Aldabra giant tortoise (left)
and hololissa (right) at Cotswolds Wildlife Park, showing shell differences (© Dr Karl Shuker)
The New
World giant tortoises famously inhabiting the Galapagos
Islands off Ecuador
in the Pacific Ocean
were once rivalled for size by several huge Old
World species native to the Indian
Ocean's granitic Seychelles
group, the coral atoll of Aldabra, the Mascarene
islands, and Madagascar.
Of these, only the Aldabra giant tortoise Aldabrachelys [=Dipsochelys]
gigantea [=dussumieri, =elephantina] is traditionally
thought to have survived into the present day, the remainder having been killed
for their meat during the 1700s and 1800s - or so it was thought, until Arnold's
giant tortoise and the hololissa unexpectedly reappeared in modern times.
There has been much debate concerning the
precise number of giant tortoise species native to the Seychelles.
Four are currently recognised (although some researchers deem them merely to be
subspecies of a single species), one of which was formally described in
September 1982, by Dr Roger Bour from France's
National Museum of Natural History. He based his description upon three old
taxiderm specimens (two at the above museum, the third at the British
Museum).
They possessed various skeletal modifications that seemed to be adaptations to
browsing, and originated from the granitic Seychelles
islands. Bour named their species Dipsochelys [now Aldabrachelys]
arnoldi, but as there did not seem to be any giant tortoises (other than
Aldabra's) in the Seychelles
today, he naturally assumed that it was extinct - belatedly recognised as a
distinct species, yet irretrievably deceased.
Aldabra giant tortoises (© Dr
Karl Shuker)
Imagine, then, his surprise when, while
still preparing his paper, Bour was shown some photos by film producer Claud
Pavard (who had taken them in August 1981) depicting two living giant
tortoises that seemed to belong to his supposedly extinct species A. arnoldi.
Nor was this the only surprise. The tortoises, males and very old, were living
in semi-captivity at a sugar estate, but not in the Seychelles
- instead, on Mauritius!
Naturally, Bour hoped to visit Mauritius,
to ascertain conclusively these potentially significant specimens' identity.
And that is where this most promising saga
seemed to come to an abrupt end. During my preparation of my book The Lost Ark, published in 1993 and the first
in my trilogy of volumes documenting new and rediscovered animals from 1900
onwards, I was unable to locate a single publication carrying any further news
regarding these tortoises, and none of my zoological colleagues and
correspondents had any details (sadly, I never succeeded in eliciting a reply
from Dr Bour himself), though they were all as intrigued by it as I was.
Happily, however, the mystery was finally solved in May 1992, when I learnt
from British
Museum
herpetologist Dr Nick Arnold (after whom A. arnoldi had been named) that
Dr Bour had indeed visited the two Mauritius
specimens, but had found that they were not representatives of A. arnoldi
after all.
The Lost Ark: New and Rediscovered Animals of the 20th Century (HarperCollins: London, 1993) (© Dr Karl Shuker)
Moreover, Dr Ian Swingland, Founding and
Research Director of the Durrell Institute of Conservation and Ecology (DICE),
informed me that giant tortoises reared in captivity sometimes have shells that
have become distorted in shape, due to the way in which these animals have been
fed. In some cases, therefore, it is possible that they may even resemble the
shells of quite unrelated species, and this is presumably what had happened in
the case of the two Mauritius
specimens, which were probably individuals originating from Aldabra.
Captivity-induced distortion of shell shape can cause problems for tortoise
taxonomists too, especially if they are dealing with specimens whose life
histories are unknown (and which, therefore, may have been reared in
captivity).
Of course, one objection that could
immediately have been raised in relation to this entire episode is the fact
that supposed specimens of A. arnoldi were discovered not in the Seychelles,
but instead in Mauritius.
As it happens, however, this objection can be effectively countered - because a
number of giant tortoises from the Seychelles
are known to have been introduced there after that island's own indigenous
species had been exterminated during the 1700s. In particular, the French
explorer Marion de Fresne transported five such specimens in 1776 from the Seychelles
to his military barracks on Mauritius.
What was assumed to be the last of this quintet died there in 1918, but there
may have been others too, whose records have failed to survive to the present
day.
A pair of Aldabra giant
tortoises mating - intriguingly, the top specimen has a markedly flat-backed shell, resembling the saddle-backed shell of Arnold's giant tortoise (public domain)
In any event, what did seem clear at the
time of writing The Lost Ark was that none of the long-lost species of Seychelles
giant tortoise had been resurrected after all. During 1995, however, another
discovery was made - one that added a new and much more dramatic chapter to
this long-running saga of mistaken and incognito identities.
In January of that year, the Nature
Protection Trust of Seychelles (NPTS) learnt of two very large, and very old,
male tortoises living in the garden of a Seychelles
hotel. When examined by Dr Justin Gerlach and K. Laura Canning, chief
scientists with the NPTS, they were found to exhibit pronounced flaring,
flattening, and scalloping of the carapace, especially over the hind legs -
characteristics that distinguished them from the Aldabra giant tortoise but
corresponded closely with those of Arnold's
supposedly long-extinct species.
Arnold's giant tortoise (© Editha@emys-home.de /Wikipedia)
Enquiries revealed that these and one other
male specimen had been purchased in 1994 from an old local man, in whose family
they had been throughout living memory. The third had died in December 1994,
but its skeleton was preserved and donated to the NPTS's scientific collections.
Cranial studies subsequently determined that it was indeed distinct from the
Aldabra species. Genetic studies were also set in motion, to bypass any
possible misclassification based solely upon morphological characteristics -
which can, as already ably demonstrated with the earlier episode of the Mauritius
specimens, be very deceptive.
By early 1997, several additional specimens
of unusual giant tortoise had been discovered in various Seychelles
localities and examined by Gerlach. Moreover, whereas some of these resembled Arnold's
giant tortoise, eight others closely recalled a second supposedly long-vanished
species - the hololissa Dipsochelys [now Aldabrachelys] hololissa.
Previously, this latter species had been known only from two shells found in
1810, described in 1877, and destroyed in the 1940s by German bombing raids
during the London Blitz. It formerly inhabited various granitic islands of the Seychelles,
where it grazed vegetation on the edges of streams and marshes, but had
vanished in the wild by 1840.
Hololissa at Prague Zoo (© travelviaitaly/Wikipedia)
In March 1997, Dr Les Noble conducted
genetic tests at Aberdeen
University
on blood samples taken by Gerlach from a large selection of live Seychelles
giant tortoises, including the controversial ones. These tests showed that
three distinct groups could be identified, revealing that eight of the
specimens were hololissas, two were Arnold's
giant tortoises, and the remainder were Aldabra giants. But this was still not
the end of the story.
A year later, Blackpool Zoo in England announced that Darwin,
the Aldabra giant tortoise that had been living there for the past 25 years,
was not a member of the Aldabra species after all. While closely scrutinising
photos of recently-discovered living specimens of the hololissa, staff at the
zoo were astonished to discover that they looked just like Darwin.
Anxious to learn more, they duly contacted Gerlach, who visited the zoo,
examined Darwin,
and confirmed that he was indeed a living hololissa. This presumably explains
why he has never successfully mated with Beagle, the female Aldabra giant
tortoise that accompanied him when he arrived at Blackpool
in 1972 - because they belong to separate species.
Hololissa at Cotswolds Wildlife Park (© Dr Karl Shuker)
Similarly, I subsequently learnt from the Cotswold
Wildlife
Park, also
in England, that one of their supposed Aldabra giant tortoises had also been unmasked as a
hololissa. Moreover, by the end of 1999 at least 12 living hololissa
individuals and 18 living individuals of Arnold's
giant tortoise had been revealed in various locations around the world,
including a very impressive specimen at Prague Zoo in the Czech
Republic.
Snapped in 1905 when its subject was still
alive on Mauritius,
a vintage black-and-white photograph still exists of what is now believed by
some researchers to have been a hololissa, taken there from its native Seychelles
homeland in 1764. Living in the Court House Garden on Mauritius, this venerable
individual was therefore at least 140 years old at the time of being
photographed, but was probably much older, because no-one knows how old it
already was at the time of its transportation there from the Seychelles.
Possible hololissa on Mauritius, vintage 1905 photograph (public domain)
All of which invites speculation as to how
many other incognito specimens of hololissa and Arnold's giant tortoise may
still be awaiting identification elsewhere. By the end of 1997, the NPTS had
introduced several specimens of hololissa and Arnold's giant tortoise to
Silhouette Island (third largest of the central Seychelles islands) in order to
initiate captive breeding programmes for both of these recently-revived species
and thus ensure their continuing survival, and it continues to search for more
possible examples in captive collections worldwide.
Officially known as the NPTS Seychelles
Giant Tortoise Conservation Project, its patron is veteran wildlife film maker
and broadcaster David Attenborough. Its long-term goal is to increase the
numbers of both species in order to permit reintroduction to secure reserve
sites within the Seychelles
group - thereby restoring in viable form two remarkable endemics to their
native island homeland after more than 150 years of 'official' non-existence.
Child riding Aldabra giant tortoise at Mount Kenya
Wildlife Conservancy, readily demonstrating just how large these tortoises are (Wikipedia/public domain)
All
that now remains to be accomplished in order for this tale of tortoise
resurrection to be complete is for the fourth species of Seychelles
giant tortoise – D. [now Aldabrachelys] daudinii, Daudin's
giant tortoise – to be rediscovered. Known only from the Seychelles
island
of Mahé
and named in honour of French zoologist François Marie Daudin (1776-1803), it
was formally described and named in 1835, but officially became extinct in 1850.
Judging
from the recent success in revealing hitherto-unrecognised living specimens of
the hololissa and Arnold's giant tortoise, however, who can say with absolute
certainty that there are no incognito A. daudinii individuals out there
somewhere too, alive and well but in blissful ignorance of the fact that their
species is officially long-extinct?! To be continued…?
This
ShukerNature article is expanded and updated from my book The Encyclopaedia of New and Rediscovered Animals
(2012).
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