J . Zool., Lond. (1987) 212,85-101

Locomotion in hatchling leatherback turtles Dermochelys coriacea

J . DAVENPORT Animal Biology Group, Marine Science Laboratories, Menai Bridge, Gwynedd, North Wales, UK

(Accepted 10 September 1986)

(With 16 figures in the text)

Hatchling leatherback turtles can only swim forwards, and employ synchronized beating of the forelimbs whether swimming slowly or quickly. The hind limbs make no contribution to propulsion. Effectively, the hatchlings have two swimming speeds; subsurface and fast (30 cm s-') or surfaced and slow (8 cm s-I). Intermediate velocities are transitory; the hatchlings were never seen to rest without movement, nor did they exhibit gliding of the type seen in green turtles. During fast ('vigorous') swimming, power is developed on both the upstroke and downstroke of the limb cycle. During slow swimming, power is only developed during the upstroke-a consequence of the orientation of the axis of limb beat which is opposite in direction to that of cheloniid sea turtles. Terrestrial locomotion is laboured and features an unstable gait which involves simultaneous movement of all four limbs and forward overbalancing during each limb cycle.

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Materials and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Collection and maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Locomotory mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vigorousswimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slow swimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Terrestrial locomotion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Swimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Vigorous swimming model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slow swimming model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comparisons with other species . . . . . . . . . . . . . . . . . . . . . . . . . . . . General considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Terrestrial locomotion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Page 85 86 86 86 86 86 87 90 93 95 95 95 97 98 99

100 101

Introduction

The leatherback turtle, Dermochelys coriacea (L.) is the most pelagic of living sea turtles, foraging widely in temperate waters as well as the tropical and subtropical areas inhabited by the other species. The anatomy of the leatherback differs considerably from that of other species (hence its placement in a separate family, the Dermochelyidae-see Gaffney (1 984) for a review

85 0022-5460/87/005085 + 17 $03'00 @ 1987 The Zoological Society of London

86 J . DAVENPORT

of chelonian relationships), and the physiology of the leatherback is also unusual since there is evidence that adult animals are at least partially endothermic (Pritchard, 1969; Frair, Ackman & Mrosovsky, 1972; Mrosovsky, 1980), which would help to explain its survival in colder waters, and its recently discovered ability to dive to considerable depths (Eckert, Nellis, Eckert & Kooyman, 1984) where it is also likely to encounter reduced environmental temperatures.

Swimming mechanisms of green and loggerhead sea turtles (Chelonia mydas L. and Curetta caretta L., respectively) have been investigated by the author (Davenport, Munks & Oxford, 1984; Davenport & Clough, 1986), and revealed a number of differences between the species, which appeared to be related to their life styles. The study reported here was performed to extend these studies to Dermochelys.

Materials and methods

Collection and maintenance Two hatchling leatherback turtles were collected from Kuala Terengganu, on the eastern coast of

peninsular Malaysia. Each weighed about 70 g and had an overall length of about 9 cm. They were flown to Penang and held in a large (3 m diameter) circular tank filled with sea water (32'100) at laboratory temperature (29-33 T). Leatherback turtles are notoriously difficult to rear in captivity and feeding them is a particular problem. No jellyfish (the ideal food) were available to us and the hatchlings would not take live or dead fish offered to them. Instead, they were hand-fed twice daily on a pelleted fish-food diet. The jaws of each hatchling were gently prised apart and about 10 soft pellets (each some 2 mm in diameter) dropped into the mouth. Usually the pellets were swallowed as soon as the hatchling was returned to sea water.

Locomotory mechanisms Most of the data given in this paper were derived from colour videotape filming of the 2 hatchlings. To

obtain the videotape, the animals were held in a long, narrow, glass aquarium ( 2 m long, 0.8 m high, 0.5 m wide) which had a 1 cm grid marked on 3 of its sides and on the bottom. The aquarium was filled with sea water and turtles placed in it one at a time. They were filmed from various aspects with a single television camera. Some additional observations, particularly of the migration of hatchlings from the nest to the sea, and the subsequent offshore swim, were made from professional television films. All videotape was analysed by making drawings of frozen frames on acetate sheet. Qualitative observations were also made upon the hatchlings in their holding tank.

Results

General observations When swimming in their holding tank, the young leatherbacks demonstrated a characteristic

previously noted by Hendrickson (1980). If placed at one side of the tank, with the head directed towards the middle, and then released, a turtle would swim across the tank until it encountered the opposite wall; it would then continue to attempt to swim in the same direction, often for many hours, repeatedly bumping into the tank wall. This inability to recognize obstacles/boundaries is not seen in other turtle species such as the green turtle Chelonia mydas and the loggerhead Caretta caretta.

All swimming in the young leatherbacks was accomplished by synchronous flapping of the foreflippers. Alternate forelimb action ('dogpaddle') was never seen; there was no involvement of

L O C O M O T I O N I N L E A T H E R B A C K T U R T L E S 87

the hind limbs whatsoever, and the turtles did not ‘glide’ (i.e. cease swimming with the foreflippers extended laterally-a common feature of green turtle swimming) as they approached the bottom or sides of tanks. The leatherbacks were never observed to swim backwards (young green turtles do so by alternate hind limb paddling while the foreflippers are held, dorsal surfaces pressed together, in front of the head).

Occasionally, the animals stopped swimming and rubbed their foreflippers (asynchronously) over the carapace and plastron for a few seconds before resuming locomotion. The reasons for this behaviour (accompanied by lateral rocking of the animal) are not obvious, though the action may help to keep body surfaces clean. The young turtles were never seen to rest motionless.

.\ E

9 ‘ u + - , 4 3

FIG. 1. Swimming track 1 . Vigorously swimming turtle. Dashed lines indicate movement of whole turtle and of tip of left foreflipper. Numbers indicate time intervals of 0.08 s. Scale bar = 10 cm. This figure is typical of several filmed sequences. Note that the head of leatherbacks does not move significantly in relation to the shell during swimming; any undulations in swimming track represent undulations of the whole animal, not just the head.

In contrast to young green and loggerhead turtles, which have poor diving capabilities until several months old (Hildebrand & Hatsel, 1927; Milsom, 1975; Davenport et al., 1984; Davenport & Clough, 1986), the hatchling leatherbacks had no difficulty in diving to the bottom of their holding tank (1.5 m deep), although they did appear to be positively buoyant.

Vigorous swimming The first type of swimming to be investigated was that shown by hatchlings when they were

released from restraint (hand holding) in the test aquarium. This was the fastest swimming observed and an average velocity of about 30 cm s-’ (c. 3.3 body lengths s-l) was recorded. A complete limb cycle occupied about 05-0.6 s. Figure 1 shows an example of the type of swimming track observed and the associated flipper tip motion. Figure 2 illustrates the changes in turtle velocity during the course of the swimming track. From these figures, it may be seen that the swimming track is undulatory, that the flipper moves more quickly on the downstroke than on the upstroke, but that increases in turtle velocity occur during the upstroke as well as the downstroke, indicating that both phases of the limb cycle yield propulsive power.

From Fig. 3 it can be seen that, in relation to the body axis of the turtle, the flippers beat downwards and forwards and upwards and backwards. However, during vigorous swimming,

88 J . DAVENPORT

Downstroke I Upstroke I Downstroke

0 ; I I 0.0 0.4 0.8

Time (s)

FIG. 2. Changes in velocity of vigorously swimming turtle during limb stroke. Velocity profile corresponds to tracks shown in Fig. 1 .

the leatherback adopts a head downltail up attitude in which the body axis is held at about 22" to the horizontal. Functionally, therefore, the flippers beat slightly backwards on the downstroke and forwards on the upstroke in relation to the swimming direction. In the middle of a typical downstroke, the flipper blade follows a path that is about 75" to the horizontal plane and the outer part of the blade is inclined (by about 47" to the horizontal) with the leading edge ventral. In the middle of a typical upstroke, the blade path is about 82" to the horizontal and the blade is inclined (by 32") with the leading edge dorsal. Blade angles at the end of the downstroke and the beginning of the upstroke could not be assessed from lateral filming, but by reference to Fig. 7 (slow swimming filmed from in front) it may be deduced that the inclination (leading edge ventral) of the blade during the downstroke is reduced as the flipper approaches the lowest point of the limb cycle and the leading edge slows down (but the flexible trailing edge continues to move quite quickly). When the leading edge begins to move upwards on the upstroke there is a rapid reversal of inclination (i.e. to a leading edge dorsal mode) as the trailing edge continues to move downwards. This results in a rather steep inclination in the early part of the upstroke until the trailing edge also starts to move upwards.

From Fig. 4 it may be seen that, during vigorous swimming, the foreflippers of young leather- backs each beat through an arc of about 128", much less than that exhibited by green turtles of similar size (204"), which are capable of crossing over the foreflippers at the bottom of the limb cycle (Davenport et al., 1984), and of nearly touching them in front of and above the head at the top of the cycle. In both the laboratory film and the videotape of hatchlings swimming offshore in the South China Sea, i t appeared that all subsurface swimming was of the vigorous type; there

LOCOMOTION IN L E A T H E R B A C K T U R T L E S 89

A

FIG. 3. Flipper blade angles in vigorously swimming turtle. Box with question mark indicates part of limb cycle where blade angle could not be assessed. Dashed line indicates path of flipper; numbers indicate intervals of 0.08 s.

F IG . 4. View (from behind) of leatherback hatchling swimming vigorously during offshore swim in South China Sea (to show arc of flipper beat). Turtle is drawn with flippers in uppermost position of limb cycle; dashed outlines represent lowermost positions.

90 J . D A V E N P O R T

seemed to be no equivalent of the 'routine swimming' observed in green turtles by Davenport et al. 1984.

Slow swimming When the leatherbacks came to the water surface, vigorous swimming was replaced within a

few limb cycles by a noticeably different and much slower (c. 8 cm s-'; 0.9 body lengths s-')

b 8 \

I

I 1

FIG. 5 . Swimming track 2. Slowly swimming turtle. Horizontal line = water surface. Dashed lines indicate movement of whole turtle and tip of right foreflipper. Numbers indicate time intervals of 0.08 s. Scale bar = 10 cm. This figure is typical of several filmed sequences. Note that the head of leatherbacks does not move significantly in relation to the shell during swimming; any undulations in swimming track represent undulations of the whole animal, not just the head.

FIG. 6. Flipper blade angles in slowly swimming turtle. Box with question mark indicates part of limb cycle where blade angle could not be assessed. Dashed line indicates path of flipper; numbers indicate intervals of 0.08 s.

LOCOMOTION IN L E A T H E R B A C K T U R T L E S 91

~ c

ul r- al m 0

7 m

II a -

2 '5 a

92 J . DAVENPORT

Upstroke I Downstroke

'* 1

0 ' I 0.0 0.4 0.8

Time (s)

FIG. 8. Changes in velocity of slowly swimming turtle during limb stroke. Velocity profile corresponds to tracks shown in Fig. 5.

swimming action. A complete limb cycle during slow swimming occupies 0.8-1.0 s, so the frequency of limb beat is lower than during vigorous swimming. The slow swimming action is illustrated from the side in Figs 5 and 6, and from the front in Fig. 7. Figure 8 shows turtle velocity during the course of a complete limb cycle (this velocity profile was similar to that of all slow swimming sequences observed). From these figures, it may be seen that the arc of the flipper beat is much reduced (to about 75") by comparison with the arc described during vigorous swimming, and that the flipper is raised little or nothing above the shoulder during the limb cycle. In consequence, the flipper blade remains continuously submerged during slow swimming, even though the carapace projects above the water surface. In the slow swimming mode, the axis of the body is close to the horizontal and the path of the flipper beat is clearly forwards and downwards; upwards and backwards. In the middle of a typical downstroke, the flipper blade follows a path that is about 54" to the horizontal and the blade is inclined by 54" with the leading edge ventral. The upstroke path is about 68" to the horizontal and the blade inclined (by 43") with the leading edge dorsal. From Fig. 8 it can be seen that turtle velocity increases during the upstroke, but falls during the downstroke, indicating that propulsive power is only developed during the upstroke in this swimming mode.

Figure 9 shows proximal and distal flipper blade angles during the course of a slow swimming limb cycle. It may be seen that the inclination of the narrow proximal part of the flipper changes

L O C O M O T I O N IN L E A T H E R B A C K T U R T L E S 93

FIG. 9. Flipper blade angles during slow swimming. Upper hydrofoil represents proximal (i.e. inner) part of flipper; lower hydrofoil represents distal (i.e. outer) part of flipper. Numbers represent intervals of 0.08 s.

much less during the course of a limb cycle than does that of the broader distal portion-which presumably generates most of the propulsion.

Terrestrial locomotion The movement of hatching leatherback turtles filmed during the beach crawl is analysed in

Fig. 10. The fore and hind limbs move synchronously, so that all four limbs push backwards against the sand simultaneously. As the limbs move backwards, the body is pushed forwards until the centre of gravity of the turtle moves ahead of the ground contact areas of the tips of the foreflippers. At this point, the hatchling overbalances, rocks forwards on to the anterior portion of the plastron and the leading edges of the proximal parts of the foreflippers; the hind legs leave the ground. Forward movement of the hind limbs starts whilst they are still in the air; fractionally afterwards the forelimbs also start to move forwards above the sand as the animals begin to rock backwards. Forward movement of the limbs continues until both sets are at right

94 J. D A V E N P O R T

FIG. 10. Limb cycle of crawling leatherback hatchling. Solid flipper outlines represent most anterior position; dashed outlines represent rearmost position. Numbers represent intervals of 0.08 s.

Downstroke

- Swimming speed 30 cm d'

Upstroke

FIG. 11. Model of vigorous of down and upstrokes.

82;cI swimming in young Dermochelys coriuceu. Angles and velocities correspond to midpoints

L O C O M O T I O N IN L E A T H E R B A C K T U R T L E S 95

angles to the body; they are then pressed downwards and backwards against the sand and the cycle is repeated. Complete limb cycles occupy 0-5-0.6 s.

On steep downhill parts of the beach crawl, the overbalancing part of the cycle was often accompanied by ‘tobogganing’ as the animals slid downhill on the anterior part of the plastron, thus gaining considerable distance. Conversely, slight uphill gradients inhibited overbalancing and forward movement of the limbs was much more laboured.

Discussion

Swimming Vigorous swimming model

Figures 1 1 , 12 and 13 display a model of vigorous swimming in young Dermochelys in which the flipper blade is considered at the midpoint of the down- and upstrokes. From the resolution of the water flows it would appear that the flipper blade has an angle of attack to the relative

(a)

Resultant

movement)

30 cm s-’

(b) (owing to forward motion)

Resultant Drag

Propulsive component

I Water flow

( 4

component s Pitch

FIG. 12. Analysis of downstroke of vigorous swimming model. (a) Resolution of water flows acting on flipper. (b) Resolution of forces produced by flipper during downstroke. Dashed arrows represent forces acting on the blade; solid arrows represent forces acting on the water. Fd = total hydrodynamic force acting on the water. (c ) Resolution of Fd into components.

96 J . D A V E N P O R T

(a) 30 cm s-' (owing to forward motion)

flipper movement)

(b) Water

J Resultant

(c)

Pitch component

U p u l s i v e component

FIG. 13. Analysis of upstroke of vigorous swimming model. (a) Resolution of water flows acting on flipper. (b) Resolution of forces produced by flipper during upstroke. Dashed arrows represent forces acting on the blade; solid arrows represent forces acting on the water. Fu = total hydrodynamic force acting on the water. (c) Resolution of Fu into components.

water flow of about + 35" on the downstroke and -22" on the upstroke. (N.B. in the resolution of water flows no account has been taken of induced water flow, which effectively reduces angles of attack a little-see Weis-Fogh (1973) and Vogel (1981) for discussion.) This situation differs from vigorous swimming in the green turtle (in which the angle of attack is +22" on the downstroke and + 7 ' on the upstroke) but is reasonably similar to the 'routine swimming' model proposed for Chelonia mydus by Davenport et al. (1984). The Dermochelys model implies that lift-based propulsion operates on both downstroke and upstroke, with the flipper generating high lift and drag resulting in overall hydrodynamic forces (Fd, F,) with considerable horizontal propulsive components. Whereas the upstroke in Cheloniu mydus produces no propulsion during vigorous swimming, and no more than 20-40% of the downstroke power during routine swimming, the upstroke of Dermochelys appears to be more powerful, so that F d and F, are less asymmetrical, though still not as equal as the corresponding forces in penguins (Clark & Bemis, 1979).

L O C O M O T I O N I N L E A T H E R B A C K T I J R T L E S 97

4 Swimming speed 7.9 cm s-l

Upstroke

FIG. 14. Model of slow swimming in young Dermochelys coriacea. Angles and velocities correspond to midpoints of down and upstrokes.

Penguin swimming is based upon stiffened, flipper-like wings flapping directly up and down close to the centre of gravity; this minimizes wastage of energy in pitching. Turtle flippers flap in front of the centre of gravity so tend to cause upward pitching on the downstroke and downward pitching on the upstroke. Pitching in vigorously swimming green turtles is opposed to some extent by compensatory movements of the head (Davenport et al., 1984). Young leatherbacks have a shorter neck and the head is much less mobile than in green or loggerhead turtles. Consequently, the swimming path is undulatory.

Slow swimming model Figures 14, 15 and 16 show a model of slow swimming in young leatherbacks. From the

resolution of water flows it appears that the flipper blade has an angle of attack to the relative water flow of about -16" on the downstroke and -35" on the upstroke. This observation implies that the downstroke does not propel the turtle forwards during slow swimming, but instead the relatively low lift and drag forces combine to generate a force (Fd) which is directed forwards and therefore has a braking component. This analysis is consistent with the turtle velocity profile shown in Fig. 8. In contrast, the upstroke, with its large angle of attack, generates much lift and drag to produce an overall hydrodynamic force (F,) with a strong propulsive

98 J . D A V E N P O R T

(owing to forward motion)

Resultant

Lift

(angle of attack)

Resultant

Lift

(angle of attack)

Pitch component

Braking

(4 component

Braking

(4

component FIG. 15. Analysis of downstroke of slow swimming model. (a) Resolution of water Row acting on Ripper. (b)

Resolution of forces produced by flipper during downstroke. Dashed arrows represent forces acting on the blade; solid arrows represent forces acting on the water. Fd = total hydrodynamic force acting on the water. (c) Resolution of Fd into components.

component. The idea of a turtle relying on the upstroke for lift-based propulsion is far removed from the concept of Gray (1953), who believed that turtles used their foreflippers as simple paddles, producing drag-based power only on the down (= back) stroke.

Comparisons with other species Vigorously swimming young leatherback turtles swim at an average velocity of about 30 cm

s-I (3.3 body lengths s-l), a similar velocity to that of green turtles of similar size (Davenport et al., 1984). Comparisons with other aquatic species are difficult because of scaling problems, but if it is assumed that peak swimming speeds are directly proportional to body length (Wu, 1977), then Dermochelys swims a little more quickly than the penguin Aptenodytes forsteri (2.3 body lengths s-l; Clark & Bemis, 1979), but rather less effectively than the flatish Pleuronectesplatessa (5.1 body lengths s-l; Blaxter & Dickson, 1959).

Davenport et al. (1984) found that a single, slightly larger ( 1 1 cm length) green turtle briefly

L O C O M O T I O N I N L E A T H E R B A C K T U R T L E S

7.9crn s-' (4 (owing to forward motion)

99

movement)

Resultant

'0' \ Lift *-

J' Drag Resultant

componeu Propulsive component

FIG. 16. Analysis of upstroke of slow swimming model. (a) Resolution of water flows acting on flipper. (b) Resolution of forces produced by flipper during upstroke. Dashed arrows represent forces acting on the blade; solid arrows represent forces acting on the water. Fu = total hydrodynamic force acting on the water. (c) Resolution of Fu into components.

achieved 8.5 body lengths s- immediately after release from restraint, and therefore approached the swimming speed of streamlined fish such as the mackerel Scomber scomber (8.6 body lengths s-l; Blaxter & Dickson, 1959). The peak velocity recorded during limb cycles in Dermochelys (9.1 cm length) did not exceed six body lengths s-l, which might suggest that young leatherbacks have a slightly lower speed capability than Chelonia mydas. However, whereas green turtles swim violently away from restraint, but slow down considerably within a few limb cycles, young leatherbacks swim away in a sustained vigorous manner, so the difference in peak swimming speed may simply reflect a difference in behavioural response rather than any fundamental difference in hydrodynamic or muscular capability.

General considerations The swimming repertoire of young leatherbacks is much simpler than that of green and

loggerhead turtles of similar age. All swimming is accomplished by synchronized flapping of the

100 J . D A V E N P O R T

foreflippers, and is effectively either subsurface and fast (30 cm s - I ) or at the surface and slow (8 cm s-l). Intermediate velocities are transitory and the turtles appear not to rest. The ‘two speed’ nature of swimming may be associated with the downwards and forwardslupwards and backwards axis of flipper beat (which is opposite in direction to the axis in green, loggerhead and hawksbill turtles), combined with the positive buoyancy of young Dermochelys.

All young sea turtles seem to be positively buoyant during the first few months of life (Daven- port & Clough, 1986) and adopt a head downltail up attitude when swimming under water. However, in Chelonia mydas and Caretta caretta, the downwards and backwardslupwards and forwards limb stroke allows positive angles of attack (and power) to be maintained over a range of swimming speeds (thus accommodating both vigorous and routine swimming). The opposite axis of flipper beat in Dermochelys is much more sensitive to the attitude of the body; if the turtle slows and the body axis becomes more nearly horizontal, there is a rapid decline in angle of attack on the downstroke, with consequent loss of power and automatic surfacing. Slow surface swimming may be somewhat inefficient (since the downstroke produces no power, indeed slows the turtle), but is not required to oppose positive buoyancy and in any case is probably no less efficient than the ‘dogpaddle’ of slow swimming green turtle hatchlings, and is appreciably quicker than the double hind limb kick ( 5 cm s-l) employed by young loggerheads (Davenport & Clough, 1986).

Davenport & Clough, 1986, suggested that young loggerhead turtles exhibit a wider repertoire of swimming styles than young green turtles because Caretta caretta is a coastal, carnivorous species whose habit demands manoeuvrability rather than the outright speed required of Chelonia mydas, which makes long periodic oceanic migrations between its coastal plant feeding grounds and island breeding areas. It seems probable that the limited range of swimming styles shown by Dermochelys may also be a reflection of lifestyle. Leatherbacks are planktonic feeders upon slow moving prey (almost exclusively jellyfish) and spend most of their life in the open ocean; they have no obvious need of great manoeuvrability, and would appear to have no requirement for sudden bursts of speed to overhaul prey. The narrow ability to swim steadily over great distances is of overriding importance to them and their propulsion system seems to be geared to this admirably.

Terrestrial locomotion Detailed analyses of terrestrial locomotion in chelonians have been few. Walker (1971)

and Zug (1972) described the locomotion of freshwater species which are agile on land and walk with the carapace entirely off the ground; Jayes & Alexander (1980) considered the slow gaits of tortoises. Many authorities have commented upon the laboured terrestrial locomotion of sea turtles (stemming from the laterally directed flippers) which Hendrickson (1980) believes to be the evolutionary price paid for large size and effective long distance swimming capability.

Although Bustard (1972) remarked that young turtles employed a ‘push-pull’ action in which all four limbs moved in unison when crawling down the beach, it appears that no detailed account of hatchlings’ locomotion has been published. The results presented here show that hatchling Dermochelys employ a fundamentally unstable gait which involves overbalancing during each limb cycle, and all four limb tips being off the ground simultaneously. The gait is suited to downhill movement on sand-other substrata would be less forgiving given the soft nature of the ventral skin of the head and flippers.

L O C O M O T I O N I N LEATHERBACK T U R T L E S 101

The author wishes to thank Dr Wong Tat Meng and Miss Chan Eng Heng for their good offices in obtaining the leatherback hatchlings. He also acknowledges the help and facilities provided by the Universiti Sains Malaysia, and the travel funding supplied by the Royal Society of London.

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