38 | New Scientist | 1 August 2020
Basically, dinosaurs were faster than the crocs
and, over time, they outcompeted them.
It is an elegant story, but as a graduate
student it didn’t sit well with me. And during
the first decade of the 21st century, it began
to seem increasingly untenable. A wealth
of new Triassic pseudosuchian fossils had
been discovered and many of them were
dead ringers for dinosaurs, a sign that both
groups were converging on the same diets
and lifestyles. In 2008, I reviewed these new
fossils to trace the evolution of both groups
and came to a startling conclusion. During
the entire Triassic, the pseudosuchians were
completely outpacing the dinosaurs. They
had more species, were more abundant in
their ecosystems and had a greater variety of
body plans, anatomical features and diets.Earth unzipped
These findings helped reframe the question
of how the dinosaurs became the world’s
pre-eminent beasts. It must have happened,
not gradually through the Triassic, but
relatively quickly, towards the end of that
period, when we know the pseudosuchians
definitely did begin to decline. This actually
makes a lot of sense because, at just this time,
something epic happened to planet Earth.
In the days of Prorotodactylus, nearly all
land was part of a supercontinent called
Pangaea (see “Triassic world”, page 40). Then,
200 million years ago, Pangaea started to
crack. The fracture began in the centre of the
land mass and unzipped it down the middle.
North America separated from Europe; South
America from Africa. As they parted, Earth
haemorrhaged lava from volcanoes in what
is now the bottom of the Atlantic Ocean for
more than 500,000 years.
Released with the lava were huge volumes
of carbon dioxide and sulphur dioxide. These
gases continually warmed the atmosphere,
while bursts of ash from the eruptions
shut out the sun’s light. This meant hot
spells “alternated with intense volcanic
winters that brought freezing for decades
at a time”, says Paul Olsen at Columbia
University in New York. At least 30 per centAn interrupted reign
The era of the dinosaurs that began around 250 million years ago was punctuated by
epic extinction events that helped shape their evolutionPERMIAN
All sorts of animals
flourished during this time,
many of them lizards that
looked like dinosaurs but
weren’t related to themTRIASSIC
Dinosaurs begin to appear,
but most were skulking
animals no bigger than a
horse. The planet was ruled
by other creatures, including
the pseudosuchians,
ancestors of modern
crocodiles (see main story)JURASSIC
Dinosaurs sail through the
end-Triassic extinction and
begin to diversify and
increase in sizeCRETACEOUS
Some of the most iconic
groups of dinosaurs such
as Tyrannosaurus and
Triceratops evolveThe Permian mass
EXTINCTION nearly
ends life on Earth, killing
95 per cent of species
in the ocean and
70 per cent on land200Giant sauropod
dinosaurs such as
Diplodocus had
spread widelyA huge asteroid smashes
into Earth, extinguishing
all dinosaurs except the
ancestors of birds252201End-Triassic EXTINCTION.
The supercontinent of
Pangaea splits apart, and
volcanoes belch gases
that unleash a wave
of global warming. The
pseudosuchians die outStegosaurus evolves70 Grasses appear145130 Flowering plants
evolve100 Earliest bees develop26022066A minor EXTINCTION
event of uncertain
cause wipes out many
of the larger dinosaurs15015562 Penguins emerge52 Bats evolve245Gorgonopsids,
distant relatives of
mammals, evolve
Some of the earliest
ichthyosaurs appearWarm-blooded
protomammals
emergeOdontochelys, one
of the earliest known
turtles, evolvesMILLION YEARS
BEFORE PRESENT