The Owl That Fell from the Sky (12 page)

Turtle bones

Wonderful things wash up on beaches. In September 1996 a woman found a large dead turtle on Waikorea Beach, an isolated spot west of Hamilton in northern New Zealand. She reported it to the local office of the Department of Conservation. Two officers, Laurence Barea and Gary Hickman, went to investigate. They took photographs of the turtle, then buried it in nearby sand dunes and marked the spot.

Turtles, with their protective armoured carapace and plastron—upper and lower halves of the shell—are distinctive animals, superbly adapted for their marine existence. They have a streamlined body and their forelimbs have evolved into large propulsive paddles. In the fossil record as far back as 200 million years there are creatures we would immediately recognise as turtles if they were alive today. The shape of the turtle's body is so successful it has proved remarkably stable in evolutionary terms: modern turtles have changed very little from their earliest ancestors. Only the destructiveness, greed and indifference of people threaten the turtles' future—as they do our own.

Turtles breed in the tropics and are widely distributed in tropical and subtropical seas. Occasionally they turn up in colder regions, including the seas around New Zealand, where five species have been recorded. Here they are most commonly seen in summer and autumn, in the warmer northern half of the North Island. Most are stragglers, assisted or carried by the East Australian Current, which flows south along Australia's east coast, east across the northern Tasman Sea, then south-east along the edge of the continental shelf off the north-eastern North Island. Roughly seventy percent are alive when found, but many have become entangled in nets or lines. Others are washed ashore, a sign of illness or cold-shock: normally they would come ashore only to lay eggs and none can breed so far south.

Commonest in New Zealand is the leathery turtle
Dermochelys coriacea
. It is the largest of all living turtles, reaching around three metres in total length and weighing up to 900 kilograms. The carapace is a mosaic of small, many-sided bony plates covered in tough skin. It has seven longitudinal ridges: swimming at the surface the turtle looks like an upturned dinghy.

The leathery turtle is the world's most widely distributed turtle, found in all tropical and temperate seas. It is the only species widely reported in southern parts of New Zealand because it deliberately seeks out temperate waters as feeding grounds. It can do this through physiological adaptations that enable it to maintain a higher core body temperature than the ambient temperature. The four other turtles recorded in New Zealand—green turtle,
Chelonia mydas
, loggerhead turtle,
Caretta caretta
, hawksbill turtle,
Eretmochelys imbricata
, and olive ridley turtle,
Lepidochelys olivacea
—are smaller and their carapaces, featuring large juxtaposed scaly scutes, are more typical. These turtles mainly turn up in northern New Zealand waters that, even in the far north, are too cold for them most of the year.

 

 

The body of the turtle at Waikorea Beach was in an advanced state of decay. One of the rangers sent me photographs and asked for an identification. I could see the carapace's individual scutes, including the row running along the mid-line, and the marginal scutes along the edges of the shell. Between these on each side was a row of five, possibly six, of the large scutes known as costal shields. The green turtle and hawksbill have only four pairs of costals, the loggerhead has five (rarely six) and the olive ridley has six. I felt the dead turtle was most likely to be a loggerhead since there were numerous records of this species in New Zealand, whereas the olive ridley had been recorded only twice.

The photographs were later seen by Raymond Coory at the Museum of New Zealand Te Papa Tongarewa. He noticed the carapace was diamond-shaped and felt it was very similar to the carapace of an olive ridley in the Te Papa collection. I sent photographs to a colleague at the Smithsonian Institution and these were seen by two other American specialists familiar with olive ridleys. All agreed that from the look of the animal it was an olive ridley.

More photographs of the Waikorea specimen then emerged. Shots of the underside showed the presence of four “inframarginal” scutes—the row of shields on each side of the plastron between the forelimb and hindlimb and next in line beside the marginal scutes. The olive ridley has four inframarginals, whereas the loggerhead usually has three. The Waikorea turtle was, therefore, a particularly interesting specimen—only the third known record of an olive ridley in New Zealand. The first had been found at Flat Point in the Wairarapa (North Island) in 1956; the second at Kaka Point Beach near Dunedin (South Island) in 1985. Olive ridleys are distributed throughout the tropics, but are most abundant in the eastern Pacific Ocean, the Indian Ocean and the Gulf of Guinea in the Atlantic.

About a year and a half after the turtle was buried, the Department of Conservation officers returned to exhume the bones. After successfully recovering the entire skeleton they kindly delivered it to Auckland Museum. The turtle had measured about 700 millimetres along the curve of the carapace, and as it was an adult its bones were fully grown and ossified. The time in the damp sand had cleaned the bones beautifully, and all Maree Johnston, the land vertebrates technician, had to do to prepare them for the collection was to wash and scrub them gently and set them out to dry. Bones in a museum collection need to be clean so it is possible to examine the bones' minute features, and so no dried tissue that could attract and sustain insect pests remains. Moth and beetle larvae that eat dried flesh in the wild and clothing and carpet fibres in people's homes will eat fur, feathers and fibre on objects in museum collections.

Skeletonisation of a fresh corpse to obtain clean bones is a time-consuming process. We normally use the simple technique of cold-water rotting. The skin, internal organs and larger muscles are removed with scalpels, and the remaining body boiled briefly to improve the subsequent rotting process. It is then placed in a vessel of cold water with the lid on. Bacteria flourish, destroying the soft tissues. The water in the jars and buckets is changed several times over the following months until clean bones are visible. After disinfection with bleach, scrubbing of any troublesome areas and final rinsing, the bones are carefully picked out and set aside to dry. Not all aspects of the task are pleasant, but the redeeming feature is the set of beautiful clean white odourless bones produced at the end.

Larger animals rotting down in large buckets generate a lot of liquid for disposal, so for a couple of wallabies, an albatross and a mute swan I tried out my compost bin at home. Ramola Prasad, the technician, fleshed out the body and had it wrapped in newspaper so I could take it straight home from the freezer one day after work. I had a hole ready in a bin of friable, well-rotted compost. I buried the package, kept the bin moist for six to twelve months, and then dug out the bones. If the neighbours ever saw me burying and exhuming strange items they never mentioned it. The bones needed a lot of scrubbing, but the end results were worthwhile.

Many large museums use colonies of dermestid beetles to clean bones. The beetles' larvae eat the surrounding tissue but leave the bones alone. For best results the animal bodies are again roughly stripped down, and this time dried before exposure to the beetles. The process takes time, and the beetle colonies need constant maintenance to keep the temperature, humidity and supply of food just right. In addition, precautions are needed to prevent the beetles escaping into the museum collections: usually the colony is kept in a separate building or outhouse.

The Waikorea turtle bones, already fully rotted down in the dunes, were therefore a great gift. Using indelible ink, Maree Johnston wrote the registration number on as many as possible and painted over each number with a clear acrylic solution to protect it. Stored loose in a large box, the bones then joined the museum's collection, ready for service in research studies, identifications and exhibitions.

At least two archaeologists, studying bones from prehistoric midden sites in the tropical Pacific, have used the Waikorea bones as reference specimens, to help determine which of many bones and bone fragments found in the middens belonged to turtles. The skull was once displayed in a temporary exhibition, and I have used the bones to help describe a forty-million-year-old turtle fossil.

Jane Hill, a secondary school teacher, had found this fossil in 2005 at a roadside cutting near Whangarei in northern New Zealand. Jack Grant-Mackie, a retired geologist still active at the University of Auckland, helped recover the fossil bones and asked me to assist in the study of them.

The fossil represented a large turtle with a carapace approaching 900 millimetres long, and was from the Late Eocene Epoch—that is, forty to forty-five million years ago. It comprised a broken right humerus—an upper forelimb bone; some bones of the right “hand”; five vertebrae, preserved in line as in life; and various other fragments. The bones were broken, incomplete, and in places still partly obscured by hard rock, but each had to be identified as to which part of the skeleton it was from, and compared in shape and size with published descriptions of fossil turtles from around the world.

The string of vertebrae was difficult to place. Fortunately, in 1879 the museum had received on exchange from the Royal College of Surgeons in London an articulated skeleton of a green turtle. Still extant, the skeleton was mounted vertically with the head pointing skyward and the belly facing out. The carapace was supported on a metal rod and all the other bones were wired into their correct positions. Guided by this green turtle skeleton and the loose bones of the Waikorea turtle, I finally pinned down the fossil vertebrae as cervical (neck) and thoracic: C6, C7, C8, T1 and T2.

 

 

The Eocene turtle from Whangarei is an important record of New Zealand's fossil history. The immense age of fossils is hard to grasp, but various analogies help us to understand the enormity of geological time. One is to consider the age of the Earth compressed into a calendar year that began on January 1 and in which the current time is midnight on December 31. It took a long time for the planet to develop conditions favourable to living organisms—the first simple forms of life appeared around the beginning of June. The dinosaurs reigned from December 13 to 26. The Whangarei turtle fossil seems very old at forty million years, but was in fact living quite recently, on about December 28. Humans, in case you were wondering, appeared on December 31 at 11.50 pm, and the whole of recorded human history has taken place in the last forty seconds before midnight.

 

The Aitutaki house geckos

In October 1995, when I visited the tiny Pacific island of Aitutaki in the Cook Islands, I went out on foot at night to look for geckos in the main village, Arutanga. I was doing a survey of reptiles in the islands and collecting voucher specimens for Auckland Museum.

The evening was warm and humid, I could smell the scent of tropical flowers and there were the sounds that typify a Pacific island settlement: barking dogs, bleating goats, snuffling pigs and the ever-strident crowing roosters. It was thirsty weather, so I called into the Seabreeze bar on the wharf for a few beers. The intake of liquid soon had me in the lavatory, which was lucky for on the walls near fluorescent lights I caught three geckos.

I was not immediately sure what species the geckos were, as many geckos appear very similar. But however similar they may look at first glance, their differences are often reflected—strange as it may sound—in the number, size and shape of the pads, or lamellae, along the underside of the toes.

Toes are very important to geckos. Batteries of microscopic hairs on the lamellae beneath the flattened and expanded toes of many kinds of geckos enable these lizards to climb along walls and ceilings. The microscopic hairs connect to the surface by inter-molecular forces to give dry adhesion. As the gecko rolls and unrolls its toes against the surface, countless connections are made and broken at the submicroscopic level. Altogether, over the area of the expanded toes, these tiny connections are enough to support the gecko's weight. Today geckos' toes are closely studied by bioengineers looking for new and improved artificial adhesive mechanisms.

Because herpetologists need to pay such close attention to toes when identifying geckos, the descriptive generic names of many geckos end in “dactylus”, from the Greek “daktylos” referring to the finger. I used a hand lens to look closely at the pattern of scales on the head and toes of the geckos from Arutanga wharf and this confirmed my suspicions that they were the Asian house gecko,
Hemidactylus frenatus
.

 

 

Geckos are one of the largest families of lizards and one of the most widespread, being common throughout the warmer regions of the world. Their body scales are small and granular, giving their skin a dull velvety appearance. Geckos have large eyes that they cannot blink: in the course of evolution the lower eyelid has fused shut. In compensation, one transparent scale on the eyelid has enlarged to cover the eye. This scale is shed and renewed regularly, along with the rest of the gecko's skin. If the eyes get dirty between moults, the gecko licks them clean with its large fleshy tongue.

In the tropics, various species of geckos enter dwellings as “house geckos”, emerging at night to feed on insects attracted to electric lights. Most reptiles are silent but geckos are an exception: some species, including many house geckos, have chirping or chattering calls.

The main house geckos in the South Pacific islands are the oceanic gecko,
Gehyra oceanica
, the sad (or mourning) gecko,
Lepidodactylus lugubris
, the fox gecko,
Hemidactylus garnotii
, the stump-toed gecko,
Gehyra mutilata,
and the Asian house gecko. These geckos form an interesting case study in biogeography—the study of the distribution of organisms and the mechanisms by which the patterns of distribution have arisen. The oceanic gecko readily enters houses but it also lives happily in forests, away from dwellings. It is found nowhere else but the Pacific so is probably native to most of the many Pacific islands where it lives, and pre-dates the arrival of humans. It is a forest gecko that enters houses opportunistically.

The sad gecko is found on islands throughout the Indian and Pacific Oceans. In the Pacific it lives in the bush as well as in buildings. Sad geckos presumably spread across the Pacific either naturally before human settlement—eggs or adults rafted between islands on debris—or were spread by the canoes of the early Polynesian voyagers as they moved out of south-east Asia to colonise the Pacific. Ancestral Polynesians reached Samoa and Tonga about 3,000 years ago and then spread east, perhaps with sad geckos as stowaways.

In the Pacific, the fox and stump-toed geckos, natives of southern Asia, are usually restricted to human habitations, the sign of an introduced species. In Polynesia, the fox gecko tends to live mainly in rural villages, suggesting it may have been introduced early—with Polynesian voyagers perhaps, or by sailing ships in the 1800s. The stump-toed gecko is fully at home in Polynesian towns and possibly arrived a little later. It is not called
Gehyra mutilata
for nothing, for if it is roughly handled it self-mutilates as a defence mechanism. It does not just shed its tail, as many lizards do, but can also slough off entire sections of skin, leaving areas of exposed slippery flesh, reminiscent, on a smaller scale, of raw skinned chicken meat. This is as disconcerting to the field herpetologist who catches these geckos as it must be confusing to the small predator.

The Pacific house geckos lay eggs that, when insinuated into crevices in cargo, are easily transported about. Many have sticky eggs that become cemented into cracks as they dry. The fox and sad geckos have another attribute that has aided their spread between islands: they exist as asexual clones that reproduce by “virgin birth”, known technically as parthenogenesis. This means only a single egg or individual is needed to found a new population. All individuals are females. Conveniently bypassing the need for any males, they lay unfertilised eggs that hatch into females. The individuals of these clones have limited genetic variation because this can happen only by mutation, not by the reassortment of parental genes that occurs in sexually breeding species.

Parthenogenesis is unsurprising in insects and is known in some fish, but it is fairly rare in reptiles and unknown in birds and mammals—the higher vertebrates. (There has been one case reported in our own species, in the eastern Mediterranean some 2,000 years ago at a town called Bethlehem. Regrettably the biological details of this remarkable birth are unknown since the accounts are purely anecdotal.)

Parthenogenesis in lizards was first discovered in the 1950s by Ilya Darevsky, a zoologist at the Leningrad Academy of Sciences, who found that certain populations of a lizard in Armenia seemed to be entirely female. Darevsky's published results were doubted until the 1960s, when American herpetologists found all-female populations of whiptail lizards in the south-west United States and some of these lizards demonstrated parthenogenesis.

It is now thought that about one percent of the world's 3,000 species of lizards are unisexual. Parthenogenetic lizard clones have mostly arisen suddenly, as the freak but functioning offspring of a rare and chance hybridisation of two different species.

 

 

The Asian house gecko, the most recent gecko to arrive in the Pacific, is easily spread by the current systems of moving international freight by sea and air. It is shaping up to be a significant invasive species throughout the warmer parts of the world. Its original distribution is thought to have been South-east Asia and New Guinea. In Australia, it was found near Darwin in the 1800s, and it has since spread widely throughout northern Australia. The first specimens in Brisbane were collected in 1983 and it is now the commonest gecko in that city. It is found in and near most Queensland ports from Cooktown to the Gold Coast, and in coastal New South Wales south to Coffs Harbour.

The Asian house gecko established itself at Acapulco in Mexico around 1930, and in Hawaii in the 1950s. It has become widespread in the southern United States. In the South Pacific, it took hold on the main island of Vanuatu sometime between 1971 and 1986. In Fiji it was recorded in the Nadi-Lautoka area in 1980 and was well established around Suva and Labasa by 1986. A specimen was collected on Rarotonga, the main island of the Cook Islands, in 1987. In the Society Islands, French Polynesia, it arrived shortly before 1990. It is now the reptile most commonly intercepted in cargo reaching New Zealand, although conditions are unsuitable for these travellers to survive.

Wherever it spreads in the Pacific, the Asian house gecko often has competitive advantages over other house geckos. At lights, where house geckos congregate to feed, it usually displaces or reduces in number whatever species of geckos were visiting the lights before. By its size and aggression it easily excludes the smaller sad gecko.

At Bamboo Bungalows, the guest house where I stayed at Arutanga, three species of house geckos were in residence—oceanic, stump-toed and sad. At nearby Arutanga wharf, the key site besides the airstrip for the arrival of cargo on the island, I did not grasp immediately that the three Asian house geckos I had caught were probably the first arrivals of that species on the island, or their recent descendants. I happened to be collecting just as this invasive gecko had established a new beachhead in its steady conquest of the Pacific. The existing house geckos of Aitutaki were in for a shake-up.

In July 2000 Tony Whitaker, a New Zealand herpetologist, visited Aitutaki. He found that Asian house geckos were now widespread over part of the island. He was unable to find any stump-toed geckos.