11 June 2022 | New Scientist | 35The ascent of mammals
The stor y of the evolutionar y origin of mammals is told with
elan in this clear, engaging book, finds Michael MarshallBook
The Rise and Reign
of the Mammals
Steve Brusatte
Picador
ANYONE writing about mammals
faces a key challenge: not making
it about us. Humans are mammals
of course, and it is easy to present
the tale of mammalian evolution
as inexorably leading to our arrival.
Palaeontologist Steve Brusatte
deftly avoids this problem in his
new history of mammals by leaving
almost all mention of humans to
the final pages, where we come
in as, essentially, a peculiar and
rather alarming twist in the tale.
Brusatte is most famous for his
work on dinosaurs. His previous
book, The Rise and Fall of the
Dinosaurs, was a widely praised
bestseller. In recent years, he has
expanded his research into other
areas, and The Rise and Reign
of the Mammals is the result.
The evolutionary origin of
mammals is a complex story,
involving technical terms such as
“mammaliaform” – meaning “an
animal that is almost a mammal but
not quite”. Worse still, many of these
kinds of animal are now extinct,
with no modern equivalent to help
us understand them. To Brusatte’s
credit, his discussion of the
emergence of mammals remains
startlingly clear and engaging.
For instance, the synapsids
come to life as a group of
reptile- like animals that, to
an inexperienced eye, might be
mistaken for oversized geckos or
primitive dinosaurs. But in fact, they
had distinctive skulls that enabled
them to grow powerful jaw muscles
for chomping on tough insects – a
trait that would be carried through
to their mammalian descendants.
The most famous synapsid is
Dimetrodon, which had a huge sail
on its back, but there were many
others and they dominated land
ecosystems for millions of years.
Brusatte is particularly good
on how we draw the line between
mammals and non-mammals.
He acknowledges that on some
level it is an arbitrary distinction,
created to help make sense
of a complex world. But he
still offers a sensible answer.
At this point, the story would
normally cover how the tiny
mammals lived in the shadow of
the huge dinosaurs for millions of
years. Brusatte engages hard with
this cliché, arguing that competition
actually went both ways: mammals
couldn’t grow very large with the
dinosaurs around, but dinosaurs
couldn’t get very small because
mammals were much better at
carving out a niche at that size.
He shows a similarly deft touch
when handling the mass extinction
of 66 million years ago that wiped
out all the dinosaurs except birds.
It is true that mammals survived,
but Brusatte shows that it wasn’t an
easy escape. Instead, he emphasiseshow much of a hit the mammals
took, with three out of four species
disappearing in one heavily studied
region. Mammals, writes Brusatte,
had many little advantages that
helped them to scrape through,
including being small and
adapted for a generalist diet.
The story ends with the primates,
the group that includes humans.
However, Brusatte’s focus here is on
non-human primates, exploring the
earliest primates that emerged soon
after the dinosaur extinction and
following their monkey and ape
descendants up to the present.
When Homo sapiens turns up,
it is presented as something of
a calamity: our hunting prowess
wipes out many mammal species,
and our hominin cousins such as
Neanderthals die out as well.
Plenty of writers have tackled
mammalian biology, but The Rise
and Reign of the Mammals stands
out for its brilliant balance of
scientific detail and lively, efficient
storytelling. Brusatte has a clear
understanding of the book he is
writing. It isn’t a long argument, like
On the Origin of Species, but rather
a story, which he tells with elan. ❚Michael Marshall is a science writer
based in Devon, UKA sail-backed Dimetrodon looked
like a primitive dinosaur, but was a
reptile-like precursor to mammalsDANIEL^ E
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