The
evolution of the group is fairly well resolved due to comprehensive analyses of
morphology,
biogeography, and
mt and
nDNA sequences (Pereira
et al. 2002, Grau
et al. 2005). The position of
Penelopina and
Chamaepetes - peculiar genera of which the former, uniquely among guans and more in line with
curassows, shows pronounced
sexual dimorphism - relative to each other is not determinable with certainty at present, but all evidence suggests that they are the
basalmost guans. Their distribution is fairly far northwards, with 2 of their 3 species living in
Central America. This indicates that the guans' origin is in the northern
Andes region, in the general area of
Colombia or perhaps
Ecuador; the date of their initial radiation is not well resolved due to the lack of
fossil evidence but can be very roughly placed around 40–25
mya (
Oligocene, perhaps some time earlier). The two basal lineages diverged during the
Burdigalian, around 20–15 mya.(Pereira
et al. 2002) The two larger genera diverged around the same time, spreading mainly southwards all over tropical South America in the process (Pereira
et al. 2002). It appears as if the present-day distribution of the piping-guans is much
relictual, due to
climate changes fragmenting lowland habitat.
Aburria were apparently being driven into refugia of suitable
habitat time and again during the
Late Pliocene by a combination of this and, possibly, competition with the more diverse and generally more adaptable
Penelope (Grau
et al. 2005). If taken as a subfamily, the group also includes the
chachalacas, but the horned guan is excluded and found in its monotypic subfamily.
Genera and species == References ==