Function in the stunted forelimbs of Mononykus olecranus (Theropoda), a dinosaurian anteater

Abstract

Mononykus olecranus, a theropod dinosaur from the Upper Cretaceous of Mongolia, ex hibits reduced forelimbs with a single functional digit. These bizarre forelimbs have aroused great curiosity as to the behavior of the animal, but until now no functional study on the forelimbs of Mononykus has been undertaken. Here I show that the orientation and range of motion in the forelimb elements of Mononykus are such that the humeri sprawl laterally, the antebrachia are held subvertically, the palms face ventrally, and intramanual movement is restricted to subparasagittal mo tion. This is a radical departure from the typical theropod condition, in which the palms face me dially and intramanual movement is transverse. The results of this study confirm that the forelimbs of Mononykus could not have been used to grasp prey or dig burrows, but were well suited for scratch-digging or hook-and-pull movements such as are used by extant anteaters and pangolins to open tough insect nests. Mononykus likely occupied a niche equivalent to that of an anteater or pangolin, an unusual niche for a dinosaur.

Morphological and functional diversity in therizinosaur claws and the implications for theropod claw evolution

“…Evidence for fossorial behaviour has been documented in a number of dinosaur taxa and for different purposes. This ranges from digging burrows in small ornithischians [30,31] to nest building in sauropods [32] and troodontids [33] and foraging in alvarezsaurids [20]. While the large body size largely rules out the possibility of burrow digging in therizinosaurs, troodontids and dromaeosaurids most probably used their hindlimbs and pedal claws for digging [33,34], as feathering on the forelimbs would have interfered with manus digging [35].…”

“…The manual unguals of theropod dinosaurs in general, and therizinosaurs in particular, however, have rarely been considered, or have been limited to range-ofmotion studies of the forelimbs [19][20][21]. This is surprising, as in bipedal animals, the manual unguals are not restricted by locomotory constraints.…”

A test of the validity of range of motion studies of fossil archosaur elbow mobility using repeated-measures analysis and the extant phylogenetic bracket

“…Despite these concerns, the practice of physically manipulating fossil archosaur (particularly dinosaur) forelimbs to obtain ROMs in degrees is currently a growing area of interest. For example, direct and indirect elbow joint ROM studies of fossil archosaur forelimbs are important sources of phylogenetic and paleoecological data (Hankin and Watson, 1914;Bramwell and Whitfield, 1974;Bennett, 1991;Sereno, 1993;Tereshchenko, 1994;Tereshchenko, 1996;Carpenter and Smith, 2001;Gishlick, 2001;Carpenter, 2002;Bonnan, 2003;Wilhite, 2003;Senter, 2005;Senter, 2006a;Senter, 2006b;Senter and Parrish, 2006;Senter and Robins, 2005;Bonnan and Senter, 2007;Langer et al, 2007;Thompson and Holmes, 2007;Senter, 2007;Carpenter and Wilson, 2008). To the best of our knowledge, previous authors have not recognized that studies of fossilized limb joint ROMs meet the requirements for a repeatedmeasures analysis, in which repeated measures between multiple observers are statistically analyzed for significant differences.…”

Using the American alligator and a repeated-measures design to place constraints onin vivoshoulder joint range of motion in dinosaurs and other fossil archosaurs

“…non-locomotor limb movements (Fischer, 1998)] in bipedal dinosaurs, such as during prey capture, displays, grooming, etc. (Welles, 1984;Nicholls and Russell, 1985;Gishlick, 2001;Carpenter, 2002;Carpenter and Smith, 2001;Senter, 2005;Senter, 2006a;Senter, 2006b;Senter, 2006c;Senter, 2007;Senter and Robins, 2005;Senter and Parrish, 2006;Bonnan and Senter, 2007;Carpenter and Wilson, 2008;Lipkin and Carpenter, 2008). Unlike early, mostly qualitative reports of humeral ROM (e.g.…”