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Journal of Vertebrate Paleontology 21(3):410–414, September 2001 q 2001 by the Society of Vertebrate Paleontology

RAPID COMMUNICATION

FIRST DEFINITIVE THERIZINOSAURID (DINOSAURIA; THEROPODA) FROM NORTH AMERICA

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JAMES I. KIRKLAND1 and DOUGLAS G. WOLFE2 Utah Geological Survey, P.O. Box 146100, Salt Lake City, Utah 86114-6100; 2 Mesa Southwest Museum, 53 N. MacDonald St., Mesa, Arizona 85012

A partial disarticulated skeleton of a large theropod from the Upper Cretaceous (Turonian) Moreno Hill Formation of New Mexico is described as Nothronychus mckinleyi, gen. et sp. nov. The specimen provides the first undisputed record of a therizinosauroid in North America and strengthens the documented paleogeographic ties between western North America and Asia throughout the Late Cretaceous. The Therizinosauroidea (5Segnosauria) are a group of derived coelurosaurian theropods known only from six or seven monospecific genera from Asia (Perle, 1979; Barsbold and Perle, 1980; Barsbold, 1983; Russell and Dong, 1994; Xu et al., 1999). These taxa are known from partial skeletons that include one skull (Clark et al., 1994). Isolated frontals and an ungual from the upper Campanian Dinosaur Park formation of Alberta, Canada (Currie, 1987, 1992) and a possible astragalus from the upper Maastrichtian Hell Creek Formation of the northern United States (Russell, 1984) are the only therizinosaurids reported from North America, albeit these identifications have been questioned (Barsbold and Maryanska, 1990; Clark et al., 1994; Maryanska, 1997). The recovery of a significant portion of a large therizinosaurid skeleton in the lower member of the Moreno Hill formation of New Mexico establishes their presence in North America, at least during the ‘‘middle’’ Cretaceous. The lower member of the Moreno Hill formation is dated as middle Turonian based on its relationship to other strata (Hook et al., 1983; Wolfe and Kirkland, 1998). Dinosaur fossils are particularly rare from the ‘‘middle’’ Cretaceous due to the global marine transgression. For that reason the Moreno Hill faunal assemblage is exceptionally important. In addition to the new therizinosaurid, it contains Zuniceratops christopheri Wolfe and Kirkland, 1998, and skeletons of as yet unnamed hadrosaurids, nodosaurids, and a basal coelurosaur. SYSTEMATIC PALEONTOLOGY THEROPODA Marsh, 1881 TETANURAE Gauthier, 1986 COELUROSAURIA von Huene, 1914 THERIZINOSAURIDAE Barsbold, 1976 NOTHRONYCHUS, gen. nov. Etymology Nothros (Greek): slothful; onyx (Greek): claw. Type Species N. mckinleyi, sp. nov. Diagnosis As for the type and only known species. Species NOTHRONYCHUS MCKINLEYI, sp. nov. (Figs. 2, 3) Etymology Species mckinleyi to honor Bobby McKinley for his support of this research.

Holotype Paleontological collections of Mesa Southwest Museum (MSM), Mesa, Arizona, MSM P-2117, partial disarticulated skeleton including isolated teeth, fragmentary skull elements, several cervical vertebrae, first? dorsal vertebra, anterior caudal vertebra, ribs, fused gastralia, scapula, right humerus, complete right and partial left ulna, metacarpals, manual phalanges, two manual unguals, two ischia, two tibia, right fibula, partial metatarsals, pedal phalanges, two pedal unguals (Fig. 1A). Locality Holotype, ‘‘Haystack Butte’’ locality (MSM 9878) southern Zuni Basin, Catron Co., New Mexico in a small bone bed preserving a minimum of five individuals of Zuniceratops. Horizon Lower member, Moreno Hill Formation, Upper Cretaceous, middle Turonian, probably Collignoniceras woollgari Zone (Wolfe and Kirkland, 1998). Diagnosis Teeth with serrations extending close to constriction with circular root; anterior dorsal vertebrae with long pedicle and large pleurocoel encasing multiple separate pneumatic foramina; scapula slender with laterally facing glenoid; slender, straight humerus with short deltopectoral crest and lacking spur on humeral shaft; manual unguals with flexor tubercle not extending below the proximal articulation and lacking dorsoproximal lip; thin ischium nearly excluded from acetabulum with large, rectangular, medially situated, obturator process; fibula with M. iliofibularis tubercle approximately at mid-shaft; ped unguals thick. Description The teeth are relatively tiny compared to the overall size of the dinosaur. The crowns are tall and nearly symmetrical (Fig. 1B). The cutting edges have low serrations that extend close to the base of crown. The nearly circular root is separated from the crown by a constriction and measures only 3.8 mm wide. Several possible cranial fragments are present based on shape, but are difficult to interpret because of poor preservation and will be discussed elsewhere. Several cervical vertebrae (Fig. 2A–E) have been recovered, but all are crushed and broken revealing the highly and finely pneumatic, camellate (sensu Britt, 1993, 1995) internal structure. Externally, the pneumatic system originates from a series of small foramina between the laminae supporting the neural arch. These openings are obscured by the poor preservation of these vertebrae. The cervical centra are longer than tall and are narrow except between the parapophyses. They are platycoelous to amphiplatyan. The centra are rectangular in cross-section and have distinct ventrolateral ridges extending posteriorly from the parapophyses. The centra are constricted medially along the ventral and lateral surfaces. The neural arch forms a broad sheet across the centrum and the pre- and postzygapophyses are well separated. The neural spines are nearly absent in anterior cervicals and are more prominent in the posterior

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TABLE 1. Measurements (in mm) of type specimen of Nothronychus mckinleyi gen. et sp. nov. Teeth Serration counts follow Farlow (1991). Best preserved Height of Length of tooth crown crown 8.4

Width of crown

4.6

3.1

10 denticles/5 mm anteriorly 13 denticles/5 mm posteriorly Cervicals (five, crushed in different directions and disarticulated) Length Length of Height of Height of between Width across centrum centrum vertebra zyg. tips anterior zygs.

FIGURE 1. A. Skeletal reconstruction of Nothronychus, gen. nov. based on Alxasaurus and preserved elements of Nothronychus (shaded). B, Tooth of Nothronychus in labial view.

cervicals. The neural canal is nearly circular in anterior view and is exposed dorsally. The diapophyses are posterior to the parapophyses and are situated above the midpoint of the centrum. The anterior dorsal centrum (Fig. 2F, G) is amphiplatyan with a well-developed hyposphene and its overall form is that of a constricted cylinder. There is a well-developed pleurocoel containing several individual openings into the centrum. The neural canal is small and the neural arch is large. It has a well developed pedicle below the zygapophyses and relatively short neural spine. The transverse processes are large and are connected to the top of the centrum by two well-developed laminae. The anterior caudal vertebra (Fig. 2H–K) is slightly opisthocoelous and has flattened sides that are somewhat constricted at mid-length. Ventrally, there is a slight medial depression that extends to the well-developed, posterior facet for the articulation of the chevron. The posterior face of the centrum is parallel to, but significantly lower than, the anterior face of the centrum. There is a small, distinct pneumatic opening below the sweptback caudal rib on each side of the centrum as in oviraptorosaurs (Sues, 1997). Posterior to this opening, toward the margin of the centrum, there is a distinct laterally directed tubercle. The slender scapula (Fig. 3A) is lightly built. Although the acromium is not preserved, it appears that this area was not large nor robustly constructed. The glenoid faces anteriolaterally. The humerus (Fig. 3B–D) is slender and relatively straight. The deltopectoral process extends for 26% of humeral length. The humeral head extends medially across the proximal end of the humerus. There is a well-developed internal process. The ulna (Fig. 3E) is also slender and is slightly bowed posteriorly. Unlike most therizinosaurids, the manual unguals (Fig. 3K–M) have no lip developed dorsal to articular surface (see Sues, 1997). Of the pelvic elements, only the ischia are preserved. They are laterally compressed, with a large, distally positioned obturator process that would have an extensive contact with the pubis (Fig. 3F). The contact areas with the ilium and pubis are extensive, leaving only a very small portion contributing to the acetabulum. Both tibia are poorly preserved, but are relatively robust, and straight (Fig. 3G, H). The slender, right fibula is nearly complete and has a straight shaft (Fig. 3I, J). The proximal end lacks the fibular fossa on its medial side. There is a large tubercle for attachment of the M. iliofibularis on the lateral side approximately at mid-shaft. The pedal unguals are relatively stout, and twisted laterally (Fig. 3N–P). Discussion The teeth of Nothronychus, with their distinc-

* 125.5 133.5 187 188

* * 52 54.0 56.5

* * * * 170

Anterior dorsal vertebra Length of Height of centrum centrum 67

120 153 * * 210.5

48 55.5 * * *

Width of centrum

Height of vertebra

75

248

73

Mid-anterior caudal vertebrae Length of centrum

Height of centrum

Width of centrum

Height of vertebra

Width across Trans. processes

64

58

50

105

114

Left scapula Length Ave. width of blade Width of distal end

518 56 69

Right humerus Length delto-pectoral process/length Proximal width Distal width

418 26% 144 107

Ulna Length Proximal lateral-medial width Distal Width

302 51 38

Manual unguals (positions uncertain) Length Length (dorsal curve) (maximum linear) 138 124

Proximal width

Height proximal articulation

21 19.5

47 49

107 101

Both Ischium Maximum length Maximum width (at obturator process)

534 225

Both Tibia (flattened) Maximum length (as preserved)

614

Metatarsal (distal portion preserved) Distal width Metatarsal I

Distal height

48

33

Pedal phalangies (identifications uncertain) Proximal Length width Left phalanx IV–3 Left phalanx IV–4

37 41

39 31

Distal width 36.5 27

Pedal unguals

Left ungual III Left ungual IV

Length (dorsal curve)

Length (maximum linear)

Proximal width

Height proximal articulation

99 92

82.5 77.5

18 20

40 38


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FIGURE 2. Vertebrae of Nothronychus mckinleyi, gen. et sp. nov. A, anterior cervical vertebra in dorsal view; B, anterior cervical vertebra in ventral view; C, posterior cervical vertebra in left lateral view; D, posterior cervical vertebra in right lateral view; E, posterior cervical vertebra in right anterior view; F, dorsal vertebrae in posterior view; G, dorsal vertebrae in left lateral view; H, anterior caudal vertebra in left lateral view; I, anterior caudal vertebra in right lateral view; J, anterior caudal vertebra in left caudal view; K, anterior caudal vertebra in ventral view. Abbreviations: h, hyposphene; if, infraprezygapophseal fossae; p, pneumatic foramen; t, tubercle.

tive tall subsymmetrical crown and constricted root, are unlike those of any other described North American dinosaur. As with Segnosaurus, the serrations on the anterior carina are larger than those on the posterior carina (Perle, 1979). Unlike in other therizinosaurids, the serrations extend most of the length of the tooth crown. Among the many thousands of dinosaur teeth collected from microvertebrate sites in western North America, not a single therizinosaurid tooth has ever been recognized (e.g., Currie et al., 1990; Eaton et al., 1997, 1999; Kirkland, 1997). The cervical vertebrae of Nothronychus resemble those of most other therizinosaurids in their large size, slightly platycoelous to amphiplatyan centra, and reduced neural spine (Perle, 1979; Russell and Dong, 1993; Xu et al., 1999). Nanshiungosaurus is the exception in that it has amphicoelous to opisthocoelous cervical vertebrae (Dong, 1979; Dong and Yu, 1997). The anterior dorsal vertebra compares closely with, but differs from, that of Alxasaurus in that the capitular facet is low

on the centrum and the centrum has a large pleurocoel and hyposphene (Russell and Dong, 1994). It differs from Nanshiungosaurus in having a high pedicoel (Dong, 1979). The scapula is more lightly built than in other therizinosaurids except Alxasaurus. However, unlike Alxasaurus, the glenoid extends onto the lateral surface as in other therizinosaurids (Barsbold, 1976; Perle, 1979; Osmolska, 2000, personal commun.). The legnth of the well-developed delto-pectoral crest is about 26% the length of the humerus, yet the crest is considerably shorter than in other known therizinosaurids (Maryanska, 1997). Unlike most other therizinosaurids (Maryanska, 1997), a spur is absent on the humeral shaft as in Alxasaurus (Russell and Dong, 1994). The manual unguals do not display the posterodorsal lip on the proximal end characteristic of Therizinosauria and Oviraptorosauria (Sues, 1997). The flexor tubercle does not extend proximally below the proximal articular facet as in other therizinosaurids. The unguals are relatively short and recurved unlike those of Therizinosaurus (Barsbold, 1976). Initially, the right ischium was misidentified as a squamosal of Zuniceratops christopheri (Wolfe and Kirkland, 1998; Wolfe, 2000) because no other identifiable therizinosaurid material was known from the site. The ischia are remarkably similar to those of Segnosaurus (Perle, 1979) in lateral view, and if they were the only elements preserved, they would likely be referred to Segnosaurus. The pedal unguals are thicker than most described therizinosaurids except for Chilantaisaurus zheziangensis (? 5Nanshiungosaurus) (Dong, 1979). A phylogenetic analysis of Nothronychus mckinleyi will be presented elsewhere (Kirkland and Wolfe, in preparation), but some preliminary observations can be made. Beipiaosaurus and Alxasaurus from the Lower Cretaceous of Asia are the most primitive known therizinosauroids (Russell and Dong, 1994; Maryanska, 1997; Xu et al., 1999). Nothronychus from the middle Turonian shares with these taxa primitive features such as a slender forelimb and scapula. However, the laterally facing glenoid on the scapula and extensive contact for pubis on the obturator process are derived characters shared by other Late Cretaceous therizinosaurids, perhaps reflecting an intermediate phylogenetic position. If the presence of Early Jurassic therizinosauroids in Asia (Zhao and Xu, 1998) is correct, it suggests that therizinosaurs may have been dispersed broadly across the globe prior to the full fragmentation of Gondwanaland. However, it has been noted that the teeth in Zhao and Xu’s jaw have a medial ridge, which is present on at least some prosauropod teeth, but is completely unknown in therizinosauroid teeth (Matt Lamanna, 2000, personal commun.). Discounting a Lower Jurassic therizinosauroid, the therizinosaurid, Nothronychus suggests that the North American–Asian connection established in the Early Cenomanian (Cifelli et al., 1997; Kirkland et al., 1997, 1998, 1999) was also a factor in the middle Turonian. ACKNOWLEDGMENTS Field work was conducted under BLM permit MSM-8172RS-1A. We thank the staff and volunteers of the Mesa Southwest Museum and Dinamation International Society for their assistance in collecting the specimens. Preparation of the specimens was under the direction of Harold and Phyllis Bollan of Grand Junction, Colorado. Robert Gaston of Gaston Design, Fruita, Colorado generously provided study casts of the material. Dan Chure provided an English translation of Barsbold (1983). Access to pertinent specimens at the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China by Dong Zhiming, Xing Xu, and Hailu You is appreciated. Brooks Britt discussed the pneumaticity in therizinosauroid vertebrae. Scott Hartman made figure 1. Ben Creisler is thanked for assistance developing the name Nothronychus. Jim Clark, Halka


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FIGURE 3. Appendicular skeletal elements of Nothronychus mckinleyi, gen. et sp. nov. A, left scapula in lateral view; B, right humerus in caudal view; C, right humerus in proximal view; D, right humerus in cranial view; E, right ulna in caudal view; F, left ischium in lateral view; G, right tibia in anterolateral view; H, left tibia in posteromedial view; I, right fibula in laterial view; J, right fibula in medial view; K, manual ungual in lateral view; L, manual ungual in lateral view; M, manual ungual in proximal view; N, pedal ungual in lateral view; O, pedal ungual in lateral view; P, pedal ungual in proximal view. Abbreviations: a, position of accetabulem; d, deltopectoral crest; g, glenoid; h, humeral head; i, contact with ilium; it, internal tuberosity; op, contact of obturator process with pubis; p, contact with pubis; t, tubercle for attachment of the M. iliofibularis.


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Osmolska, Martha Hayden, Mike Lowe, Mike Hyland, and Ken Carpenter read drafts of the manuscript. Thoughtful reviews by Hans Dieter-Sues and Jim Clark are appreciated. Page costs were provided by Discovery Channel. Hazel Wolfe is thanked for her constant support in the field and throughout the project. LITERATURE CITED Barsbold, R. 1976. [New information on Therizinosaurus (Therizinosauridae, Theropoda)]. [Soviet–Mongolian Palaeontological Expedition, Transactions] 3:76–92. [in Russian] ——— 1983. [Carnivorous dinosaurs from the Cretaceous of Mongolia]. [Soviet–Mongolian Palaeontological Expedition, Transactions] 19:5–117. [in Russian] ———, and T. Maryanska. 1990. Segnosauria; pp. 408–415 in D. B. Weishampel, P. Dodson, and H. Osmolska (eds.), The Dinosauria. University of California Press, Berkeley. ———, and A. Perle. 1980. Segnosauria, a new infraorder of carnivorous dinosaurs. Acta Palaeontologica Polonica 25:187–195. Britt, B. B. 1993. Postcranial bones in dinosaur and other archosaurs, Ph.D. dissertation, University of Calgary, Alberta, Canada, pp. ——— 1995. The nature and distribution of pneumatic vertebrae in the Theropoda. Journal of Vertebrate Paleontology 15(3, suppl.):20A. Cifelli, R. L., J. I. Kirkland, A. Weil, A. R. Deinos, and B. J. Kowallis. 1997. High-precision Ar40/Ar39 geochronology and the advent of North America’s Late Cretaceous terrestrial fauna. Proceedings National Academy of Science USA 94:11163–11167. Clark, J. M., A. Perle, and M. A. Norell. 1994. The skull of Erlikosaurus andrewsi a Late Cretaceous ‘‘Segnosaur’’ (Theropoda: Therizinosauridae) from Mongolia. American Museum Novitates 3115: 1–39. Currie, P. J. 1987. Theropods of the Judith River Formation of Dinosaur Provincial Park, Alberta. Fourth Symposium on Mesozoic Terrestrial Ecosystems, Short Papers. Occasional Paper of the Tyrrell Museum of Palaeontology 3:52–60. ———, 1992. Saurishian dinosaurs of the Late Cretaceous of Asia and North America; pp. 237–249 in N. J. Mateer and C. Pei-Ji (eds.), Aspects of Nonmarine Cretaceous Geology. China Ocean Press, Beijing. ———, J. K. Rigby, Jr., and R. E. Sloan. 1990. Theropod teeth from the Judith River Formation of southern Alberta, Canada; pp. 107– 125 in K. Carpenter and P. J. Currie (eds.), Dinosaur Systematics— Approaches and Perspectives. Cambridge University Press, Cambridge. Dong, Z. 1979. [Cretaceous dinosaurs of Huanan (south China)]; pp. 342–350 in Mesozoic and Cenozoic Redbeds in Southern China. Science Press, Beijing. [in Chinese] ———, and H. Yu. 1997. A new segnosaur from Mazongshan area, Gansu Province, China; pp. 90–95 in Z. Dong (ed.), Sino-Japanese Silk Road Dinosaur Expedition. China Ocean Press, Beijing. Eaton, J. G., J. I. Kirkland, J. H. Hutchinson, R. Denton, R. C. O’Neill, and M. J. Parrish. 1997. Nonmarine extinction across the Cenomanian–Turonian (C–T) boundary, southwestern Utah, with a comparison to the Cretaceous–Tertiary (K–T) extinction event. Geological Society of America Bulletin 59:129–151. ———, R. L. Cifelli, J. H. Hutchinson, J. I. Kirkland, and J. M. Parrish. 1999. Cretaceous vertebrate faunas of the Kaiparowits Basin (Cen-

omanian–Campanian), southern Utah; pp. 345–353 in D. Gillette (ed.), Vertebrate Paleontology in Utah. Utah Geological Survey, Miscellaneous Publication 99-1. Farlow, J. O., D. L. Brinkman, W. L. Abler, and P. J. Currie. 1991. Size, shape, and serration density of theropod dinosaur lateral teeth. Modern Geology 16:161–198. Hook, S. C., C. M. Molenaar, and W. A. Cobban. 1983. Stratigraphy and revision of nomenclature of upper Cenomanian to Turonian (upper Cretaceous) rocks of west-central New Mexico; pp. 7–28 in S. C. Hook (ed.), Contributions to Mid Cretaceous Paleontology and Stratigraphy of New Mexico. New Mexico Bureau of Mines and Mineral Resources Circular 185. Kirkland, J. I., B. Britt, D. L. Burge, K. Carpenter, R. Cifelli, F. DeCourten, J. Eaton, S. Hasiotis, and T. Lawton. 1997. Lower to middle Cretaceous dinosaur faunas of the central Colorado Plateau: a key to understanding 35 million years of tectonics, sedimentology, evolution, and biogeography. Brigham Young University Geology Studies 42:69–103. ———, S. G. Lucas, and J. W. Estep. 1998. Cretaceous dinosaurs of the Colorado Plateau; pp. 67–89 in S. G. Lucas, J. I. Kirkland, and J. W. Estep (eds.), Lower to Middle Cretaceous Non-marine Cretaceous Faunas. New Mexico Museum of Natural History and Science Bulletin 14. ———, R. Cifelli, B. Britt, D. L. Burge, F. DeCourten, J. Eaton, and J. M. Parrish. 1999. Distribution of Vertebrate faunas in the Cedar Mountain Formation, east-central Utah; pp. 201–217 in D. Gillette (ed.), Vertebrate Paleontology in Utah. Utah Geological Survey, Miscellaneous Publication 99-1. Maryanska, T. 1997. Segnosaurs (Therizinosaurs); pp. 234–241 in J. O. Farlow and M. K. Brett-Surman (eds.), The Complete Dinosaur. Indiana University Press, Bloomington. Perle, A. 1979. [Segnosauridae a new family of theropods from the Late Cretaceous of Mongolia]. [Soviet–Mongolian Palaeontological Expedition, Transactions] 8:45–55. [in Russian] Russell, D. A. 1984. A check list of families and genera of North American dinosaurs. Syllogeus 53:1–43. ———, and Z. Dong. 1994. The affinities of a new theropod from the Alxa Desert, Inner Mongolia, People’s Republic of China. Canadian Journal of Earth Science 30:2107–2127. Sues, H.-D. 1997. On Chirostenotes, a Late Cretaceous oviraptorosaur (Dinosauria: Theropoda) from western North America. Journal of Vertebrate Paleontology 17:698–716. Wolfe, D. G. 2000. New Information on the skull of Zuniceratops christopheri, a neoceratopsian dinosaur from the Cretaceous Moreno Hill Formation, New Mexico; pp. 93–94 in S. G. Lucas (ed.), Dinosaurs of New Mexico. New Mexico Museum of Natural History and Science Bulletin 17. ———, and J. I. Kirkland. 1998. Zuniceratops christopheri n. gen. & n. sp., A ceratopsian dinosaur from the Moreno Hill Formation (Cretaceous, Turonian) of west-central New Mexico; pp. 303–317 in S. G. Lucas, J. I. Kirkland, and J. W. Estep (eds.), Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin 14. Xu, X., Z. Tang, and X. Wang. 1999. A therizinosauroid dinosaur with integumentary structures from China. Nature 399:350–354. Zhao, X., and X. Xu. 1998. The oldest coelurisaurian. Nature 394:234– 235. Received 28 January 2001; accepted 18 April 2001.


Kirkland & Wolfe, 2001