[Taxacom] Primates and toads

[John Grehan]

As another example of primates acting as the uppermost geological layer in
South East Asia is the distribution of monkeys of Sulawesi which shows
evidence of allopatric differentiation of a widespread ancestor and a
tectonic correlation within the island that also involves other taxa. While
one may imagine competitive exclusion to explain absence of Macaca
elsewhere, it is biogeographically unnecessary as the evidence points to
the ancestral Macaca having a particular range that included some areas and
not others. And what was good for primates was also good for toads.

Excerpt from Heads (2012)

In Sulawesi, the seven endemic Macaca species have distributions that are,
as Evans et al. (2003) emphasized, “virtually identical” with clades of
toads. The authors concluded that the pattern indicates general vicariance
in the whole fauna and is comparable to that found at other major
biogeographic boundaries. In studies of the nymphalid butterfly Cethosai in
Wallacea (i.e., Sulawesi and neighboring islands), Müller and Beheregary
(2010: 314) concluded that the high levels of island endemism and the
essentially allopatric groupings are best explained by “vicariant processes
linked to the history of formation of micro-continent and associated paleo
islands.”

One of the biogeographic boundaries within Sulawesi occurs in the
southewestern arm of the island, where the highest point on the islands
(Mount Rantemaio, 3,440 m, in the Latimojong Mountains; Fig. 5-16) is
located. There is an important biogeographic break between the biota of the
Latimojong Mountains and that of Mount Lompobatang in the south. The break
is known in plants, amphibians, primates, and many other groups and
represents a classic problem in biogeography. Although biologists have
challenged geologists to explain the pattern, until recently there was no
known geological basis for it. Now there is good evidence from dated
zircons in xenoliths that a fragment of Gondwana lies buried beneath on of
the volcanic arcs of East Java. Smyth et al. (2007) proposed that this
extends northeast to northern Sulawesi, beneath Latimojong but west of
Lompobatang (Fig. 5-16). This Gondwana fragment could have collided with
Sundaland during Late Cretaceous¬ northwest-directed subduction. A mélange
of arc and ophiolitic material was accreted first to the Sundaland margin,
in Java and eastern Borneo, but the arrival and accretion of the Gondwana
fragment would have terminated subduction here. In the Paleogene,
subduction shifted to take place along the Java trench in a northeastward
direction. The suture shown by Metcalfe (2008) running through central
Sulawesi also separates Latimojong from Lompobatang (Fig. 5-16).

John Grehan