Marginated Tortoise - Taxonomy

Taxonomy

The marginated tortoise was formally described by German naturalist Johann David Schoepf in 1789, its specific epithet marginata a straightforward derivation from the Latin term for 'marginated'.

The nominate subspecies is the Greek marginated tortoise, Testudo marginata marginata. Three additional taxa of marginated tortoises have been named:

The Sardinian marginated tortoise (Testudo marginata sarda) is the name usually used to separate the population on Sardinia. These tortoises have less strongly bent tiles in the posterior of the carapace, and the posterior of the carapace is almost smooth compared with the saw-like Testudo marginata marginata. Clearly distinct according to morphology and entirely allopatric, it cannot be distinguished by mtDNA cytochrome b and nDNA ISSR sequence analysis. Lineage sorting has not occurred to a considerable degree; consequently, the more geographically isolated Sardinian population is presumably of quite recent origin.

Indeed it appears to derive from a deliberate introduction by humans. Though it is not clear whether this occurred in prehistoric times or more recently, this might be resolved by dating subfossil remains. Sequence evolution at least in mtDNA is known to proceed much more slowly in some turtles and tortoises than in others; the rate of the mitochondrial 12S rRNA gene in Testudo is probably a rather low 1-1.63% per million years (as this fits best the paleobiogeographical situation), limiting the resolution provided by molecular systematics.

An extinct subspecies described as T. marginata cretensis persisted on Crete before the end of the last ice age and perhaps into early historic times

A population of small and light-colored marginated tortoises exists on the southwestern coast of the Peloponnesus, between Kalamata and south of Stoupa. The so-called "Dwarf marginated tortoise" was described as a new species Testudo weissingeri, but it is not recognizably distinct phylogenetically. Unlike the Sardinian population, it occupies an extremely restricted range with very arid habitat, and its apomorphies seem related to this. Considering ice age-associated climate and sea level changes, this population is probably not older than a few thousand years; as it is not geographically isolated, it should be considered a local form, and not even a subspecies Testudo marginata weissingeri. It is notable that a similar situation is found in Hermann's Tortoises living in the same region.

Testudo marginata is also closely related to the Greek tortoise or ppur-thighed tortoise (Testudo graeca). Both have very similar bodily characteristics, an oblong carapace, large scales on the front legs, large covering for the head and cone-like scales on the upper thigh, undivided tail covering, moveable stomach plates, and lack of a tail spike. Presumably, Testudo marginata diverged from ancestral Testudo graeca as a population more suited for life in the mountainous regions. Evidence in favor of this is the wide geographical region and the extremely large number of subspecies of Testudo graeca, including a subspecies in Turkey with strongly bent carapace tiles, like the marginated tortoise. Testudo marginata on the other hand, despite the two subspecies, presents a much more unified appearance, which points toward an earlier appearance in evolutionary history. In captivity, the two species often cross-breed, but this should be avoided.

According to the 2005 DNA sequence data, these species do not seem to hybridize to a notable extent in the wild, though they are obviously very close relatives, and as evidenced bby morphology some allele flow still occurs, but slowly. The Egyptian tortoise appears to represent a lineage that diverged from the same ancestral stock southwards into northeastern Africa around the same time as the marginated tortoise's ancestors diverged in Greece. These two are actually more similar to each other than to T. graeca regarding DNA sequence data, but considering biogeography, this is either due to (rather unlikely) dispersal across the Mediterranean, or the supposed "clade" is invalid and the similarity due to convergent evolution.