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Australia: The Land Where Time Began |
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Valley of whales In this location in Egypt the fossils of 15 whale
species have been found, some up to 10 m long. Their full skeletons,
encased in lime-rich mudstone or siltstone preserved them where they
died. There are also fossils of other animals such as dugongs, manatees
and turtles, as well as a variety of small fish, sharks’ teeth and a
number of invertebrates. There are fossil mangrove roots in the same
layer, though they are more common just above the layer with the whale
fossils. The author3 suggests this indicates that the early
whales were near-shore feeders that fed in shallow water around
coastlines. He also suggests they were the forerunners of the modern
toothed whales that include dolphins and killer whales that fed mainly
on fish and crustaceans. The baleen whales didn’t evolve until much
later. The finding of several proto-whale fossils in
Egypt, and a few million years later in Pakistan, as well as from
scattered finds from the northern and southern margins of the Tethys
Ocean from about this time, their ancestry can be derived. Following the
KT boundary there were significant numbers of ecological voids left
empty. On land the mammals diversified explosively, and appear to have
done so in more than 1 episodes of diversifcation, to fill many of these
empty niches. In the oceans the radiations were slower to occur, the
teleosts (bony fish) growing larger and moving up the food chain to join
the more ancestral lineage of sharks. The return of mammals to the sea took longer. The
first mammals to arise included some bizarre and cumbersome forms, some
of which resembled dinosaurs that had gone extinct not long before.
Indricotherium was an
enormous browser of tree tops, a member of the same family as
rhinoceroses. These replaced the dinosaurian sauropods in Europe.
Arsinoitherium was a
browsing herbivore from Africa that had magnificent horns, that was very
similar to the dinosaur
Triceratops. Fossils of
this animal were found in the Sahara, in rocks that were slightly older
than those of the Valley of Whales, named after the ancient Egyptian
queen Arsinoe.
Pachyaena is a large
hyena-bear from South Africa that is believed to have scavenged along
the sea shore as the modern brown hyena (or strand wolf) does, is
believed to be ancestral to the whales. Rapid, progressive evolution
from these strand hunters to wading and walking whales, to paddle
swimmers, and eventually fully marine mammals that swam with their tails
and were streamlined, have been shown in the fossils of some of the
early proto-whale fossils. As with the wales in Egypt and all whales
since, these were true whales. Baleen and
echo location The evolution of the whales began around the same
time as our ancestral primates. There is another fossil site near
Calvert, Maryland, USA, where the younger rocks and contain a diverse
assemblage of marine mammals including toothed whales, early dolphins,
baleen whales and some pinnipeds that were at a primitive stage of
evolution (family that includes seals and sea lions). These have all
been dated to the Miocene (Neogene age), and represent a snapshot of
evolution about 20 My later than those in the deposits in the Valley of
the Whales in Egypt. By that time the Tethys Ocean had narrowed greatly,
and the climate had cooled as it closed progressively, leading to a
great radiation that was caused by the temperature decline in the ocean,
that included adaptations to colder conditions in the polar regions, as
well as to freshwater habitats of estuaries and rivers. There were also
new types of food such as plankton. The author3 suggests that at the present
the baleen whales are possibly the ultimate in evolutionary perfection
when it comes to harvesting the plankton of the oceans. The largest
living animal on Earth is the blue whale that eats about 4 tonnes of
plankton per day. It eats mostly krill, small shrimp-like animals that
is a member of the zooplankton that feeds on the phytoplankton. When the
blue whale opens its mouth all in its path enters and when it closes its
mouth the water is filtered through the baleen that is made of keratin
and is in the form of a tight mesh, the same protein in the nails and
hair of other mammals). The krill and everything else that remains after
the water has been forced through the baleen mesh is swallowed. Humpback whales have a different method of feeding;
they rise slowly beneath a rich patch of plankton while exhaling to form
bubbles in a ring that tends to gather the krill into a dense mass that
can be easily taken in a gulp. It is not known if the bubble net method
of feeding on krill had been evolved by the Miocene. The author3 suggests that the more
sophisticated use of sound may have evolved during the Miocene. At the
present it is the main retrieval system among dolphins and whales of the
present. The technique of emitting high frequency sounds, in the form of
audible clicks and ultrasonic vibrations of more than 100 KHz, then
detecting the returning reflections of the sound has been evolved by
dolphins. They form extremely accurate images of the sea around them,
together with the distance, size and shape of objects in the water, and
even the texture and density, the species of fish and their movements.
The author3 suggests recycled compressed air may be used by
dolphins to produce the clicks that are produced by the dolphin’s large
forehead region, the received signal being received over a broader area
around the sides of the head and lower jaw. The sound is better refined
by asymmetry of the jaw. The complex array of signals is decoded with
the aid of a gigantic auditory lobe in the brain. The echo-location
capacity of the fossil genus
Kentriodon, one of the
dolphin-like species recovered from the deposits in Maryland was
relatively rudimentary as indicated by the perfect symmetry of its lower
skull region. Lineages arose from
Kentriodon that
eventually gave rise to dolphins of more modern in appearance, that had
echo-location that was highly developed, and to porpoises, killer
whales, belugas, and narwhals.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |