Hadrosaurus paucidens Marsh, 1889

Prieto-Márquez, Albert, Weishampel, David B. & Horner, John R., 2006, The dinosaur Hadrosaurus foulkii, from the Campanian of the East Coast of North America, with a reevaluation of the genus, Acta Palaeontologica Polonica 51 (1), pp. 77-98 : 93-94

Hadrosaurus paucidens Marsh, 1889 .

Holotype: USNM 5457 , a nearly complete left squamosal and right maxilla.

Type locality: As indicated by Ostrom (1964), USNM 5457 came from the Dog Creek locality, “about a quarter mile east of the freight road from Judith to Maiden, about 12 miles southeast of Judith, Fergus County, Montana ”.

Type horizon: Judith River Formation, Upper Cretaceous (Campanian). Comments.—This species was first described by Marsh (1889), who later assigned it to a ceratopsian dinosaur ( Marsh 1890). More recently, Ostrom (1964) referred USNM 5457 to Lambeosaurus on the basis of the erect and high squamosal and the similar morphology of both the maxilla and the squamosal to those of L. lambei . Likewise, Ostrom (1964) erected L. paucidens for USNM 5457. We did not have the opportunity to examine USNM 5457, but we could make comparisons between the illustrations in Ostrom’s 1964 paper and first hand examination of other hadrosaurids. The maxilla is typically lambeosaurine in structure, with a sloping rostral shelf, but otherwise does not lend itself to a lower level diagnosis of USNM 5457. Whereas it is true that in both USNM 5457 and L. lambei CMN 2869 the squamosal is remarkably high, this condition is variable among and within lambeosaurine taxa. Thus, for example, the skull of another L. lambei (ROM 1218) does not have a squamosal that is higher than in other lambeosaurines and is comparable in this regard to the squamosal of C. casuarius (e.g., CMN 8676), P. tubicen (e.g., PMU R222), H. altispinus (e.g., CMN 8501), and H. stebingeri (e.g., MOR 548). On the other hand, there are taxa such as Amurosaurus riabinini Bolotsky and Kurzanov, 1991 ( Godefroit et al. 2004) in which some specimens whose squamosal is as high as that in USNM 5457. Therefore, we reject the great height and erect form of the USNM 5457 squamosal as a character for referring this specimen to Lambeosaurus . Additionally, there are remarkable differences between USNM 5457 and L. lambei that make these two forms less similar than pointed out by Ostrom (1964). Thus, the dorsal border of the infratemporal fenestra in USNM 5457 is much wider than in L. lambei , but comparable to the breadth seen in the other lambeosaurines mentioned above. The quadrate cotylus is about 35% narrower in USNM 5457 than in L. lambei (e.g., CMN 2869) and the other lambeosaurines mentioned above. For a detailed osteology of USNM 5457 the reader is referred to Ostrom (1964).

Conclusion: USNM 5457 lacks characters to distinguish L. paucidens from Lambeosaurus species and other Lambeosaurinae. Thus, it is more appropriate to consider USNM 5457 a Lambeosaurinae indeterminate.