Saurornitholestes

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[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]

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.[5] 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
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[7] and weighed approximately 10 kilograms (30 pounds).[8] At the hip it stood 0.6 meters (2 feet), or around as tall as the length of a terrier.