The leatherback sea turtle (Dermochelys coriacea), sometimes called the lute turtle, leathery turtle or simply the luth, is the largest of all living turtles and the heaviest non-crocodilian reptile, reaching lengths of up to 2.7 metres (8 ft 10 in) and weights of 500 kilograms (1,100 lb).[5][6][7] It is the only living species in the genus Dermochelys and family Dermochelyidae. It can easily be differentiated from other modern sea turtles by its lack of a bony shell; instead, its carapace is covered by oily flesh and flexible, leather-like skin, for which it is named.[8] Leatherback turtles have a global range, although there are multiple distinct subpopulations. The species as a whole is considered vulnerable, and some of its subpopulations are critically endangered.
Dermochelys coriacea is the only species in genus Dermochelys. The genus, in turn, contains the only extant member of the family Dermochelyidae.[9]
Domenico Agostino Vandelli named the species first in 1761 as Testudo coriacea after an animal captured at Ostia and donated to the University of Padua by Pope Clement XIII.[10] In 1816, French zoologist Henri Blainville coined the term Dermochelys. The leatherback was then reclassified as Dermochelys coriacea.[11] In 1843, the zoologist Leopold Fitzinger put the genus in its own family, Dermochelyidae.[12] In 1884, the American naturalist Samuel Garman described the species as Sphargis coriacea schlegelii.[13] The two were then united in D. coriacea, with each given subspecies status as D. c. coriacea and D. c. schlegelii. The subspecies were later labeled invalid synonyms of D. coriacea.[14][15]
Both the turtle's common and scientific names come from the leathery texture and appearance of its carapace (Dermochelys coriacea literally translates to "Leathery Skin-turtle"). Older names include "leathery turtle"[7] and "trunk turtle".[16] The common names incorporating "lute" and "luth" compare the seven ridges that run the length of the animal's back to the seven strings on the musical instrument of the same name.[17] But probably more accurately derived from the lute's ribbed back which is in the form of a shell.[citation needed]
Relatives of modern leatherback turtles have existed in relatively the same form since the first true sea turtles evolved over 110 million years ago during the Cretaceous period.[18] The dermochelyids are relatives of the family Cheloniidae, which contains the other six extant sea turtle species. However, their sister taxon is the extinct family Protostegidae that included other species that did not have a hard carapace.[19][20]
Leatherback turtles have the most hydrodynamic body of any sea turtle, with a large, teardrop-shaped body. A large pair of front flippers powers the turtles through the water. Like other sea turtles, the leatherback has flattened forelimbs adapted for swimming in the open ocean. Claws are absent from both pairs of flippers. The leatherback's flippers are the largest in proportion to its body among extant sea turtles. Leatherback's front flippers can grow up to 2.7 m (8.9 ft) in large specimens, the largest flippers (even in comparison to its body) of any sea turtle.
The leatherback has several characteristics that distinguish it from other sea turtles. Its most notable feature is the lack of a bony carapace. Instead of scutes, it has thick, leathery skin with embedded minuscule osteoderms. Seven distinct ridges rise from the carapace, crossing from the cranial to caudal margin of the turtle's back. Leatherbacks are unique among reptiles in that their scales lack β-keratin. The entire turtle's dorsal surface is colored dark grey to black, with a scattering of white blotches and spots. Demonstrating countershading, the turtle's underside is lightly colored.[21][22] Instead of teeth, the leatherback turtle has points on the tomium of its upper lip, with backwards spines in its throat (esophagus) to help it swallow food and to stop its prey from escaping once caught.
D. coriacea adults average 1–1.75 m (3.3–5.7 ft) in curved carapace length (CCL), 1.83–2.2 m (6.0–7.2 ft) in total length, and 250 to 700 kg (550 to 1,540 lb) in weight.[21][23] In the Caribbean, the mean size of adults was reported at 384 kg (847 lb) in weight and 1.55 m (5.1 ft) in CCL.[24] Similarly, those nesting in French Guiana, weighed an average of 339.3 kg (748 lb) and measured 1.54 m (5.1 ft) in CCL.[25][26] The largest verified specimen ever found was discovered on the Pakistani beach of Sandspit and measured 213 cm (6.99 ft) in CCL and 650 kg (1,433 lb) in weight.[27] A previous contender, the "Harlech turtle", was purportedly 256.5 cm (8.42 ft) in CCL and 916 kg (2,019 lb) in weight,[28][29] however recent inspection of its remains housed at the National Museum Cardiff have found that its true CCL is closer to 1.5 m (4.9 ft), casting doubt on the accuracy of the claimed weight, as well.[27] On the other hand, one scientific paper has claimed that the species can weigh up to 1,000 kg (2,200 lb) without providing more verifiable detail.[30] The leatherback turtle is scarcely larger than any other sea turtle upon hatching, as they average 61.3 mm (2.41 in) in carapace length and weigh around 46 g (1.6 oz) when freshly hatched.[24]
D. coriacea exhibits several anatomical characteristics believed to be associated with a life in cold waters, including an extensive covering of brown adipose tissue,[31] temperature-independent swimming muscles,[32] countercurrent heat exchangers between the large front flippers and the core body, and an extensive network of countercurrent heat exchangers surrounding the trachea.[33]
The carapace of the leatherback sea turtle has a unique design which enables the sea turtles to withstand high hydrostatic pressures as they dive to depths of 1200 m.[34] Unlike other sea turtles, the leatherback sea turtle has a soft, leathery skin which covers the osteoderms rather than a hard keratinous shell. The osteoderms are made up of bone-like hydroxyapatite/collagen tissue and have jagged edges, referred to as teeth. These osteoderms are connected by a configuration of interpenetrating extremities called sutures that provide flexibility to the carapace, enabling in plane and out of plane movement between osteoderms. This is important since the lungs, and thus the carapace, expand when taking in air and contract when deep diving.[34]
The sutures connect rigid elements and flexible joints in a zig-zag configuration, so there is no region where teeth can easily penetrate the carapace. There are two main failure mechanisms for the tires in tension:[clarification needed] tooth failure corresponding to mineral-brittle failure; and interfacial failure between teeth corresponding to collagen-ductile failure.[34] The triangular tooth geometry is able to evenly distribute load and absorb energy.[34] This leads to a high strength in tension since this geometry takes advantage of the tensile strength of bone and the interface.[34][35] Additionally, the carapace is tough because sutures prevent crack propagation. Under load, cracks interact with the sutures which can resist crack growth via crack bridging. This phenomenon was observed in sequential compression of osteoderm samples.[36]
Leatherbacks have been viewed as unique among extant non-avian reptiles for their ability to maintain high body temperatures using metabolically generated heat, or endothermy. Initial studies on their metabolic rates found leatherbacks had resting metabolisms around three times higher than expected for reptiles of their size.[37] However, recent studies using reptile representatives encompassing all the size ranges leatherbacks pass through during ontogeny discovered the resting metabolic rate of a large D. coriacea is not significantly different from predicted results based on allometry.[38]
Rather than using a high resting metabolism, leatherbacks appear to take advantage of a high activity rate. Studies on wild D. coriacea discovered individuals may spend as little as 0.1% of the day resting.[39] This constant swimming creates muscle-derived heat. Coupled with their countercurrent heat exchangers, insulating fat covering, and large size, leatherbacks are able to maintain high temperature differentials compared to the surrounding water. Adult leatherbacks have been found with core body temperatures that were 18 °C (32 °F) above the water in which they were swimming.[40]
Leatherback turtles are one of the deepest-diving marine animals. Individuals have been recorded diving to depths as great as 1,280 m (4,200 ft).[41][42]Typical dive durations are between 3 and 8 minutes, with dives of 30–70 minutes occurring infrequently.[43]
They are also the fastest-moving non-avian reptiles. The 1992 edition of the Guinness Book of World Records lists the leatherback turtle moving at 35.28 km/h (21.92 mph) in the water.[44][45] More typically, they swim at 1.80–10.08 km/h (1.12–6.26 mph).[39]
The leatherback turtle is a species with a cosmopolitan global range. Of all the extant sea turtle species, D. coriacea has the widest distribution, reaching as far north as Alaska and Norway and as far south as Cape Agulhas in Africa and the southernmost tip of New Zealand.[21] The leatherback is found in all tropical and subtropical oceans, and its range extends well into the Arctic Circle.[46]
The three major, genetically distinct populations occur in the Atlantic, eastern Pacific, and western Pacific Oceans.