Taxonomic Status Of Stephanosaurus

[DD1991]

Has anybody figured out the exact systematic placement of Stephanosaurus marginatus? As far as I can recall, the holotype of S. marginatus (CMN 419) consists of bones of the forelimb and the foot as well as fragments of neck vertebrae, teeth, and ribs (disassociated bones cataloged under CMN 419 [including a theropod ischium] were provisionally referred to T. marginatus by Lambe 1902, but were later referred to Lambeosaurus by Gilmore 1924). The two editions of the Dinosauria list Stephanosaurus and its type species as a nomen dubium (probably based on the assessment of Stephanosaurus as gen. et. sp. indet. in Brett-Surman's 1989 thesis), but without comment. As pointed out by Gilmore (1924), Stephanosaurus differs from Gryposaurus notabilis only in that the humerus and radius are almost equally proportional to each other in length (ratio of humerus length to radius length in Stephanosaurus 1:0.953 versus 1:0.881 in Gryposaurus notabilis) and the radius and ulna are larger than those of Gryposaurus. Since mid-late Campanian of Montana and Canada is starting to become crowded with saurolophines belonging to different tribes (Brachylophosaurini, Kritosaurini, Saurolophini) and no edmontosaurins have been found in the Dinosaur Park Formation yet, I'd be curious to see if Stephanosaurus could be its own thing or not.

[Regg Cato]

Last I understood it's still considered a junior synonym of Lambeosaurus. The original description (a short 9-page paper which also describes Gorgosaurus libratus) illustrates the skull of S. marginatus, which almost certainly belongs to Lambeosaurus.

Edited August 30, 2013 by Regg Cato

[DD1991]

Last I understood it's still considered a junior synonym of Lambeosaurus. The original description (a short 9-page paper which also describes Gorgosaurus libratus) illustrates the skull of S. marginatus, which almost certainly belongs to Lambeosaurus.

Hi,

The synonymy of Stephanosaurus with Lambeosaurus in some books is due to the fact that the type specimen of Lambeosaurus lambei was thought by Lambe to be the same animal as the type species of Stephanosaurus, Trachodon marginatus, since Lambe believed that the teeth included in CMN 419 were similar to those of Lambeosaurus for CMN 2869 to be considered conspecific with CMN 419. Therefore, Stephanosaurus should not be used in synonymy lists for Lambeosaurus, though you didn't answer my question as to whether CMN 419 is saurolophine or lambeosaurine.

[Regg Cato]

Hi,

The synonymy of Stephanosaurus with Lambeosaurus in some books is due to the fact that the type specimen of Lambeosaurus lambei was thought by Lambe to be the same animal as the type species of Stephanosaurus, Trachodon marginatus, since Lambe believed that the teeth included in CMN 419 were similar to those of Lambeosaurus for CMN 2869 to be considered conspecific with CMN 419. Therefore, Stephanosaurus should not be used in synonymy lists for Lambeosaurus, though you didn't answer my question as to whether CMN 419 is saurolophine or lambeosaurine.

Right; Gilmore (1924) and Russell (1930) synonymized it with Gryposaurus, while other authors considered it a synonym of Lambeosaurus.

Given the material (and the fact that, as you said, CMN 2869 is not Stephanosaurus), I think at this point the conservative view would be to consider Stephanosaurus as a nomen dubium. I haven't personally seen CMN 419, so I can't comment on its subfamilial assignment.