Letters to Nature

Nature 406, 716-718 (17 August 2000) | doi:10.1038/35021041; Received 8 February 2000; Accepted 24 May 2000

Cursoriality in bipedal archosaurs

Terry D. Jones1,2, James O. Farlow3, John A. Ruben1, Donald M. Henderson4 & Willem J. Hillenius5

  1. Zoology Department, Oregon State University, Corvallis, Oregon 97331, USA
  2. Department of Geosciences, Indiana-Purdue University, Fort Wayne, Indiana 46805, USA
  3. Department of Cell Biology and Anatomy, School of Medicine, The Johns Hopkins University, Baltimore, Maryland 21205, USA
  4. Biology Department, College of Charleston , Charleston, South Carolina 29424, USA
  5. Present address: Department of Biology, Stephen F. Austin State University, Nachogdoches, Texas 75962, USA.

Correspondence to: Terry D. Jones1,2 Correspondence and requests for materials should be addressed to T.D.J. (e-mail: Email: tdjones@sfasu.edu).

Modern birds have markedly foreshortened tails and their body mass is centred anteriorly, near the wings1, 2, 3, 4, 5. To provide stability during powered flight, the avian centre of mass is far from the pelvis, which poses potential balance problems for cursorial birds. To compensate, avians adapted to running maintain the femur subhorizontally, with its distal end situated anteriorly, close to the animal's centre of mass; stride generation stems largely from parasagittal rotation of the lower leg about the knee joint6, 7, 8, 9, 10, 11, 12. In contrast, bipedal dinosaurs had a centre of mass near the hip joint and rotated the entire hindlimb during stride generation4, 5, 6, 7, 8, 11, 12, 13. Here we show that these contrasting styles of cursoriality are tightly linked to longer relative total hindlimb length in cursorial birds than in bipedal dinosaurs. Surprisingly, Caudipteryx , described as a theropod dinosaur14, 15, possessed an anterior centre of mass and hindlimb proportions resembling those of cursorial birds. Accordingly, Caudipteryx probably used a running mechanism more similar to that of modern cursorial birds than to that of all other bipedal dinosaurs. These observations provide valuable clues about cursoriality in Caudipteryx , but may also have implications for interpreting the locomotory status of its ancestors.