Saurornitholestes ("lizard-bird thief") is a genus of carnivorous dromaeosaurid theropod dinosaur from the late Cretaceous of Canada (Alberta and Saskatchewan) and the United States (Montana, New Mexico, Alabama, and South Carolina). Two species have been named that are regarded as valid: Saurornitholestes langstoni in 1978 and Saurornitholestes sullivani in 2015. Saurornitholestes was a small, bipedal, meat-eating dinosaur, equipped with a sickle-like claw on each foot.

Saurornitholestes robustus, a species named in 2006, was regarded as a dubious troodontid in 2014 and tentatively assigned to the genus Xenovenator in 2026.

Discovery and naming

In 1974, Canadian amateur paleontologist Irene Vanderloh discovered the skeleton of a small theropod near Steveville in Alberta. She showed it to John Storer of the Provincial Museum of Alberta, who brought it to the attention of Hans-Dieter Sues. In 1978, Sues named and described the specimen as the type species Saurornitholestes langstoni. The generic name is in reference to the Saurornithoididae, due to the resemblance with this group that is today seen as part of the Troodontidae, and combines their name with a Greek lestes, "thief". The specific name honours Wann Langston, Jr.

Additional specimens

thumb|left|Foot of an assigned S. langstoni specimen

Two more complete and larger partial skeletons (RTMP 88.121.39 and MOR 660), dozens of isolated bones, and scores of teeth are known from the badlands of Dinosaur Provincial Park in Alberta; most of these are housed at the Royal Tyrrell Museum of Palaeontology, in Drumheller, Alberta and remain undescribed. The Alberta and Montana remains are usually attributed to the single species Saurornitholestes langstoni, though they come from a variety of rock formations indicating a wide span of time; for example, the Oldman Formation (dated to about 77 million years ago but whether they represent S. langstoni or a different, related species is unknown. Neonate-sized Saurornitholestes fossils have been reported in the scientific literature.

Saurornitholestes sullivani is known from the Hunter Wash fauna of the Kirtland Formation in New Mexico, based on the frontal SMP VP-1270. It differs from S. langstoni in the characters of the frontal.

A well-preserved skeleton of Saurornitholestes (specimen UALVP 55700) discovered in 2014 is currently under preparation by University of Alberta paleontologists working in Japan. After examining the skull of that specimen, Currie and Evans announced in 2019 that the Zapsalis teeth from the Dinosaur Park Formation represented the second premaxillary tooth of S. langstoni.

Formerly assigned species

In 2006, Robert Sullivan named and described a second nominal species, Saurornitholestes robustus, based on holotype SMP VP-1955, a left frontal. The specific name refers to the great thickness of this bone, the only trait in which the species is known to differ from S. langstoni. The holotype was found in the Willow Wash fauna of the Kirtland Formation in New Mexico, dated to about 73 million years ago. and a study published in 2014 took the conclusion a step further by demonstrating that S. robustus was assignable to Troodontidae based on similarities with troodontids. In 2026, Rivera-Sylva and colleagues tentatively assigned S. robustus to their new genus Xenovenator based on shared cranial anatomy, a conclusion supported by their phylogenetic analyses.

Possible indeterminate fossils are known from the Hell Creek Formation in Montana, North Dakota, and South Dakota, dated to about 66 million years ago.

Description

thumb|left|Size of S. langstoni compared to a human

Saurornitholestes was a small dromaeosaur, with the type species S. langstoni measuring about long and weighing approximately between . At the hip it stood tall. Like other theropods in the Dromaeosauridae, Saurornitholestes had a long, curving, blade-like claw on the second toe. Saurornitholestes was more long-legged and lightly built than other dromaeosaurids such as Velociraptor and Dromaeosaurus. It resembles Velociraptor in having large, fanglike teeth in the front of the jaws. Saurornitholestes most closely resembles Velociraptor, although the precise relationships of the Dromaeosauridae are still relatively poorly understood.

Classification

thumb|Reconstructed S. langstoni skull

thumb|Dentary of S. langstoni specimen TMP 1988.121.0039

In 1978, Sues assigned Saurornitholestes to the Dromaeosauridae. Later studies most often found it a member of the dromaeosaurid Velociraptorinae, but a cladistic analysis by Philip J. Currie in 2009 recovered a position in a more basal dromaeosaurid clade that was named the Saurornitholestinae.

The cladogram below is the result of a 2019 analysis by Philip J. Currie and David C. Evans. Currie and Evans recovered Saurornitholestes as the sister taxon of Atrociraptor.

A tooth of Saurornitholestes has been found embedded in the wing bone of a large pterosaur, possibly a juvenile Quetzalcoatlus.

References

  • Currie P.J. & Koppelhus E.B., Dinosaur Provincial Park: a spectacular ancient ecosystem revealed, Vol. 1 (Indiana University Press, 2005), p. 372–373.
  • Jacobsen, A.R. 2001. Tooth-marked small theropod bone: An extremely rare trace. p. 58-63. In: Mesozoic Vertebrate Life. Ed.s Tanke, D. H., Carpenter, K., Skrepnick, M. W. Indiana University Press.
  • Longrich N.R. & Currie P.J. (2009), "A microraptorine (Dinosauria–Dromaeosauridae) from the Late Cretaceous of North America", PNAS 106(13): p. 5002-5007.
  • Norell, Mark A. and Makovicky, Peter J. "Dromaeosauridae." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 208.
  • Saurornitholestes - Dinosaur Saurornitholestes Characteristics, Behavior and Habitat ; <small>Subheadings: Habitat, Historical Period, Size and Weight</small>
  • Sullivan, R.M. (2006). "Saurornitholestes robustus, n. sp. (Theropoda:Dromaeosauridae) from the Upper Cretaceous Kirtland Formation (De-Na-Zin member_), San Juan Basin, New Mexico." NMMNH Bulletin 35: 253–256.
  • Sullivan, R.M. and Lucas, S.G. (2006). "The Kirtlandian land-vertebrate "age" – faunal composition, temporal position and biostratigraphic correlation in the nonmarine Upper Cretaceous of western North America." New Mexico Museum of Natural History and Science, 35: 7-29.
  • Tanke, D.H. and Brett-Surman, M.K. 2001. Evidence of Hatchling and Nestling-Size Hadrosaurs (Reptilia:Ornithischia) from Dinosaur Provincial Park (Dinosaur Park Formation: Campanian), Alberta, Canada. pp.&nbsp;206–218. In: Mesozoic Vertebrate Life—New Research Inspired by the Paleontology of Philip J. Currie. Edited by D.H. Tanke and K. Carpenter. Indiana University Press: Bloomington. xviii + 577 pp.