If tortoises could not survive the MIS 9 high stand,
then they could not have survived the much more
severe previous high stand of MIS 11 that nearly
submerged all of Bermuda. It is quite possible that
another population of tortoise could have inhabited
Bermuda during the long period (approximately
500,000 yr) of low sea level that preceded MIS 11,
but there is no fossil record of vertebrates from this
entire interval. Thus, the earliest that the progenitor ofH. bermudae could have colonized Bermuda was
toward the end of the regressive phase of the MIS 11
highstand, when sea levels were falling rapidly
(Hearty et al., 1999). Tortoises then had only the MIS
10 glacial interval to evolve into an endemic species
before being exterminated by the following rise in sea
level during MIS 9. If so, the entire existence of H.
bermudae would have been confined to a maximum
span of approximately 100,000 yr. To date, no fissure
fills or cave deposits have been found dating to the
MIS 10 glacial period (Olson et al., 2005), which may
explain why no other tortoise remains are yet known
from Bermuda.