The Deinonychosaurs are the group of dinosaurs most closely related to the birds. They are divided into two groups, the Dromaeosaurs (popularly known as 'Raptors') and the Troodontids, which share a common hindlimb morphology, with two digits used to support weight during locomotion, and a third supporting a large, sickle-shaped claw, which was held clear of the ground.
In a forthcoming paper in the journal Acta Paleontologica Polonica, a team of scientists led by Lida Xing of the Department of Biological Sciences at the University of Alberta describe the discovery of a group of tracks made by dinosaurs with two walking toes, in the Liujiaxia Dinosaur National Geopark in Ganzu Province, China.
Liujiaxia Dinosaur National Geopark in Ganzu Province.
The tracks are located in fine sandstone/siltstone in the Early Cretaceous Yanguoxia Formation, on the southeastern edge of the Lanzhou-Minhe Basin. The site contains six dinosaur trackways, made by dinosaurs with two walking toes, with feet measuring approximately 14.8 cm in length and 6.4 cm wide and step lengths of 35.7-37.5 cm.
One of the prints. (A) Photograph. (B) Computerized Photogrammetry image with 0.2 mm contour lines. (C) Outline drawing with 10 cm scale bar. From Xing et al. (2012).
Deinonychosaurs are thought to have been capable of considerable speed when chasing prey, but none of the Liujiaxia track-makers appears to have been moving fast when making the tracks. This has no particular significance, since no modern predator runs all, or even most, of the time. There has been an ongoing debate over whether these dinosaurs were pack or solitary hunters; again this site is somewhat ambivalent, as most of the tracks are of solitary animals, but one track apparently shows six animals moving as a group.
Turning trackway. Left, photograph. Centre, outline drawing. Right, pace angulations. Scale bar is 50 cm. From Xing et al. (2012).
It is not possible to say with confidence what the actual track-maker was. The print are within the size range of a large Troodontid or a small-to-medium sized Dromaeosaur, though Xing et al. feel that the most likely track-maker was a Dromaeosaur.