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Saurornitholestes

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Saurornitholestes
Temporal range: Late Cretaceous, 77–68 Ma Possible Cretaceous-Paleogene boundary record
Skeletal reconstruction of S. langstoni
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Dromaeosauridae
Clade: †Eudromaeosauria
Subfamily: †Saurornitholestinae
Genus: †Saurornitholestes
Sues, 1978
Type species
†Saurornitholestes langstoni
Sues, 1978
Other species
  • †S. sullivani
    Jasinski, 2015
Synonyms

Saurornitholestes ("lizard-bird thief") is a genus of carnivorous dromaeosaurid theropod dinosaur from the late Cretaceous of Canada (Alberta) and the United States (Montana, New Mexico, Alabama, North Carolina, and South Carolina).

Two species have been named: Saurornitholestes langstoni in 1978 and Saurornitholestes sullivani in 2015. Saurornitholestes was a small bipedal meat-eating dinosaur, equipped with a sickle-claw on the foot.

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.[1]

The holotype specimen, TMP 1974.10.5, was uncovered in a layer of the Dinosaur Park Formation dating to the late Campanian. It consists of a very fragmentary skeleton including teeth, skull elements, two vertebrae, ribs, tail elements and a part of the hand. Also three paratypes were assigned: CMN 12343, CMN 12354, and UA 5283, all frontals.[1]

Additional specimens

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[2]) and the upper Two Medicine Formation (about 72 million years ago). Similar teeth are found in younger deposits, dated to around 70 to 69 million years ago,[3] but whether they represent S. langstoni or a different, related species is unknown. Neonate-sized Saurornitholestes fossils have been reported in the scientific literature.[4]

Fragmentary fossils of Saurornitholestes have also been found from the eastern half of North America. A tooth found in the Mooreville Chalk of Alabama has been assigned to the genus. In 2015, Schwimmer et al. identified the existence of Saurornitholestes langstoni from the Tar Heel, Coachman, and Donoho Creek formations of North and South Carolina based on diagnostic teeth and a pedal ungual. This also makes S. langstoni currently the only dromaeosaurid taxon reported with certainty from the East Coast.[5]

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.[6]

A well-preserved skeleton of Saurornitholestes (specimen UALVP 55700) discovered in 2014 is currently under preparation by University of Alberta paleontologists working in Japan.[7] 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.[8]

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.[9] However, a subsequent overview of dromaeosaurid phylogeny asserted that S. robustus lacked dromaeosaurid characters and should be considered an indeterminate theropod,[10] 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.[11]

Possible indeterminate fossils are known from the Hell Creek Formation in Montana, North Dakota, and South Dakota, dated to about 66 million years ago.[12]

Description

Size of S. langstoni compared to a human

Saurornitholestes was about 1.8 m (5 ft 11 in) long[13] and weighed approximately 10 kg (22 lb).[14] At the hip it stood 60 cm (2 ft) 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

Reconstructed S. langstoni skull
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.[8]

Eudromaeosauria

Paleobiology

Senses

Saurornitholestes sullivani is thought to have had a keen sense of smell, due to its skull suggesting an unusually large olfactory bulb.[6]

Teeth function

The second premaxillary teeth of (at least) Saurornitholestes, Velociraptor, and Bambiraptor may have been structurally specialized for preening feathers. This may also have been the function of the unusual premaxillary teeth of the oviraptorosaurs Protarchaeopteryx and Incisivosaurus.[8]

Feeding habits

Restoration of an S. langstoni digging a multituberculate out of a burrow

Saurornitholestes' feeding habits were discovered to be typical of coelurosaurian theropods, with a characteristic "puncture and pull" feeding method. Studies of wear patterns on the teeth of this animal by Angelica Torices et al. in a study regarding theropod feeding habits indicate that dromaeosaurid teeth share similar wear patterns to those seen in the tyrannosauridae and troodontidae, respectively. However, micro-wear on the teeth indicated that Saurornitholestes likely preferred larger prey items than the troodontids it shared their environment with. Such differentiations in its diet likely allowed the theropod to inhabit the same environment as its more distant maniraptoran relations. The same study also indicated that both Saurornitholestes and the related Dromaeosaurus (also analyzed in the study) likely included bone in their diet and were better adapted to handle the stresses associated with attacking struggling prey while troodontids, equipped with weaker jaws, preyed on softer animals and prey items such as invertebrates and carrion. This feeding strategy and ability to handle struggling prey was also a feature that the dromaeosaurid also shared with tyrannosaurids such as Gorgosaurus, which was also analyzed in said study alongside these smaller theropods.[15][16]

A tooth of Saurornitholestes has been found embedded in the wing bone of a large pterosaur, probably a juvenile Quetzalcoatlus.[17] Because the pterosaur was so much larger than Saurornitholestes, Currie and Jacobsen suggest that the theropod was probably scavenging the remains of an already dead animal.[17]

Paleopathology

In 2001, Bruce Rothschild and others published a study examining evidence for stress fractures and tendon avulsions in theropod dinosaurs and the implications for their behavior. They found that only two of the 82 Saurornitholestes foot bones checked for stress fractures actually had them. Two of the nine hand bones examined for stress fractures were found to have them.[18]

Aase Roland Jacobsen published a description of a Saurornitholestes dentary in 2001.[19] The dentary is about 12 cm long and preserves fifteen tooth positions, of which only ten preserve teeth.[20] Three toothmarks were visible on the inner "lingual" surface of the dentary.[20] Two of the three marks are series of grooves made by the serrations on the maker's teeth.[20] The striations are between 0.37 mm and 0.40 mm thick with cuboidal cross-sections.[21]

The shape of the preserved serrations are too different from those of Saurornitholestes for the marks to be the result of injuries incurred during intraspecific face biting behaviors.[22] Although the right shape for Dromaeosaurus tooth serrations, the preserved marks are too coarse to have been left by that genus.[22] Although a specific identification cannot be made, the most likely perpetrator would be a juvenile individual of one of the Dinosaur Park Formation's tyrannosaurids, like Gorgosaurus, or Daspletosaurus.[23]

Paleoenvironment

Restoration of a pair of Saurornitholestes hunting Cerasinops

Saurornitholestes was found on both sides of the Western Interior Seaway. Alberta, the location of Saurornitholestes langstoni, had a habitat similar to the United States Middle West being plains[24] and floodplain swamps.[25] In its eastern range, Saurornitholestes lived alongside hadrosaurs like Eotrachodon and Hypsibema, large theropods like Appalachiosaurus and Dryptosaurus, an unidentified ornithomimosaur, and another unidentified small theropod that was likely either a dromaeosaurid or a troodontid. Saurornitholestes appears to have been the most common small theropod in Dinosaur Provincial Park, and teeth and bones are much more common than those of its more robust contemporary, Dromaeosaurus.[5]

See also

Footnotes

  1. ^ a b H.-D. Sues, 1978, "A new small theropod dinosaur from the Judith River Formation (Campanian) of Alberta Canada", Zoological Journal of the Linnean Society 62: 381-400
  2. ^ Arbour, et al. (2009).
  3. ^ "3.33 Alaska, United States; 3. Prince Creek Formation," in Weishampel et al. (2004). Page 587.
  4. ^ "Abstract," Tanke and Brett-Surman (2001). Page 207.
  5. ^ a b Brownstein, Chase D. (2018-02-08). "The biogeography and ecology of the Cretaceous non-avian dinosaurs of Appalachia". Palaeontologia Electronica. 21 (1): 1–56. doi:10.26879/801. ISSN 1094-8074.
  6. ^ a b Steven E. Jasinski (2015) A new dromaeosaurid (Theropoda: Dromaeosauridae) from the Late Cretaceous of New Mexico. in Sullivan, R.M. and Lucas, S.G., eds. Fossil Record 4. New Mexico Museum of Natural History and Science Bulletin 67: 79-88
  7. ^ "Small but vicious Alberta dinosaur to be discussed in Red Deer - Red Deer Advocate". Red Deer Advocate. 2018-03-09. Retrieved 2018-03-11.
  8. ^ a b c Currie, Philip J.; Evans, David C. (2020). "Cranial Anatomy of New Specimens of Saurornitholestes langstoni (Dinosauria, Theropoda, Dromaeosauridae) from the Dinosaur Park Formation (Campanian) of Alberta". The Anatomical Record. 303 (4): 691–715. doi:10.1002/ar.24241. PMID 31497925. S2CID 202002676.
  9. ^ Sullivan and Lucas (2006).
  10. ^ Turner, A.H., Makovicky, P.J. and Norell, M.A., 2012, A review of dromaeosaurid systematics and paravian phylogeny: Bulletin of the American Museum of Natural History, v. 371, p. 1–206.
  11. ^ Evans, D.C., Larson, D.W., Cullen, T.M. and Sullivan, R.M., 2014. "Saurornitholestes" robustus is a troodontid (Dinosauria: Theropoda): Canadian Journal of Earth Sciences, v. 51, p. 730–734.
  12. ^ Dinosaur distribution (Late Cretaceous; North America; North Dakota). Weishampel, et al. (2004). Page 585
  13. ^ Currie and Koppelhus (2005). Pages 372–373.
  14. ^ Longrich and Currie (2009).
  15. ^ "Dinosaurs' tooth wear sheds light on their predatory lives". ScienceDaily. April 2018. Retrieved 14 February 2019.
  16. ^ "Scratches on dinosaur teeth reveal their fierce, efficient eating habits - The Washington Post". The Washington Post.
  17. ^ a b Currie and Jacobsen (1995).
  18. ^ "Table 23.1," in Rothschild, et al. (2001); page 333.
  19. ^ "Abstract," Jacobsen (2001). Page 58.
  20. ^ a b c "Description," Jacobsen (2001). Page 59.
  21. ^ "Description," Jacobsen (2001). Page 60.
  22. ^ a b "Discussion," Jacobsen (2001). Page 60.
  23. ^ "Discussion," Jacobsen (2001). Page 61.
  24. ^ Strauss, Bob. "Meet the Raptor Dinosaurs of the Mesozoic Era". ThoughtCo. Retrieved 14 February 2019.
  25. ^ Norell and Makovicky.

References

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