from Wiktionary, Creative Commons Attribution/Share-Alike License
- proper n. a taxonomic family, within superfamily Testudinoidea - the tortoises
Some Americans use ‘tortoise’ in a strict taxonomic sense to refer to the Testudinidae, which is the scientific name for modern land tortoises.
We are already pretty confident of the remarkable fact that the turtles accomplished an evolutionary doubling back to the land: an early marque of land ‘tortoises’ went back to the watery environment of their even earlier fish ancestors, became sea turtles, then returned to the land yet again, as a new incarnation of land tortoises, the Testudinidae.
Sterrer W (2000) Hesperotestudo (Testudines: Testudinidae) from the Pleistocene of Bermuda, with comments on the phylogenetic position of the genus.
In Britain, we’d be inclined to call any land-dwelling chelonian a tortoise, whether it is a member of the Testudinidae or not as we shall see, there are fossil ‘tortoises’ that lived on land but are not members of the Testudinidae.
If you look at the family tree, you’ll notice that, in addition to the Testudinidae all modern land tortoises there are two fossil genera of fully shelled animals called Proganochelys* and Palaeochersis.
Land tortoises are represented by bold type, and you can see that today’s land tortoises constitute a single branch, the Testudinidae, deeply nested within rich branchings of otherwise aquatic chelonians.