Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

Bipedalism, Flight, and the Evolution of Theropod Locomotor Diversity

Stephen M. Gatesy and Kevin M. Middleton
Journal of Vertebrate Paleontology
Vol. 17, No. 2 (Jun. 19, 1997), pp. 308-329
Stable URL: http://www.jstor.org/stable/4523809
Page Count: 22
  • Subscribe ($19.50)
  • Cite this Item
Bipedalism, Flight, and the Evolution of Theropod Locomotor Diversity
Preview not available

Abstract

The evolution of theropod flight has been characterized as a shift from one to three locomotor modules. Basal theropods, which were terrestrial bipeds, had a single locomotor module composed of the hind limb and tail. In birds, aerial locomotion was acquired with the origination of the wing module and a decoupling of the hind limb and tail into separate pelvic and caudal modules. This increase in modularity is thought to have granted birds more locomotor "options" than non-avian theropods. More specifically, an aerial loco system could have eased constraints on the hind limb and allowed specialization for habitats and lifestyles unavailable to non-birds. If so, bird hind limbs should be more disparate than those of non-avian theropods. We addressed this hypothesis by visualizing one aspect of limb design, the proportions of the three main segments, using ternary diagrams. Our results show that avian hind limb proportions are much more disparate than those of non-avian theropods. This broad range of limb design correlates with a radiation in locomotor diversity founded on three locomotor modules. We propose that birds have reached regions of proportion morphospace that are off limits to bipeds with only one locomotor module. In comparison, the limbs of non-avian theropods are conservatively proportioned. Despite great variation in body size, theropods other than birds do not exhibit specializations for locomotion other than terrestrial bipedalism. Although other aspects of size and shape need to be analyzed, the relationship between modular flexibility and morphological disparity appears to play an important role in theropod locomotor evolution.

Page Thumbnails

  • Thumbnail: Page 
308
    308
  • Thumbnail: Page 
309
    309
  • Thumbnail: Page 
310
    310
  • Thumbnail: Page 
311
    311
  • Thumbnail: Page 
312
    312
  • Thumbnail: Page 
313
    313
  • Thumbnail: Page 
314
    314
  • Thumbnail: Page 
315
    315
  • Thumbnail: Page 
316
    316
  • Thumbnail: Page 
317
    317
  • Thumbnail: Page 
318
    318
  • Thumbnail: Page 
319
    319
  • Thumbnail: Page 
320
    320
  • Thumbnail: Page 
321
    321
  • Thumbnail: Page 
322
    322
  • Thumbnail: Page 
323
    323
  • Thumbnail: Page 
324
    324
  • Thumbnail: Page 
325
    325
  • Thumbnail: Page 
326
    326
  • Thumbnail: Page 
327
    327
  • Thumbnail: Page 
328
    328
  • Thumbnail: Page 
329
    329