[D] Osmakasaurus depressus [sG] [T]
Cretaceous Early Barremian Aptian
Ornithischia Ornithopoda Iguanodontia Camptosauridae
Chilson Member, Buffalo Gap, Lakota Formation, South Dakota, US
Osmakasaurus depressus (McDonald 2011) > Planicoxa depressus (Carpenter and Wilson,Y. 2008) >> Camptosaurus depressus (Gilmore, 1909)
The generic name is derived from ósmaka, which means “canyon” in the language of the Lakota People, in reference to the name of the type locality in western South Dakota, an area inhabited by the Lakota. Saurus comes from the transliterated Greek meaning “lizard”. The gender of the generic name is masculine.
Locality and horizon
Calico Canyon, near Buffalo Gap, Custer County, South Dakota (Gilmore 1909); Lakota Formation, Barremian–Aptian (Tschudy et al. 1984).
Basal styracosternan distinguished from all other iguanodontians by the following unique combination of characters: cranial end of preacetabular process of ilium modified into horizontal boot, straight dorsal margin of ilium, dorsal margin of ilium thickens mediolaterally towards the M. iliocaudalis platform.
Camptosaurus depressus was originally distinguished from other species of Camptosaurus chiefly by the “narrowness or depressed nature of the ilia” (Gilmore 1909:293). This condition is exhibited by only the left ilium of USNM 4753, on which the dorsal margin of the ilium above the acetabulum faces dorsolaterally and the postacetabular process is nearly horizontal (Fig. 8A). Carpenter & Wilson (2008) considered the horizontal postacetabular process of USNM 4753 similar to that of DMNH 42504, the holotype ilium of Planicoxa venenica (DiCroce & Carpenter 2001); thus, they referred C. depressus to Planicoxa, as P. depressa. However, the horizontal postacetabular process of USNM 4753 is more likely a product of distortion.
Carpenter & Ishida (2010) Early and “Middle” Cretaceous Iguanodonts in Time and Space Journal of Iberian Geology 36 (2) 145-164
Buffalo Gap, South Dakota, USA
Valanginian (Sohn, 1979; Dahlstrom and Fox, 1995.
Originally named Camptosaurus depressus by Gilmore (1909) for the depressed nature of the ilium, it was reassigned to the genus Planicoxa by Carpenter and Wilson (2008). The short, truncated postacetabular process is folded laterally to a horizontal position that is characteristic of the genus. It differs however, from Planicoxa venenica in straighter dorsal margin, proportionally shorter (less than 50%) and more robust preacetabular blade relative to ilium length, shallower acetabular notch, and proportionally narrower brevis shelf relative to ilium length. The ischial peduncle is expanded onto the lateral surface.