridges. Furthermore, the tooth crown was wrinkled in Ostafrikasaurus , Baryonyx , and Suchomimus , and Asian spinosaurids, but smooth in Spinosaurus , with only some specimens of the latter ...
They used the clade name Megalosauria (Bonaparte, 1850) in their analysis and defined it as the node comprising Megalosaurus, Spinosaurus, their most recent common ancestor, and all its descendants. Furthermore, a new megalosauroid family Piatnitzkysauridae was named to include all megalosauroids more closely related to Piatnitzkysaurus than to ...