This is a speculative reconstruction of a subadult Deinonychus displaying semi-arboreal characteristics. It's based on the tenuous assumption that the type specimen (YPM 5205) represents an immature animal, as compared to later specimens with slightly different morphological characteristics, most notably the Harvard specimen (MCZ 4371) described in 1976. Ostrom noted in the description for this newer specimen that one of the major differences between this and the type is the angle of curvature for the second pedal claw: the newer specimen had a much straighter sickle claw, while the original was very strongly curved. However, he had no opinion at the time on whether this difference in morphology represented individual, ontogenetic, or sexual variation.(1)
(Comparison diagram of two second pedal claw specimens, redrawn by me from Parsons & Parsons 2009)
In 2006, Parsons & Parsons demonstrated unequivocally that the Harvard specimen is a sexually mature adult, and identified some unique adult characters associated with this and other mature Deinonychus specimens.(2) Further study by the same authors in 2009 tentatively indicates that the type specimen—a possible subadult—may be associated with arboreal characteristics. Adult specimens are also found to have proportionally shorter arms, leaving room to speculate whether the longer arms of subadults could have been a semi-volant adaptation involved in some incipient gliding (or, perhaps more accurate for an animal that size, "descent-slowing") capabilities. The more strongly recurved second pedal claw is implicated in climbing, and its lateral compression and inner arc are compared in this paper to the same ungual in Melanerpes, the red-headed woodpecker (a highly scansorial modern bird).(3)
Behavior rarely fossilizes, and the idea that immature Deinonychus occupied a partially arboreal niche is still highly speculative, especially given that few modern archosaurs possess markedly different ecologies at different ontogenic stages. And while I don't usually support copying extant birds this precisely for serious paleoart, it proved to be an excellent practice piece to flesh out a highly speculative idea.
This piece is based directly on an excellent photograph by my most admired living scientist, experimental psychologist Steven Pinker, who was kind enough to grant me permission to do so. Pinker is a world-renowned cognitive scientist as well as a talented photographer, and you can check out more of his better angles of our nature on his website at stevepinker.com.
It's interesting to note that of all known specimens of deinonychosaurs, a sizable percentage of them represent juveniles or subadults, animals that lived very brief lives before succumbing to nature's indifference. For the life of a Deinonychus was surely solitary, poor, nasty, brutish and short.
1. Ostrom, J. H. (1976). "On a new specimen of the Lower Cretaceous theropod dinosaur Deinonychus antirrhopus". Breviora 439: 1–21.
2. Parsons, W. L.; Parsons, K. M. (2006). "Morphology and size of an adult specimen of Deinonychus antirrhopus, (Saurischia, Theropoda)". Journal of Vertebrate Paleontology 26 (3 sup.): 109A.
3. Parsons, W. L.; Parsons, K. M. (2009). "Further descriptions of the osteology of Deinonychus antirrhopus (Saurischia, Theropoda)". Bulletin of the Buffalo Society of Natural Sciences 38: 43–54.
I personally suspect that different groups, genus, species had their own tactics, since competition always inspires a range of lifestyles. In some areas/times it may have been different species to each niche/lifestyle, while in others it was just a few species living different ways at different ages, or even different genders (females in trees, males on ground for all we know). The difficult part is finding and correctly interpreting the evidence of any of the fragments we can find after so long.
VERY NICE JOB!!!
Great art!!! but perhaps a bit too avian?
It would make sense that Deinonychus would have an arboreal arboreal development, it would be a greater insurance policy for the maturation of offspring in comparison to other fauna restricted to the linear plane of ground dwellers. Having feathers would also lessen the effects of falling damage if mistakes occur.
It seems though, that the less curved claw would be a trait of adults with a higher emphasis on living on the ground. Cassowaries exhibit a long but straight pedal claw on each foot, the claw grows straight and distally from the toe. The straightened claws of Cassowaries may show some parallelism with the idea of ontogenic transformation of Deinonychus into a more ground dwelling emphasis.
This is so beautifully done and so well made! I love it!!!!!
Keep up this awesome work!!!
Oh my goodness. By the way, how do you put those textures on digital art?
There are other ways to use filters to achieve a similar textured effect, but that's what I find most useful!
There are, theoretically, a few things that could be tested to further probe this hypothesis: did both adult and subadult Deinonychus have quill knobs in the ulna? Are they same kind of quill knobs? Did subadults have greater range of motion in the arms or the hips than adults? Do adults have different stomach contents than subadults? Answering some of these questions could give us greater resolution into what was going on with these unusual ontogenic variations, but for now it remains what it is: speculation.
aloha from kauai