254 FIGURE 1. Saurornitholestes <strong>robustus</strong>, n. <strong>sp</strong>. SMP VP-1955 (holotype), nearly complete left frontal, from SMP loc. # 388, De-na-zin Member, Kirtland Formation. A, dorsal view (stereo pair); B, ventral view (stereo pair); C, orbital rim (lateral view) (dorsal direction is to the right); D, medial view of midline sutural surface (dorsal direction is to the left). Bar scale = 10 mm.
FIGURE 2. Cf. Saurornitholestes <strong>robustus</strong>, n. <strong>sp</strong>. SMP VP-1901 (referred <strong>sp</strong>ecimen), islolated tooth, from SMP loc. # 350, De-na-zin Member, Kirtland Formation. Bar Scale = 5 mm. Median suture thickness is 8 mm, measured at the confluence of the posterior margin of the olfactory bulb and the anterior margin of the cerebral hemi<strong>sp</strong>here impression. The maximum thickness of the frontal is where the posterior border descends ventrally. Here, the frontal measures 10 mm thick, and is more than twice the thickness of the holotype (TMP 74.10.5) in this region. The median suture surface is very rugose. The lateral surface of the orbital wall is weathered. No foramina are visible, due to the condition of the lateral surface. Comments— The massive nature of the holotype frontal (SMP VP- 1955) clearly distinguishes it from the holotype of Saurornithololestes langstoni (TMP 74.10.5), leaving little doubt as to its <strong>sp</strong>ecific distinctiveness. The ratio of the length (measured along the midline) to the thickness (posterior part of the frontal) is 6:1 for S. <strong>robustus</strong> and 10:1 for S. langstoni. Moreover, the holotype of S. <strong>robustus</strong> differs from referred <strong>sp</strong>ecimens of Velociraptor mongoliensis (Barsbold and Osmólska, 1999), although they share a number of features (i.e., length/width ratio; shallow depression along mid-length of frontal; strong frontal nasal contact; lacrimal overlapping the frontal dorsally, etc.), which are herein considered characters of velociraptorines in general. Thus, there are sufficient reasons to retain both Saurornitholestes and Velociraptor as distinct genera. The frontal, once attributed to the <strong>sp</strong>ecies S. langstoni, has all the morphological attributes of the genus. These include: 1) triangular shape; 2) posteroventral projection of the frontoparietal contact; 3) sigmoidally curved ridge running anterolaterally onto the frontal margin of the postorbital process; and 4) posterior concavity around the supratemporal fossae (Sues, 1978; Currie, 1987; <strong>Sullivan</strong> and Lucas, 2000). The <strong>sp</strong>ecific difference is the massive thickness of the frontal and somewhat larger size. Cf. Saurornitholestes <strong>robustus</strong> Material— SMP VP-1901, tooth (Fig. 2), SMP loc #350; and SMP VP-1741, left second pedal ungual (Fig. 3), SMP loc. #361. Both <strong>sp</strong>ecimens were collected from the De-na-zin Member, Kirtland Formation, San Juan Basin, New Mexico Comments— The tooth (SMP VP-1901) is nearly complete and is characteristically laterally compressed and strongly recurved. It has a FABL (fore-aft basal length) of 6.5 mm. The height of the tooth is 12 mm, mea- 255 FIGURE 3. Cf. Saurornitholestes <strong>robustus</strong>, n. <strong>sp</strong>. SMP VP-1741 (referred <strong>sp</strong>ecimen), left pes ungual (digit II), from SMP loc. # 361, De-na-zin Member, Kirtland Formation. A, medial view; B, lateral view. Bar Scale = 10 mm. sured from the base to the tip of the crown along the posterior carina; 15 mm along the anterior carina. Denticles are present along both the anterior and posterior carinae, and they are slightly hooked toward the tip. Some of the denticles are damaged, e<strong>sp</strong>ecially along the anterior edge towards the base. The enamel veneer is largely missing, with only remnants adhering to the tooth in the vicinity of the denticles on both the anterior and posterior carinae. Although somewhat larger than most Saurornitholetes teeth, this tooth cannot be distinguished from those of Saurornitholestes (S. langstoni) as illustrated by Currie et al. (1990), Sankey et al. (2002) and Brinkman (2005). The second pedal ungual (SMP VP-1741) is incomplete both proximally and distally, making it difficult to accurately determine its total size. However, it measures 69 mm along the preserved outside curvature. It is laterally compressed and possesses a prominent lateral groove on each side. This groove is situated slightly higher on the left lateral side compared to the right side, thus it is from the left pes (Kirtland et al., 1993; Rahut and Werner, 1995; Norell and Makovicky, 1997). The pedal ungual is deeper than that of Velociraptor mongoliensis (IGM 100/985) described and illustrated by Norell and Makovicky (1997, fig. 6). DISCUSSION This is the second frontal of Saurornitholestes known from the San Juan Basin, New Mexico, and arguably it is the most important, as it documents features that serve to distinguish it from its presumed predecessor Saurornitholestes langstoni. The previous report of Saurornitholestes from the Kirtland Formation was also based on a left frontal from the San Juan Basin (<strong>Sullivan</strong> and Lucas, 2000). However, this <strong>sp</strong>ecimen (SMP VP-1270) was smaller, slightly water-worn, and in some re<strong>sp</strong>ects, similar to the holotype of S. langstoni. At the time of its report, some minor differences were noted, but these were relegated to individual variation (<strong>Sullivan</strong> and Lucas, 2000). A re-evaluation of SMP VP-1270, compared to the holotype of S. langstoni (TMP 74.10.5), which are the same size, shows it to be more like the holotype of S. <strong>robustus</strong> in having a thicker frontal. A single tooth (SMP VP-1901) and a left second pedal ungual (SMP VP-1714) are both from the De-na-zin Member of the Kirtland Formation and clearly pertain to Saurornitholestes (Figs. 2, 3). They are provisionally referred to S.
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