Dinosaur Locomotion in Nature

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Nature 415, 494 - 495 (2002)  
 
 
Biomechanics: Dinosaur locomotion from a new trackway 


Ardley Quarry in Oxfordshire, UK, contains one of the most extensive
dinosaur-trackway sites in the world, with individual trackways extending
for up to 180 metres. We have discovered a unique dual-gauge trackway from a
bipedal theropod dinosaur from the Middle Jurassic in this locality, which
indicates that these large theropods were able to run and that they used
different hindlimb postures for walking and running. Our findings have
implications for the biomechanics and evolution of theropod locomotion.

The Ardley trackways are preserved on a single horizon of the Middle
Bathonian (163 million years old)1 white-limestone formation and include
those from large theropods and at least two types of sauropod dinosaur.
Three of the trackways (numbered 13, 29 and 80; J.J.D., unpublished
observations) comprise large tridactyl ('three-toed') prints, with narrow
claw impressions typical of theropod dinosaurs (Fig. 1). All three trackways
(except for a section of track 13) are wide-gauge, with the prints
indicating that the hind feet were placed sequentially in a zig-zag
arrangement separated widely from the midline (Fig. 1a). Stride length (2.70
m) and pace angulation (117°-132°; Fig. 1) remain constant throughout the
wide-gauge tracks. This pattern contrasts strongly with the more usual
narrow-gauge form of theropod trackway2, 3 in which pace-angulation values
range between 160° and 170°: the hind-foot impressions are located close to
the midline of the trackway.

Trackway 13 is unique because one section shows the theropod gait switching
from wide to narrow gauge (the stride length increases to 5.65 m and pace
angulation increases to 173°; Fig. 2). The orientation of the feet also
changes from positive rotation (toes directed forwards and inwards; Fig. 1a)
during wide-gauge locomotion, to a small negative rotation (toes directed
slightly outwards) during the narrow-gauge phase (Fig. 1b).

Estimating the speed of movement of the track-maker requires information on
hip height (h) and stride length3, 4. Hip height can be calculated from foot
length3 (which equals the length of the middle toe, 'digit III'). For
trackway 13, this gives an h value of 1.93 m, giving estimated speeds of 6.8
km h-1 and 29.2 km h-1 for the wide- and narrow-gauge segments,
respectively.

Placing the hind feet close to, or on, the midline5, optimizes locomotor
efficiency by maximizing the effective stride length and reducing the energy
lost through lateral displacement of the centre of gravity. The Ardley
trackways therefore have important implications for the locomotor styles of
large theropod dinosaurs. The simultaneous alteration of stride length and
pace angulation (Fig. 2), foot orientation and estimated speeds all suggest
that the large Ardley theropod used the wide-gauge gait while walking but
was capable of a 'gear change' to maximize running ability by employing the
more efficient, narrow-gauge gait.

Greater stability was probably achieved during walking by shortening the
stride length, placing the hind feet further from the midline and rotating
the feet inwards. Although providing more stability, the wider spacing of
the hindlimbs would decrease the maximum stride length and therefore the
attainable speed, so faster locomotion would have called for a change to the
narrow-gauge gait.

Trackway evidence of the running ability of large bipedal dinosaurs is
scant6. Estimates of maximum speeds obtained from biomechanical studies of
skeletal material are controversial, particularly for large theropods3. The
increase in stride length evident in trackway 13 indicates that at least
some large theropods were capable of running at speeds close to previous
maximum estimates.

Other issues concerning locomotion in large theropods remain to be resolved.
The narrow-gauge (running) section of trackway 13 is only 35 m long and
leaves unanswered the question of how long a large theropod could sustain a
running gait. It is also uncertain whether the wide-gauge gait was
habitually adopted by large theropods while walking, or only when the ground
was very soft or unstable. Furthermore, the anatomical correlations between
leg and hip anatomy associated with the adoption of wide- and narrow-gauge
gaits are not yet known and we are therefore unable to determine the
phylogenetic distribution of these locomotor styles. Nevertheless, the
Ardley trackways offer new insight into dinosaur locomotor capacity and will
stimulate enquiry into the evolution and biomechanics of large theropod
dinosaurs.


JULIA J. DAY*, DAVID B. NORMAN*, PAUL UPCHURCH* & H. PHILIP POWELL? 
* Department of Earth Sciences, University of Cambridge, Downing Street,
Cambridge CB2 3EQ, UK
? Oxford University Museum of Natural History, Parks Road, Oxford OXD1 3PW,
UK


References 
1. Cope, J. C. W. et al. Geol. Soc. Spec. Rep. 15 (1980). 
2. Padian, K.& Olsen, P. E. Copeia 1984, 662-671 (1984). 
3. Thulborn, R. A. Dinosaur Tracks (Chapman & Hall, London, 1990). 
4. Alexander, R. M. Nature 261, 129-130 (1986). 
5. Alexander, R. M. Zool. J. Linn. Soc. 83, 1-25 (1986). 
6. Thulborn, R. A. Nature 292, 273-274 (1981).