Leptorhynchos sp.

Funston, Gregory F., Currie, Philip J. & Burns, Michael E., 2016, New elmisaurine specimens from North America and their relationship to the Mongolian Elmisaurus rarus, Acta Palaeontologica Polonica 61 (1), pp. 159-173 : 169

Leptorhynchos sp.

Fig. 10

Material.—RSM P2600.1, partial skeleton including? scapula, partial proximal tibia, distal end of left tibia, proximal end of fibula, right astragalocalcaneum, partial left astragalocalcaneum, distal end of metatarsal II, and distal end of metatarsal III. Frenchman Formation (Maastrichtian), Chambery Coulee, Frenchman River Valley, Saskatchewan, Description.—The Frenchman Formation material is referable to elmisaurines and is likely congeneric with Leptorhynchos elegans . The partial skeleton (RSM P2600.1) is composed mostly of hindlimb elements, including the distal end of a left tibia and some of the metatarsals ( Fig. 10 ). The distal end of the tibia is similar in shape to Leptorhynchos elegans from Alberta, but is relatively wider where it contacts the astragalus and calcaneum, which are fused. The astragalocalcaneum lacks a horizontal groove distal to the ascending process and extends far onto the posterior surface of the tibia ( Fig. 10A 2 , A 4 ). The distal condyle of metatarsal II faces ventromedially, and there is a rugosity for M. tibialis cranialis proximal to the condyle. The shaft of metatarsal III is broader transversely than the distal condyle and is anteriorly concave. The posterior surface has two cruciate ridges, as in Leptorhynchos elegans and Elmisaurus rarus . The facets for the contacts with metatarsals II and IV appear asymmetrical, as in other elmisaurines, and suggest a closer association between metatarsals II and III than metatarsals II and IV. The distal condyle is as mediolaterally wide as it is anteroposteriorly deep, whereas in Leptorhynchos elegans from Alberta, it is deeper than wide.

Metatarsal II (RSM P2161.1) from the left foot was recovered from Grasslands National Park in Saskatchewan. The proximal end has a flat posterior surface for the contact with distal tarsal III, which does not appear to have coossified in this individual. The proximal end lacks the posterior process of Caenagnathus collinsi , and is nearly identical in shape to Leptorhynchos elegans (TMP 1982.016.0006). The shaft, however, is straight and not deflected medially at its distal end, unlike Leptorhynchos elegans . There is a large posteromedial ridge on the shaft, as in Leptorhynchos elegans and Elmisaurus rarus .

Figures

Fig. 10. Elmisaurine dinosaur Leptorhynchos sp. from Upper Maastrichtian Frenchman Formation, Saskatchewan, Canada. A. RSM P2600.1, distal portion of left tibia and astragalocalcaneum in posterior (A1), lateral (A2), and medial (A3) views; distal portion of right second metatarsal in anterior (A4) and posterior (A5) views; distal portion of third metatarsal in anterior (A6), posterior (A7), and distal (A8) views. B. RSM P2161.1, left second metatarsal in anterior (B1), medial (B2), posterior (B3), lateral (B4), distal (B5), and proximal (B6) views.

Fig. 2. Cross section demonstrating the deep plantar concavity of the tarsometatarsus of elmisaurine dinosaur Leptorhynchos elegans (Parks, 1933) (ROM 781) from the Upper Campanian Dinosaur Park Formation, Dinosaur Provincial Park, Alberta, Canada.

Fig. 4. Posterior surface of metatarsal III in elmisaurine dinosaurs. A. Leptorhynchos elegans (Parks, 1933) (TMP 1986.036.0186) from Upper Campanian Dinosaur Park Formation, Dinosaur Provincial Park, Alberta, Canada. B. Chirosenotes pergracilis Gilmore, 1924 (TMP 1979.020.0001) from Upper Campanian Dinosaur Park Formation, Dinosaur Provincial Park, Alberta, Canada. C. Ingenia yanshini Barsbold, 1981 (MPC-D 102/011), provenance unknown: confiscated specimen. Photographs (A1–C1), annotated photographs (A2–C2), black lines indicate longitudinal ridges; arrow indicates cruciate ridge feature of Leptorhynchos elegans.