The Predatory Ecology of Deinonychus and the Origin of Flapping in Birds

Abstract

Most non-avian theropod dinosaurs are characterized by fearsome serrated teeth and sharp recurved claws. Interpretation of theropod predatory ecology is typically based on functional morphological analysis of these and other physical features. The notorious hypertrophied ‘killing claw’ on pedal digit (D) II of the maniraptoran theropod Deinonychus (Paraves: Dromaeosauridae) is hypothesized to have been a predatory adaptation for slashing or climbing, leading to the suggestion that Deinonychus and other dromaeosaurids were cursorial predators specialized for actively attacking and killing prey several times larger than themselves. However, this hypothesis is problematic as extant animals that possess similarly hypertrophied claws do not use them to slash or climb up prey. Here we offer an alternative interpretation: that the hypertrophied D-II claw of dromaeosaurids was functionally analogous to the enlarged talon also found on D-II of extant Accipitridae (hawks and eagles; one family of the birds commonly known as “raptors”). Here, the talon is used to maintain grip on prey of subequal body size to the predator, while the victim is pinned down by the body weight of the raptor and dismembered by the beak. The foot of Deinonychus exhibits morphology consistent with a grasping function, supportive of the prey immobilisation behavior model. Opposite morphological trends within Deinonychosauria (Dromaeosauridae + Troodontidae) are indicative of ecological separation. Placed in context of avian evolution, the grasping foot of Deinonychus and other terrestrial predatory paravians is hypothesized to have been an exaptation for the grasping foot of arboreal perching birds. Here we also describe “stability flapping”, a novel behaviour executed for positioning and stability during the initial stages of prey immobilisation, which may have been pivotal to the evolution of the flapping stroke. These findings overhaul our perception of predatory dinosaurs and highlight the role of exaptation in the evolution of novel structures and behaviours.

Pedal Claw Curvature in Birds, Lizards and Mesozoic Dinosaurs – Complicated Categories and Compensating for Mass-Specific and Phylogenetic Control

“…Manning et al [32] concluded that “the feet and hands of dromaeosaurs functioned both for locomotion (walking, running, and climbing) and as prey capture/grappling devices”, though our data for digit III supports only a terrestrial interpretation. Deinonychus , however, does fall within the predatory category, suggesting that its foot may have been used in prey immobilisation behaviour analogous to modern Accipitridae [66], [69].…”

Getting a grip on tetrapod grasping: form, function, and evolution

“…With the specialization of the forelimbs for flight throughout the evolutionary history of birds, the capacity for manipulating objects progressively became relegated to the hindlimbs (Fig. Fowler et al (2011) hypothesized that selection for grasping prey, as evidenced by claw and foot morphology of deinonychosaurian ancestors of Aves, might have formed the basis for arboreal perching, and possibly even flapping flight. This formulates an intriguing departure, in that a few birds have achieved comparable levels of digital dexterity in the pes as other tetrapods have in the manus, and consequently most birds are restricted to the execution of a power grip.…”

“…However, Iwaniuk & Whishaw (2000) suggested that prey-handling behaviour, even in basal amphibian lineages, might have been an important driving force for the evolution of manual grasping. Fowler et al, 2011) have been implicated in the evolution of pedal grasping across taxa. Gebo, 1985;Feduccia, 1999;Youlatos, 2008) and feeding (e.g.…”

Claw morphometrics in monitor lizards: Variable substrate and habitat use correlate to shape diversity within a predator guild

“…Large comparative studies of mammals have used claws/unguals to determine locomotor, and in particular fossorial, adaptations (MacLeod & Rose, 1993). Modern claws are often correlated with those of nonavian dinosaurs to extrapolate paleo‐behavior (Burnham, Feduccia, Martin, & Falk, 2011; Fowler, Freedman, Scannella, & Kambic, 2011; Lautenschlager, 2014). These studies quantified claw morphology in several ways, including Euclidean distance measures, claw curvature based on triangles, outline‐based morphometrics, and digital modelling (respective examples in Ribas et al., 2004; Feduccia, 1993; MacLeod & Rose, 1993; Manning et al., 2009).…”