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Saurornitholestes langstoni
Topic Started: Nov 13 2012, 08:24 AM (2,458 Views)
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Saurornitholestes langstoni

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Temporal range: Late Cretaceous, 77-72 Ma

Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Theropoda
Family: †Dromaeosauridae
Clade: †Eudromaeosauria
Subfamily: †Saurornitholestinae
Genus: †Saurornitholestes Sues, 1978

Saurornitholestes ("lizard-bird thief") is a genus of carnivorous dromaeosaurid theropod dinosaur from the late Cretaceous of Alberta, Montana and New Mexico.

Two species have been named: Saurornitholestes langstoni in 1978 and Saurornitholestes robustus in 2006. 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.

The holotype specimen, RTMP 74.10.5, 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 hand. Also three paratypes were assigned: CMN 12343, CMN 12354, and UA 5283, all frontals.

Two more complete and larger partial skeletons (RTMP 88.121.39 and MOR 660), dozens of isolated bones, and scores of teeth are today 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) and the upper Two Medicine Formation (about 72 million years ago). Similar teeth are found in younger deposits, but whether they represent S. langstoni or a different, related species is unknown. Neonate-sized Saurornitholestes fossils have been reported in the scientific literature.

In 2006 Robert Sullivan named and described a second 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 and additional remains referred to S. robustus, were found in the Willow Wash fauna of the Kirtland Formation in New Mexico, dated to about 73 million years ago.

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.

Saurornitholestes was about 1.8 meters (6 feet) long and weighed approximately 10 kilograms (30 pounds). At the hip it stood 0.6 meters (2 feet), or around as tall as the length of a terrier.
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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.

Alberta, the location of Saurornitholestes langstoni, had a habitat similar to the United States Middle West being plains and floodplain swamps.

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 massive contemporary, Dromaeosaurus. Little is known about what it ate and how it lived, but a tooth of Saurornitholestes has been found embedded in the wing bone of a large pterosaur, probably a juvenile Quetzalcoatlus. 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.

Bite marks from tyrannosaur
Aase Roland Jacobsen published a description of a dentary referred to Saurornitholestes with tooth marks in 2001. In the Dinosaur Park Formation, small theropods are rare due to the tendency of their thin-walled bones to be broken or poorly preserved, this increases the scientific value of the discovery of a small theropod dinosaur with preserved tooth marks. The dentary is about 12 cm long and preserves fifteen tooth positions, ten of these have teeth, with five of those teeth fully erupted and intact, two broken but functional as evidenced by the presence of wearfacets, three are only partially erupted. Three toothmarks were visible on the lingual surface of the dentary. Two of the three marks are series of grooves made by the serrations on the maker's teeth.

The first consists of 6-7 parallel grooves within a 4 x 1.3 mm area beneath the alveolus of the third tooth and angled at forty-five degrees to the dentary's longitudinal axis. The striations are between .37 mm and .40 mm thick with cuboidal cross-sections.

The second tooth mark lies between the fifth and sixth alveoli and consists of two smaller grooves separated 1.8 and 1.6 mm respectively from a larger central groove, with a V-shaped groove beneath it at an angle of sixty degrees to the longitudinal axis of the jaw.

The third mark consists of four parallel grooves in a 2 x 2 mm area on the seventh tooth oriented at ninety degrees to the longitudinal axis of the tooth.

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. Although the right shape for Dromaeosaurus tooth serrations, the preserved marks are too coarse to have been left by that genus. 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. All of the marks on the jawbone seem to have been left by the same animal because the serration marks all share the same morphology.

Stress fractures
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 was found to have them.
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Mounted skeleton cast, Royal Tyrrell Museum
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Edited by Taipan, Nov 14 2012, 04:45 PM.
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Dinosaurs' tooth wear sheds light on their predatory lives

April 26, 2018, Cell Press

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This illustration shows puncture-and-pull feeding in predatory theropod dinosaurs, based on the results of the researchers' microwear analysis and finite element analyses. Credit: Sydney Mohr/Current Biology

Predatory, bird-like theropod dinosaurs from the Upper Cretaceous (100.5-66 million years ago) of Spain and Canada all relied on a puncture-and-pull bite strategy to kill and consume their prey. But close examination of patterns of wear and modeling of their serrated, blade-like teeth reported in Current Biology on April 26 also suggest that these dinosaurs weren't necessarily in direct competition for their next meal. Some of them apparently preyed on larger, struggling prey, while others stuck to softer or smaller fare.

"All these dinosaurs were living at the same time and place, so it is important to know if they were competing for food resources or if they were aiming for different prey," says Angelica Torices of Universidad de La Rioja, Spain. "Through this work we [can] begin to understand the interactions between these predatory dinosaurs in the ecosystem a bit better.

"We find that, in general, predatory coelurosaurian dinosaurs bite in the same way through a puncture-and-pull system, but troodontids and dromaeosaurids may have preferred different prey," she adds, noting that troodontids apparently favored requiring lower bite forces in comparison to dromeosaurs. Coelurosaurians include a group of theropod dinosaurs more closely related to birds than to other dinosaurs, including the allosaurs.

Torices has always had an interest in the teeth of carnivorous dinosaurs. At first, her goal was to match tooth remains to the dinosaur species they had come from. Over time, she grew curious about how various dinosaur species used their teeth, how that related to specific tooth shapes and sizes, and what she might learn about dinosaurs' lives based on that.

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Microwear patterns on the teeth of three theropods. Credit: Angelica Torices and Victoria Arbour/Current Biology

Torices first examined the microwear, or patterns of small scratches on the teeth, to see whether she could establish any pattern in the way various dinosaurs were eating. She, along with colleagues including Ryan Wilkinson from the University of Alberta, Canada, also used a modeling approach called finite elements analysis, commonly used to solve problems in engineering and mathematical physics, to explore how the dinosaurs' teeth most likely behaved at different cutting angles.

Both approaches led to the same general conclusion, she says. All of the dinosaurs studied employed a puncture-and-pull feeding movement, in which parallel scratches form while they bite down into prey, followed by oblique scratches as the head is pulled backwards with the jaws closed, the researchers report. However, they found, the different tooth shapes performed differently under a variety of simulated biting angles.

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Different theropod dinosaurs, their teeth, and their different denticle shapes. All teeth are scaled to the same crown height for comparative purposes. Credit: Victoria Arbour/Current Biology

The evidence suggests that Dromaeosaurus and Saurornitholestes were well adapted for handling struggling prey or for processing bone as part of their diet. By comparison, Troodon teeth were more likely to fail at awkward bite angles. The findings suggest that troodontids may have preferred softer prey such as invertebrates, smaller prey that required a less powerful bite or could be swallowed whole, or immobile prey such as carrion.

Torices says they are now working to develop more complex models to include teeth along with their roots and jaws to better understand the biting process.


Journal Reference:
Torices et al.: "Puncture-and-Pull Biomechanics in the Teeth of Predatory Coelurosaurian Dinosaurs" Current Biology,http://www.cell.com/current-biology/fulltext/S0960-9822(18)30371-3 , DOI: 10.1016/j.cub.2018.03.042

•Theropods used puncture-and-pull feeding movements, based on microwear analyses
•Troodontid teeth were most likely to fail at non-optimal bite angles
•Troodontids may have favored prey requiring lower bite forces than dromaeosaurids

The teeth of putatively carnivorous dinosaurs are often blade-shaped with well-defined serrated cutting edges (Figure 1). These ziphodont teeth are often easily differentiated based on the morphology and density of the denticles. A tearing function has been proposed for theropod denticles in general, but the functional significance of denticle phenotypic variation has received less attention. In particular, the unusual hooked denticles found in troodontids suggest a different feeding strategy or diet compared to other small theropods. We used a two-pronged approach to investigate the function of denticle shape variation across theropods with both congruent body shapes and sizes (e.g., dromaeosaurids versus troodontids) and highly disparate body shapes and sizes (e.g., troodontids versus tyrannosaurids), using microwear and finite element analyses (Figure 1). We found that many toothed coelurosaurian theropods employed a puncture-and-pull feeding movement, in which parallel scratches form while biting down into prey and oblique scratches form as the head is pulled backward with the jaws closed. In finite element simulations, theropod teeth had the lowest stresses when bite forces were aligned with the oblique family of microwear scratches. Different denticle morphologies performed differently under a variety of simulated biting angles: Dromaeosaurus and Saurornitholestes were well-adapted for handling struggling prey, whereas troodontid teeth were more likely to fail at non-optimal bite angles. Troodontids may have favored softer, smaller, or immobile prey.
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Attachments: Puncture_and_Pull_Biomechanics_in_the_Teeth_of_Predatory_Coelurosaurian_Dinosaurs.pdf (3.08 MB)
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