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]

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.^[17][18]

A tooth of Saurornitholestes has been found embedded in the wing bone of a large pterosaur, probably a juvenile Quetzalcoatlus.^[19] 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.^[19]

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.^[20]

Aase Roland Jacobsen published a description of a Saurornitholestes dentary in 2001.^[21] The dentary is about 12 cm long and preserves fifteen tooth positions, of which only ten preserve teeth.^[22] Three toothmarks were visible on the inner "lingual" surface of the dentary.^[22] Two of the three marks are series of grooves made by the serrations on the maker's teeth.^[22] The striations are between 0.37 mm and 0.40 mm thick with cuboidal cross-sections.^[23]

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.^[24] Although the right shape for Dromaeosaurus tooth serrations, the preserved marks are too coarse to have been left by that genus.^[24] 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.^[25]