Pterodactyloidea

Haluza, Alejandro & Canale, Juan I., 2013, A Partial Pterosaur Ulna From The Candeleros Formation (Neuquén Group), Late Cretaceous Of Argentina, Historia Natural 3 (1), pp. 5-12 : 1

Pterodactyloidea Plieninger, 1901

Genus and species indeterminate

Referred material. MMCH-Pv 53 , proximal part of a left ulna .

Locality and horizon. The material was collected at Cabo Alarcón (S 39º 24´16,4” - W 68º 58´27,6”) between Villa El Chocón and Picún Leufú ( Fig. 1 ), from the lower levels of the Candeleros Formation (Early Cenomanian), Neuquén Group ( Garrido, 2010).

DESCRIPTION AND COMPARISONS

The ulna is anteroposteriorly crushed and deformed, mainly in the proximal end, and the distal portion of the bone is lost ( Figure 2 ). The bone is thin-walled (about 1 mm thick) as seen in all other pterosaurs. In anterior view the dorsal margin is straight, and the ventral margin is concave due to a ventral expansion of the proximal end. Below this expansion there is a prominence, the tuberculum musculi bicipitis (TMB), which is more ventrally displaced than in the ulna of Santanadactylus pricei (AMNH 22552: Wellnhofer, 1985, 1991a; Kellner and Tomida, 2000; BSP 1980 I 122: Wellnhofer, 1985). A small pneumatic foramen is present proximal to the TMB of the abovementioned species, but the preservation of MMCH-Pv 53 does not allow observation of this foramen. The preserved portion of the shaft shows in its anterior face two longitudinal low ridges that suggest the contact area with the radius ( Figure 2 B, G ). In proximal view there are two concave, anteroproximally facing articular surfaces: a dorsal one, the capitular cotyle (sensu Bennett, 2001), and the ventrally located trochlear cotyle (sensu Bennett, 2001), separated by a sharp prominence. Posterior to this small prominence is a dorsoventrally elongated depression. The posterior margin of the proximal end shows an overhanging rounded and dorsoventrally elongated prominence, the olecranon process: that corresponds to the insertion area for the M. triceps brachii ( Figure 2 A, F ). Dorsal to this prominence is a wide, posteriorly orientated depression, also present in BSP 1982 I 93 ( Wellnhofer, 1985).

Figures

Figure 1. Map of Argentina showing the Cabo AlarcÓn fossil locality. The black arrow indicates the fossil site.

Figure 2 - MMCH-Pv 53 Pterosaur proximal ulna found at Cabo AlarcÓn in A,F, proximal, B,G, anterior, C,H, dorsal, D,I, posterior, and E,J, ventral views. Abbreviations: csr: contact surface with radius; cc: capitular cotyle; tc: trochlear cotyle; ol: olecranon; pd: posterior depression; tmb: tuberculum musculi bicipitis.