Question about Extinct Tortoises

[theholocenefallen]

I'm putting this here in case someone can help point me in the right direction. I have been conducting research about the extinct giant tortoises of Mauritius. I came across the Tortoise and Freshwater Turtle research document "Turtles of the Wild: Annotated Checklist and Atlas of Taxonomy, Synonymy, Distribution, and Conservation Status."

Specifically, I was looking for details of the extinct saddle-backed Mauritius giant tortoise, which most sources I've come across refer to as cylindraspis inepta, and then the domed Mauritius tortoise, which sources call cylindraspis triserrata. However, the above source calls the inepta the domed tortoise, and the triserrata the flat-shelled tortoise (p. 277-278). The NCBI also calls the inepta the domed tortoise but with a common name of saddle-backed!

Am I missing something? Is there confusion/ disagreement within the scientific community about what to call these species? I was pretty sure the two were different yet related species, but the inconsistencies across sources is a bit confusing. Could someone clarify to me which name belongs to which species, and maybe even explain the difference? I would greatly appreciate it.

 

[TammyJ]

Maybe @TeamZissou would be able to help?

 

[ZEROPILOT]

Yes. I'd like to help. Also.
But that's a question that I can't even PRETEND to answer.
Welcome to the forum

 

[mark1]

pritchard wrote about them in his book , "living turtles of the world".......inepta and triserrata apparently lived in the same place at the same time , there have been 8 species described on a single island , pritchard wrote they were of "dubious distinctness"....... he wrote inepta , triserrata and gadowi were "tolerably" distinct, but may just represent extremes of variation .......geochelone gadowi he wrote had forked gulars and was extinct before the island was ever discovered , inepta had two cutting edges on the maxilla , triserrata had 3 cutting edges .... this was from 1967, before dna tech., their distinctness may have been proven since ?


you may have already read the link below , if not .....

Ancient DNA Study Elucidates Lost World of Indian Ocean Giant Tortoises​

 

[turtlesteve]

I think the article Mark posted is your best reference on this. It is not surprising that there were numerous extinct Cylindrapsis species, but it is only through DNA work that we will be able to accurately confirm them.

Morphological delineation of closely related tortoises is often not accurate even for living species. This was found in particular with the Testudo genus. There were many species and a proposed new genus that were invalidated when DNA testing showed all of the tortoises in question to be closely related clades of Testudo graeca. And it is also common for tortoise species to have vast differences in size and shape across their range; leopard tortoises S. pardalis can reach 30" or more in size in some parts of their range, but only reach 12" in other locales. If we had only fossil shells to describe, these would almost certainly be considered separate species.

It's more debatable, but you can also have shape differences that are not accompanied by genetics (see the disputed species Aldabrachelys arnoldi, the saddle-backed aldabra tortoise). One could argue that A. arnoldi is valid at least as a subspecies (since the morphology is heritable and seemingly consistent), but it would imply that we have witnessed essentially the beginning of a fairly rapid speciation, where the tortoises have become functionally different despite having very little genetic differentiation.

From the DNA work it seems that there are at least three deeply divided lineages (e.g. definite species) in Cylindrapsis. Anything beyond this is debatable, but might be subspecies territory (again my opinion).

Steve