Gr. chieros [hand] + Gr. stenotes [= Gr. stenos (narrow)]. = "narrow hand."

Formation and Stratigraphy: the Judith River Formation, the Dinosaur Park Formation, the Horseshoe Canyon Formation, the Hell Creek Formation, the Lance Formation, and the Frenchman Formation, Upper Cretaceous.

Geography and Locality: at the Dinosaur Provincial Park ["Steveville" and Bow River] in Alberta and Sasketchewan, and near Drumheller, in Alberta, all in Canada, and in the Big Horn Basin area of Montana, and the Sandy locality in Wyoming and South Dakota, USA.

Age: the middle Campanian to late Maastrichtian, in the Late Cretaceous.

a small (~6 to 7 feet) with unusally slender and narrow feet and hands, and a pinched third metatarsal bone not fully hidden from view in the front, unlike that seen in ornithomimosaurs or tyrannosauroids. An oviraptorosur with a very long, slender jaw, highly arched ilium, and two pleurocoels in each cervical vertebra. A caenagnathid with an unusually low, shallow, and long jaw with a prominent symphysial ridge.



Fig. 1: a composite skeleton of Chirostenotes
pergracilis, about 6.5 feet in length.

Gr. Chirostenotes; per- [= peri- (thoughroughly or completely)] + gracilis [slender or delicate]. = "very slender narrow hands."

the Judith River Formation in the middle to late Campanian, middle to late Upper Cretaceous, at the Dinosaur Provincial Park, Bow River, and Sandy Point localities, southern Alberta, Canada.

Holotype:
• CMN 2367: two incomplete hands of a single individual.

  Refered specimens:

• CMN 8538: a complete metatarsus and toes with astragalus and very incomplete distal end of the tibia (= holotype of Macrophalangia canadensis [Sternberg, 1932]).
• CMN 8776: complete lower jaw lacking the left angular/dentary bar (= holotype of Caenagnathus collinsi [Sternberg, 1940]).
• CMN 9570: incomplete metatarsal II.
• ROM 43250: partial skull including an occiput, maxilla, and palatine bones, and a skeleton including vertebrae from all areas of the body, including a sacrum, some ribs, a narly complete pelvis, and partial hindlimb.
• RTMP 79.20.1: partial skeleton including most of a pelvis, hindlimbs, a hand, and several vertebrae, including a sacrum.
• RTMP 92.36.53: an anterior caudal vertebra.
  
  Fig. 2: composite skull of Chirostenotes
  pergracilis, comprising the jaw of CMN
  8776 and the upper jaws of ROM 43250.

the largest of the Chirostenotes species so far named, C. pergracilis is distinctly different from th other species in that the dentary is very shallow, more shovel-shaped than scoop-shaped as in C. sternbergi (see below), or even Caenagnathasia or the oviraptorids. The claws are especially deeply curved and display remarkably tall "lips," having the first and third fingers closer in size than the second finger, and a distinctively tall ilium.

Chirostenotes pergracilis was synonymized with Macrophalangia canadensis Sternberg, 1932 (= "large toes from Canada") in 1988 by Currie and Russell. based on a new skeleton rescribed with both hands and feet (RTMP 79.20.1). Later, Chirostenotes was synonymized with Caenagnathus Sternberg, 1940 (= "recent jaw"), a long-suspected issue, based on another skeleton (ROM 43250) described by Sues in 1997, which included a partial skull and postcrania.

Gr. Chirostenotes; Lat. sternbergi [for {C. H.} Sternberg]. = "Sternberg's narrow hands."

the Judith River Formation in the middle to late Campanian, middle to late Upper Cretaceous, at the Dinosaur Provincial Park, Bow River, and Sandy Point localities, southern Alberta, Canada.

Holotype:
• CMN 2690: right articular region of the lower jaw.

  Refered specimens:

• RTMP 79.8.622: a dentary symphysis, broken in the back.
• RTMP 90.56.6: nearly complete fused dentaries, lacking part of the right side.
• RTMP 91.144.1: fused dentaries without the posterior processes.
• RTMP 92.36.390: fused dentaries without the posterior ventral processes.
• RTMP 92.40.44: a dentary symphysis, broken in the back.

a far more robust species than C. pergracilis, C. sternbergi is both more deeper jawed and more shorter of skull than the type species (see above). Smaller, nearly by half, C. sternbergi displays several inique differences from C. pergracilis, including proportions of the jaw and relative morphology of the symphysis that distinguishes the taxa. Basic gross similarity to Caenagnathasia is mostly superficial, as morphology indicates it is a species of Chirostentoes.

Rough similarity to Caenagnathasia, though, does suggest that C. sternbergi could be a transitional species between C. pergracilis and Caenagnathasia, a conclusion not well supported phylogenetically, as the two species of Chirostenotes share too many features for either to be closer to another genus (known) than to each other, including the shape of the symphysis, with the prescence of an hourglass-shaped depression on the bottom near the rear of the elongated symphysis, the reduced foramina on the surface, longer posterior processes, etc.

C. sternbergi was referred to Chirostenotes from a species of Caenagnathus when that genus was synonymized with Chirostenotes (Sues, 1997), forming a new combination.

Gr. Chirostenotes; sp. [abbreviation of "species"]. = "species of Chirostenotes."

the Hell Creek Formation in the middle to late Maastrichtian, late Upper Cretaceous, South Dakota, USA.

• BHM 2033: the articular, surangular, and coronoid region of the left jaw.
  
  

  Fig. 4: the angular-surangular-coronoid
  complex of Chirostenotes sp. (BHM 2033).

  
  

  Fig. 5: the reconstructed jaw of
  Chirostenotes sp., based on BHM 2033
  (above). Scale bar equals 10cm.

based on a partial jaw, C. sp. is both larger than the two other Chirostenotes species, and deeper relatively than C. pergracilis by ~20% or C. sternbergi by ~40%. Proportions indicate a new unique form, but the material is fragmentary. The jaw approaches the oviraptorids in depth to length, but this appears to be convergence.

Discussion:

Chirostenotes offers the first small theropod from the Judith River, a contemporary of long-jawed Ricardoestesia, more robust and toothy Dromaeosaurus, and much larger Albertosaurus. A small toothless theropod, Chirostenotes would not have offered any dietary competition to either Ricardoestesia or Dromaeosaurus, perhaps similarly sized but toothed, and especially not to Albertosaurus, the only large contemporaneous theropod. Therefore, Chirostenotes would have been fairly well-off. The possible diety habits of Chirostenotes can be found at the section titled "What did Oviraptors eat?"

Chirostenotes is a fairly derived oviraptorosaur, and an even more derived caenagnathid, given the shapes of the jaws of other oviraptorosaurs tend to be more short and deep, while those of Chirostenotes, and especially C. pergracilis, is long and shallow, with a typical upturned jaw in C. sternbergi reminiscent of all other oviraptorosaurs; in C. pergracilis in particular, the jaw is very shallow and low, with a forwardly inclined symphysis.

--+--Oviraptorosauria
     +--+--Caenagnathasia
        +--+--Oviraptoridae
           +--+--Caenagnathidae
              +--+--Chirostenotes         <---\
                 |  +--+--C. pergracilis  <---|___
                 |     |--C. sternbgeri   <---|
                 |     +--C. sp.          <---/
                 +--Elmisaurus

• Barsbold R.; Maryanska, T.; and Osmolska, H. 1990. Oviraptorosauria. p. 249-258 (in Weishampel, D.A.; Dodson, P.; and Osmolska, H. (eds.) The Dinosauria [University of California Press, Berkeley (Los Angeles, Oxford)]).
• Cracraft, J. 1971. Caenagnathiformes: Cretaceous birds convergent in jaw mechanism in dicynodont reptiles. Journal of Paleontology 45: 805-809.
• Currie, P.J. 1990. Elmisauridae. p. 245-248 (in Weishampel, D.A.; Dodson, P.; and Osmolska, H. (eds.) The Dinosauria) University of California Press, Berkeley [Los Angeles, Oxford].
• Currie, P.J.; Godfrey, S.J.; and Nesov, L.A. 1994. New caenagnathid (Dinosauria: Theropoda) specimens from the Upper Cretaceous of North America and Asia. Canadian Journal of Earth Sciences 30: 2255-2272. [Issue printed with "1993" as the date, but published in 1994.]
• Currie, P.J.; Rigby, J.K. Jr.; and Sloan, R.E. 1990. Theropod teeth from the Judith River Formation of southern Alberta, Canada. p. 107-125 (in Carpenter, K. and Currie, P.J. (eds.) Dinosaur Systematics: Approaches and Perspectives) Cambridge University Press.
• Currie, P.J. and Russell, D.A. 1988. Osteology and relationships of Chirostenotes pergracilis (Saurischia, Theropoda) from the Judith River (Oldman) Formation of Alberta, Canada. Canadian Journal of Earth Sciences 25: 972-986.
• Eberth, D.A. 1997. Judith River Wedge. p. 379-385. (in Currie, P.J. and Padian, K. (eds.). Encyclopedia of Dinosaurs. [Academic Press]).
• Gilmore, C.W. 1924. Contributions of vertebrate paleontology. Geological Survey of Canada, Bulletin 38: 1-89.
• Glut, D.F. 1997. Dinosaurs: the Encyclopedia (Brett-Surman, M.K. (ed.)). [McFarland & Company]. pp. 1,190.
• Paul, G.S. 1988b. Predatory Dinosaurs of the World: a Complete Illustrated Guide. [Simon & Schuster, New York]. pp. 464.
• Sternberg, C.M. 1932. Two new theropod dinosaurs from the Belly River Formation of Alberta. The Canadian Field-Naturalist 46 (5): 99-105.
• Sternberg, R.M. 1940. A toothless bird from the Cretaceous of Alberta. Journal of Paleontology 14: 81-85.
• Sues, H.-D. 1997. On Chirostenotes, a Late Cretaceous oviraptorosaur (Dinosauria: Theropod) from western North America. Journal of Vertebrate Paleontology 17: 698-716.

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