專四晨讀美文：The Belly of the Beast

The Belly of the Beast
WHAT dinosaurs ate is, of course,
a question as interesting and illuminating
as what ate dinosaurs.
In the case of one particular dinosaur,
Microraptor, the matter was addressed
in a presentation to the annual meeting
of the Society of Vertebrate Palaeontology
by Jingmai O'Connor of the Institute
of Vertebrate Palaeontology and Palaeoanthropology, in Beijing.
Microraptor is one of many small, feathered dinosaurs
found in what is now China
that were alive during the Cretaceous period
more than 66m years ago.
Being feathered, it and its kind were cousins to birds.
The actual split between the two groups,
though, had happened much earlier,
during the Jurassic period
(the first known bird is Archaeopteryx, from 150m years ago),
and by the late Cretaceous
there were many species of bird around.
What Dr O'Connor and her colleagues have found is
the remains of one of those birds,
of an as-yet-unidentified species,
in the stomach of a specimen of Microraptor.
That is interesting.
Discovering direct evidence of what a fossil animal ate,
rather than having to infer it from details
such as the shape of its teeth,
is always valuable.
But the find's true significance
is a small detail of the prey's anatomy:
the third toe of its foot.
The size of the prey's third toe is important because,
among birds, long third toes are helpful
for grasping branches and perching in trees.
Indeed, the trait is so useful for arboreal life
that it is used by many avian palaeontologists
to decide whether newly excavated species of fossil birds
lived in trees or on the ground.
And the last meal of this particular specimen of Microraptor did,
indeed, have a long third toe.
That elongated toe suggests to Dr O'Connor that
Microraptor, too, was arboreal,
and hints that its feathers may have helped it to move
through an environment
where hops, jumps and flaps between branches
were a regular part of its daily activity.
Whether the first birds
evolved from arboreal or terrestrial ancestors
is a matter of lively debate among palaeontologists.
A fossil formed so long after birds emerged does not,
in truth, shed much light on that debate.
But it does suggest
feathers may have helped promote life in the trees,
even for creatures that could not actually fly.