Late Cretaceous Theropod Dinosaurs of Southern Utah

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Late Cretaceous Theropod Dinosaurs of Southern Utah Lindsay E. Zanno, Mark A. Loewen, Andrew A. Farke, Gy-Su Kim, Leon P. A. M. Claessens, and Christopher T. McGarrity

Recent interest in Upper Cretaceous formations of southern Utah including intense collection efforts by the Kaiparowits Basin Project – a joint collaboration between the Utah Museum of Natural History, the University of Utah, and the Bureau of Land Management – has added considerably to our understanding of dinosaur diversity in the Western Interior Basin. These taxonomically unique and historically underrepresented ecosystems document a relatively high diversity of theropods, including a minimum of seven taxa known from the Kaiparowits Formation alone. Recent discoveries include at least five new taxa: Hagryphus giganteus, the first diagnostic North American oviraptorosaurian south of Montana; a new species of troodontid paravian; Nothronychus graffami, the most complete therizinosaurid skeleton yet discovered; and two new tyrannosaurid taxa, including Teratophoneus curriei and an undescribed taxon that represents the oldest North American tyrannosaurid recovered to date. Presently, data-rich paleobiogeographical comparison of latitudinally arrayed, coeval Western Interior Basin formations can only be made for a short temporal window that includes the upper Campanian Kaiparowits Formation. These investigations reveal that theropod diversity is relatively homogenous at higher taxonomic levels. Yet new discoveries also demonstrate a high degree of interformational, species-level endemism, indicating that the southern Utah theropod fauna is surprisingly unique and that theropod ranges in the upper Campanian Western Interior Basin were more restricted than previously understood. On the basis of these data, we argue against the referral of fragmentary dinosaur remains and teeth recovered from upper Campanian strata of the Western Interior Basin to taxa from other Western Interior Basin formations without substantial morphological evidence. I n t roduc t io n

Campanian exposures of the Wahweap and Kaiparowits formations of Grand Staircase–Escalante National Monument. This collaborative effort – known as the Kaiparowits Basin Project (KBP) – has documented at least 11 definitively new dinosaur taxa (with many more currently under study) that are challenging previous ideas regarding Late Cretaceous dinosaur evolution and diversity within Western Interior Basin. Although the recent work undertaken by the KBP along with several other institutions, including the Raymond M. Alf Museum of Paleontology (RAM) and the Utah Geological Survey, represents the first concerted effort to collect and research the dinosaurian fauna of the Kaiparowits Basin, decades of microvertebrate studies were conducted in this and other areas of southern Utah by Richard Cifelli, Jeffrey Eaton, and their colleagues, who were studying the region’s mammalian fauna before the project’s initiation (Eaton and Cifelli, 1988; Eaton, Munk, and Hardman, 1998; Eaton, 1999; Eaton, Cifelli, et al., 1999; Eaton, Diem, et al., 1999). Concomitant fieldwork by J. Howard Hutchison and colleagues (Hutchison et al., 1997) involved surface reconnaissance in addition to microvertebrate screening and a greater focus on identifying the lower vertebrate fauna, including dinosaurs. Such early studies provided the first insight into the dinosaurian fauna of the region and the first (and in some cases only) comprehensive faunal lists for the formations reviewed here (Tables 22.1–22.5). These foundational contributions notwithstanding, the dinosaurian identifications generated by these studies are restricted almost entirely to surface float and isolated teeth, which recent discoveries indicate to be of limited taxonomic utility for theropods. Table 22.1. Historical survey of the theropod fauna of the Iron Springs Formation derived from the literature Taxon

Reference

Theropoda

In 2000, field crews of the Utah Museum of Natural History, the University of Utah, and the Bureau of Land Management embarked on an exhaustive research project to survey and document the Late Cretaceous dinosaur fauna of the Kaiparowits Basin, southern Utah, with a focus on upper 504

Theropoda indet.

Eaton, 1999

Paraves ?Dromeosauridae ?Dromeosauridae indet.

Eaton, 1999

Troodontidae Troodontidae indet.

Eaton, 1999


Table 22.2. Historical survey of the theropod fauna of the Dakota Formation derived from the literature

Table 22.4. Historical survey of the theropod fauna of the Wahweap Formation derived from the literaturea

Taxon

Taxon

Reference

Reference

Theropoda

Theropoda cf. Richardoestesia sp.

Eaton, Cifelli, et al., 1999

Theropoda indet.

Eaton, Munk, and Hardman, 1998

cf. Paranychodon sp.


cf. Richardoestesia sp.

Kirkland, 2001


Kirkland, 2001

Tyrannosauridae Tyrannosauridae indet.


Tyrannosauridae Tyrannosauridae indet.b

Eaton, Cifelli, et al., 1999; Parrish, 1999


?Tyrannosauridae indet.

Eaton, Diem, et al., 1999


Tyrannosaurinae indet.

Kirkland, 2001

Troodontidae

Aublysodontinae indet.

Kirkland, 2001

cf. Troodon sp.

cf. Aublysodon sp.

Parrish, 1999

?Aublysodon sp.b


Paraves Dromeosauridae Velociraptorinae indet. Dromeosaurinae indet.


Paraves Table 22.3. Historical survey of the theropod fauna of the Straight Cliffs Formation derived from the literature Taxon

Reference

Theropoda

Dromeosauridae Dromeosauridae indet.c


Velociraptorinae indet.

Kirkland, 2001; Eaton, Cifelli, et al., 1999; Parrish, 1999

Dromeosaurinae indet.

Kirkland, 2001; Eaton, Cifelli, et al., 1999; Parrish, 1999

Theropoda indet.

Eaton and Cifelli, 1988

cf. Richardoestesia sp.



Parrish, 1999

Troodontidae indet. Troodon sp.


Tyrannosauridae indet.

Parrish, 1999

cf. Troodon sp.

Parrish, 1999

cf. Aublysodon sp.


Tyrannosauridae

Troodontidae

a

Kirkland, 2001

E dward G. Sable, U.S. Geological Survey (pers. comm., 1994, in Eaton et al., 1999).

Paraves

b

Equivalent to Wahweap Formation.

Dromeosauridae

c

Equivalent to Wahweap Formation or younger.







Table 22.5. Historical survey of the theropod fauna of the Kaiparowits Formation derived from the literature Taxon

Here we provide a review on the theropod fauna of the Upper Cretaceous formations in southern Utah with a focus on macrovertebrate materials recovered during the 2001–2009 field seasons by KBP crews and isolated teeth collected by the KBP and the RAM. KBP fieldwork is currently concentrated in the middle and upper Campanian Wahweap and Kaiparowits formations. As a result, the Wahweap and Kaiparowits formations have undergone the greatest recent advances in elucidating dinosaur diversity and comprise the bulk of this review. However, we also summarize the Late Cretaceous theropod fauna of southern Utah’s Iron Springs, Dakota, and Straight Cliffs formations based almost exclusively on the aforementioned microvertebrate collections. Summaries of the chronostratigraphic relationships and radiometric ages of these formations and equivalent formations to the north and south on Laramidia are presented elsewhere in this volume. Finally, we discuss the surprising discovery of a dinosaur skeleton from the Upper Cretaceous marine Tropic Shale of Late Cretaceous Theropod Dinosaurs

Reference

Theropoda cf. Richardoestesia sp.

Parrish, 1999


Parrish, 1999

Tyrannosauridae Tyrannosauridae indet.


cf. Albertosaurus sp.

Hutchison et al., 1997

Ornithomimidae Ornithomimus velox


Ornithomimus sp.


Paraves Dromeosauridae Dromeosauridae indet.





Parrish, 1999


Hutchison et al., 1997; Parrish, 1999

Troodon sp.


Aves Avisaurus sp.

Hutchison, 1993 505


southern Utah, Nothronychus graffami, a member of a rare group of predominantly plant-eating theropods known as therizinosaurians. A preliminary report representing an earlier, less comprehensive version of this chapter and restricted to the theropod fauna of the Kaiparowits Formation was published as part of a symposium on Grand Staircase–Escalante National Monument in 2006 (Zanno et al., 2010). This work greatly expands upon that review and includes recent discoveries as well as updated research results for nearly all theropod subclades, specimen reevaluations, and new tooth morphotypes. Institution Abbreviations BYU, Brigham Young University, Provo, Utah, U.S.A.; CMN, Canadian Museum of Nature, Ottawa, Ontario, Canada; MNA, Museum of Northern Arizona, Flagstaff, Arizona, U.S.A.; RAM, Raymond M. Alf Museum of Paleontology, Claremont, California, U.S.A.; UCMP, University of California Museum of Paleontology, Berkeley, California, U.S.A.; UMNH, Natural History Museum of Utah (formerly Utah Museum of Natural History), Salt Lake City, Utah, U.S.A.; YPM, Yale Peabody Museum, New Haven, Connecticut, U.S.A.

22.1. Reconstruction of the holotype skull of Teratophoneus curriei (BYU 8120) from the Kaiparowits Formation. Reconstruction and original photograph by Rob Gaston of Gaston Design, Inc., Fruita, Colorado.

Tyrannosaurids (tyrant reptiles) are a group of large-bodied theropods bearing massive skulls, diminutive arms, and stereoscopic vision (Holtz, 2004; Stevens, 2006). These highly specialized dinosaurs presumably functioned, alongside the alligatoroid Deinosuchus, as top predators within Late Cretaceous terrestrial ecosystems of the Western Interior Basin. At ~6300 kg, the Maastrichtian-aged Tyrannosaurus rex falls among the top body masses known for any terrestrial carnivore (Christiansen and Fariña, 2004; Therrien and Henderson, 2007); however, tyrannosaurids from preceding Campanian Age Western Interior Basin deposits were typically much smaller bodied (~2500 kg). Emerging evidence from China and Europe suggests that the group was more morphologically and ecologically diverse than previously appreciated. This evidence has complicated our understanding of the evolution of the tyrannosaurid body plan (Hutt et al., 2001; Xu et al., 2004, 2006; Li et al., 2009; Rauhut, Milner, and Moore-Fay, 2009; Sereno et al., 2009). Although small-bodied, Early Cretaceous tyrannosauroids possessed protofeathers (Xu et al., 2004), integument may have varied across the clade or during ontogeny. Late Campanian tyrannosaurids have been well represented in northern Western Interior Basin formations for

more than a century (Osborn, 1905; Lambe, 1914; Currie, 2003); however, tyrannosaurid species inhabiting southern Western Interior Basin ecosystems during this interval have remained enigmatic. Before the initiation of the KBP, the only diagnostic tyrannosaurid material recovered from the Kaiparowits Basin consisted of a partial associated skull and postcranial skeleton (BYU 8120/9396, BYU 8120/9397, BYU 8120/9398, BYU 826/9402, and BYU 13719, hereafter collectively referred to as BYU 8120) collected from the Kaiparowits Formation by BYU masters student Sam Webb in 1981 (Fig. 22.1). This material was recently described and named Teratophoneus curriei (Carr et al., 2011), three decades after its initial discovery (Carr, 2005). Exact locality data for BYU 8120 are not available; however, a contemporary newspaper article describing the location of the site places the specimen in the middle member of the Kaiparowits Formation in The Blues outcrop area northeast of Henrieville, Utah (Webb, 1981). The skull of Teratophoneus curriei includes the left maxilla and lacrimal, the right jugal, frontal, and squamosal, both occipitals, the left prootic, the basioccipital, the right basisphenoid, both quadrates, the left articular, and the left dentary (Carr et al., 2011; Fig. 1). Postcranial materials assigned to this species include a single cervical vertebra (C3), a single midcaudal centrum, the left scapula, coracoid, humerus, and ulna, and the left femur (Carr et al., 2011; Loewen et al., in prep.). Although many of the elements of BYU 8120 are incomplete, this specimen provides the first clear evidence of a unique tyrannosaurid taxon from the Kaiparowits Formation, and its unusually short, deep skull sheds new light on

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T h e rop od Di v e r s i t y i n t h e K a i pa row i t s B a s i n Tyrannosauridae


22.2. Skeletal reconstructions of the two new tyrannosaurid genera from the Late Cretaceous of Utah with recovered materials shown in white. (A), new species from the Wahweap Formation based entirely on UMNH VP 20200 and (B), Teratophoneus curriei from the Kaiparowits Formation based on UMNH VP 16690, with supplementary elements from the type and other specimens. Adapted with permission from artwork by Scott Hartman.

the ecomorphological diversity in tyrannosaurids during this time period (Carr et al., 2011). Recent fieldwork in the Wahweap and Kaiparowits formations by the UMNH and RAM has produced numerous isolated tyrannosaurid elements as well as eight associated specimens that vastly augment our knowledge of Teratophoneus and southern Campanian tyrannosaurid diversity more generally. The most complete Wahweap specimen (UMNH VP 20200) was discovered in the lower part of the Middle Member in 2009 (Fig. 22.2A). The specimen preserves portions of the skull including the right maxilla, both co-ossified nasals, the right frontal, the left laterosphenoid, the left jugal, the right quadrate, the left palatine, the left dentary, the left splenial, the left surangular, and the left prearticular. Postcranial elements include a single caudal chevron; both pubes; the left tibia, fibula, and metatarsals II, III, and IV (Loewen et al., in prep.). UMNH VP 20200 was recovered from sediments

dated to approximately 80 Ma (Jinnah et al., 2009), making it the oldest definitive tyrannosaurid yet known from the Western Interior Basin. As such, the specimen promises to provide valuable information on the origin and early evolution of Tyrannosauridae on the North American continent. In contrast to the paucity of materials known from the Wahweap Formation, tyrannosaurid remains are abundant in the Kaiparowits. An exceptionally well-preserved associated subadult skeleton referable to Teratophoneus curriei (Loewen et al., in prep.) was discovered in 2004 (UMNH VP 16690; Fig. 22.2B). Not only does UMNH VP 16690 vastly expand our understanding of the anatomy of Teratophoneus, it also represents one of the most complete and phylogenetically informative tyrannosaurid individuals thus far collected from the southern Western Interior Basin formations. The subadult specimen of Teratophoneus (UMNH VP 16690) is approximately 65% complete and preserves most

Late Cretaceous Theropod Dinosaurs

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of the skull, axial column, pelvis, and a portion of the right leg (Fig. 22.2B). Recovered cranial materials include the following: the left maxilla; both lacrimals and postorbitals; the right squamosal; the left quadratojugal and quadrate; both frontals, parietals, angulars, and surangulars; a complete braincase; the left prearticular and articular, and multiple teeth (Fig. 22.3). In total, the skull lacks only the premaxillae, right maxilla, nasals, jugals, left squamosal, palatines, vomers, dentaries, splenials, and right prearticular and articular. Preserved axial materials include the atlas, seven cervical vertebrae and ribs, eight dorsal vertebrae and 14 dorsal ribs, two sacral vertebrae, 34 caudal vertebrae, and 19 chevrons. The appendicular skeleton is known from parts of both ilia, both pubes, both ischia, the right femur, tibia, and fibula, a single pedal phalanx, and an ungual (Wiersma and Loewen, this volume, Chapter 27). A number of associated but shattered elements from the rostral portion of the skull, in addition to several shattered teeth, suggest that the facial skeleton of UMNH VP 16690 may have been trampled before burial (Wiersma, Loewen, and Getty, 2009; Wiersma and Loewen, this volume, Chapter 27). The reconstructed body size of this individual (approximately 6 m) (Fig. 22.2B), together with partial neurocentral fusion in preserved dorsal and sacral vertebrae, is suggestive of a subadult age for the animal at the time of death (Brochu, 1996). The UMNH and RAM have collected other associated, less complete tyrannosaurid individuals and isolated tyrannosaurid elements from the Kaiparowits Formation during the course of the KBP. Specimens include: a partial subadult

dentary (RAM 8395), associated hind limb materials including a left femur, partial right tibia, complete right astragalus and calcaneum, partial right metatarsal III, and complete pedal PIII-1 and PIII-2 (RAM 9132); associated juvenile cranial material, including fused parietals, a partial unfused frontal, and partial dentary (UMNH VP 12586); partial limb elements and teeth (UMNH VP 16161); fragmentary limb elements, a pedal phalanx, and an ungual (UMNH VP 16692); associated limb and skull fragments, including a partial dentary, pedal phalanx, and ungual (UMNH VP 16693); a tooth, caudal vertebrae, left femur, tibia, fibula, metatarsal III, single pedal phalanx, and ungual of a large adult individual (UMNH VP 11302); isolated fused parietals (UMNH VP 16225); an isolated humerus (UMNH VP 12223); an isolated lacrimal from a large adult; and an isolated jugal from a large adult (UMNH VP 16691). The taxonomic identity of these specimens is currently under review (Loewen et al., in prep.). Recent phylogenies (Brusatte et al., 2010; Carr et al., 2011) recover Teratophoneus as a derived tyrannosaurine tyrannosaurid just basal to a clade composed of the Campanian–Maastrichtian taxa Daspletosaurus, Tyrannosaurus, and Tarbosaurus. These authors also recover the southern laramidian taxon Bistahieversor (Carr and Williamson, 2000, 2010) from the late Campanian of New Mexico as a derived tyrannosauroid outside of Tyrannosauridae proper. Research on UMNH VP 16690 supports the distinction between Teratophoneus, Bistahieverser sealeyi, and the Wahweap tyrannosaurid (UMNH VP 20200), documenting the presence of at least three distinct tyrannosauroid taxa from the southern Western Interior Basin. Moreover, preliminary phylogenetic analyses suggest that these three southern tyrannosauroid species form a clade to the exclusion of all other Campanian tyrannosaurids known from northern formations (i.e., Gorgosaurus, Albertosaurus, Daspletosaurus, Daspletosaurus n. sp. from the Dinosaur Park Formation and Daspletosaurus n. sp. from the Two Medicine Formation), lending critical information to the geographic distribution of theropod taxa across the Late Cretaceous Western Interior Basin (Loewen et al., in prep.). The abundance of tyrannosaurid material collected during the relatively brief time span of the KBP challenges previous statements that the upper Campanian formations of New Mexico exceed those of Utah with regard to tyrannosaurid preservation (Carr and Williamson, 2000), and highlights the importance of fossil-bearing strata of southern Utah in understanding dinosaur evolution in the Western Interior Basin. Study of the diagnostic tyrannosaurid material recovered from the Kaiparowits Formation will permit a more comprehensive understanding of tyrannosauroid diversity, biogeography, and evolution during the Late Campanian.

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22.3. Reconstruction of the skull of a juvenile Teratophoneus curriei (UMNH VP 16690) from the Kaiparowits Formation. Reconstruction and original photograph by Rob Gaston of Gaston Design, Inc.


Ornithomimids (ostrich mimics) were medium-bodied (200– 700 kg; Christiansen and Fariña, 2004), lightly built dinosaurs, estimated to be among the fastest theropods (Coombs, 1978; Thulborn, 1982; Christiansen, 1998). They are generally regarded as close relatives of tyrannosauroids, falling within Coelurosauria but outside of Maniraptora, the more derived subclade that includes modern birds. Advanced members of the group possess toothless, keratinous covered beaks, elongate necks, and gracile limbs. The discovery of Sinornithomimus in a mass-death assemblage prompted speculation that ornithomimids were social animals, congregating in large groups (Kobayashi et al., 1999; Varricchio et al., 2008). The diet of ornithomimids has been a matter of some debate; hypotheses have been put forth ranging from myrmecophagy (Russell, 1972) to filter feeding (Norell, Clark, and Makovicky, 2001). However, most recent studies make a strong argument for herbivory (Kobayashi et al., 1999; Barrett, 2005; Zanno, Gillette, et al., 2009; Zanno and Makovicky, 2010), based in part on the recovery of stomach stones in several remarkably preserved specimens (Kobayashi et al., 1999; Ji et al., 2003; Wings, 2007). Owing to a lack of teeth, ornithomimids are not generally represented in faunal lists generated on the basis of microvertebrate studies. Thus, no ornithomimids have been reported from the Iron Springs, Dakota, Straight Cliffs, or Wahweap formations (Tables 22.1–22.4). However, their absence from these formations is almost certainly the result of collection and/or taphonomic biases because ornithomimid remains have been recovered from both older and younger formations within the Colorado Plateau (Marsh, 1890; Ostrom, 1970). Ornithomimid skeletal remains form an abundant constituent of the theropod materials recovered from the Kaiparowits Formation, and along with those of tyrannosaurids, they are among the most commonly recovered. Despite their relative abundance, little progress has been made in identifying the ornithomimid remains from the Kaiparowits Formation. Thirty years ago, an ornithomimid specimen consisting of a nearly complete hind limb, fragmentary pelvis, and partial axial column (MNA PI.1762A) was collected from the Kaiparowits Formation by the Museum of Northern Arizona and subsequently referred to the late Maastrichtian taxon Ornithomimus velox by DeCourten and Russell (1985). The holotype of O. velox (YPM 542) is fragmentary, comprising a distal tibia with astragalus, incomplete left metatarsus and second pedal digit, together with potentially associated manual elements (YPM 548). Its taxonomic status is currently uncertain. Russell (1972) noted that the two supposedly diagnostic characteristics of O. velox provided by

previous authors (shortness of the metatarsus and metatarsal II longer than metatarsal IV) were derived from a reconstruction of the incompletely preserved metatarsus (Marsh, 1890). At the time, the length and proportion of the metatarsals of O. velox could not be determined from the type specimen; therefore, these traits could not be evaluated with confidence (Russell, 1972). Moreover, Makovicky, Kobayashi, and Currie (2004) note only a single manual character as potentially diagnostic for O. velox – metacarpal I being the longest in the metacarpus. However, this trait is shared with Ornithomimus edmontonicus, and therefore, it would only be diagnostic to species level if these taxa were to prove synonymous. Although it is currently unclear whether O. velox can be regarded as a valid taxon, work on the status of this enigmatic taxon is forthcoming. Additional preparation of the holotype metatarsus (YPM 542) is permitting accurate measurements of its proportion, and detailed morphometric analyses of the manus (YPM 548) (Neabore et al., 2007; Lavender et al., 2010) is offering valuable insights that may help resolve these issues. Even if O. velox is upheld as a valid taxon by additional research, the referral of the Kaiparowits specimen MNA PI.1762A to this species is dubious. DeCourten and Russell’s (1985) justification for the referral of MNA PI.1762A to O. velox lies in pedal ungual morphology (which they identify as similar in both specimens), relative proportions of the pes, and temporal equivalence (at the time, palynological evidence supported a Lancian age for the Kaiparowits Formation [Lohrengel, 1969], suggesting that the Kaiparowits and the Denver Formation of Colorado, from which the type specimen of O. velox is described [Marsh, 1890] are coeval). The specific ratio used by DeCourten and Russell (1985) to assign the Kaiparowits specimen to O. velox (ratio of the length of the second pedal ungual to the basal phalanx of digit II) is given by the authors as 0.61–0.64 in “pre-Lancian” North American taxa (Ornithomimus edmontonicus, sensu Makovicky, Kobayashi, and Currie, 2004, and Struthiomimus altus), 0.78 in MNA PI.1762A, and 0.88 in the holotype of O. velox. Given that the proportions of MNA PI.1762A are in fact closer to other North American ornithomimid species than to O. velox (as given), we do not see the justification for this association. Moreover, although proportional characteristics have been proposed as diagnostic for individual ornithomimid taxa (Russell, 1972), recent studies (Kobayashi, Makovicky, and Currie, 2006) have challenged the validity of most of these differentiations. Kobayashi, Makovicky, and Currie (2006) cite characteristics of the skull, forelimb, and caudal vertebrae as diagnostic for ornithomimids; however, they do not identify any diagnostic features of the pes among North American taxa. Finally, although Longrich (2008b) outlines differences between the pedal unguals of several species of


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22.4. Skeletal reconstruction of Ornithomimus, showing ornithomimid elements recovered from the Kaiparowits Formation in white (multiple specimens and individuals represented). Adapted with permission from artwork by Greg Paul.

North American ornithomimids that may ultimately prove useful in discerning the evolutionary relationships of MNA PI.1762A, it is unclear how large of a sample was considered in the study and whether these distinctions can be discretely quantified by gap coding (Archie, 1985). Ultimately, additional study of Western Interior Basin ornithomimid materials is needed to confirm or refute these various distinctions. Recent fieldwork conducted by the KBP has added significant morphological data to bear upon the identity of Kaiparowits ornithomimid materials (Fig. 22.4), including the contentious specimen MNA PI.1762A. Newly recovered

elements include associated caudal vertebrae, metatarsal fragments, and phalanges (UMNH VP 12223), two isolated tibiae (UMNH VP 9553 and UMNH VP 16698), an isolated articulated foot with an associated limb bone (UMNH VP 19467); an associated partial rear skeleton including caudal vertebrae, a partial pelvis, and partial foot (UMNH VP 20188); a badly damaged skull (UMNH VP unnumbered), as well as the first articulated forelimb material from the formation (UMNH VP 16385). The forelimb materials (UMNH VP 16385) consist of an incomplete and partially crushed manus, carpus, and antebrachium (Fig. 22.5). Additional material recently collected

22.5. Three-dimensional surface scan of the left ornithomimid manus (UMNH VP 16385) from the Kaiparowits Formation in dorsal view, showing subequal metacarpals I and II and straight ungual morphology. Placement and identity of phalangeal fragments in digit III is approximate. Scale bar = 10 mm. 510

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22.6. Morphological variation in distal caudal vertebrae of late Campanian ornithomimids from the Western Interior of North America. (A–C, F, I) Ornithomimidae incertae cedis from the Kaiparowits Formation (UMNH VP 16260); (D, G) and (J) CMN 12228 Dromiceiomimus brevetertius, Kobayashi, Makovicky, and Currie, 2006; (Ornithomimus edmontonicus sensu Makovicky, Kobayashi, and Currie, 2004); and (E, H, K) Struthiomimus altus (CMN 2102/8902). Kaiparowits ornithomimid shown in (A) dorsal, (B) right lateral, and (C) ventral views. Late Campanian ornithomimid caudals in right lateral views (F–H) showing the absence of lateral groove for the prezygapophyses in all but Dromiceiomimus (G). Prezygapophyses of ornithomimid caudal vertebrae in ventral views (I–K) showing presence of a ventral groove in Dromiceiomimus (J). lg, lateral groove on the centrum caused by articulation with the prezygapophyses; ns, neural spine remnant; prz, prezygapophysis; pzg, ventral groove on the prezygapophysis; vg, ventral groove on centrum. Upper left scale bar = 4 mm (A–C). Upper right scale bar = 5 mm (E). All other views not to scale.


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by the Raymond M. Alf Museum (RAM 6794) includes the left pelvis (complete ilium, partial pubis and ischium), left hind limb (including partial femur, partial tibia, fibula, metatarsals II–V, and incomplete set of phalanges), partial right hind limb (complete femur, tibia, with partial metatarsals and incomplete set of phalanges), 15 caudal vertebrae, and several incomplete ribs. RAM 6794 thus provides useful comparative material to MNA PI.1762A. Preliminary examination of the forelimb materials (UMNH VP 16385) reveals similarities to O. edmontonicus in the relative size of metacarpal I and in ungual morphology. However, isolated caudal vertebrae collected by the UMNH (UMNH VP 16260; Fig. 22.6A–C, F, I) lack the diagnostic, deeply grooved articulation between pre- and postzygapophyses (Fig. 22.6F–H), as well as the prezygapophyseal ventral groove (Fig. 22.6I–K) of Dromiceiomimus brevetertius (Kobayashi, Makovicky, and Currie, 2006) (O. edmontonicus sensu Makovicky, Kobayashi, and Currie, 2004). A more comprehensive investigation of ornithomimid materials from the Kaiparowits Formation, including reevaluation of MNA PI.1762A, is currently being undertaken by researchers at the UMNH, RAM, and the College of the Holy Cross (Zanno, Sampson et al., 2005; Zanno, Loewen, et al., 2009; Neabore et al., 2007; Lavender et al., 2010) and is expected to provide additional insights regarding the taxonomic and systematic relationships of North American ornithomimids. Therizinosauria Therizinosaurians (scythe reptiles) are regarded as one of the most enigmatic theropod subclades owing to their remarkably bizarre anatomy. Derived members are characterized by a keratinous beak, a potbelly, and over 1-m-long scytheshaped claws on the hands. With some species weighing in at over 6 tons, therizinosaurians achieve some of the largest body sizes among maniraptoran theropods (Zanno and Makovicky, in prep.) and are generally considered chiefly herbivorous, partly as a result of their enlarged gut and small, leaf-shaped teeth (Paul, 1984; Weishampel and Norman, 1989; Russell, 1997; Zhang et al., 2001; Kirkland et al., 2005; Zanno, Gillette, et al., 2009; Zanno and Makovicky, 2010). At least early members of the clade were feathered (Xu, Tang, and Wang, 1999). For the first half century after their discovery, therizinosaurians were known exclusively from Asia. However, recent years have seen the discovery of three therizinosaurian species in western North America (Kirkland and Wolfe, 2001; Kirkland et al., 2005; Zanno, Gillette, et al., 2009). In addition, although still controversial, several isolated elements from Upper Cetaceous formations of the northern Western Interior Basin have been referred to the clade including two 512

isolated frontals, an ungual, an astragalus, and a cervical vertebra (Russell, 1984; Currie, 1987b, 1992; Ryan and Russell, 2001). Only a single discovery marks the presence of therizinosaurians in the Late Cretaceous of Utah – the recently described species Nothronychus graffami, from the lower Turonian portion of the Tropic Shale (Gillette et al., 2001; Zanno, Gillette, et al., 2009) – although description of its sister species Nothronychus mckinleyi from middle Turonian sediments in nearby New Mexico (Kirkland and Wolfe, 2001) confirmed the existence of the group in the Late Cretaceous of North America nearly a decade earlier. Nothronychus graffami is a large-bodied member of the derived subclade Therizinosauridae and is represented by the most complete skeleton yet discovered for the clade (Fig. 22.7). Recent phylogenetic studies indicate that this taxon is more closely related to Late Cretaceous taxa from Asia than to the Early Cretaceous North American therizinosaurian Falcarius utahensis, supporting the idea of faunal interchange between western North America and Asia in the late Early Cretaceous (Russell, 1993; Cifelli et al., 1997; Kirkland et al., 1997, 1999; Zanno and Makovicky, 2011). As therizinosaurids were not unequivocally recognized as North American inhabitants until relatively recently, and given that their morphology (especially the teeth) is highly convergent with other clades of herbivorous dinosaurs, it is possible that therizinosaurid remains have been collected in other Upper Cretaceous formations in the Western Interior Basin and that future investigation may reveal a more widespread presence than currently recognized. Oviraptorosauria Oviraptorosaurians (egg thieves) are a predominantly endentulous group of feathered maniraptoran dinosaurs that are often adorned with a cranial crest, keratinous beak, and powerful arms bearing formidable claws.. Members of the group are predominantly small (3 kg) to medium bodied (250 kg); however, an exemplary Late Cretaceous species from China (Gigantoraptor, Xu et al., 2007) is estimated at over 3000 kg (Zanno and Makovicky, in prep.). Oviraptorosaurians are widely known in Asia, where upward of a dozen taxa have been named, many from remarkably complete skeletons. In contrast, only a few North American members of the clade have been described (generally referred to as caenagnathids, although this taxonomy is currently contentious; Zanno and Sampson, 2005), and almost all are known from isolated and fragmentary materials. An exception to this is a new Maastrichtian-age species from South Dakota, which is represented by two partial skeletons awaiting description (Triebold, Nuss, and Nuss, 2000). Zanno et al.


22.7. Skeletal reconstruction of the therizinosaurid Nothronychus graffami based on the holotype (UMNH VP 16420) from the Upper Cretaceous Tropic Shale, southern Utah. Modified from Zanno, Gillette, et al. (2009).

Although the dietary preference of advanced members of the clade is presently unclear, primitive members of the group possess incisiform front teeth and stomach stones indicative of an herbivorous component to the diet (Ji et al., 1998; Xu et al., 2002; Barrett, 2005; Zanno, Gillette, et al., 2009; Longrich, Currie, and Dong, 2010; Zanno and Makovicky, 2010). Several other rarely elucidated aspects of dinosaur paleobiology are known for oviraptorosaurians, including details about egg laying (Sato et al., 2005; Erickson et al., 2007) and brooding behavior (Norell et al., 1994, 1995). Although these dinosaurs are remarkably similar to birds in anatomy and behavior, current phylogenetic analyses demonstrate that these similarities are the result of convergence rather than ancestry (Sues, 1997; Makovicky and Sues, 1998; Norell, Makovicky, and Currie, 2001; Rauhut, 2003; Lu et al., 2004). Because derived oviraptorosaurians lack teeth, their remains are not commonly recovered in microvertebrate assemblages. This bias may explain their absence from prior faunal surveys of Upper Cretaceous formations of southern Utah (Tables 22.1–22.5). Thus, as is the case with toothless

ornithomimids, oviraptorosaurians are not yet recognized in the Iron Springs, Dakota, Straight Cliffs, or Wahweap formations, although they too are known from both earlier and later formations in the Western Interior (Sues, 1997; Makovicky and Sues, 1998). Definitive oviraptorosaurian remains were not known from the prolific Kaiparowits Formation until UMNH crews recovered the first diagnostic skeletal material in 2002. A nearly complete left manus (missing only the second ungual), carpus, and distal antebrachium (UMNH VP 12765) of a new oviraptorosaurian were recovered in articulation within a remnant of channel sandstone (Fig. 22.8). As is often the case with Kaiparowits specimens (Lund et al., 2008), exceptional soft tissue preservation makes allusion to the keratinous sheath of one ungual. Additional elements – including fragmentary metatarsals and pedal phalanges, and a partial, articulated pedal digit with ungual – were salvaged from the surrounding hillside. The specimen, dubbed Hagryphus giganteus, represents the first dinosaur taxon to be named from Grand Staircase–Escalante National Monument and


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is notably larger than its named northern cousins Chirostenotes and Elmisaurus (Fig. 22.9), with an estimated body size increase of 30–40% (Zanno and Sampson, 2005) and an estimated mass of ~180 kg (Zanno and Makovicky, in prep.). Proportionally gigantic isolated unguals of oviraptorosaurians are also known from Alberta (P. Currie, pers. comm., 2003) and the undescribed skeleton of a new oviraptorosaurian from South Dakota (Triebold, Nuss, and Nuss, 2000) represents another relatively large-bodied species akin to Hagryphus. Hagryphus is the first North American oviraptorosaurian described from south of Montana and South Dakota and represents the southernmost limit yet identified for this enigmatic group of theropods within the Western Interior Basin. Although the holotype represents the only published account of oviraptorosaurian materials from the formation, the recent recognition of a distal second right metatarsal (RAM 12433) closely comparing to an oviraptorosaurian specimen CMN 8538 (formerly Macrophalangia) from Alberta, Canada, suggests that other fragmentary oviraptorosaurian materials may have been collected that await identification. Dromaeosauridae Dromaeosaurid theropods (running reptiles) are swift smallto medium-bodied predators (0.6–350 kg; Turner et al., 2007) distinctive in possessing lightly built skeletons, an enlarged sickle claw on the second digit of the foot, and stiff tails reinforced by dramatically elongated bony struts. Dromaeosauridae is one of the more diverse maniraptoran clades, and its members are considered to be among the closest extinct cousins to birds. Several small-bodied, feathered species have been found within exceptionally prolific Lower Cretaceous lake beds in China (Xu, Wang, and Wu, 1999; Xu, Zhou, and Wang, 2000) – including the miniature “four-winged” dinosaur Microraptor – and the majority of dromaeosaurid species are known from Asia. Yet the group has a relatively diverse North American representation, with at least five documented species, including the largest dromaeosaurid known to date, Utahraptor, recovered from Lower Cretaceous beds in central Utah (Kirkland, Gaston, and Burge, 1993). Dromaeosaurids are known to have been widespread across the Upper Cretaceous Western Interior Basin (Norell and Makovicky, 2004). Their serrated, blade-like teeth are commonly recovered in microvertebrate localities within Upper Cretaceous beds of southern Utah. At least one species is known from the Iron Springs Formation on the basis of isolated teeth (Eaton, 1999; Table 22.1), whereas at least two dromaeosaurid tooth morphotypes representing a minimum of two species are known from the Dakota, Straight Cliffs, and Wahweap formations (Tables 22.2–22.5). These teeth 514

22.8. Holotype manus of the oviraptorosaurian Hagryphus giganteus (UMNH VP 12765) in dorsal view. DI, digit I; DII, digit II; DIII, digit III. Scale bar = 5 cm.

have commonly been referred to the subclades Dromaeosaurinae and Velociraptorinae (Eaton, 1999; Eaton, Cifelli, et al., 1999; Eaton, Diem, et al., 1999; Parrish, 1999; Kirkland, 2001). However, recent studies of dromaeosaurid evolutionary relationships vary, and many no longer recover these two major divisions (Hwang et al., 2002; Senter et al., 2004; Norell et al., 2006; Senter, 2007; Xu et al., 2009). Furthermore, it is Zanno et al.


22.9. Skeletal reconstruction of Hagryphus giganteus, showing recovered portions of the skeleton (UMNH VP 12765) in white. Missing sections filled in with skeletal materials recovered from the Hell Creek Formation and adapted with permission from artwork by Scott Hartman.

not clear that these divisions are reflected with consistency in tooth morphology. For instance, Currie and Varricchio (2004:table 4.2) demonstrate that the dimensions and denticle counts of the teeth of the Late Cretaceous North American “velociraptorine” Saurornitholestes fall within the range of variation observed in the dromaeosaurid Atrociraptor from the Horseshoe Canyon Formation, which is often recovered as closer to Dromaeosaurus (the internal specifier for Dromaeosaurinae) than Velociraptor (the internal specifier for Velociraptorinae) (Makovicky, Apesteguia, and Agnolin, 2005; Senter, 2007; Zhang et al., 2008; Xu et al., 2009). They also note that the maxillary teeth of the North American dromaeosaurids Bambiraptor (Burnham et al., 2000), Deinonychus (Ostrom, 1969), Saurornitholestes (Currie, Rigby, and Sloan, 1990), Atrociraptor, and the Asian species Velociraptor (Barsbold and Osmólska, 1999) are all “closely comparable in terms of tooth shape, carina position, denticles size, and denticles shape” (Currie and Varricchio, 2004:122), yet current phylogenetic analyses recover these taxa as spread across the dromaeosaurid family tree (Hu et al., 2009) suggesting caution in the taxonomic assignment of isolated teeth of this morphotype beyond Dromaeosauridae. Collection of teeth from microvertebrate localities suggested the presence of “dromaeosaurine” and “velociraptorine” dromaeosaurids in the Kaiparowits Formation over a decade ago (Hutchison et al., 1997; Table 22.5). Subsequent

collection and detailed examination of UMNH and RAM collections has verified the existence of at least two dromaeosaurid species in the formation on the basis of isolated teeth recovered as surface float or within burial sites of herbivorous dinosaurs (Fig. 22.10A–D). In earlier publications (Zanno, Sampson et al., 2005; Gates et al., 2010), we provisionally referred these to cf. Dromaeosaurus and cf. Saurornitholestes


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Table 22.6. Revised theropod fauna of the Wahweap and Kaiparowits formations, this study Wahweap Formation

Kaiparowits Formation

Theropoda

Theropoda

Theropoda indet.

Theropoda indet.

Tyrannosauridae

Tyrannosauridae

Genus et sp. nov.

Genus et sp. nov.

Paraves

Ornithomimidae

Dromeosauridae

Ornithomimidae indet.

Morphotype A

Oviraptorosauria

Morphotype B

Hagryphus giganteus

Troodontidae

Paraves

Troodontidae indet.

Dromeosauridae indet. Morphotype A Morphotype B Troodontidae Talos sampsoni Aves ? cf. Avisaurus


22.10. Paravian theropod teeth from the Kaiparowits Formation. (A) UMNH VP 16306 Dromaeosauridae morphotype A, (B) RAM 9136 Dromaeosauridae morphotype A, (C) UMNH VP 11803 Dromaeosauridae morphotype B, (D) RAM 12084 Dromaeosauridae morphotype B, (E) UMNH VP 12507 Troodontidae maxillary tooth, (F) UMNH VP 12507 Troodontidae dentary tooth, and (G) RAM 12083 Theropoda incertae sedis (cf. “Richardoestesia”). Scale bar = 1 cm.

(sensu Sankey, 2001; Sankey et al., 2002) based on comparisons with teeth from the approximately coeval Dinosaur Park and Aguja formations. Here we adopt a more general nomenclature that considers new information regarding the limited paleogeographical ranges of Western Interior Basin theropods by restricting the taxonomic identify of these teeth to Dromaeosauridae indet. morphotype A (Dromaeosaurus type) and morphotype B (Saurornitholestes/Atrociraptor/ Bambiraptor type) (Table 22.6). Dromaeosauridae postcranial materials remain rare in the Kaiparowits Formation and include an isolated pedal phalanx PII-I (UMNH VP 12494) and isolated unguals.

Troodontids (wounding teeth) are a group of feathered maniraptoran dinosaurs, notable for exhibiting some of the smallest body sizes (0.1 kg; Therrien and Henderson, 2007; Turner et al., 2007) and the largest relative brain sizes (Currie, 2005) within Dinosauria. The group is known almost exclusively from Asia, and until recently, only two genera were recognized in North America: Troodon (sensu Currie, 1987a, 2005) and Pectinodon (Carpenter, 1982; Longrich, 2008a), although other potentially valid troodontid species have been described and or subsumed into existing taxa (e.g.,

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Troodontidae


22.11. Morphology of troodontid frontals from the late Campanian of the Western Interior of North America. (A–B) UMNH VP 16303 troodontid incertae cedis from the Kaiparowits Formation of Utah in (A) ventral and (B) dorsal views. (C) CMN 12340, Troodon formosus cranium from the Dinosaur Park Formation, Alberta, Canada, in ventral view. apo, articular surface for the postorbital; la, articular surface for the lacrimal; lf, left frontal; na, articular surface for the nasal; ol, olfactory lobe; or, orbital margin; pa; parietal; po; postorbital; rf, right frontal; sfr, ridge on the rostral margin of the supratemporal fenestra. Scale bar = 4 cm.

Stenonychosaurus, Koparion). As a result of their distinctive teeth and the possible presence of seeds preserved as gut contents in the primitive species Jinfengopteryx (Xu and Norell, 2006), several authors have proposed an omnivorous or herbivorous diet for at least some members of the clade (Holtz, Brinkman, and Chandler, 1998; Zanno, Gillette, et al., 2009; Zanno and Makovicy, 2010). However, other species possess blade-like teeth, suggesting that dietary diversity, including carnivory, likely characterized the group (Currie and Dong, 2001; Zanno and Makovicy, 2010). Several troodontid specimens preserve remarkable evidence of behavior. Perhaps the most intriguing troodontid is the miniature Chinese species Mei long. The subadult holotype was discovered preserved in a distinctive avianlike sleeping posture with its head rotated back toward the tail and tucked under its wing-like forelimb (Xu and Norell, 2004). Although not as widely touted, the holotype specimen of another Asian species, Sinornithoides youngi (Currie and Dong, 2001), is also preserved in this posture. Troodontid nests, eggs, and embryos are known from Upper Cretaceous formations in the Western Interior Basin, and studies on clutch volume, reproductive physiology, and egg-laying behavior (Varricchio et al., 1997; Varricchio, Horner, and Jackson, 2002; Varricchio and Jackson, 2004) have yielded important information on the reproductive biology of these rare theropods.

Troodontid teeth, which are widely recognized as diagnostic for the clade (Currie, 1987a; Makovicky and Norell, 2004), have been collected from the Iron Springs, Dakota, and Straight Cliffs formations and exclusively referred to Troodontidae (Eaton, 1999; Eaton, Cifelli, et al., 1999; Tables 22.1–22.3), whereas troodontid teeth from the Wahweap Formation have been identified as Troodontidae indet. (Kirkland, 2001), cf. Troodon (Parrish, 1999), and Troodon sp. (Eaton, Cifelli, et al., 1999; Table 22.4). The presence of troodontid theropods in the Kaiparo wits Formation was originally documented on the basis of isolated teeth (Hutchison et al., 1997; Eaton, Cifelli, et al., 1999). Numerous troodontid teeth have been collected by the UMNH and RAM over the past decade (Fig. 22.10E, F), adding to those collected during earlier microvertebrate surveys (Hutchison et al., 1997; Eaton, Cifelli, et al., 1999). Several authors referred these teeth to Troodon sp. (Hutchison et al., 1997; Eaton, Cifelli, et al., 1999; Table 22.5). However, troodontid cranial and postcranial materials have been recovered from the Kaiparowits Formation recently that shed doubt on this referral. During the field season of 2005, an isolated left frontal of a troodontid (UMNH VP 16303) was recovered (Zanno, 2007; Fig. 22.11A, B), and 3 years later, in 2008, a partially articulated, partial postcranial skeleton representing a subadult troodontid individual (UMNH VP 19479) was found (Zanno,


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22.12. Skeletal reconstruction of the Kaiparowits Formation troodontid Talos sampsoni showing extent of holotype material (UMNH VP 19479) in white. Adapted with permission from artwork by Scott Hartman.

Varricchio, et al., 2009; Zanno et al., 2011). The frontal shares several features with Troodon formosus (CMN 12340) from the contemporaneous Dinosaur Park Formation in Alberta, such as an elongate, triangular morphology, an extensive orbital rim, a prominent ridge defining the rostral limit of the supratemporal fenestra, and a large, laterally extensive postorbital process (Fig. 22.11B, C). However, UMNH VP 16303 also varies from CMN 12340 and other troodontid frontals recovered from coeval formations across the Western Interior Basin (particularly the Two Medicine Formation) in the shape of the orbital margin, supratemporal ridge, and orbital bulbs. The partial postcranial skeleton (UMNH VP 19479; Fig. 22.12) also differs from specimens currently considered part of the T. formosus paradigm and was recently made the holotype for the new genus and species Talos sampsoni (Zanno et al., 2011). In particular UMNH VP 19479 is significantly more gracile in metatarsal morphology (Fig. 22.13) when compared to materials from T. formosus individuals of smaller and larger body size, which indicates that its slender nature is not solely attributable to ontogenetic variation (Zanno et al., 2011). The specimen also exhibits autapomorphic features of the foot and ankle. Additional work is currently underway to determine whether UMNH VP 16303 is distinguishable from other Western Interior Basin troodontid frontals and to investigate possible variation between the teeth of T. formosus and troodontid teeth from the Kaiparowits formation to determine whether late Campanian Western Interior Basin troodontid teeth are diagnostic beyond the level of Troodontidae. Finally, a poorly preserved, partial paravian skeleton collected by Howard Hutchison of the University of California at Berkeley’s Museum of Paleontology in 1994 was

identified by him as a dromaeosaurid, and this identification was retained in earlier KBP publications (Zanno, Sampson et al., 2005; Zanno et al., 2010). The specimen, UCMP 149171, consists of a proximal tibia, fragmentary metatarsals, pedal phalanges, and pedal unguals, as well as some fragmentary skull material, including the basioccipital, fused parietals, and portions of the squamosals. The tibial morphology of UCMP 149171 suggests that these materials represent another troodontid specimen (Zanno et al., 2011). Further study is needed to determine how these specimens, along with additional isolated materials such as isolated caudal vertebrae, compare to troodontid materials across the Western Interior Basin.

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Aves Abundant evidence exists in support of the hypothesis that birds are the direct descendants of maniraptoran theropods, and thus represent a specialized clade of living dinosaurs (Padian and Chiappe, 1998). Just as living birds comprise one of the most diverse vertebrate groups in our modern ecosystems, the group is known to have had a strong representation during the Cretaceous. Over 30 genera of Cretaceous birds, most preserving evidence of feathers, are known from the Early Cretaceous of China alone (Zhou and Li, 2010, and references therein). Many of these taxa retain primitive morphology such as teeth, clawed fingers on the hand, and a long tail, such as the famous Jurassic bird Archaeopteryx. To date, avian remains have not been documented in the Iron Springs, Dakota, Straight Cliffs, and Wahweap formations (Tables 22.1–22.4). A number of fragmentary avian skeletal elements have been collected during the KBP. A single paravian tooth (RAM 11906) possessing a constricted junction


22.13. Left foot of the holotype (UMNH VP 19479) of Talos sampsoni in dorsal view, illustrating its gracile proportions, arctometatarsalian condition, subequal third and fourth metatarsals, and well-developed raptorial digit II. Phalanges of digits I and II inverted from right foot. Scale bar = 10 mm.

between root and crown was collected from the Kaiparowits Formation by the RAM and may be referable to Aves. A proximal portion of a right coracoid referable to Enantiornithines (RAM 14306) is also known. Currently, the only named avian taxon known from the Kaiparowits Formation is Avisaurus (Hutchison, 1993). Two species of Avisaurus are known from Upper Cretaceous formations in Montana, A. archibaldi (Brett-Surman and Paul, 1985) from the Hell Creek Formation (formerly also known from the Lecho Formation in Argentina, now separated into a new species Soroavisaurus australis; Chiappe, 1993) and A. gloriae (Varricchio and Chiappe, 1995) from the Upper Two Medicine Formation. Both are known solely from the tarsometatarsus. By comparison, the Kaiparowits specimen represents the most complete enantiornithine bird fossil known from North America to date, preserving a large portion of the skeleton including a partial axial column with pygostyle, a well-developed pectoral girdle and forelimb with a robust keel, U-shaped furcula, and papillae remigiales, and a robust tarsometatarsus with highly recurved unguals (Hutchison, 1993). Preliminary study indicates that this specimen represents a new species of Avisaurus, but after publication of an abstract describing the find (Hutchison, 1993), no subsequent research has been undertaken to name the specimen. Theropoda indet. The San Diego Museum of Natural History and Jeff Eaton recovered a theropod specimen consisting of limb material, including metatarsals (UMNH VP 19477) from the John Henry Member of the Straight Cliffs Formation, Cedar Canyon (J. Kirkland, pers. comm., 2010). However, UMNH VP 19477 was not fully prepared when we wrote this chapter and is not yet assignable beyond Coelurosauria.


Teeth similar to the enigmatic theropod tooth morphotypes “Richardoestesia” and “Paronychodon” are reported throughout the Dakota, Straight Cliffs, Wahweap, and Kaiparowits formations (Hutchison et al., 1997; Eaton, Cifelli, et al., 1999; Eaton, Diem, et al., 1999; Parrish, 1999; Kirkland, 2001; Tables 22.2–22.5). The KBP and RAM crews also collected teeth sharing features with the morphotype “Richardoestesia” from the Kaiparowits Formation (UMNH VP 12684; RAM 12083; Fig. 22.10G). These teeth exhibit minute denticles on the distal carinae (~0.14–0.15 mm wide as in “R. gilmori” sensu Currie, Rigby, and Sloan, 1990), slight recurvature, and either minute, low-relief denticles on mesial carinae (UMNH VP 12684) or no denticles on the mesial carinae (RAM 12083). However, tooth morphotypes similar to “Paronychodon” have not yet been confirmed in UMNH or RAM collections. The taxonomy of isolated teeth is problematic. Teeth falling within the parameters of the “Richardoestesia” and “Paronychodon” morphotypes from multiple Upper Cretaceous formations across the Western Interior Basin (including those of southern Utah) may represent multiple theropod taxa and these taxa may or may not represent natural evolutionary groupings. Furthermore, some disparate tooth types referred to these two taxa and found within the same formation may belong to the same species (Longrich, 2008a). At minimum, given the distinct taxonomic composition of the geographically intervening Kaiparowits Formation, teeth referred to “Richardoestesia” and “Paronychodon” from the Kaiparowits Formation and Aguja Formation of Texas (Sankey, 2001) probably represent taxa distinct from those in Upper Cretaceous formations of Alberta, Canada. Here we refer these isolated teeth to the suprageneric level, as we have done in other instances in this chapter, considering them theropod indet. (Table 22.6).

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Di s c u s s io n Isolated Tooth Taxonomy and Fragmentary Western Interior Basin Remains

Western Interior Basin was low and that many taxa probably had pan-Laramidian geographic ranges. Now that it has been demonstrated that coeval formations in the upper Campanian of the Western Interior Basin exhibit unique dinosaur faunas with unexpectedly limited geographic ranges (Smith et al., 2003, 2004; Sampson et al., 2004, 2009, 2010; Gates and Evans, 2005; Zanno, Gates, et al., 2005; Zanno, Sampson, et al., 2005; Lucas et al., 2006; Gates and Sampson, 2007; Zanno, 2007; Wagner and Lehman, 2009; Zanno, Loewen, et al., 2009; Gates et al., 2010; Sampson and Loewen, 2010; Sampson et al., this volume, Chapter 28), it is more reasonable to assume that teeth or fragmentary skeletal remains from Western Interior Basin formations with poorly known faunas are more likely to represent new species than be referable to existing taxa.

Although proposals have been put forth supporting the taxonomic utility of tooth morphology in small theropods (Currie, Rigby, and Sloan, 1990; Fiorillo and Currie, 1994; Sankey, 2001; Sankey et al., 2002; Samman et al., 2005; Smith, 2005; Larson, 2008; Longrich, 2008a), these studies have focused either on the intraformational identification of isolated theropod teeth, which are generally referred to an existing species of the same formation on the basis of similarity, or intraspecific variation in tooth morphology (ontogenetic or tooth positional studies). Thus far, broad-scale studies of interspecific, interformational diagnostic utility have not been considered. Indeed, such a study would require a sufficient sample of dentigerous small theropod skeletons of closely related species across the Western Interior Basin, and although our knowledge of Western Interior Basin theropods is fast improving, we still lack the accompanying skeletal evidence to conduct such a query for most theropod clades. Data arguing against taxonomic utility of isolated theropod teeth are found in Farlow et al. (1991) and Currie and Varricchio (2004), who demonstrate significant overlap in morphological parameters of isolated dromaeosaurid teeth from different genera, and detailed studies by Samman et al. (2005), which fail to identify isolated tyrannosaurid teeth from the same formation even to genus level. Indeed, the recent recovery of diagnostic troodontid skeletal material from the Kaiparowits Formation (i.e., Talos sampsoni) indicates that previous referral of isolated troodontid teeth from that formation to Troodon sp. (Eaton, Cifelli, et al., 1999) is dubious. The same may be true for the referral of Wahweap troodontid teeth to Troodon sp. (Eaton, Cifelli, et al., 1999) and the problematic taxon Aublysodon sp. (Eaton, Diem, et al., 1999). Whether or not the Kaiparowits and/or Wahweap troodontid teeth show significant morphological variation as to merit distinction from T. formosus without associated skeletal material is currently under study. This single example underscores the larger potential problem of assigning isolated teeth to genus or species over broad geographic areas within the Western Interior Basin, and we caution against the referral of any isolated teeth and/or undiagnostic skeletal remains to existing genera or species (Eaton, Cifelli, et al., 1999; Eaton, Diem, et al., 1999; Lucas, Heckert, and Sullivan, 2000; Sullivan and Lucas, 2000, 2006; Sankey, 2001; Sullivan, 2006) without more substantive morphological evidence. In the past, this practice was born out of the assumption that theropod diversity across the

Nearly all Late Cretaceous theropod clades known to have inhabited North America can now be documented in Upper Cretaceous formations of southern Utah, including tyrannosaurids (except Iron Springs), ornithomimids (Kaiparowits), therizinosaurids (Tropic Shale), oviraptorosaurians (Kaiparowits), dromaeosaurids, troodontids, and avians (Kaiparowits). Thus far, comprehensive, quantitative biogeographical studies of dinosaurs across the Western Interior Basin have been conducted only for coeval upper Campanian formations (Gates et al., 2010, 2012). As the theropod fauna of earlier Upper Cretaceous formations are poorly known at the present time, we focus on identifying biogeographical patterns of theropods inhabiting the Kaiparowits and coeval Western Interior Basin ecosystems here. Recent radiometric dates derived from several bentonite horizons within the Kaiparowits Formation establish the formation as coeval with fossiliferous portions of the upper Campanian Dinosaur Park, upper Judith River, and upper Two Medicine formations (Roberts, Deino, and Chan, 2005). As such, the ecological diversity preserved in the Kaiparowits offers essential insight into the phylogeny and biogeographic patterns of theropod dinosaurs within the Western Interior Basin during this interval. Results of the KBP demonstrate that all major groups of theropod dinosaurs known from northern upper Campanian formations were present in the Kaiparowits ecosystem (Zanno, Sampson et al., 2005). However, despite the apparent homogeneity among theropod subclades within upper Campanian Western Interior Basin formations, taxa that can be identified to the species level appear to be endemic to

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Biogeography and Diversity Patterns in the Western Interior Basin


restricted geographic areas. Over the last ten years, enough diagnostic material has been collected to verify that the Kaiparowits tyrannosaurids, troodontids, and oviraptorosaurs are local endemics. The identity of Kaiparowits ornithomimid materials are, as of yet, unconfirmed; however, our preliminary work suggests they may be referable to a new taxon. Dromaeosaurid materials remain too fragmentary to assess taxonomically. Thus, only a single theropod taxon from the Kaiparowits Formation is presently referred to a previously named Western Interior Basin genus – Avisaurus – and no formal study of this specimen has been conducted to confirm this assignment. Additional study of dromaeosaurid and ornithomimid materials may identify regionally distributed genera or species inhabiting the Kaiparowits; however, the currently confirmed theropod fauna of the Kaiparowits Formation was endemic to a small geographic area. Paleoenviromental interpretations of upper Campanian Western Interior Basin formations suggest they span a range of habitats, from wet alluvial to arid coastal plain settings (Eberth, 1990; Rogers, 1990; Roberts, 2007). Yet this substantial environmental variation appears to have had little effect upon the subclade composition of the theropod fauna (although they may be affecting local endemicity and speciation patterns). Rather than determining the diversity of theropods, paleoenvironmental conditions may have impacted the relative abundance of these clades within Western Interior Basin formations, especially if depositional regimes were sampling different primary habitat or driving selective taphonomic processes. Preliminary evidence seems to support this hypothesis, as tyrannosaurids (Gorgosaurus), and paravians (Saurornitholestes and Troodon) are reported as the most abundant theropods in the Dinosaur Park Formation (Currie, 1987b, 2005), whereas tyrannosaurids and ornithomimids are the most commonly recovered theropods in the Kaiparowits Formation. Ultimately, although we find these patterns of interest, a larger sample size and greater taphonomic control is needed to determine whether these differences are reflections of variation in regional ecology or simply the result of skewed sampling or preservational biases.

The newly recovered theropod fauna of Upper Cretaceous formations of southern Utah is dramatically augmenting our understanding of the taxonomy, biogeography, and phylogeny of theropod taxa from the Western Interior Basin. Recent discoveries include: (1) two new tyrannosaurid genera, including Teratophoneus curriei and an unnamed Wahweap taxon, which represents the oldest North American member

of the clade discovered to date; (2) the large-bodied oviraptorosaurian Hagryphus giganteus (Zanno and Sampson, 2005); (3) the troodontid Talos sampsoni, which provides the first substantial evidence for troodontid diversity in the Western Interior Basin during the Campanian (Zanno et al., 2011); and (4) the most complete therizinosaurid skeleton recovered to date, Nothronychus graffami. Research in progress on the first diagnostic ornithomimid forelimb material confirms a close relationship between the Kaiparowits ornithomimid and the genus Ornithomimus, although study is ongoing. Reinvestigation of ornithomimid specimens from the Kaiparowits Formation raises considerable questions about the referral of these materials to the Maastrichtian species Ornithomimus velox and suggests that they represent a new taxon. Finally, although isolated teeth substantiate the presence of at least two dromaeosaurids in the Kaiparowits Formation, new paleobiogeographical evidence suggests that the previous referral of these teeth to Dromaeosaurus and Saurornitholestes (Zanno, Sampson et al., 2005; Gates et al., 2010) is dubious. The presence of Troodon sp. in the Wahweap and Kaiparowits formations (Eaton, Cifelli, et al., 1999) is not supported by skeletal data. Finally, we find considerable problems with the utility of isolated theropod tooth “taxa” and caution against the use of these morphotypes in paleoecological and paleobiogeographical studies of Western Interior Basin theropods. Although dinosaur diversity data for other Upper Cretaceous formations of southern Utah are predominantly limited to microvertebrate samples, our increased understanding of the Kaiparowits theropod fauna permits broad paleobiogeographical comparisons with other coeval upper Campanian formations in the Western Interior Basin. Such comparisons demonstrate a surprising amount of homogeneity in theropod taxa at the subclade level, particularly given the perceived variation in paleoenvironments. However, the data also establish a high degree of endemicity at the species level. As a result, we hypothesize that unique paleoenvironmental signatures may be better expressed through relative abundance rather than presence/absence data for theropod clades within the Western Interior Basin. Finally, in stark contrast to previous assumptions of faunal homogeneity across the Western Interior Basin, the latest faunal data from the Kaiparowits Formation indicate geographically restricted theropod species ranges for most groups during at least the late Campanian. This pattern provides a new evolutionary context for the preliminary identification of isolated theropod materials and raises doubts regarding the referral of fragmentary theropod materials to existing genera or species from other Western Interior Basin formations without substantial morphological evidence.


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Ac k now l e d gm e n t s We thank Grand Staircase–Escalante National Monument and the Bureau of Land Management for their continued support throughout the duration of this project. Special thanks go to A. Titus (Grand Staircase–Escalante National Monument) for his ongoing efforts both in and out of the field. Without dozens of dedicated students, faculty, and museum volunteers from the UMNH, the University of Utah, the Raymond M. Alf Museum of Paleontology, and other collaborating institutions, this project could never have achieved the success we document here. Additional thanks go to M. Getty, E. Lund, J. Gentry, E. Roberts, J. Wiersma,

D. Lofgren, M. Stokes, and T. Gates for their substantial contributions in the field and in the lab. We are grateful to H. Hutchison and the University of California at Berkeley’s Museum of Paleontology for access to specimens. Skeletal drawings were modified from artwork by S. Hartman and G. Paul. Funding was provided by Grand Staircase–Escalante National Monument, UMNH, Discovery Channel, University of Utah Graduate Research Fellowships (L.E.Z., M.A.L.), National Science Foundation (NSF 0745454, Kaiparowits Basin Project), J. Caldwell-Meeker Postdoctoral Fellowship at the Field Museum (L.E.Z.), and by the Sherman Fairchild Foundation and the Fisher Foundation for Holy Cross student fieldwork.

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