Day number 4 showcases one of my favorite dinosaurs, Ornitholestes! It has been alerted to the sound of a larger animal nearby as it forages.

"A biomechanical study conducted by Phil Senter (2006) used articulated casts of the Ornitholestes type specimen's right forelimb to determine its range of motion.[57] Senter found that the antebrachium (forearm) could swing freely within a 95° range.[58] When flexed (bent inward) at the elbow joint to the maximum possible extent, the humerus (upper arm bone) and radius (a lower arm bone) formed a 53° angle.[58] The ability of Ornitholestes to bend the forearm to an angle significantly more acute than 90° is characteristic of Maniraptoriformes, but absent in more primitive theropods such as Coelophysis and Allosaurus.[59]

Even when fully extended (straightened) at the elbow, the forearm did not form a straight angle, falling short of this by 22°.[58] Pronation (twisting to make the palmar side of the hand face downwards) of the forearm was impossible, because the radius and ulna lacked rolling surfaces, meaning the forearm was in a permanent state of supination.[24]

When Ornitholestes bent its elbows, this would cause the forearms to move inward, towards its midline.[60] It may have used that ability to grasp prey with both hands simultaneously." - Wikipedia

Art © 2015 Stephanie Dziezyk.