Comments on the proposed conservation of usage of Testudo gigantea Schweigger, 1812 (currently Geochelone (Aldabrachelys) gigantea; Reptilia, Testudines) 19

Frazier’s petition to fix the name of the Aldabra tortoise as Aldabrachelys gigantea (incorrectly petitioned as Geochelone (Aldabrachelys) gigantea) rests on three points: questions over the status of the type specimen of Testudo gigantea Schweigger,
1812, arguments of nomenclatural stability and the wider impacts of
nomenclature. The arguments put forward by Frazier are flawed on all
three points.

Status of the type specimen of Testudo gigantea Schweigger, 1812

The contentious and complicated history of the nomenclature of the
Aldabra giant tortoise derives from the misplacing of the type specimen
described by Schweigger (1812). Schweigger described a large (but not
gigantic) tortoise from Brazil originating from the King of Lisbon’s
collection. On historical grounds this is unlikely to have been a
tortoise from the Indian Ocean, which had been dominated by the French
and Dutch since the mid 17th century. Much of the material originally
held in Lisbon is South American in origin, reflecting Lisbon’s role as
a colonial power in South America. Accordingly the origin ‘Brasilia’ is
highly plausible. Furthermore the description given by Schweigger notes
three distinctive features: the lack of projecting marginal scutes, the
lack of a cervical or nuchal scute and the presence of notably large,
thickened scales on the limbs. In contrast the Aldabra tortoise has
flared marginals, usually (but not always) has a nuchal scute and has
no distinctively enlarged scales on the limbs. However all of these
features are highly distinctive in South American tortoises,
particularly Chelonoidis denticulata.
Although the type was misplaced in the Muséum National d’Histoire
Naturelle, Paris probably in the 1800s, Bour (2006) describes a
specimen which corresponds extremely closely to the type. His account
of this specimen leaves no reasonable doubt that it is indeed the type
of Testudo gigantea. This specimen is also easily identifiable as a South American red-footed tortoise Chelonoidis denticulata. On this basis the original description and the holotype of Testudo gigantea are identifiable as Chelonoidis denticulata and
cannot be applied to the Aldabra tortoise without a fundamental
changing of taxonomic history. A very strong case would be needed for
such a change to be acceptable.

Nomenclatural stability

As noted by Frazier Testudo gigantea was
applied to the tortoises on Aldabra from the late 19th century. Frazier
cites Hubrecht (1881) as being the first person to associate T. gigantea with Aldabra. However, in reality Hubrecht referred the type of T. dussumieri (from Aldabra) to T. gigantea. This is at best a very tenuous association and the first clear statement that T. gigantea could
be applied to the tortoises specifically from Aldabra is that of
Rothschild (1915). Other names were explicitly associated with Aldabra
from an earlier date: T. dussumieri (1831), T. elephantina (from 1835) and T. daudinii (1896). T. dussumieri was overlooked for the next 150 years, and T. daudinii was
only associated with Aldabra tortoises four times, last in 1967 (Bolau
1896; Rothschild 1915; Wermuth & Mertens 1961; Honegger 1967). T. elephantina was applied to the Aldabra population regularly until 1954, followed by a 30 year gap until its reappearance in 1983. Thus T. gigantea has only been associated with Aldabra for 94 years, compared to 178 years for T. dussumieri and 174 years for T. elephantina. Testudo gigantea has
no claim to priority or to uniquely regular use. The extent of the
current confusion and lack of stability is shown by Frazier’s own
listing of five generic names (Aldabrachelys, Dipsochelys, Geochelone, Megalochelys and Testudo)
with 7 combinations used in the past decade and a total of 9 names in
the past two decades. Frazier gives a list of 31 citations in support
of the continued use of gigantea since 1986, but only 11 of
these have any connection to taxonomy, the others mentioning Aldabra
tortoises only in passing. The same is true of the statements relating
to non taxonomic aspects of biology; the majority of citations concern
other species and the name used in their passing reference to Aldabra
tortoises is essentially irrelevant. Frazier’s list is also misleading
in that it does not consider the number of citations of other names. A
wider comparison shows that over the past 10 years, peer-reviewed
publications including discussion of the taxonomy of Aldabra tortoises
have used gigantea 4 times and dussumieri 9 times. In the same time period non-taxonomic papers (ecology and behaviour) including Aldabra tortoises have used gigantea 9 times and dussumieri 7
times. This means that in the total scientific literature of the past
decade no name has had significantly greater currency or stability,
with gigantea being used 13 times and dussumieri 16
times. Frazier (2006) himself noted the ‘general instability and chaos
regarding the valid name of the Aldabra Tortoise’ and this is borne out
by the present analysis. There is no stability to protect.

Wider impacts of nomenclature

Although Frazier is correct in noting that international bodies and conventions use Geochelone gigantea for
the Aldabra tortoise this has little practical relevance; the tortoises
referred to are explicitly the Aldabra tortoises, for which there is no
significant identification issue whatever name is applied. Of the three
citations given for the use of G. gigantea in Seychelles
government documents, one is primary legislation specifically
concerning tortoises, the other two have no relevance to tortoises and
only refer to tortoises as examples of the biodiversity of the islands.
Other examples can be cited where different names have been used, for
example the Seychelles Biodiversity Strategy and Action Plan (Republic
of Seychelles 1997) uses Dipsochelys (without a species name) and the reports of the Seychelles Islands Foundation which manages Aldabra have variously used Geochelone gigantea, Testudo gigantea and Dipsochelys dussumieri (e.g.
Betts, 2000). A further implication of this nomenclatural issue is the
unintended consequence of potentially validating a misleading name. In
1957 Loveridge & Williams created Aldabrachelys as a subgenus of Geochelone, designating Testudo gigantea as the type species. This name was rejected by Bour (1982) on the basis of the misidentification of T. gigantea. Rejection of gigantea required the rejection of Aldabrachelys and the creation of a new generic name, Dipsochelys. Since then Aldabrachelys has been very rarely used (only twice in the past decade in relevant systematic literature) and Dipsochelys remains the most widely applied distinct generic name for the Madagascar-Seychelles-Aldabra tortoises. Validation of gigantea, as proposed by Frazier, would also validate Aldabrachelys as the generic name based on gigantea.
This is highly undesirable as it would require the adoption of a
currently rarely used name, and would apply to all giant tortoises
(living and extinct) from Madagascar, Seychelles and Aldabra, not only
to the Aldabran population. The name Aldabrachelys is very
unfortunate in that it clearly ties the genus to Aldabra; whilst
Aldabra supports the largest wild population of giant tortoises in the
world it has only been occupied by giant tortoises for the past 115,000
years, compared to some 10 million years for Madagascar. There is
little doubt that the genus originated on Madagascar and has only a
recent history on Aldabra. To promote Aldabrachelys over Dipsochelys would
have a confusing effect on interpretations of a substantial part of the
evolutionary history of the genus. Whilst this is not a taxonomic
point, it would be very unfortunate for public education and
comprehension of nomenclature. In conclusion, the original description
and holotype of Testudo gigantea demonstrate that this name applies to the South American Chelonoidis denticulata.
Setting aside the existing holotype specimen in favour of the neotype
proposed by Frazier would be a significant nomenclatural act and should
only be undertaken with a strong justification and unequivocal support.
The claim that Testudo gigantea is a stable name cannot be
justified as even Frazier notes that there has not been any stability
in the nomenclature of the Aldabra tortoise for the past 27 years.
Although Frazier states that his neotype designation was undertaken
after ‘after extended consultation with numerous specialists in
chelonian systematics’ he did not include any of the specialists who
have worked specifically on the nomenclature of the Aldabran tortoises
in the past 25 years, all of whom would have been expected to urge
against proposal of a neotype and this petition. Accordingly I
recommend that the International Commission on Zoological Nomenclature
reject the petition of Case 3463 and allow the Code to operate,
validating Testudo dussumieri Gray, 1831 (now Dipsochelys dussumieri) as the valid name for the Aldabra giant tortoise and retaining Testudo gigantea Schweigger, 1812 as a junior synonym of Chelonoidis denticulata (Linnaeus, 1766).

Additional references

Betts, M. 2000. Research Officer’s Annual Report. June 1999 – July 2000. Seychelles Islands Foundation, [unpublished report].

Bolau, H. 1896 Glandula thyroidea und Glandula thymus. Zoologischer Jahrbuch, Abteilung Anatomie, 12: 658–709.

Honegger, R.E. 1967. Beobachtungen an den Riesenshildkroten (Testudo gigantea Schweigger)

der Inseln im Indishen Ozean. Salamandra, 3: 101–121.

Republic of Seychelles. 1997. Seychelles biodiversity strategy and action plan. Republic of Seychelles, UNEP & IUCN.