Tanycolagreus

Tanycolagreus is a genus of coelurid theropod from the Late Jurassic of North America. The holotype is a partial skeleton recovered from the Bone Cabin Quarry West locality, Albany County, Wyoming, from the Morrison Formation (Oxfordian-Tithonian). The holotype (TPII 2000-09-29, Thanksgiving Point Institute, Inc.) includes an incomplete skull and mandibles and much of the postcranial skeleton, and two paratypes have also been named — an incomplete hand originally referred to Ornitholestes hermanni, also collected from Bone Cabin Quarry, and a premaxilla, originally referred to Stokesosaurus clevelandi, from the Cleveland-Lloyd Quarry of Utah. Present in stratigraphic zone 2. Remains possibly referrable to Stokesosaurus have been recovered from stratigraphic zone 5. of the Morrison Formation. The skull of Tanycolagreus is less well known than its postcranial anatomy, and only the following elements have been found: left nasal, left lacrimal, left premaxilla and one premaxillary tooth, left postorbital, left quadratojugal, incomplete left squamosal, right quadrate, right splenial, left articular, and two cheek teeth. The etymology of Tanycolagreus is based upon the structure of its long forelimbs ((Greek tany - 'long, stretched out', kolon - 'limb' and agreus - 'hunter'); the species is named for George "Top" Wilson. Carpenter et al. (2005, pp. 43–44) determined that the holotype of Tanycolagreus represents a subadult individual which measured approximately 3.3 meters (11 ft) long in life. However, one of the paratypes, the premaxilla from the Cleveland-Lloyd Quarry, would have belonged to a larger individual, measuring 4 meters (13 ft) long. It cannot be determined whether or not the Cleveland-Lloyd specimen represents a fully mature adult, so the upper size limit for the taxon remains unknown. Though a detailed phylogenetic analysis of Tanycolagreus has yet to be carried out, Carpenter et al. (2005, p. 44) state that, of the other known Morrison theropods, this genus most closely resembles Coelurus, though it retains more primitive features. A life restoration of Tanycolagreus is on display at the North American Museum of Ancient Life (Lehi, Utah), where it is portrayed as preying upon a small ornithischian dinosaur, Othnielia rex.

[edit] Diagnosis & Description

Carpenter et al. (2005; pp. 27 & 29) diagnosed Tanycolagreus topwilsoni as follows: "Medium-sized tetanuran having short, deep-bodied premaxilla pierced by narial foramen at base of nasal process, orbital process on postorbital, T-shaped quadratojugal, centrodiapophyseal lamina on dorsals. Differs from Coelurus in the absence of pleurocoel on anterior dorsals; posterior caudal prezygapophyses elongated to one-third centrum length, rather than short; straight, rather than sigmoidal, humeral shaft; bowed, rather than straight, radius; flat-bottomed rather than arced pubic foot; straight rather than sigmoidal femoral shaft; metatarsal length subequal to humeral length, rather than 1.75 times humeral length. Differs from Ornitholestes in straight anterior margin of premaxilla, rather than rounded; T-shaped rather than L-shaped quadratojugal; elongate neural spine; posterior caudal prezygapophyses only one-third centrum length, rather than one-half centrum length; bowed, slender radius, rather than straight, robust radius." The single premaxillary tooth preserved with the holotype is badly damaged, but does exhibit the asymmetrical cross-section typical in theropod teeth; the cheek teeth are too poorly preserved to show any detail.