First, several of our analyses (a maximum likelihood reconstruction
using data from all three coding regions: Fig. 3A, a Bayesian
reconstruction using data from the NAD5 and cytochrome B loci:
Fig. 3D, and our the maximum clade credibility tree associated
with our Bayesian dating analysis: Fig. 4) all robustly suggest that
the common ancestor of the A. belzebuth + A. chamek clade was the
next lineage to diverge following the initial split of A. marginatus
from the earliest Ateles. Under this scenario, populations of early
Ateles probably would have expanded eastward from the southern
Amazon to the eastern part of the Brazilian Amazon and westward
giving rise (4.5 Ma) to the common ancestor of A. chamek (currently
found in the southwestern Amazon of Peru and Bolivia)
and A. belzebuth (currently found in the northwestern Amazon of
Ecuador and Colombia as well as Amazonian Venezuela and northern
Brazil). Other populations would have expanded north and
west across the western Amazonian lowlands into present-day
Venezuela and northern Colombia before the completion of the
Andes (4.0 Ma), giving rise to the common ancestor of A. hybridus
(which is now confined to the Río Magdalena valley), the trans-
Andean forms, and A. paniscus. From there, spider monkeys would
have expanded east to the Guianas and to northeastern Brazil,
north of the mouth of the Amazon River, giving rise to A. paniscus
3.5 Ma (95% credibility interval 2.0–5.2 Ma). Other populations in
northern Colombia would have expanded westward, skirting the
north coast of Colombia, and then both southward into the forests
along the Pacific coast of Colombia and Ecuador (giving rise to
extant A. fusciceps) and northward through the Isthmus of Panama
into Mesoamerica (giving rise to A. geoffroyi)