1 August 2020 | New Scientist | 37of the worst mass extinctions ever. A blast
of global warming, fuelled by volcanic
eruptions of unimaginable scale in Siberia,
had caused more than 95 per cent of Earth’s
species to die. From this catastrophe sprang
the dinosaurs’ ancestors and closest cousins,
including Prorotodactylus. Within 20 million
years, they had evolved and diversified into
the three main subgroups of dinosaurs: the
meat-eating theropods, the long-necked,
plant-guzzling sauropodomorphs and
the beaked, herbivorous ornithischians.
Much later, these lineages would spawn
recognisable dinosaurs: Tyrannosaurus,
Brontosaurus and Triceratops, respectively
(see “An interrupted reign”, page 38).
Before this, in the Triassic period, most
dinosaurs were horse-sized or smaller.
And they weren’t alone. Proliferating
alongside them were all sorts of other
reptiles, including a particularly successful
group called the pseudosuchians. This is
the lineage to which modern crocodiles
and alligators belong. They are a paltry
bunch today, about 25 species all told, living
in warm, semiaquatic environments. But
back in the Triassic, there were scores of
them, including armoured ones that ate
plants, toothless omnivores that sprinted
on their hind legs and apex predators called
rauisuchians that were 9 metres from nose
to tail and had teeth like steak knives.
See you later, alligator
If the pseudosuchians sound impressive,
that’s because they were. So how did
dinosaurs replace them as the dominant
creatures on land? Back in the 1970s,
some palaeontologists thought that early
dinosaurs were unusually well-adapted to
rapid running compared with their close
relatives, says John Hutchinson, an expert on
animal muscles and locomotion at the Royal
Veterinary College in London. They tended
to walk on long, erect legs and were often
bipedal. This view was articulated by leading
dinosaur experts such as Robert Bakker,
then at Harvard University, and Alan Charig
at London’s Natural History Museum. >