Pectinodon bakkeri, Carpenter, 1982

Carpenter, Kenneth, 1982, Baby dinosaurs from the Late Cretaceous Lance and Hell Creek formations and a description of a new species of theropod, Contributions to Geology, University of Wyoming 20, pp. 123-134 : 129-130

Pectinodon bakkeri new species

Fig. 3 a-c

Synonymy: Saurornithoides sp. Estes, 1964 (in part).

Diagnosis: As for genus.

Material: Holotype tooth, UCM 38445 (UCMP- V 5711) H 6.2 mm, W 3.7 mm. Paratype teeth: UCM 38446 (UCMP-V 5711) H 1.8 mm, W 2 mm; UCMP 73098 (UCMP-V 5815) H 2.8 mm, W 1.8 mm; and UCMP 125239 (UCMP-V 5815) H 3.2 mm. W 2.5 mm. Referred teeth (all adults and all from UCMP-V5620): UCMP 125240 - 125247 .

Distribution: Apparently restricted to Lance Formation of eastern Wyoming. Holotype from UCMP- V 5711, Bushy Tailed Blowout, Sl/z, sec. 20, T 37 N., R. 64 W., Niobrara County.

Etymology: Specific name in honor of Dr. Robert T Bakker, who has contributed considerably to the study of dinosaurs.

Discussion: The large holotype tooth ( Fig. 3 a ) is not from a juvenile. The paratypes ( figs. 3 b, c ), however, are small and probably are from babies. Estes (1964) referred teeth with large posterior denticulations to Saurornithoides sp., but later noted that this identification was incorrect (personal communication). Reexamination of Estes’ material revealed the presence of three different kinds of small theropod teeth. One group has large posterior serrations and are clearly referable to Pectinodon bakkeri (e. g., Estes, 1964, Fig. 69 a). Another group of teeth has smaller posterior serrations which are directed obliquely upward. The tip of the crown is oblique to the vertical axis of the tooth, but does not project posteriorly as in Pectinodon ; the crown has a piercing tip. The first serration is significantly smaller than the crown tip. There may be poorly developed serrations on the anterior edge or a sharp translucent keel. These teeth are similar to those in the dentary of Saurornithoides ínequalis (ROM 1445) previously referred to Troodon formosus by Russell (1948), and to Saurornithoides junior by Barsbold (1974). This group of teeth from the Lance Formation is referred to S. inequalis . The third group of teeth has well developed serrations on the anterior and posterior margins; however, these serrations are smaller than those in Pectinodon or Saurornithoides . As in Saurornithoides , the crown tip functions in piercing. Furthermore, the first serration is significantly smaller than the crown tip. In many respects, these teeth resemble those of Velociraptor mongoııensıs (e. g.-, AMNH 6515 ), except that the anterior serrations are not significantly smaller than the posterior serrations.

Pectinodon bakkeri is provisionally placed in the family Saurornithoididae because the crowns are strongly compressed laterally and serrations are well developed only on the posterior edge.

Figures

Figures 1-11. Fig. 1, Dromaeosauridae, tooth, UCM 39502. Fig. 2a-h, Sauromithoides inequalis: 20,, buccal view of hatchling left dentary, UCM 41666; c, lingual view; e, dorsal view; b, buccal view of left dentary, NMC 8540 (cast); d, lingual view; f, dorsal view; g, lateral view of hatchling basioccipital, UCM 43218; and h, ventral view. Fig. 3a-c, teeth of Pectinodon bakkeri: a, holotype, UCM 38445; b, paratype, UCM 38446; and c, paratype, UCMP 73098. Fig. 4, Pararıychodon lacustris, tooth, UCMP 124990. Fig. 5a, b, Tyrannosauridae: a as lateral view of UCMP 119853; and b, posterior view. Fig. 6, Theropoda, tooth, UCMP 124987. Fig. 7a, b, tooth of Aublysodon mirandus: a! lateral view of UCMP 124406; and b, posterior view. Fig. 8, Thescelosaurus sp., tooth, UCMP 124973. Fig. 9, Hadrosauridae, tooth, UCM 45060. Fig. 10, Ceratopsidae, tooth, UCM 45057. Fig. 11, Ankylosaurus magniventris, tooth, UCMP 124399. Heavy bars to left of specimens = 2 mm.