Page 231 - (DK) Ocean - The Definitive Visual Guide

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Today: Life in GRAY REEF SHARK
Like its close relative the
Modern Oceans Caribbean reef shark (below),
this shark lives in warm,
shallow waters, near coral
We know much more about life in today’s oceans atolls and in adjacent lagoons.
because, as well having entire organisms to study, we can It is found in the Indian and
also observe life cycles, locomotion, and behavior. Each Pacific oceans, but it is cut
of the five oceans supports a wide variety of life. Some off from the Atlantic.
species are very specialized and are restricted to a small
area, while others are migratory or generalists and have a
wider distribution. Sometimes, closely related species live
in the same habitat in different oceans, separated by land
or other physical barriers (see right).
By studying living organisms and the characteristics of the water they CARIBBEAN REEF SHARK
live in, scientists can also better understand ancient ocean environments Like the gray reef shark (above), this
and organisms. The deep ocean is still poorly known, but it contains species lives in shallow water near
an ecosystem that could be crucial to our understanding of life—black coral reefs. Its range is isolated from
the Indo-Pacific by the deep, cold ocean
and white smokers (see p.188). Isolated from sunlight and from the
around South Africa, so it is restricted
surrounding water by a steep thermal gradient, it is possible that this is to warm parts of the Atlantic, from
the type of environment in which life first evolved 3.5 billion years ago. the Caribbean to Uruguay.

252–199.5 MYA
199.5–142 MYA
23.3–1.8 MYA
1.8–PRESENT
635–542 MYA
354–323 MYA
323–290 MYA
542–490 MYA
290–252 MYA
443–418 MYA
418–354 MYA
490–443 MYA
EDIACARAN CAMBRIAN ORDOVICIAN SILURIAN DEVONIAN MISSISSIPPIAN PENNSYLVANIAN PERMIAN TRIASSIC JURASSIC CRETACEOUS PALAEOGENE NEOGENE QUATERNARY
65–23.3 MYA
142–65 MYA
earliest sharks
appear
fourth mass earliest whales
extinction
penguins evolve from
terrestrial
Cambrian Explosion: rapid first armored first lobe-finned third mass first turtles
evolution of body forms fish appear fish appear extinction appear mammals
635 600 550 500 450 400 350 300 250 200 150 100 50
second mass whales
extinction diversify
first mass
Ediacaran fossils show plactodonts (earliest
early multicellular life extinction marine reptiles) appear plesiosaurs replace
earliest jawless fish, placodonts
representing the first fifth mass
vertebrates, appear ichthyosaurs appear mosasaurs replace extinction kills
ichthyosaurs last ammonites
2,000 MYA 1,500 MYA 1,000 MYA 700 MYA 635 MYA PRESENT
PHANEROZOIC EON 542 MYA–PRESENT DAY
first fossil evidence of beginning of the Ediacaran period, which
mineralized skeletons soon features the first multicellular life
Mass Extinctions VOLCANIC ARMAGEDDON
Volcanic activity in the western Ghats of India is now
The history of life is punctuated by five mass extinctions—catastrophic events thought to have been a factor in the most recent mass
extinction. The eruptions would have caused destruction
in which many life forms died out. The first occurred 443 million years ago,
and climate change on a global scale.
when prominent marine invertebrates disappeared from the fossil record. About
368 million years ago, global cooling and an oxygen shortage in shallow seas
caused about 21 percent of marine families to disappear, including corals,
brachiopods, bivalves, fishes, and ancient sponges. At the end of the
Permian Period, 252 million years ago, the cooling and shrinking of
oceans killed over half of all marine life. Another mass-extinction
event at the end of the Triassic Period, 199.5 million years ago,
caused major losses of cephalopods, especially the ammonites.
The fifth extinction, 65 million years ago,
caused the demise of the dinosaurs;
in the oceans, it caused the giant
marine reptiles to disappear. The
next mass extinction is likely to
be a result of human activity. OCEAN LIFE

AMMONITE FOSSIL
This ammonite species is one
of the few to survive the late-
Triassic mass extinction event.