![]() |
||||||||||||||
Australia: The Land Where Time Began |
||||||||||||||
Biogeography of Australia – Northwestern
Australia Among the clades of southern Australia there are
many that are endemics, distinctive and isolated, though in northern
Australia plants and animal are often allied with groups from Asia,
which has often been attributed to recent immigration from Asia to
Australia. Camaenidae .lat., a family of land snails with a distribution
from Asia to Australia is a typical example. It is the most diverse
family of snails in Australia with 80 genera and 400 species. In both
rainforest and desert these snails are widespread, though as the group
is a northern one, it is absent from southwestern Australia and
Tasmania. According to the traditional model for the Australian
contingent it is suggested that dispersal occurred in the Miocene from a
Laurasian centre of origin (Hugall & Stanisic, 2011), and this model
depends on an evolutionary clock and interprets a basal, paraphyletic
group’s locality as a centre of origin. Heads1 suggests it is
also possible that rather than invading Australia by dispersal the
Camaenidae ‘invaded’ the region by evolving there. If this is indeed the
case, the family’s geographic connections with related groups in
Southeast Asia and elsewhere would therefore represent ancestral
distributions, hence reflecting aspects of former geography. In
northwestern Australia there are several groups that have been
interpreted in this way and in northwestern Australia examples of
camaenid distribution are cited in what follows.
Subterranean endemism - Hamersley Range (Pilbara Region) and Tethyan
connections The discovery of a diverse subterranean fauna in
the northwest of the continent is said by Heads1 to be one of
the most interesting developments in Australian biogeography (Eberhard
et al., 2005; Humphreys,
2008). This fauna is comprised of a wide range of groups, which includes
fish, though the fauna is best known for its wide diversity of unusual
Crustacea. Stygobionts make up many of these subterranean clades found
in groundwater. Species that breathe air that are found in groundwater
are called troglobionts. Cape Range and Barrow Island were the first
places where this fauna was found, then further inland at the Hamersley
Range, as well as other parts of the Pilbara region. This is the area
where most of the iron ore is mined, especially in and around the
Hamersley Range. Above and below ground the local flora and fauna are
important for understanding the evolutionary history of Australia, and
it is the groundwater abstraction and the dewatering of aquifers that
takes place before mining begins that is threatening the existence of
the stygofauna. A striking feature of this stygobiont fauna, apart
from its unexpected and wide diversity, is the high proportion of
species that have affinities with Tethyan or Gondwanan species (Eberhard
et al., 2005). Coastal caves
of the Mediterranean, the Canary Islands and the Caribbean, are the
places where the Tethyan clades that are sister groups of the Australian
clades are found. The ‘full Tethyan track’ is the name often given to
the distribution that extends from Australia to the Caribbean via the
Mediterranean by biologists working on the fauna (Jaume et
al., 2001; Jaume, 2008;
Humphreys et al., 2009;
Karanovich & Eberhard, 2009). Sandstone or limestone aquifers that are anchialine
– having a subterranean connection to the sea – are the habitats of the
stygobionts of the northwest. These aquifers have been described as
underground estuaries; they are salinity-stratified and affected by
marine tides. The origin of the cave fauna have been explained (Page et
al., 2008) as being by a
process by which a local marine species is stranded in a new,
terrestrial habitat as it emerges, the process occurring either as a
result of uplift or marine regression, and for stygobiotic faunas is one
of the most significant causes of vicariance (Craw et
al., 1999; Culver & Pipan,
2009). Heads, Michael, 2014,
Biogeography of Australasia: A
Molecular Analysis, Cambridge University Press
|
|
|||||||||||||
|
||||||||||||||
Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |