Sankey, J.T. and S. Baszio, eds. 2008. Vertebrate Microfossil Assemblages: Their Role in Paleoecology and Paleobiogeography. Indiana University Press.

Diversity of Latest Cretaceous (Late Maastrichtian) Small Theropods and Birds: Teeth from the

Lance and Hell Creek Formations

Julia T. Sankey

Department of Physics and Geology, California State University, Stanislaus, Turlock, California

95382. Julia@geology.csustan.edu

1. Abstract

Late Maastrichtian (latest Cretaceous) small theropod dinosaur and bird diversity has

been difficult to determine because of scarcity or skeletal remains. Numerous teeth of small

theropods and birds from the Hell Creek (Montana) and Lance (Wyoming) Formations were

analyzed. Relative abundances are: dromaeosaurids (23%), troodontids (14%), cf.

Richardoestesia isosceles (35%), cf. Paronychodon (20%), and bird (8%). This Maastrichtian

theropod assemblage is different from the late Campanian one from Alberta in three ways: 1) the

abundance (55%) of two unusual small theropods, cf. Richardoestesia isosceles and

Paronychodon; 2) the abundance of teeth, from all taxa, with a flat side and longitudinal ridges;

3) the lower abundance and diversity of dromaeosaurids. The late Maastrichtian had a lower

diversity of small theropods compared to the late Campanian possibly due to competition for

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prey between dromaeosaurids and juvenile tyrannosaurids and climatic and/or climatic and

environmental changes during the latest Cretaceous.

Key Words

Theropod, dinosaur, Maastrichtian, Late Cretaceous, Teeth, Diversity

2. Introduction

2.1. Previous work

The first detailed descriptions of small theropod teeth was done by CURRIE et al. (1990)

based on collections from the late Campanian Judith River Group of Alberta. Identification and

reference of isolated teeth to known taxa was possible due to the existence of jaws with teeth

from some of the small theropods. This work has been used to identify isolated theropod teeth

from Late Cretaceous sites ranging from Texas to Alaska (e.g. ROWE et al. 1992; FIORILLO &

CURRIE 1994; FIORILLO & GANGLOFF 2000; SANKEY 2001).

After CURRIE et al.’s 1990 paper, the numbers of theropod teeth from the Judith River

Group increased, especially because of screen washing by Donald Brinkman and crews from the

Royal Tyrrell Museum of Paleontology. BASZIO (1997a-b) studied this larger sample from the

Judith River Group and also samples from Maastrichtian sites in Alberta. He documented

changes in the relative abundance of small theropods under different paleoclimatic and

paleoenvironmental conditions from the mid-Campanian through the late Maastricthian. SANKEY

et al. (2002) studied an even larger sample (1700+ specimens) of small theropod and bird teeth

from the Judith River Group, described and quantified new morphological groups, and

documented a higher diversity of small theropods and birds than previously recognized.

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2.2 Importance of Microsites

This research project is an excellent example of why microsite studies are important,

especially for particular groups of fossils with sparse fossil records. Prior to this work, late

Maastrichtian (latest Cretaceous) small theropod dinosaur and bird diversity had been difficult to

determine because of the scarcity of skeletal remains. However, due to the extensive collection

of microvertebrate sites, especially through screen-washing, from the Lance Formation of

Wyoming and the Hell Creek Formation of Montana by William Clemens and his students from

the University of California at Berkeley Museum of Paleontology (UCMP), a large collection of

late Maastrichtian small theropod and bird teeth was produced. This paper describes these teeth,

both qualitatively and quantitatively, determines the relative abundance of the major groups of

taxa, compares this to the late Campanian, and estimates the small theropod and bird diversity in

the latest Cretaceous of North America, just prior to the K/T extinctions.

3. Materials and Methods

3.1. Fossil sites

Fossils were collected by the University of California at Berkeley Museum of

Paleontology (UCMP), and resulted from extensive surface collection and screen washing by

William Clemens and his students from microsites in the Lance Formation of Wyoming and the

Hell Creek Formation of Montana. Locality information is on file at the UCMP, and is available

to qualified researchers.

Photographed specimens were coated with vaporized amonium chloride to highlight

surface detail. Tooth measurements are illustrated and described in Figure 1. The dimensions

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measured on each tooth and analyzed are: fore aft basal length (FABL), curvature (Curv), tooth

height (Ht), cross-sectional thickness (CST), denticles per millimeter (dent/mm), and denticle

width (Wd) and height (Ht) (Table 1). The following abbreviations are used: RTMP (Royal

Tyrrell Museum of Paleontology) and UCMP (University of California at Berkeley Museum of

Paleontology).

(((FIGURE 1 NEAR HERE)))

4. Selected Systematic Paleontology

Order Saurischia SEELY 1888

4.1 Family Dromaeosauridae MATTHEW & BROWN 1922

4.1.1 cf. Dromaeosaurus MATTHEW & BROWN 1922

Figures 2.14-2.17

Table 1

Description.

Teeth are long and narrow, slightly recurved, oval in cross section, and have denticles on

both carinae, with larger posterior denticles. Denticles are short and wide, unworn tips are

slightly rounded, and interdenticle spaces are present.

Discussion.

Teeth resemble Dromaeosaurus albertensis from the Judith River Group (SANKEY et al.

2002) in tooth shape, size, and denticle morphology (i.e. denticles larger on posterior carinae,

denticles usually 0.2 mm wide and 0.3 mm high, and unworn tips are slightly rounded to

straight). However, because no UCMP teeth possess a twisted anterior carina, which is a

characteristic of Dromaeosaurus albertensis teeth, these are referred to cf. Dromaeosaurus.

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CURRIE et al. (1990) described the variation of teeth along the tooth row of the type specimen of

Dromaeosaurus albertensis. They noted that premaxillary teeth are smaller and less recurved

than maxillary teeth. UCMP 187037 (Fig. 2.14-2.17) resembles premaxillary teeth from D.

albertensis (SANKEY et al. 2002, fig. 4.5-4.7).

4.1.2 cf. ?Dromaeosaurus – Morphotype A SANKEY et al. 2002

Table 1

Description.

Teeth are long and wide, straight (i.e. not recurved), lingual side is flat, weakly developed

longitudinal ridges on both sides, but especially the convex side, and cross section shape is oval.

Anterior side of tooth tip is worn. Denticles present on posterior carina are minute or absent on

anterior. Denticles short and wide, square-shaped, with straight to rounded tips.

Discussion.

Teeth closely resembles those referred to as ?Dromaeosaurus Morphotype A in SANKEY

et al. (2002; fig. 4.9-13) in shape and size, and in particular in possessing the distinctive

characteristics of one flattened side, longitudinal ridges, anterior tip worn, and in denticle size

and shape. CURRIE et al. (1990) considered teeth with one flat side to be growth abnormalities

and referred them to known taxa based on their denticle morphology. For example, they referred

flat-sided teeth with Dromaeosaurus-like denticles to Paronychodon-like Dromaeosaurus.

However, enough differences were documented in flat-sided teeth that SANKEY et al. (2002)

referred them to ?Dromaeosaurus Morphotype A. These teeth were noted to have the following

distinctive characteristics: one flat tooth surface, longitudinal ridges, distinctive shape (posterior

tooth edge is straight), large size, and long fore-aft basal lengths relative to heights. Support for

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the validity of this grouping came from the following evidence: 1) No teeth of this flat

morphology are present in the type specimen of D. albertensis. 2) Flat morphology teeth have a

stratigraphic distribution through the late Maastrichtian (this paper and BASZIO 1997b, Plate VI,

88), and D. albertensis is restricted to the mid-Campanian. 3) The pattern of wear on these teeth

is different from that of D. albertensis, suggesting that they functioned differently (SANKEY et al.

2002).

(((FIGURE 2 NEAR HERE)))

4.1.3 cf. Saurornitholestes SUES 1978

Figures 2.1-2.13

Table 1

Description.

Tooth shape varies from strongly recurved (Fig. 2.5) to only slightly recurved (Fig. 2.3).

Teeth are flattened (labial-lingually) and are oval in cross section. Denticles are large on the

posterior carinae, and are minute or absent on the anterior. Posterior denticles are long and

slender, and vary in size along the carina (Fig. 2.12). Denticle tips are clearly pointed in unworn

teeth or rounded in outline (Fig. 2.2). Weakly developed longitudinal ridges are present on both

sides of many teeth (Fig. 2.3; 2.10), but not all (Fig. 2.12).

Discussion.

Teeth resemble Saurornitholestes cf. S. langstoni from the Judith River Group in shape,

size, and denticle morphology (SANKEY et al. 2002). However, the UCMP teeth are distinct in

having longitudinal ridges, which are not present in Saurornitholestes from the Judith River

Group. Many of the UCMP teeth are more strongly recurved (e.g. Fig. 2.5) and wider (i.e.

FABL) than those from the Judith River Group. Additionally, in many of the UCMP teeth,

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denticles are wider and less distinctly pointed than in typical Saurornitholestes langstoni teeth

from the Judith River Group (SANKEY et al. 2002). Because of these differences, the UCMP teeth

do not resemble any currently described Saurornitholestes taxa from either the Campanian or

Maastricthian.

(((FIGURE 3 NEAR HERE)))

(((TABLE 1 NEAR HERE)))

4.2 Troodontidae

4.2.1 Genus Troodon LEIDY 1856

Troodon sp.

Figures 3.9-3.12; 3.20-3.21

Table 2

Description.

Teeth are recurved, laterally compressed, and oval in cross-section. Denticles are large

and pointed on the posterior carina. Denticles are minute or absent on the anterior carina.

Discussion.

Troodon jaws and teeth have been described and illustrated by CURRIE et al. (1990),

BASZIO (1997b), RYAN et al. (1998), PENG et al. (2001), and SANKEY et al. (2002). The UCMP

Troodon teeth are different: they are longer and not strongly recurved, and their denticles are

longer and wider. Although the tooth shape is most similar to Saurornitholestes from the Judith

River Group (fig. 4.14-18; SANKEY et al. 2002), the UCMP teeth are clearly referable to Troodon

because of their large and pointed denticles. However, they represent a distinct taxon from the

Campanian ones.

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4.2.2 Troodon sp. Flat Morph.

Figures 3.1-3.8

Table 2

Description.

Teeth are straight, with round cross-sections. One side of the tooth is flattened to concave

and the other side is convex. Well-developed longitudinal ridges are present, often on both sides,

but sometimes only on the flat side. The anterior carina is typically smooth and unserrated, but

can have minute denticles. Denticles on the posterior carina are large, larger than any other

theropod. Denticle tips vary from rounded to pointed in outline. Base of the crown is constricted.

Discussion.

These teeth are similar to the other Troodon sp. teeth in the collection in size, shape, and

denticle morphology. The main differences are the presence of a flat side and the well-developed

longitudinal ridges. Given this similarity, they are considered to be a flat morphology of the

Troodon sp. present in the Maastrichtian and not a separate taxon.

4.2.3 Troodon sp. Large Morph.

Figures 3.13-3.16

Table 2

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Description.

Tooth is large, recurved, and round in cross-section. Large denticles are present on both

carinae. Longitudinal ridges occur on both sides of teeth.

Discussion.

The tooth is easily referred to Troodon based on the tooth shape and large denticles.

However, it is considerably larger than any other Troodon tooth from these Maastrichtian

collections (see Table 2). However, teeth of similar size have been collected by UCMP from

Campanian sites from the North Slope of Alaska (pers. obs, 2002).

(((TABLE 2 NEAR HERE)))

Infraorder Maniraptora GAUTHIER 1986

4.3 Family unknown

4.3.1 cf. Richardoestesia isosceles SANKEY 2001

Figure 4.1-4.10

Table 3

Description.

These teeth are long and narrow, straight or slightly recurved. Recurvature, when present,

is slight (Fig. 4.5-4.7). Straight teeth are shaped like an isosceles triangle in lateral view (Fig.

4.8-4.9). Cross-sectional shape is oval (Fig. 4.4). A slight depression or sulcus is present on the

labial and lingual sides of some teeth, extending from tooth base towards tooth tip (Fig. 4.2; 4.6).

Slight longitudinal ridges are present on the sides of some teeth (Fig. 4.5-4.7). Denticles are

minute (Fig. 4.10), uniformly-sized along tooth, extend the length of the carinae, and are similar

in size on both the anterior and posterior carinae. Interdenticle spaces are minute. Denticles are

square-shaped, with tips that are straight or slightly rounded, but not pointed.

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Discussion.

Richardoestesia gilmorei is known from a partial jaw with teeth (CURRIE et al. 1990). Its

teeth are small, recurved, oval in cross-section, slightly flattened (labial-lingually), and with

small denticles (SANKEY et al. 2002). BASZIO (1997a) demonstrated that teeth similar to R.

gilmorei, but that are straight, represent a distinct taxon because they have different relative

abundance patterns (i.e. when the recurved teeth are common, the straight teeth are rare).

SANKEY (2001) named the straight form Richardoestesia isosceles. The UCMP teeth are similar

to Richardoestesia isosceles from the Judith River Group (SANKEY et al. 2002), except the

UCMP teeth are considerably bigger.

BASZIO (1997a) found that Richardoestesia sp. (=R. isosceles) is rare (less than 5%) in

most Late Cretaceous (Campanian and Maastrichtian) theropod assemblages. However, from the

Lance Formation of Wyoming, he found that R. isosceles had 45% relative abundance. This is

similar to the UCMP collections. BASZIO (1997a) and SANKEY (2001) suggest that R. isosceles,

with its straight to slightly recurved teeth, was a fish-eater, so its high abundance in near coastal

deposits like the Hell Creek and Lance Formations is not surprising.

SUES et al. (2002) describe the teeth of Irritator challengeri, a spinosaurid from the lower

Cretaceous of Brazil as: conical, straight to slightly recurved, round in cross-section, no

denticles, with small enamel wrinkles on the labial surface, and vertical ridges on both the labial

and lingual surfaces. They suggest that these teeth were probably well-adapted for impaling and

holding prey (vs. ripping), such as fish and other vertebrates (SUES et al. 2002).

Spinosaurids are known from England, Africa, and South America. Based on similarities

in the teeth between Irritator challengeri and R. isosceles, the latter may have been a spinosaurid

also (SANKEY 2002). If this is the case, then this is the first record of spinosaurids in North

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America. Alternatively, R. isosceles may represent a case of convergent evolution with

spinosaurids.

(((TABLE 3 NEAR HERE)))

4.4 Family Unknown

4.4.1 Genus Paronychodon COPE 1876

cf. Paronychodon lacustris Morphotype A SANKEY et al. 2002

Figure 4.11-4.22

Table 4

Description.

Teeth are recurved, oval in cross-section, with one side that is flattened (4.11) to concave

and the other that is convex (Fig. 4.12). Well-developed longitudinal ridges are present, often on

both surfaces, but usually better developed on the flat surface (Fig. 4.16). The carinae are

typically smooth and unserrated, but can have minute denticles, especially on the posterior carina

(Fig. 4.13).

Discussion.

CURRIE et al. (1990) considered flat sided teeth from the Judith River Group as growth

abnormalities and referred those with characteristic denticles to known taxa like Dromaeosaurus.

They referred teeth with flat sides, longitudinal ridges, and no denticles to Paronychodon

lacustris (CURRIE et al., 1990). SANKEY et al. (2002; fig. 5.25-5.30) separated Paronychodon

lacustris into two morphotypes, A and B. These UCMP teeth are similar in shape and denticle

morphology (if present) to teeth referred to Paronychodon lacustris Morphotype A in SANKEY et

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al. (2002; fig. 5.28-5.30). The main differences are that the UCMP teeth are considerably bigger

and some of the teeth have small denticles present on the posterior carina (Fig. 4.13).

4.4.1 Genus Paronychodon COPE 1876

cf. Paronychodon lacustris Morphotype B SANKEY et al. 2002

Figures 4.32-4.34

Table 4

Description.

Teeth are small, slightly recurved, with one flat side, indented at the base (at posterior

and anterior ends), well developed longitudinal ridges (especially on the lingual side), no

denticles, and round in cross section.

Discussion.

These teeth closely resemble those referred to as Paronychodon lacustris Morphotype B

in SANKEY et al. (2002; fig. 5.25-5.27).

(((FIGURE 4 NEAR HERE)))

(((TABLE 4 NEAR HERE)))

4.4 Class Aves LINNAEUS 1758

4.4.1 Order indeterminate

Figures 4.24-4.31

Table 5

Description.

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The teeth are small, flattened (labial-lingually), oval in cross-section, straight to slightly

recurved, and with no or minute denticles. Longitudinal ridges and a sulcus (indentation) are

present on both sides of the teeth (Fig. 4.25).

Discussion.

Isolated bird teeth were identified from the Campanian Judith River Group (SANKEY et al.

2002) based on similarity to Hesperornis teeth. However, bird teeth and small teeth of

Richardoestesia gilmorei and R. isosceles can be difficult to distinguish. Bird teeth are usually

the smallest teeth, are the base of the crown is indented, denticles are absent or minute, and a

sulcus is present on both sides of the tooth. Bird teeth have been overlooked in many Late

Cretaceous microsite collections, yet they are present, and they are important in order to

document bird diversity in the Late Cretaceous.

(((TABLE 5 NEAR HERE)))

5. Discussion

A collection of over 500 small theropod and bird teeth were examined and identified

from the late Maastrichtian Lance Formation of Wyoming and the Hell Creek Formation of

Montana. A subsample of these teeth were measured (Tables1-5). Relative abundances are:

dromaeosaurids (23%), troodontids (14%), cf. Richardoestesia isosceles (35%), cf.

Paronychodon (20%), and bird (8%).

One of the unique things about this late Maastrichtian assemblage, in contrast to the late

Campanian, is the abundance of two unusual small theropods, cf. Richardoestesia isosceles and

Paronychodon. Together they make up 55% of the assemblage, yet were uncommon in the late

Campanian. Another important difference in this assemblage is the abundance, in most of the

small theropod taxa, of teeth with a flat side and longitudinal ridges. This interesting

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phenomenon is rare in Campanian teeth and is poorly understood. Another difference in this

assemblage is that dromaeosaurids only make up 23% of this assemblage, but are considerably

more diverse and abundant in the late Campanian.

In the late Maastrichtian, Tyrannosaurus rex was also present and teeth from juveniles

are common in this assemblage. Juvenile T. rex would have passed through the same size ranges

as taxa of smaller theropods, and would have fed on the same prey. Competition with juvenile T.

rex may partly explain the lower diversity of dromaeosaurids in the late Maastrichtian vs the late

Campanian. Richardoestesia isosceles, as a probable piscivore, would not have competed with

juvenile T. rex for prey, and this may be why it was one of the most common small theropods in

the late Maastrichtian.

Determining the diversity of small theropods and birds for the late Maastrichtian

compared to the late Campanian can only be estimated based on this project for two reasons: 1)

despite this large sample of teeth from late Maastrichtian small theropods, the sample is still

considerably smaller for the late Campanian; 2) because fewer skeletal remains of late

Maastrichtian small theropods have been found, identifications of isolated teeth is still less

definite. However, based on this sample, the late Maastrichtian had a slightly lower diversity of

small theropods compared with the late Campanian. Competetion for prey may have played role,

especially between juvenile tyrannosaurids and adult dromaeosaurids. Climatic and

environmental changes from the late Campanian to late Maastrichtian were also factors.

6. Acknowledgments

This work was supported by the Haslem Postdoctoral Fellowship at the South Dakota

School of Mines and Technology (SDSMT), the Welles Fund from the University of California

Berkeley Museum of Paleontology (UCMP), and the Jurassic Foundation. I thank William

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Clemens, Kevin Padian, Pat Holroyd, Samantha Hopkins, Tom Stidham, and Anthony Barnosky

(UCMP), Gale Bishop (SDSMT), Lisa Pond (illustrator at Louisiana State University), and

Donald Brinkman and Philip Currie (Royal Tyrrell Museum of Paleontology). The fossil

specimens were collected by William Clemens and his students at UCMP; this work was

financially supported by UCMP and NSF grants to William Clemens, most recently EAR-

9505841.

7. References

BASZIO, S. 1997a. Investigations on Canadian dinosaurs: palaeoecology of dinosaur

throughout the Late Cretaceous of south Alberta, Canada. - Courier Forschungsinstitut

Senckenberg 196: 1-31.

BASZIO, S. 1997b. Investigations on Canadian dinosaurs: systematic palaeontology of isolated

dinosaur teeth from the Latest Cretaceous of south Alberta, Canada. - Courier

Forschungsinstitut Senckenberg 196: 33-77.

COPE, E.D. 1876a. Descriptions of some vertebrate remains from the Fort Union beds of

Montana. - Proceedings of the Academy of Natural Sciences of Philadelphia 248-261.

CURRIE, P. J., RIGBY, JR., J.K., & SLOAN, R.E. 1990. Theropod teeth from the Judith River

Formation of southern Alberta, Canada. - In: CARPENTER, K & CURRIE, P.J., eds.,

Dinosaur Systematics: Perspectives and Approaches: 107-125. Cambridge University

Press, Cambridge.

FIORILLO, A. R., & CURRIE, P.J. 1994. Theropod teeth from the Judith River Formation (Upper

Cretaceous) of south-central Montana. - Journal of Vertebrate Paleontology 14: 74-80.

FIORILLO, A.R. & GANGLOFF, R.A. 2000. Theropod teeth from the Prince Creek Formation

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(Cretaceous) of northern Alaska, with speculations on Arctic dinosaur paleoecology.

- Journal of Vertebrate Paleontology 20(4): 675-682.

GAUTHIER, J. 1986. Saurischian monophyly and the origin of birds. - In: PADIAN, K. ed, The

Origin of Birds and the Evolution of Flight: 1-55. - Memoirs of the California Academy

of Science 8.

LEIDY, J. 1856. Notice of remains of extinct reptiles and fishes, discovered by Dr. F. V. Hayden

in the Bad Lands of the Judith River, Nebraska Territory. - Academy of Natural Sciences

Philadelphia Proceedings 8: 72-73.

LINNAEUS, C. 1758. - Systema naturae per regna tri naturae, 10th edition, revised, 2 volumes.

Holmiae, L. Salmii.

MATTHEW, W. D. & BROWN, B. 1922. The family Deinodontidae, with notice of a new genus

from the Cretaceous of Alberta. - Bulletin of the American Museum of Natural History

46: 367-385.

PENG, J. -H., RUSSELL, A.P. & BRINKMAN, D.B. 2001. Vertebrate microsite assemblages

(exclusive of mammals) from the Foremost and Oldman Formations of the Judith River

Group (Campanian) of Southeastern Alberta: An Illustrated Guide. - The Provincial

Museum of Alberta, Natural History Occasional Paper No. 25:1-54.

ROWE, T., CIFELLI, R.L., LEHMAN, T.M., & WEIL, A. 1992. The Campanian Terlingua local

fauna, with a summary of other vertebrates from the Aguja Formation, Trans-Pecos,

Texas. - Journal of Vertebrate Paleontology 12: 472-493.

RYAN, M. J., CURRIE, P.J., GARDNER, J.D., VICARIOUS, M.K., & LAVING, J.M. 1998. Baby

hadrosaurid material associated with an unusually high abundance of Troodon teeth from

the Horseshoe Canyon Formation, Upper Cretaceous, Alberta, Canada. - Gaea 15: 123-

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133.

SANKEY, J.T. 2001. Late Campanian southern dinosaurs, Aguja Formation, Big Bend, Texas.

- Journal of Paleontology 75(1): 208-215.

SANKEY, J.T. 2002. Theropod dinosaur diversity in the Latest Cretaceous (Maastrichtian) of

North America. - Journal of Vertebrate Paleontology Abstracts of Papers 22(3): 103A.

SANKEY, J.T., BRINKMAN, D.B., GUENTHER, M. & CURRIE, P.J. 2002. Theropod and bird teeth

from the Judith River Group (Late Cretaceous), Alberta. - Journal of Paleontology 76(4):

751-763.

SEELEY, H.G. 1888. The classification of the Dinosauria. - Report British Association for the

Advancement of Science 1887: 698-699.

SUES, H.-D. 1978. A new small theropod dinosaur from the Judith River Formation

(Campanian) of Alberta Canada. - Zoological Journal of the Linnaean Society 62: 381-

400.

SUES, H.– D., FREY, E., MARTIAL, D.M., & SCOTT, D.M. 2002. Irritator challengeri, a

spinosaurid (Dinosauria: Theropod) from the Lower Cretaceous of Brazil. - Journal of

Vertebrate Paleontology 22(3): 535-527.

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FIGURE 1. Measurements of teeth. A, FABL, fore-aft basal length, not including denticles. B, Greatest height, from crown tip to base (not including root, if unshed tooth) and measured from posterior side. C, Curvature, the greatest distance from posterior carinae (not including the denticles) to a perpendicular line from tooth tip to base. D, Cross-sectional thickness, the greatest lateral-lingual cross-sectional tooth thickness. E, Greatest denticle width. F, Greatest denticle height. Denticles/mm, measured midway along the posterior carinae. (from SANKEY et al., 2002).

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FIGURE 2. Theropod teeth from the Lance Formation (Wyoming) and Hell Creek Formation (Montana) with views of lingual and labial sides, cross section through the base of tooth, and close up of denticles. 1-13, cf. Saurornitholestes sp.; 1-4, UCMP 187048; 5-8, UCMP 187027; 9-11, UCMP 124401; 12-13, UCMP 174796; 14-17, cf. Dromaeosaurus, UCMP 187037.

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FIGURE 3. Theropod teeth from the Lance Formation (Wyoming) and Hell Creek Formation (Montana) with views of lingual and labial sides, cross section through the base of tooth, and close up of denticles. Troodon sp. Flat Morph.; 1-4, UCMP 187181; 5-8, UCMP 126518; Troodon sp.; 9-12, UCMP 187186; 20-21, UCMP 187178; Troodon sp. Large Morph.; 13-16, UCMP 186979; Troodon sp. premax.; 17-19 UCMP 187184.

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FIGURE 4. Theropod teeth from the Lance Formation (Wyoming) and Hell Creek Formation (Montana) with views of lingual and labial sides, cross section through the base of tooth, and close up of denticles. cf. Richardoestesia; 1-4, UCMP 186892; 5-7, UCMP 186847; 8-10, UCMP 187175; cf. Paronychodon lacustris Morphotype A, 11-14, UCMP 187142; 15-19, UCMP 187080; 20-23, UCMP 187135; Bird; 24-26, UCMP 186945; 27-28, UCMP 123545; 29-31, UCMP 109018; Paronychodon lacustris Morphotype B, 32-34, UCMP 187094.

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Table 1. Dromaeosaurid measurements.

Spec. No Local. No. FABL HT Dent/mm186838 V77118 6.5 >13.0 -187047 V73102 2.3 - 9187070 5620 2.5 5 6128941 75157 3.7 6 6120338 73085 5.5 7.5 5119921 72208 3.7 5.7 6124987 73087 6 15 4134801 73092 3.7 10 5187048 73102 5.8 13 5187049 80091 3 6 7128913 74118 3.8 7 6186967 87049 7 13 4186968 87038 6 10 3.5186972 87067 6 10 4186970 87153 7 13 4186973 87072 2.8 7 5120153 72215 3 4.8 5186971 87040 7 13 4120287 73078 5 8 4.5174796 90084 3.4 5 4.5186944 76167 3.5 6 6186891 5618 7 17 4.5120339 73085 9 17 4186899 83118 - - 3.5187194 82013 3.2 5.5 6123543 73093 7 6 4187201 77118 3.5 - 7187200 87098 2.2 3.5 7187197 87022 3.5 5.5 5.5124401 5620 4.5 8 5186957 75175 3.3 5 5.5187199 87022 3.6 5 5.5119788 72206 8 17 -187198 87022 2.6 4 7187079 5620 2.2 4 6187054 5815 3 4.5 7187143 87084 3.6 8 5187139 87105 3.2 7 5.5186957 75161 4.5 7 4.5119926 72203 - - 3.5120305 73083 9 17 3.5186958 87098 2.6 4 6186959 87038 3 5 7186961 87030 3.2 8 5186962 73090 3.4 5 5.5186964 87098 3.3 - 4.5186960 75178 5 10 4.5187037 72213 3.6 10 4.5187039 75173 4.5 9 5129085 75173 5 - 4.5

79095 870401 4 7 6187041 73087 4 8 6

22

187042 72208 3 5 6187043 72208 2.5 4.5 6.5187044 72208 3 4 6187045 72208 3 5 5187046 73102 2.3 4 8187036 82060 5 8 5187034 91051 6 12 4.5187033 87059 5 12 4187030 83256 5 8 5187027 5818 4 7 6187025 91051 4 6 7187006 76157 6 12 5187038 75178 4 7 5.5187010 75165 3 6 6123565 73097 4 7 6119718 72199 6 10 5187083 75165 5 8 6187125 56201 7 4 4187129 5620 4 9 4.5187124 5620 6 12 4187105 5620 5 8 5187163 73087 2.5 5 7

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Table 2. Troodon measurements. Spec. No. Local. No. Curv. FABL HT CST Dent/mm Dent. W Dent. Ht.

187076 V5620 0.4 2.2 3.0 1 4 0.2 0.3187071 V5620 - 2.4 - 0.9 4 0.3 0.3187078 V5620 - 2.5 - 0.9 4 0.3 -187075 V5620 0.9 2.7 4.5 1 3.5-4 0.3 0.3187072 V5620 - 2.2 - 1 4 0.3 0.2187073 V5620 1.1 2.9 4.3 1.1 3.5 0.3 0.3187074 V5620 0.7 2.7 4.2 1.1 4 0.3 0.3187071 V5620 - 2.9 - 0.9 3 0.3 0.3187067 V5620 0.9 2.7 3.8 1 3.5 0.3 0.2187068 V5620 1.0 2.6 3.1 1 4.5 0.2 0.1187069 V5620 1.0 2.7 4.1 1 4 0.3 0.3187066 V5620 1.6 3.0 3.5 1 3 0.4 0.4187062 V5620 - 2.2 - 0.8 3.5 0.3 0.3187063 V5620 - 2.4 3.9 0.9 4 0.3 0.3187065 V5620 1.5 0.2 4.1 1 3 0.3 0.3187061 V5620 - 2.7 - 1.1 4.5 0.3 0.3187060 V5620 - 2.4 - 0.9 3.5 0.3 0.2187058 V5620 1.0 - 2.5 0.8 3.5 0.3 0.4187059 V5620 0.9 2.1 3.2 0.8 5 0.2 0.2186904 V84130 0.4 2.0 3.0 0.7 3.5 0.3 0.2187057 V72208 - 3.1 - 1.1 4 0.3 0.3128845 V74116 1.6 3.2 4.6 1.1 4 0.3 0.3119919 V72208 - - - 1 4 0.3 0.2128787 V73102 1.1 3.6 4.6 1.7 2.5 0.4 0.4214059 V5616 0.1 1.9 3.4 1.3 3 0.3 0.2214060 V73087 - 2.0 - 0.8 5 0.2 0.2214061 V75172 - 2.6 - 0.9 4 0.3 0.2214062 V75172 - 2.4 - 0.9 4.5 0.3 0.2186868 V75172 0.6 2.2 2.9 0.9 4 0.3 0.3186885 V73087 0.9 2.1 3.0 0.7 4.5 0.2 0.3186886 V5616 >1.2 3.2 4.0 1 3 0.4 0.4

24

Table 3. Richardoestesia isosceles measurements.

Spec. No Local. No. Curv. FABL HT CST Dent/mm Dent. W Dent. Ht.186834 V82060 - 5.6 - 3.2 11.5 0.2 0.2186835 V80091 0.0 4.2 8.5 10 minute186836 V87030 0.0 4.1 - 2.1 * -186837 V77118 0.2 3.3 6.7 1.7 10.5 0.2 0.2186839 V82060 - 3.6 - 1.8 9 minute186840 V87082 0.0 4.4 9.2 2 6.5 0.2 0.2186842 V73103 0.3 2.7 5.3 1.4 8 0.2 0.1186833 V82023 0.0 3.3 1.5 9 0.2 0.2186825 V80092 0.2 3.3 9.1 1.8 8 0.2 0.1186824 V80092 0.0 2.9 >6.1 1.5 * -186829 V83044 - 5.9 - 2.9 8 0.2 0.1186827 V80088 0.0 4.5 >10.5 2.1 6 0.2 0.1213922 V73087 >0.3 2.4 - 1.2 * -213923 V73087 - - - 2 9 0.1 0.1213924 V73087 >0.5 3.6 >7.7 1.8 8 0.2 0.1213925 V73087 0.0 1.8 - 1.5 8 0.2 0.1213926 V73087 0.2 2.4 - 1.2 10 0.2 0.1213927 V73087 0.0 3.2 6.2 1.5 6.5 0.2 0.1213928 V73087 0.0 2.4 - 1.2 7.5 0.2 0.2213929 V73087 0.0 4.1 >9.5 2 7 0.2 0.1213930 V73087 0.0 2.4 - 1.2 9.5 0.2 0.1213931 V73087 0.2 3.6 >7.6 1.7 8 0.2 0.2213932 V73087 >0.5 3.8 >10.3 8.5 0.2 0.2213933 V73087 0.0 3.0 4.8 1.5 8 0.2 0.2213934 V73087 >0.3 2.4 >4.5 0.9 * -213935 V73087 0.2 2.3 4.4 1.4 8 0.2 0.2213936 V73087 0.0 2.9 5.6 1.5 * -213937 V73087 0.2 2.6 5.5 1.1 * -213938 V73087 0.6 2.1 >3.5 0.9 8.5 0.2 0.2213939 V73087 >0.5 1.7 - 3.2 9 0.2 0.1213940 V73087 0.0 2.4 - 1.4 * -213941 V73087 0.0 2.6 5.2 1.1 * -213942 V73087 0.0 2.7 5.9 1.5 * -213943 V73087 0.0 4.5 >11.1 2.3 7 0.2 0.2213944 V73087 0.0 3.8 >9.1 2 9 0.2 0.1213945 V73087 0.5 3.0 >6.7 1.7 9 0.2 0.2213946 V73087 >0.3 3.2 >7.0 1.5 8.5 0.1 0.2213947 V73087 0.2 2.6 >5.3 1.4 * -213948 V73087 0.0 2.6 - 1.4 9 0.2 0.2213949 V73087 >1.1 3.0 >6.8 1.5 7 0.2 0.2213950 V73087 0.2 4.4 >13.9 2 9 0.2 0.1213951 V73087 0.0 4.2 13.0 1.8 8 0.2 0.1213952 V73087 0.0 2.9 - 1.5 7.5 0.2 0.1213953 V73087 0.0 3.8 8.9 1.7 7.5 0.2 0.2213954 V73087 0.0 2.3 - 1.4 * -213955 V73087 0.0 3.0 - 1.5 7 0.2 0.2213956 V73087 0.0 3.9 >8.5 2 7 0.2 0.2213957 V73087 >0.9 3.3 - 1.7 10 0.2 0.2213958 V73087 >0.8 2.7 - 1.4 8 0.2 0.2213959 V73087 >0.3 3.9 - 1.8 8 0.2 0.1213960 V73087 0.3 3.9 9.1 1.8 7.5 0.2 0.2213961 V73087 0.2 2.4 >5.2 0.9 * -

25

213962 V73087 0.2 4.7 >9.7 2.1 8 0.2 0.1213963 V73087 0.0 3.2 - 1.4 12 0.1 0.1213964 V73087 - 2.9 - 1.5 * -213965 V73087 >0.5 3.9 >7.7 1.7 9 0.2 0.1213966 V73087 0.2 3.8 >8.6 2 7.5 0.2 0.2213967 V73087 - 3.2 - 1.5 10 0.2 0.2213968 V73087 0.2 2.4 5.3 * -213969 V73087 0.2 2.1 >4.4 1.1 12.5 0.1 0.1213970 V73087 0.0 2.7 - 1.5 7 0.2 0.1213971 V73087 0.5 3.0 >6.1 1.7 9.5 0.2 0.2213972 V73087 0.0 4.1 8.5 2 8 0.2 0.2213973 V73087 0.0 2.3 - 1.4 6.5 0.2 0.2213974 V73087 >0.2 - - 8 0.2 0.2213975 V73087 0.3 4.4 8.9 2 7 0.2 0.2213976 V73087 - 1.8 - 1.1 * -213977 V73087 0.0 4.2 - 2.1 6 0.2 0.2213978 V73087 >0.2 3.5 - 2 8.5 0.2 0.1213979 V73087 0.0 3.0 >8.3 1.5 * -213980 V87072 1.1 2.7 5.2 1.4 6.5 0.2 0.2213981 V87072 - 1.8 - 1.2 * -213982 V87072 - 3.9 - 1.8 7.5 0.2 0.2213983 V5620 0.0 3.6 >8.8 2 8 0.2 0.1213984 V5620 0.5 4.4 8.6 1.8 6.5 0.2 0.2213985 V5620 0.0 3.2 - 1.7 * -213986 V5620 0.0 4.1 - 2.1 7.5 0.2 0.1213987 V73077 0.5 2.4 >5.2 1.4 10.5 0.1 0.1213988 V73077 - - - 2.3 4 0.2 0.2213989 V73077 0.0 2.6 >4.7 1.5 6 0.2 0.2213990 V73077 0.0 1.8 - 0.9 7 0.2 0.1213991 V73077 0.0 3.0 - 1.7 6 0.2 0.2213992 V73087 0.3 3.9 >8.9 1.7 8 0.2 0.2213993 V73087 0.0 2.1 - 1.2 10 0.1 0.1213994 V73087 0.6 2.9 5.8 1.4 10 0.2 0.2213995 V73087 1.8 3.5 8.6 1.8 5.5 0.2 0.2213996 V73087 0.0 5.3 >12.3 2.7 5.5 0.2 0.2213997 V73087 0.2 2.9 5.9 1.5 10 0.1 0.1213998 V73087 0.2 2.7 >6.2 2.1 * -213999 V73087 0.0 2.7 >5.3 1.4 10 0.1 0.1214000 V73087 0.0 3.5 - 1.7 7.5 0.2 0.2214001 V73087 0.0 2.0 - 1.1 * -214002 V73087 - 2.9 - 7 0.2 0.2214003 V73087 0.0 4.1 - 2 7 0.2 0.1214004 V73087 0.0 1.8 - 1.1 12 0.1 0.0214005 V73087 >0.3 3.3 - 1.7 7 0.2 0.2214006 V73087 0.2 2.0 >4.7 1.1 * -186842 V73103 0.5 2.7 5.9 1.4 9 0.2 0.1120257 V73077 0.0 3.2 - 1.4 7 0.2 0.1186833 V82023 - 3.3 - 1.4 5.5 0.2 0.2

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Table 4. Paronychodon measurements. Spec. No. Local. No. Curv. FABL HT CST Dent/mm Dent. W Dent. Ht.

187120 V5620 - 2.3 - 0.9 - -187123 V5620 1.5 3.3 6.5 1.5 - -187128 V5620 - 3.8 - 1.8 - -187112 V5620 - 2.0 - 0.9 - -187114 V5620 0.4 3.9 8.7 1.8 - 0.1187102 V5620 0.5 2.5 5.2 1.8 8.5 0.1 -187108 V5620 - 3.3 - 1.8 - -187096 V5620 - 4.5 - 2.1 - 0.1187098 V5620 - 3.8 - 1.6 6 0.1 -187099 V5620 0.5 3.0 5.4 1.6 - -187100 V5620 - 2.8 - 1.6 - -187091 V5620 >0.4 2.4 6.6 1.8 - 0.1187085 V5620 - 5.0 - 2.7 7 0.1 -187092 V5620 - 2.2 - 1.3 - -187093 V5620 - 2.8 - 1.5 - 0.1187086 V5620 - 4.5 - 2.4 7.5 0.1 0.1187087 V5620 - 5.2 - 2.7 5.5 0.2 -187089 V5620 0.8 1.6 4.7 1.2 - -187159 V73087 >1.0 3.3 >13.3 1.8 - -123342 V73087 - 6.0 - 3.2 - -187130 V5620 0.6 2.1 6.7 1.5 - -187133 V5620 - 2.7 - 1.4 - -187134 V5620 - 2.8 - 1.2 minute -187150 V77131 - 2.7 - 2.1 - -187151 V80091 >0.5 4.7 >10.7 2.6 minute -187144 V87084 >0.9 4.1 >10.2 1.5 - -187145 V82013 - 4.1 - 1.8 - -187146 V82013 0.7 2.5 8.1 1.9 - -187082 V82022 - 5.1 - 1.9 - -187162 V73087 >0.2 3.9 - 1.8 - -187156 V73087 - 4.4 - 1.9 - -187164 V73087 - 4.9 - 2.4 - 0.1120254 V73077 - 3.0 - 1.3 5.5 0.2 0.1

53283 V5620 - 3.5 - 1.8 5.5 0.1 0.187141 V87038 >1.3 5.5 >12.1 2.5 6.5 0.1 -

124400 V5620 - 4.4 - 2.4 - -124405 V74107 1.0 2.7 9.6 1.9 - -187214 V87034 - 4.2 - 2.1 - -187121 V5620 >1.9 2.8 >5.6 1.6 - -187126 V5620 >1.6 4.7 >9.6 2.1 - -120192 V73076 - 2.0 - 1.2 - -

53065 V5821 - 4.8 - 2.1 - 0.2186931 V77131 ~0.1 3.8 - 1.7 6.5 0.1 -

46585 V5616 - 2.8 - 1.3 - -73076 V5815 - 4.5 - 1.9 - 0.1

186908 V87151 >0.9 3.5 >6.1 1.8 6 0.2 0.1119787 V72206 - 3.9 - 1.9 6.5 0.1 0.1123525 V73092 1.9 3.9 7.3 1.5 10 0.1 0.1186913 V87035 - 5.0 - 2.4 5 0.2 0.1186911 V80119 0.0 3.9 >6.3 1.7 9.5 0.1 -186900 V83118 0.7 5.4 >10.8 2.5 - 0.1214007 V65238 - 3.9 - 1.6 9 0.1 0.1

27

214008 V65238 0.7 2.2 >4.2 1.1 8 0.1 0.1214009 V65238 1.0 2.2 - 1.3 10 0.1 0.1214010 V65238 - 3.3 - 1.6 6 0.1 0.1214011 V65238 >0.7 2.4 >3.3 0.9 8 0.1 0.1214012 V65238 0.0 3.8 7.3 1.8 5.5 0.1 0.1214013 V65238 0.2 2.5 5.4 1.4 8.5 0.1 0.1214014 V65238 0.0 - 4.4 1 8 0.1 0.1214015 V65238 0.7 2.6 >6.1 1.3 8 0.1 0.1214016 V65238 0.5 2.7 3.9 1.2 9 0.1 0.1214017 V65238 0 4.1 - 1.7 8.5 0.1 0.1214018 V65238 1.4 3.0 >4.4 1.2 9 0.1 0.1214019 V65238 0.0 3.4 - 1.4 6 0.2 -214020 V65238 1.0 2.7 5.0 1.4 minute 0.1214021 V65238 2.0 2.9 5.4 1.4 10 0.1 0.1214022 V65238 0.2 3.5 7.2 1.5 8 0.1 0.1214023 V65238 0.7 3.2 6.3 1.4 8 0.1 0.1214024 V65238 0.8 2.7 >5.3 1.2 7.5 0.1 -214025 V65238 0.0 4.1 - 1.8 minute 0.1214026 V65238 >0.4 2.7 >3.8 1.2 8 0.1 -214027 V65238 1.5 2.7 5.3 1.6 - -214028 V65238 >1.5 3.3 >7.5 1.8 - 0.1214029 V65238 0.1 3.1 - 1.3 10 0.1 0.1214030 V65238 0.0 2.6 >5.0 1.3 9 0.1 0.1214031 V65238 1.0 3.6 >7.2 1.7 6 0.1 0.1214032 V65238 0.4 3.6 >7.8 1.6 8 0.1 0.1214033 V65238 0.2 2.7 >5.1 1.2 10 0.1 0.2214034 V65238 0.8 2.9 - 1.3 7 0.1 0.1214035 V65238 0.8 2.2 4.0 1 9 0.1 0.1214036 V65238 1.0 2.7 - 1.2 7.5 0.1 -214037 V65238 1.5 4.2 - 2.1 minute 0.1214038 V65238 - 3.6 - 1.7 6.5 0.1 0.1214039 V65238 0.7 2.8 6.5 1.6 6.5 0.1 -214040 V65238 0 2.4 - 1.2 - 0.1214041 V65238 0.2 2.4 - 1.1 8.5 0.1 0.1214042 V65238 0.4 3.0 >5.6 1.2 9 0.1 0.1214043 V65238 0.2 3.2 7.3 1.6 8 0.1 -214044 V65238 1.2 3.2 >6.1 1.7 0.1214045 V65238 2.2 3.5 >5.9 1.8 9 0.1 0.1214046 V65238 1.2 2.8 >5.5 1.3 8 0.1 0.1214047 V84130 - - - 1.5 7 0.1 0.1214048 V84130 - 2.7 - 1.2 8 0.1 0.0214049 V84130 - 2.4 - 1.1 8 0.1 0.1214050 V84130 0.0 2.1 - 0.9 8 0.1 -214051 V5713 0.1 3.2 7.7 1.5 - 0.1214052 V5713 0.8 3.3 >6.0 1.5 7 0.1 0.1214053 V5713 0.0 3.9 >7.8 1.8 8 0.1 0.1214054 V5713 0.0 2.0 >4.2 1 12 0.1 0.1214055 V5713 0.1 3.3 - 1.6 10 0.1

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Table 5. Bird measurements. Spec. No. Local. No. Curv. FABL HT CST Dent/mm Dent. W Dent. Ht.

186826 V73087 0 2.6 >4.8 1.1 - - -214056 V73087 0 2.5 - 1.2 - - -214057 V73087 0 2.4 >5.1 1.5 - - -214058 V73087 0.8 3.8 >8.2 2.1 - - -

29