Biology Reference
In-Depth Information
emerging from so many different ancillary sources is not only fascinating,
but it supports the general accuracy of individual approaches, and it estab-
lishes a context for interpreting results from other studies. For example,
Hughes and Eastwood used DNA sequence data to identify a monophyletic
group of 81 species of
Lupinus
(lupine, bluebonnet) endemic to the Andes
Mountains. The age of the clade is dated to 1.76-1.18 Ma, giving a diversi-
fi cation rate of 2.49-3.72 species per million years and “providing the most
spectacular example of plant species diversifi cation documented to date”
(Hughes and Eastwood 2006, 10334). The conclusions are supported by
the geologic and varied biologic evidence documenting the recent origin of
the High Andes.
In northwestern Argentina, climates were responding to the rise of the
Southern Andes to a height of around 5500 m toward the end of the Neo-
gene, and the effects are preserved in sediments of the Santa María Basin
(Kleinert and Strecker 2001). They reveal cooling and seasonally dry cli-
mates with trees and shrubs circa 7 Ma, then herbs and grasses between 5
and 3 Ma, and fi nally vegetation of cold and arid environments at 2.6 Ma
(latest Pliocene). Dry-habitat caviomorph rodents are also prominent in the
late Pliocene San Andrés Formation of east-central Argentina (Verzi and
Quintana 2005), and sediments from the Lauca Basin of northern Chile
show increasing desiccation between 6.4 and 3.7 Ma (Gaupp et al. 1999).
The expectations of ecosystem change in southern Argentina (e.g., in
Chubut and Santa Cruz Provinces, Patagonia) are for cooling, drying, and
more seasonal climates between the early and late Miocene; a change from
warm and humid shrubby vegetation to cold and drier grassy communi-
ties; and a corresponding increase in dry-land faunas, browsers, and graz-
ers. In the early Miocene Chenque Formation, there is pollen resembling
Acacia
and
Anadenanthera
that today are common in warm humid climates
(Barreda and Caccavari 1992; Palamarczuk and Barreda 1998). In the early
Miocene Santa Cruz Formation, fossil vertebrate faunas are present. From
the base of the section toward the top, however, they show a decrease in
diversity; euhypsodont species increase; and brachyodont, glyptodontids,
and toxodontids become more diverse. Megathroideid body size is re-
duced, and protheroteid diversity decreases. These faunal shifts are inter-
preted as responses to an environment that was becoming seasonally dry
(Tauber 1997a, b; Barreda and Bellosi 2003). Elsewhere in the vicinity,
increasing pollen of the herbaceous grasses and shrubby Amaranthaceae-
Chenopodiaceae and Asteraceae also indicate drying and more seasonal
climates, as does pollen of
Ephedra
refl ecting edaphically drier coastal
dunes, probably with strong winds and high evapotranspiration, and inland
